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Press Kit/JULY 2012

Mars Science Laboratory Landing

Media Contacts
Dwayne Brown

NASA’s Mars
202-358-1726
Steve Cole Program 202-358-0918
Headquarters


dwayne.c.brown@nasa.gov
Washington


stephen.e.cole@nasa.gov
Guy Webster

Mars Science Laboratory

818-354-5011
D.C. Agle Mission 818-393-9011
Jet Propulsion Laboratory guy.webster@jpl.nasa.gov
Pasadena, Calif. agle@jpl.nasa.gov
Science Payload Investigations
Alpha Particle X-ray Spectrometer: Ruth Ann Chicoine, Canadian Space Agency, Saint-Hubert, Québec,
Canada; 450-926-4451; ruthann.chicoine@asc-csa.gc.ca
Chemistry and Camera: James Rickman, Los Alamos National Laboratory, Los Alamos, N.M.; 505-665-9203;
elvis@lanl.gov
Chemistry and Mineralogy: Rachel Hoover, NASA Ames Research Center, Moffett Field, Calif.; 650-604-0643;
rachel.hoover@nasa.gov
Dynamic Albedo of Neutrons: Igor Mitrofanov, Space Research Institute, Moscow, Russia;
011-7-495-333-3489; imitrofa@space.ru
Mars Descent Imager, Mars Hand Lens Imager, Mast Camera: Michael Ravine, Malin Space Science
Systems, San Diego; 858-552-2650 extension 591; ravine@msss.com
Radiation Assessment Detector: Donald Hassler, Southwest Research Institute; Boulder, Colo.;
303-546-0683; hassler@boulder.swri.edu
Rover Environmental Monitoring Station: Luis Cuesta, Centro de Astrobiología, Madrid, Spain;
011-34-620-265557; cuestacl@cab.inta-csic.es
Sample Analysis at Mars: Nancy Neal Jones, NASA Goddard Space Flight Center, Greenbelt, Md.;
301-286-0039; nancy.n.jones@nasa.gov

Engineering Investigation
MSL Entry, Descent and Landing Instrument Suite: Kathy Barnstorff, NASA Langley Research Center,
Hampton, Va.; 757-864-9886; kathy.barnstorff@nasa.gov

Contents
Media Services Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Quick Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Mars at a Glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Mars Science Laboratory Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Mission Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Comparing Two Mars Rover Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Curiosity’s Landing Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Recent, Current and Upcoming Missions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Mars Science: A Story of Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Historical Mars Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Program and Project Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Media Services Information
NASA Television Transmission

News Conferences

NASA Television is available in continental North
America, Alaska and Hawaii by C-band signal via
Satellite AMC-18C, at 105 degrees west longitude,
transponder 3C, 3760 MHz, vertical polarization. A
Digital Video Broadcast-compliant Integrated Receiver
Decoder is needed for reception. Transmission format
is DVB-S, 4:2:0. Data rate is 38.80 Mbps; symbol rate
28.0681, modulation QPSK/DVB-S, FEC 3/4.

An overview of the mission will be presented in a
news conference broadcast on NASA TV and on
http://www.ustream.tv/nasajpl, originating from NASA
Headquarters in Washington, at 1 p.m. EDT on
July 16, 2012. Back-to-back briefings on Aug. 2, 2012,
at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.,
will present information about the mission’s science
goals and capabilities at 10 a.m. PDT, and about
the flight and planned landing at 11 a.m. Pre-landing
update briefings at JPL are scheduled for 9:30 a.m.
PDT on Aug. 4 and 9:30 a.m. on Aug. 5. A post-launch
briefing at JPL will begin within about an hour of the
anticipated landing time (10:31 p.m. PDT) under most
conditions, and within about three hours of the landing
time if the spacecraft’s status is unknown. All of these
briefings will be carried on NASA TV and on http://
www.ustream.tv/nasajpl. Specific information about
upcoming briefings, as they are scheduled, will be kept
current on the Internet at http://www.nasa.gov/msl.

NASA-TV Multichannel Broadcast includes: Public
Channel (Channel 101) in high definition; Education
Channel (Channel 102) in standard definition; and Media
Channel (Channel 103) in high definition.
For digital downlink information for each NASA TV channel, access to all three channels online, and a schedule
of programming for Mars Science Laboratory activities,
visit http://www.nasa.gov/ntv.
Media Credentialing

Live Feed

News media representatives who would like to cover
the launch in person must be accredited through the
NASA Jet Propulsion Laboratory’s Media Relations
Office. To apply for credentials, visit http://mediacredentials.jpl.nasa.gov. Specific questions about the
credentialing process may be submitted to mediacredentials@list.jpl.nasa.gov. Journalists may contact the JPL newsroom at 818-354-5011 for more
information.

A live feed of video during key landing activities from
the mission control room at JPL will be carried on
NASA TV and on http://www.ustream.tv/nasajpl between about 9 and 11 p.m. PDT on Aug. 5 (midnight
and 2 a.m. EDT on Aug. 6).
Internet Information
Information about NASA’s Mars Science Laboratory
mission, including an electronic copy of this press kit,
press releases, status reports and images, is available
at http://www.nasa.gov/mars and http://marsprogram.
jpl.nasa.gov/msl. Frequent updates about the mission,
together with public feedback, are available by following Curiosity on Twitter at http://www.twitter.com/
marscuriosity and on Facebook at http://www.
facebook.com/marscuriosity.

Mars Science Laboratory Landing

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Press Kit

Quick Facts
Spacecraft

Mission

Cruise vehicle dimensions (cruise stage and aeroshell
with rover and descent stage inside): Diameter: 14 feet,
9 inches (4.5 meters); height: 9 feet, 8 inches (3 meters)

Time of Mars landing: 10:31 p.m. Aug. 5 PDT (1:31
a.m. Aug. 6 EDT, 05:31 Aug. 6 Universal Time) plus or
minus a minute. This is Earth-received time, which includes one-way light time for radio signal to reach Earth
from Mars. The landing will be at about 3 p.m. local
time at the Mars landing site.

Rover name: Curiosity
Rover dimensions: Length: 9 feet, 10 inches (3.0 meters)
(not counting arm); width: 9 feet, 1 inch (2.8 meters);
height at top of mast: 7 feet (2.1 meters); arm length:
7 feet (2.1 meters); wheel diameter: 20 inches (0.5
meter)

Landing site: 4.6 degrees south latitude, 137.4 degrees
east longitude, near base of Mount Sharp inside Gale
Crater
Earth–Mars distance on landing day: 154 million miles
(248 million kilometers)

Mass: 8,463 pounds (3,893 kilograms) total at launch,
consisting of 1,982-pound (899-kilogram) rover;
5,293-pound (2,401-kilogram) entry, descent and landing system (aeroshell plus fueled descent stage); and
1,188-pound (539-kilogram) fueled cruise stage

One-way radio transit time, Mars to Earth, on landing
day: 13.8 minutes
Total distance of travel, Earth to Mars: About 352 million
miles (567 million kilometers)

Power for rover: Multi-mission radioisotope thermoelectric generator and lithium-ion batteries

Primary mission: One Martian year (98 weeks)

Science payload: 165 pounds (75 kilograms) in 10 instruments: Alpha Particle X-ray Spectrometer, Chemistry
and Camera, Chemistry and Mineralogy, Dynamic
Albedo of Neutrons, Mars Descent Imager, Mars Hand
Lens Imager, Mast Camera, Radiation Assessment
Detector, Rover Environmental Monitoring Station, and
Sample Analysis at Mars

Expected near-surface atmospheric temperatures at
landing site during primary mission: minus 130 F to 32
F (minus 90 C to zero C)
Program
Cost: $2.5 billion, including $1.8 billlion for spacecraft
development and science investigations and additional
amounts for launch and operations.

Launch
Launch Time and Place: Nov. 26, 2011, 10:02 a.m.
EST, from Launch Complex 41, Cape Canaveral Air
Force Station, Fla.
Launch Vehicle: Atlas V 541 provided by United Launch
Alliance
Earth–Mars distance at launch: 127 million miles
(204 million kilometers)

Mars Science Laboratory Landing

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Mars at a Glance
General

Environment

• One of five planets known to ancients; Mars was
the Roman god of war, agriculture and the state

• Atmosphere composed chiefly of carbon dioxide
(95.3 percent), nitrogen (2.7 percent) and argon
(1.6 percent)

• Yellowish brown to reddish color; occasionally the
third-brightest object in the night sky after the moon
and Venus

• Surface atmospheric pressure less than 1/100th
that of Earth’s average

Physical Characteristics

• Surface winds of 0 to about 20 miles per hour (0 to
about 9 meters per second), with gusts of about
90 miles per hour (about 40 meters per second)

• Average diameter 4,212 miles (6,780 kilometers);
about half the size of Earth, but twice the size of
Earth’s moon

• Local, regional and global dust storms; also whirlwinds called dust devils
• Surface temperature averages minus 64 F (minus
53 C); varies from minus 199 F (minus 128 C)
during polar night to 80 F (27 C) at equator during
midday at closest point in orbit to sun

• Same land area as Earth, reminiscent of a cold,
rocky desert
• Mass 1/10th of Earth’s; gravity only 38 percent as
strong as Earth’s

Features

• Density 3.9 times greater than water (compared with
Earth’s 5.5 times greater than water)

• Highest point is Olympus Mons, a huge shield volcano about 16 miles (26 kilometers) high and 370
miles (600 kilometers) across; has about the same
area as Arizona

• No planet-wide magnetic field detected; only localized ancient remnant fields in various regions
Orbit

• Canyon system of Valles Marineris is largest and
deepest known in solar system; extends more than
2,500 miles (4,000 kilometers) and has 3 to 6 miles
(5 to 10 kilometers) relief from floors to tops of surrounding plateaus

• Fourth planet from the sun, the next beyond Earth
• About 1.5 times farther from the sun than Earth is
• Orbit elliptical; distance from sun varies from a minimum of 128.4 million miles (206.7 million kilometers)
to a maximum of 154.8 million miles (249.2 million
kilometers); average is 141.5 million miles (227.7
million kilometers)

Moons
• Two irregularly shaped moons, each only a few
kilometers wide

• Revolves around sun once every 687 Earth days

• Larger moon named Phobos (“fear”); smaller is
Deimos (“terror”), named for attributes personified
in Greek mythology as sons of the god of war

• Rotation period (length of day): 24 hours, 39 minutes, 35 seconds (1.027 Earth days)
• Poles tilted 25 degrees, creating seasons similar to
Earth’s

Mars Science Laboratory Landing

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Press Kit

Mars Science Laboratory Investigations
Mars Science Laboratory Investigations

croorganisms or their fossil equivalents. However, if this
mission finds that the field site in Gale Crater has had
conditions favorable for habitability and for preserving
evidence about life, those findings can shape future
missions that would bring samples back to Earth for
life-detection tests or for missions that carry advanced
life-detection experiments to Mars. In this sense, the
Mars Science Laboratory is the prospecting stage in a
step-by-step program of exploration, reconnaissance,
prospecting and mining evidence for a definitive answer about whether life has existed on Mars. NASA’s
Astrobiology Program has aided in development of the
Mars Science Laboratory science payload and in studies of extreme habitats on Earth that can help in understanding possible habitats on Mars.

NASA’s Mars Science Laboratory mission will study
whether the Gale Crater area of Mars has evidence of
past and present habitable environments. These studies
will be part of a broader examination of past and present
processes in the Martian atmosphere and on its surface.
The research will use 10 instrument-based science
investigations. The mission’s rover, Curiosity, carries the
instruments for these investigations and will support their
use by providing overland mobility, sample-acquisition
capabilities, power and communications. The primary
mission will last one Mars year (98 weeks).
The payload includes mast-mounted instruments to
survey the surroundings and assess potential sampling
targets from a distance; instruments on Curiosity’s
robotic arm for close-up inspections; laboratory instruments inside the rover for analysis of samples from
rocks, soils and atmosphere; and instruments to monitor the environment around the rover. In addition to the
science payload, engineering sensors on the heat shield
will gather information about Mars’ atmosphere and the
spacecraft’s performance during its descent through the
atmosphere.

Three conditions considered crucial for habitability are
liquid water, other chemical ingredients utilized by life
and a source of energy. The Mars Science Laboratory
mission advances the “follow the water” strategy of
NASA Mars exploration since the mid-1990s to a
strategy of determining the best settings for seeking an
answer to whether Mars ever supported life.
Every environment on Earth where there is liquid water
sustains microbial life. For most of Earth’s history, the
only life forms on this planet were microorganisms, or
microbes. Microbes still make up most of the living matter on Earth. Scientists who specialize in the search for
life on other worlds expect that any life on Mars, if it has
existed at all, has been microbial.

To make best use of the rover’s science capabilities, a
diverse international team of scientists and engineers will
make daily decisions about the rover’s activities for the
following day. Even if all the rover’s technology performs
flawlessly, some types of evidence the mission will seek
about past environments may not have persisted in the
rock record. While the possibility that life might have
existed on Mars provokes great interest, a finding that
conditions did not favor life would also pay off with valuable insight about differences and similarities between
early Mars and early Earth.

Curiosity will land in a region where this key item on the
checklist of life’s requirements has already been determined: It was wet. Observations from Mars orbit during
five years of assessing candidate landing sites have
made these areas some of the most intensely studied
places on Mars. Researchers have used NASA’s Mars
Reconnaissance Orbiter to map the area’s mineralogy,
finding exposures of clay minerals. Clays, other phyllosilicates and sulfates form under conditions with adequate
liquid water in a life-supporting, medium range between
very acidic and very alkaline.

Habitability
The mission will assess whether the area Curiosity explores has ever been a potential habitat for Martian life.
Whether life has existed on Mars is an open question
that this mission, by itself, is not designed to answer.
Curiosity does not carry experiments to detect active
processes that would signify present-day biological
metabolism, nor does it have the ability to image mi-

Mars Science Laboratory Landing

Curiosity will inventory other basic ingredients for life,
seek additional evidence about water and investigate
how conditions in the area have changed over time.
The wet environment in which the clay minerals formed

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Press Kit

process would favor increased concentration of heavier
isotopes in the retained, modern atmosphere. Such
processes can be relevant to habitability and biology.
Curiosity will assess isotopic ratios in methane if that
gas is in the air around the rover. Methane is an organic
molecule, and its carbon isotope ratio can be very
distinctive. Observations from orbit and from Earth indicate traces of it may be present in Mars’ atmosphere.
Isotopic ratios could hold clues about whether methane
is being produced by microbes or by a non-biological
process.

is long gone, probably occurring more than 3 billion
years ago. Examining the geological context for those
minerals, such as the minerals in younger rock layers,
could advance understanding of habitat change to drier
conditions. The rover can also check for traces of water
still bound into the mineral structure of rocks at and near
the surface.
Carbon-containing compounds called organic molecules are an important class of ingredients for life that
Curiosity can detect and inventory. This capability adds
a trailblazing “follow the carbon” aspect to the Mars
Science Laboratory, as part of the sequel to the “follow
the water” theme.

The mission has four primary science objectives to
meet NASA’s overall habitability assessment goal:
• Assess the biological potential of at least one target
environment by determining the nature and inventory of organic carbon compounds, searching for
the chemical building blocks of life and identifying
features that may record the actions of biologically
relevant processes.

Organic molecules contain one or more carbon atoms
bound to hydrogen and, in many cases, additional elements. They can exist without life, but life as we know
it cannot exist without them, so their presence would
be an important plus for habitability. If Curiosity detects
complex organics that are important to life on Earth,
such as amino acids, these might be of biological origin,
but also could come from non-biological sources, such
as carbonaceous meteorites delivered to the surface of
the planet.

• Characterize the geology of the rover’s field site at
all appropriate spatial scales by investigating the
chemical, isotopic and mineralogical composition of
surface and near-surface materials and interpreting
the processes that have formed rocks and soils.
• Investigate planetary processes of relevance to past
habitability (including the role of water) by assessing
the long-time-scale atmospheric evolution and determining the present state, distribution and cycling
of water and carbon dioxide.

Curiosity will also check for other chemical elements
important for life, such as nitrogen, phosphorus, sulfur
and oxygen.
The rover will definitively identify minerals, which provide
a lasting record of the temperatures, pressures and
chemistry present when the minerals were formed or
altered. Researchers will add that information to observations about geological context, such as the patterns
and processes of sedimentary rock accumulation, to
chart a chronology of how the area’s environments have
changed over time. Energy for life on Mars could come
from sunlight, heat or mixtures of chemicals (food) with
an energy gradient that could be exploited by biological
metabolism. The information Curiosity collects about
minerals and about the area’s modern environment will
be analyzed for clues about possible past and present
energy sources for life.

• Characterize the broad spectrum of surface radiation, including galactic cosmic radiation, solar
proton events and secondary neutrons.
Preservation and Past Environments
Some of the same environmental conditions favorable
for life can, paradoxically, be unfavorable for preserving evidence about life. Water, oxidants and heat, all of
which can contribute to habitability, can destroy organic
molecules and other possible markers left by life, or
biosignatures.
Life has thrived on Earth for more than 3 billion years,
but only a miniscule fraction of Earth’s past life has
left evidence of itself in the rock record on this planet.
Preserving evidence of life from the distant past has
required specific, unusual conditions. On Earth, these
windows of preservation have included situations such
as insects encased in amber and mastodons im-

Curiosity will measure the ratios of different isotopes of
several elements. Isotopes are variants of the same element with different atomic weights. Ratios such as the
proportion of carbon-13 to carbon-12 can provide insight into planetary processes. For example, Mars once
had a much denser atmosphere than it does today, and
if the loss occurred at the top of the atmosphere, that
Mars Science Laboratory Landing

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Press Kit

mersed in tar pits. Mars won’t have fossils of insects or
mastodons; if Mars has had any life forms at all, they
were likely microbes. Understanding what types of
environments may have preserved evidence of microbial
life from billions of years ago, even on Earth, is still an
emerging field of study.
To determine whether Mars ever supported life, a key
step is learning where biosignatures could persist.
Curiosity’s findings about windows of preservation will
serve this mission’s prospector role: identifying good
hunting grounds for possible future investigations about
Martian life’s existence and characteristics. They can
also guide this mission’s own course, informing decisions about where to drive and which rocks to sample
in Curiosity’s search for organics.
Accumulation of rock-forming sediments writes a record
of environmental conditions and processes into those
sedimentary rocks. The layers of the mountain inside
Gale Crater provide a record of events arranged in
the order in which they occurred. Researchers using
Curiosity can look at how environments changed over
time, possibly including transitions from habitable conditions to non-habitable conditions. Some of the clues are
in the textures of the rocks, and Curiosity will be looking for distinctive rock textures. Other clues are in the
mineral and chemical compositions.
Some conditions and processes, such as low temperatures and rapid entrapment in the sediments, can favor
preservation of organics and evidence about life. As
Curiosity looks for organics by analyzing samples drilled
from sedimentary rocks, it will be reading the history of
past environments whether or not it finds organics.
Some minerals and other geologic materials, such as
sulfates, phosphates, carbonates and silica, can help
preserve biosignatures. All of these materials, forming
under just the right balance of environmental conditions,
have the potential to preserve fragments of organic molecules derived from microbes or carbonaceous meteorites. But not just any rock formed of suitable minerals
will do. Most on Earth do not. Expectations for Mars are
similar, and the chances of a discovery — even if life had
been present — are very small. If this sounds sobering,
it should be, but this is the only known way to prospect
for the vestiges of life on the early Earth.
The area at Gale Crater accessible to Curiosity as it
drives during the mission contains rocks and soils
that may have been originally deposited under differMars Science Laboratory Landing

ing conditions over a range of times. Analyzing samples
from different points in that range could identify which, if
any, hold organics. The rover might find that the answer
is none. While such an answer could shrink prospects
for finding evidence of ancient life on Mars, it would
strengthen the contrast between early Mars and early
Earth. The history of environmental changes on an
Earth-like planet without life would be valuable for understanding the history of life’s interaction with Earth’s
environment.
Modern Environment
The Mars Science Laboratory will study the current environment in its landing region as well as the records left by
past environments. Curiosity carries a weather station, an
instrument for monitoring natural high-energy radiation
and an instrument that can detect soil moisture and water-containing minerals in the ground beneath the rover.
The investigations of organics and other potential ingredients for life can analyze samples of modern-day soil for
what nutrients would be available to soil microbes. The
ability to check for methane in the atmosphere is a study
of modern processes, too. Methane would break down
and disappear from the atmosphere within a few centuries if not replenished by an active source, so its presence would be surprising.
Selection of Curiosity’s landing site was not based on
traits favoring present-day habitability. However, much of
the information this mission contributes about the modern environment will enhance our general understanding
of Mars. For example, can organic compounds delivered
by meteorites persist in the soil close to the surface?
How does the modern atmosphere affect the ultraviolet
and high-energy radiation that reaches the surface, posing a hazard to life and to preservation of organics? How
might we better estimate levels in the past? The rover’s
monitoring of radiation levels from cosmic rays and the
sun also is designed to address astronaut safety on
eventual human missions to Mars.
Science Payload
On April 14, 2004, NASA announced an opportunity
for researchers to propose science investigations for
the Mars Science Laboratory mission. The solicitation
for proposals said, “The overall science objective of the
MSL mission is to explore and quantitatively assess a
potential habitat on Mars.” Eight months later, the agency
announced selection of eight investigations proposed
competitively. In addition, Spain and Russia would each
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Press Kit

provide an investigation through international agreements. The instruments for these 10 investigations make
up the science payload on Curiosity.
The two instruments on the mast are a versatile,
high-definition imaging system, and a laser-equipped,
spectrum-reading camera that can hit a rock with a
laser and observe the resulting spark for information
about what chemical elements are in the rock. The
tools on the turret at the end of Curiosity’s 7-foot-long
(2.1-meter-long) robotic arm include a radiation-emitting
instrument that reads X-ray clues to targets’ composition and a magnifying-lens camera. The arm can deliver
soil and powdered-rock samples to an instrument that
uses X-ray analysis to identify minerals in the sample
and to an instrument that uses three laboratory methods
for assessing carbon compounds and other chemicals
important to life and indicative of past and present processes. For characterizing the modern environment, the
rover also carries instruments to monitor the weather,
measure natural radiation and seek evidence of water
beneath the surface. To provide context for all the other
instruments, a camera will record images of the landing
area during descent.
The 10 science instruments on the Mars Science
Laboratory have a combined mass of 165 pounds (75
kilograms), compared with a five-instrument science
payload totaling 11 pounds (5 kilograms) on each of the
twin rovers, Spirit and Opportunity, that landed on Mars
in 2004. The mass of just one of Curiosity’s 10 instruments, 88 pounds (40 kilograms) for Sample Analysis at
Mars, is nearly four times the 23-pound (10.6-kilogram)
total mass of the first Mars rover, 1997’s Sojourner on
the Mars Pathfinder mission.
Assessing past and present habitability of environments
at sites visited by Curiosity will require integrating the
results of the various instruments, not any single instrument. Science operations and analysis will be coordinated through the Mars Science Laboratory Project
Science Group, whose members are Project Scientist
John Grotzinger, of the California Institute of Technology,
Pasadena, Calif.; Program Scientist Michael Meyer of
NASA Headquarters, Washington; and the principal
investigator for each of the following investigations.
Mast Camera (Mastcam)
Two two-megapixel color cameras on Curiosity’s mast
are the left and right eyes of the Mast Camera, or
Mastcam investigation. These versatile cameras have
Mars Science Laboratory Landing

complementary capabilities for showing the rover’s surroundings in exquisite detail and in motion.
The right-eye Mastcam looks through a telephoto lens,
revealing details near or far with about three-fold better
resolution than any previous landscape-viewing camera
on the surface of Mars. The left-eye Mastcam provides
broader context through a medium-angle lens. Each
can acquire and store thousands of full-color images.
Each is also capable of recording high-definition video.
Combining information from the two eyes can yield 3-D
views where the images overlap.
Mastcam imaging of the shapes and colors of landscapes, rocks and soils will provide clues about the history of environmental processes that have formed them
and modified them over time. Images and videos of the
sky will document contemporary processes, such as the
movement of clouds and dust.
The telephoto Mastcam is called “Mastcam 100” for its
100-millimeter focal-length lens. Its images cover an area
about six degrees wide and five degrees tall, in 1,600 pixels by 1,200 pixels. This yields a scale of 2.9 inches (7.4
centimeters) per pixel at a distance of about six-tenths of
a mile (1 kilometer) and about 0.006 inch (150 microns)
per pixel at a distance of 6.6 feet (2 meters). The camera
provides enough resolution to distinguish a basketball
from a football at a distance of seven football fields, or to
read “ONE CENT” on a penny on the ground beside the
rover.
Its left-eye partner, called “Mastcam 34” for its 34-millimeter lens, catches a scene three times wider — about
18 degrees wide and 15 degrees tall — on an identical
detector. It can obtain images with 8.7 inches (22 centimeters) per pixel at a distance of about six-tenths of a
mile (1 kilometer) and 0.018 inch (450 microns) per pixel
at a distance of 6.6 feet (2 meters).
The centers of Mastcam’s lenses sit about 6.5 feet (2.0
meters) above ground level. The eyes are farther apart —
about 10 inches (25 centimeters) — than the stereo eyes
on earlier Mars surface robots. The cameras can focus
on features at any distance from about 6 feet (just under
2 meters) to infinity.
When Curiosity drives to a new location, the Mastcam 34
can record a full-color, full-circle panorama showing everything from the nearby ground to the horizon by taking
150 images in about 25 minutes. For a first look, these
may be sent to Earth initially as compressed “thumbnail”
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versions. Mastcam thumbnail frames — roughly 150-by150-pixel versions of each image — can be sent as
an index of the full-scale images held in the onboard
memory.
Using the Mastcam 100, the team will be able to see
farther off to the sides of the rover’s path, compared with
what has been possible with earlier Mars rovers. That
will help with selection of the most interesting targets to
approach for analyzing with Curiosity’s other instruments
and will provide additional geological context for interpreting data about the chosen targets.

include science spectral filters for examining the ground
or sky in narrow bands of visible-light or near-infrared
wavelengths. These science filters can be used for
follow-up observations to gain more information about
rocks or other features of interest identified in red-greenblue images. One additional filter on each camera allows
it to look directly at the sun to measure the amount of
dust in the atmosphere, a key part of Mars’ weather.

The Mastcams will provide still images and video to
study motions of the rover — both for science, such
as seeing how soils interact with wheels, and for engineering, such as aiding in use of the robotic arm. In
other videos, the team may use cinematic techniques
such as panning across a scene and using the rover’s
movement for “dolly” shots. Video from the cameras is
720p high definition at four to seven frames per second,
depending on exposure time.

Mastcam’s color-calibration target on the rover deck
includes magnets to keep the highly magnetic Martian
dust from accumulating on portions of color chips and
white-gray-balance reference chips. Natural lighting on
Mars tends to be redder than on Earth due to dust in
Mars’ atmosphere. “True color” images can be produced that incorporate that lighting effect — comparable to the warm, orange lighting that is experienced at
sunset on Earth. Alternatively, a white-balance calculation can be used to adjust for the tint of the lighting, as
the human eye tends to do and digital cameras can do.
The Mastcams are capable of producing both true-color
and white-balanced images.

Malin Space Science Systems, San Diego, built the
Mastcams and two of Curiosity’s other science instruments: the Mars Hand Lens Imager and the Mars
Descent Imager.

The Mastcam principal investigator is Michael Malin, a
geologist who founded Malin Space Science Systems
and has participated in NASA Mars exploration since the
Mariner 9 mission in 1971–72.

The four cameras from Malin Space Science Systems
share several design features. They use a Bayer pattern
filter, as found in many commercial digital cameras, for
color imaging. Bayer filtering means that the chargecoupled device (CCD) that detects each pixel of the
image is covered with a grid of green, red and blue filters
so that the camera gets the three color components
over the entire scene in a single exposure. This is a
change from color cameras on earlier Mars landers and
rovers, which took a series of exposures through different filters to be combined into color composites by processing on Earth. The filter design used for Curiosity’s
science cameras results in pictures in which the color
closely mimics the way the average human eye sees the
world. Each of the cameras uses a focusing mechanism
from MDA Information Systems Space Division, formerly
Alliance Spacesystems, Pasadena, Calif. Each uses
a Kodak CCD with an array of 1,600 by 1,200 active
pixels. Each has an eight-gigabyte flash memory.

Chemistry and Camera (ChemCam)

Besides the affixed red-green-blue filter grid, the
Mastcams have wheels of other color filters that can be
rotated into place between the lens and the CCD. These

Mars Science Laboratory Landing

The investigation using a rock-zapping laser and a telescope mounted atop Curiosity’s mast is the Chemistry
and Camera suite, or ChemCam. It also includes spectrometers and electronics down inside the rover.
The laser can hit rock or soil targets up to about 23
feet (7 meters) away with enough energy to excite a
pinhead-size spot into a glowing, ionized gas, called
plasma. The instrument observes that spark with the
telescope and analyzes the spectrum of light to identify
the chemical elements in the target.
The telescope, with a diameter of 4.33 inches (110
millimeters), doubles as the optics for the camera of
ChemCam, which records monochrome images on
a 1,024-pixel-by-1,024-pixel detector. The telescopic
camera, called the remote micro-imager, or RMI, will
show context of the spots hit with the laser. It can also
be used independently of the laser for observations of
targets at any distance.

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extreme environments, such as inside nuclear reactors
and on the sea floor, and has had experimental
applications in environmental monitoring and cancer
detection, but ChemCam is its first use in interplanetary
exploration.

Information from ChemCam will help researchers survey
the rover’s surroundings and choose which targets to
approach for study with the tools on the arm and the
analytical laboratory instruments. ChemCam can also
analyze many more targets than those instruments
can. It can be used on multiple targets the same day,
while the analytical laboratory investigations — SAM
and CheMin — take multiple days per target. It can also
check the composition of targets inaccessible to the
rover’s other ingredient-identifying instruments, such as
rock faces beyond the reach of Curiosity’s robotic arm.

Roger Wiens, a geochemist with the U.S. Department
of Energy’s Los Alamos National Laboratory in
Los Alamos, N.M., is the principal investigator for
ChemCam. For developing, building and testing the
instrument, Los Alamos partnered with researchers in
France funded by the French national space agency,
Centre National d’Études Spatiales. The deputy principal investigator is Sylvestre Maurice, a spectroscopy
expert with the Institut de Recherche en Astrophysique
et Planétologie at the Observatoire Midi-Pyrénées,
Toulouse, France.

The spot hit by ChemCam’s infrared laser gets more
than a million watts of power focused on it for five
one-billionths of a second. Light from the resulting flash
comes back to ChemCam through the telescope, then
through about 20 feet (6 meters) of optical fiber down
the mast to three spectrometers inside the rover. The
spectrometers record intensity at 6,144 different wavelengths of ultraviolet, visible and infrared light (wavelengths from 240 to 850 nanometers). Different chemical
elements in the target, in their ionized state, emit light
at different wavelengths. Dozens of laser pulses on the
same spot will be used to achieve the desired accuracy
in identifying elements. Among the many elements that
the instrument can identify in rocks and soils are sodium,
magnesium, aluminum, silicon, calcium, potassium,
titanium, manganese, iron, hydrogen, oxygen, beryllium,
lithium, strontium, nitrogen and phosphorus.

France provided ChemCam’s laser and telescope. The
laser was built by Thales, Paris, France. Los Alamos
National Laboratory supplied the spectrometers and
data processors. The optical design for the spectrometers came from Ocean Optics, Dunedin, Fla. NASA’s Jet
Propulsion Laboratory, Pasadena, Calif., provided fiberoptic connections linking the two parts of the instrument and a cooling machine to keep the spectrometers
cold. The ChemCam team includes experts in mineralogy, geology, astrobiology and other fields, with some
members also on other Curiosity instrument teams.
Alpha Particle X-Ray Spectrometer (APXS)

If a rock has a coating of dust or a weathered rind,
hundreds of repeated pulses from the laser can remove
those layers to provide a reading of the rock’s interior
composition and a comparison between the interior and
the coating.

The Alpha Particle X-Ray Spectrometer (APXS) on
Curiosity’s robotic arm, like its predecessors on the
arms of all previous Mars rovers, will identify chemical
elements in rocks and soils.

Researchers also plan to use ChemCam to study the
soil at each place Curiosity stops. These observations
will document local and regional variations in the soil’s
composition and — from images taken through the
telescope by the remote micro-imager — in the size
distribution of soil particles.

The APXS instruments on Sojourner, Spirit and
Opportunity produced important findings from those
missions, including salty compositions indicative of a
wet past in bedrocks examined by Opportunity and
the signature of an ancient hot spring or steam vent in
soil examined by Spirit. The APXS on Curiosity delivers greater sensitivity, better scheduling versatility and a
new mode for optimal positioning.

Another capability will be to check for water, either
bound into mineral composition or as frost. By quickly
identifying hydrogen and oxygen, ChemCam can provide unambiguous identification of water if any is on the
surface in the area Curiosity explores.

The Canadian Space Agency contributed this
Canadian-made instrument for the Mars Science
Laboratory. A pinch of radioactive material emits radiation that “queries” the target and an X-ray detector
“reads” the answer.

ChemCam uses a technology called laser-induced
breakdown spectroscopy. This method of determining
the composition of an object has been used in other
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The APXS sensor head, about the size of a cupcake,
rides on the multi-tool turret at the end of Curiosity’s arm.
The rover will place the spectrometer’s contact-sensing
surface directly onto most rock targets selected for
APXS readings or just above some soil targets.
The instrument determines the abundance of elements
from sodium to strontium, including the major rockforming and soil-forming elements sodium, magnesium,
aluminum, silicon, calcium, iron and sulfur. In 10-minute
quick looks, it can detect even minor ingredients down
to concentrations of about one-half percent. In threehour readings, it can detect important trace elements
down to concentrations of 100 or fewer parts per million.
It has a high sensitivity to salt-forming elements such as
sulfur, chlorine and bromine, which can indicate interaction with water in the past.
The APXS will characterize the geological context and
inform choices about acquiring samples for analysis inside the mission’s analytical laboratory instruments: SAM
and CheMin. Learning which elements, in what concentrations, are in the targets will help researchers identify
processes that formed the rocks and soils in the area of
Mars where Curiosity is working.
The spectrometer uses the radioactive element curium
as a source to bombard the target with energetic alpha
particles (helium nuclei) and X-rays. This causes each element in the target to emit its own characteristic X-rays,
which are then registered by an X-ray detector chip
inside the sensor head. The investigation’s main electronics package, which resides inside the rover, records
all detected X-rays with their energy and assembles the
detections into the X-ray spectrum of this sample.
On Spirit and Opportunity, the need for the X-ray detector chip to stay cold, and the length of time necessary
for acquiring a measurement, have restricted most
APXS measurements to Martian nighttime hours. One
change in Curiosity’s APXS is the possibility to activate a
solid-state electric cooler for the detector, for use of the
APXS during Martian daytime.
Curiosity’s APXS can make measurements in about
one-third the time needed for equivalent readings by its
predecessors. This improvement in sensitivity results
mainly from shrinking the distance between the X-ray
detector and the sample by about one-third, to 0.75
inch (19 millimeters).

Mars Science Laboratory Landing

Additional improvement in sensitivity, mainly for heavy
elements such as iron, comes from increasing the
amount X-rays emitted by the curium. Curiosity’s APXS
has about 700 micrograms (in mass) or 60 millicuries
(in radioactivity), which is twice as much as Spirit’s or
Opportunity’s. Curium is a synthetic element first identified in a laboratory in 1944. The specific isotope used in
all Mars rovers’ APXS instruments is curium 244, which
has a half-life of 18.1 years. This makes it ideal for longduration missions, where even after more than seven
years of the Opportunity mission, the loss in activity is
hardly noticeable.
The additional X-ray intensity will benefit use of a technique called the scatter peak method, which was
developed by physicist Iain Campbell, an APXS coinvestigator at the University of Guelph, Ontario, Canada.
This method extracts information about elements invisible to X-rays, such as oxygen. It was used to detect and
quantify water bound in the minerals of salty subsurface
soils examined by Spirit at Gusev Crater.
When the spectrometer is in contact with the target, it
examines a patch about 0.7 inch (1.7 centimeters) in
diameter. It detects elements to a depth of about 0.0002
inch (5 microns) for low-atomic-weight elements and to
about 10 times that depth for heavier elements. The dust
removal tool on Curiosity’s arm turret can be used to
brush some rock surfaces clean before APXS examines
them.
For some soil targets, to avoid pushing the instrument
into the soil, the spectrometer will not be placed in direct
contact with the target. In those cases, placement will
use a standoff distance of about 0.4 inch (1 centimeter)
or less.
Another new feature for Curiosity’s APXS is an autonomous placement mode. With this software, as the arm
moves the spectrometer step-by-step closer to the soil,
the instrument checks X-rays from the target for several
seconds at each step. When the count rate reaches a
predetermined criterion of what would be adequate for a
good compositional reading, the software knows, “OK.
That’s close enough.” The arm’s approach movements
cease and the longer-duration APXS reading begins. A
more complex variation of this autonomous placement
mode may use brief readings at several positions parallel
to the ground surface, scanning a larger area for certain
compositional criteria, such as ratio of iron to sulfur, and
quickly selecting the most distinctive spots for longerduration readings.
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Besides examining rocks and soils in place, the science
team can use the APXS to check processed samples
that the arm places on the rover’s observation tray and
soil freshly exposed by action of the rover’s wheels. An
onboard basaltic rock slab, surrounded by nickel plate,
will be used periodically to check the performance and
calibration of the instrument.
The principal investigator for Curiosity’s APXS is Ralf
Gellert, a physicist at the University of Guelph in Ontario,
Canada. He was part of the team that designed and
built the Spirit and Opportunity APXS instruments at
the Max Planck Institute in Mainz, Germany, and provided the new scientific design for the Mars Science
Laboratory APXS based on the experience gained
through the long operation of those predecessors. MDA,
in Brampton, Ontario, Canada, built the instrument as
the prime contractor for the Canadian Space Agency.
Mars Hand Lens Imager (MAHLI)

lights and adjustable focus. Also, it sits on a longer arm,
one that can hold MAHLI up higher than the cameras
on the rover’s mast for seeing over an obstacle or capturing a rover self-portrait.
When positioned at its closest range — about 0.8 inch
(21 millimeters) from its target — the camera’s images
have a resolution of slightly less than one one-thousandth of an inch (14 microns) per pixel. The field of
view for that close-up is a rectangle about 0.9 inch (2.2
centimeters) by 0.7 inch (1.7 centimeters).
The camera can be held at a series of different distances from a target to show context as well as detail
by adjusting the focus. At about 3 feet (1 meter) from
a target, it still has a pixel resolution of about 0.02 inch
(half a millimeter) in a view covering an area about 2 feet
(70 centimeters) wide. By manipulation of arm position
and focus, the camera can be used to examine hardware on the rover or record time-lapse views of activities such as opening a sample inlet cover.

The Mars Hand Lens Imager, or MAHLI, is a focusable
color camera on the tool-bearing turret at the end of
Curiosity’s robotic arm. Researchers will use it for magnified, close-up views of rocks and soils, and also for
wider scenes of the ground, the landscape or even the
rover. Essentially, it is a hand-held camera with a macro
lens and autofocus.

MAHLI has two sets of white light-emitting diodes to
enable imaging at night or in deep shadow. Two other
light-emitting diodes on the instrument glow at the ultraviolet wavelength of 365 nanometers. These will make it
possible to check for materials that fluoresce under this
illumination.

The investigation takes its name from the type of hand
lens magnifying tool that every field geologist carries for
seeing details in rocks. Color, crystal shapes, mineral
cleavage planes and other visible details from such
close-up observation provide clues to a rock’s composition. In sedimentary rocks, the sizes and shapes of the
grains in the rock, and the scale of fine layering, provide
information about how the grains were transported
and deposited. Sharp-edge grains have not been worn
down by tumbling long distances, for example. The size
of grains can indicate whether the water or wind that
carried them was moving quickly or not.

Malin Space Science Systems, San Diego, developed,
built and operates MAHLI. This camera shares some
traits with three other cameras on Curiosity from the
same company. It uses a red-green-blue filter grid like
the one on commercial digital cameras for obtaining a
full-color image with a single exposure. Its image detector is a charge-coupled device with an array of 1,600 by
1,200 active pixels. It stores images in an eight-gigabyte
flash memory, and it can perform an onboard focus
merge of eight images to reduce from eight to two the
number of images returned to Earth in downlink-limited
situations.

These clues garnered from MAHLI images can aid both
in selection of which targets to analyze with other instruments and in directly reading the environmental history
recorded in the rocks and soils the rover encounters.

Curiosity carries a vertically mounted calibration target
for MAHLI, for checking color, white balance, resolution,
focus and the ultraviolet illumination.

As a close-up magnifying camera, MAHLI resembles
the Microscopic Imager instrument mounted at the
end of the robotic arm on each of the twin Mars rovers
Spirit and Opportunity. MAHLI has significantly greater
capabilities than those predecessors, however: full color,
Mars Science Laboratory Landing

Ken Edgett of Malin Space Science Systems, a geologist who has helped run cameras on several Mars
orbiters, is the principal investigator for MAHLI. A unified
imaging-science team for the three Malin-supplied instruments combines experience in geologic field work,
Mars exploration and space cameras.
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Chemistry and Mineralogy (CheMin)
The Chemistry and Mineralogy experiment, or CheMin,
is one of two investigations that will analyze powdered
rock and soil samples delivered by Curiosity’s robotic
arm. It will identify and quantify the minerals in the
samples. Minerals provide a durable record of past
environmental conditions, including information about
possible ingredients and energy sources for life.
CheMin uses X-ray diffraction, a first for a mission to
Mars. This is a more definitive method for identifying
minerals than was possible with any instrument on previous missions. The investigation supplements the diffraction measurements with X-ray fluorescence capability to
determine further details of composition by identifying
ratios of specific elements present.
X-ray diffraction works by directing an X-ray beam at
a sample and recording how X-rays are scattered by
the sample at the atomic level. All minerals are crystalline, and in crystalline materials, atoms are arranged
in an orderly, periodic structure, causing the X-rays to
be scattered at predictable angles. From those angles,
researchers can deduce the spacing between planes
of atoms in the crystal. Each different mineral yields a
known, characteristic series of spacings and intensities,
its own fingerprint.
On Curiosity’s deck, near the front of the rover, one funnel with a removable cover leads through the deck top
to the CheMin instrument inside the rover. The instrument is a cube about 10 inches (25 centimeters) on
each side, weighing about 22 pounds (10 kilograms).
The rover acquires rock samples with a percussive drill
and soil samples with a scoop. A sample processing
tool on the robotic arm puts the powdered rock or soil
through a sieve designed to remove any particles larger
than 0.006 inch (150 microns) before delivering the material into the CheMin inlet funnel. Vibration helps move
the sample material — now a gritty powder — down
the funnel. Each sample analysis will use about as much
material as in a baby aspirin.
The funnel delivers the sample into a disc-shaped cell,
about the diameter of a shirt button and thickness of a
business card. The walls of the sample cell are transparent plastic. Thirty-two of these cells are mounted around
the perimeter of a sample wheel. Rotating the wheel can
position any cell into the instrument’s X-ray beam. Five
cells hold reference samples from Earth to help calibrate
Mars Science Laboratory Landing

the instrument. The other 27 are reusable holders for
Martian samples.
Each pair of cells is mounted on a metal holder that resembles a tuning fork. A tiny piezoelectric buzzer excites
the fork to keep the particles in the sample moving inside
the cell during analysis of the sample. This puts the particles in a random mix of orientations to the X-ray beam,
improving detection of how the mineral crystals in the
sample scatter the X-rays. The piezoelectric vibration,
at about 200 cycles per second (middle C on a piano
is 261 cycles per second) also helps keep the powder
flowing during filling and dumping of the cell.
CheMin generates X-rays by aiming high-energy electrons at a target of cobalt. The X-rays emitted by the
cobalt are then directed into a narrow beam. During
analysis, the sample sits between the incoming beam
on one side and the instrument’s detector on the other.
The detector is a charge-coupled device like the ones in
electronic cameras, but sensitive to X-ray wavelengths
and cooled to minus 76 degrees Fahrenheit (minus 60
degrees Celsius).
Each CheMin analysis of a sample requires up to
10 hours of accumulating data while the X-rays are
hitting the sample. The time may be split into two or
more Martian nights of operation.
The X-ray diffraction data show the angles at which the
primary X-rays from the beam are deflected and the
intensity at each angle. The detector also reads secondary X-rays emitted by the sample itself when it is excited
by the primary X-rays. This is the X-ray fluorescence
information. Different elements emit secondary X-rays at
different frequencies. CheMin’s X-ray fluorescence capability can detect elements with an atomic number greater
than 11 (sodium) in the periodic table.
Instruments that previous missions to Mars have used
for studying Martian minerals have not been able to
provide definitive identification of all types of minerals.
CheMin will be able to do so for minerals present in
samples above minimal detection limits of about 3 percent of the sample composition. The instrument will also
indicate the approximate concentrations of different minerals in the sample. X-ray fluorescence can add information about the ratio of elements in types of minerals with
variable elemental composition, such as the proportion
of iron to magnesium in iron magnesium silicate (olivine).
It can also aid in identifying non-crystalline ingredients in
a sample, such as volcanic glass.
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Each type of mineral forms under a certain set of
environmental conditions: the chemistry present (including water), the temperature and the pressure. Thus,
CheMin’s identification of minerals will provide information about the environment at the time and place where
the minerals in the rocks and soils formed or were altered. Some minerals the instrument might detect, such
as phosphates, carbonates, sulfates and silica, can
help preserve biosignatures. Whether or not the mission
determines that the landing area has offered a favorable
habitat for life, the inventory of minerals identified by
CheMin will provide information about processes in the
evolution of the planet’s environment.
David Blake, an expert in cosmochemistry and exobiology at NASA’s Ames Research Center, Moffett Field,
Calif., is the principal investigator for CheMin. He began
work in 1989 on a compact X-ray diffraction instrument
for use in planetary missions. His work with colleagues
has resulted in commercial portable instruments for use
in geological field work on Earth, as well as the CheMin
investigation. The spinoff instruments have found applications in screening for counterfeit pharmaceuticals in
developing nations and in analyzing archaeological finds.
NASA Ames Research Center won the 2010 Commercial Invention of the Year Award from NASA for the
tuning-fork powder vibration system used on CheMin.
Blake and Philippe Sarazin of inXitu Inc., Campbell,
Calif., a co-investigator on the CheMin team, developed
the technology while Sarazin was working as a postdoctoral fellow at Ames.

SAM’s analytical tools fit into a microwave-oven-size box
inside the front end of the rover. While it is the biggest
of the 10 instruments on Curiosity, this tightly packed
box holds instrumentation that would take up a good
portion of a laboratory room on Earth. One focus during
development was power efficiency. For example, the
two ovens can heat powdered samples to about 1,800
degrees Fahrenheit (1,000 degrees Celsius) drawing a
maximum power of just 40 watts. More than a third of a
mile (more than 600 meters) of wiring is inside SAM.
SAM can detect a fainter trace of organics and identify
a wider variety of them than any instrument yet sent to
Mars. It also can provide information about other ingredients of life and clues to past environments.
One of SAM’s tools, a mass spectrometer like those
seen in many TV crime-solving laboratories, identifies
gases by the molecular weight and electrical charge of
their ionized states. It will check for several elements
important for life as we know it, including nitrogen, phosphorous, sulfur, oxygen, hydrogen and carbon.
Another tool, a tunable laser spectrometer, uses absorption of light at specific wavelengths to measure concentrations of methane, carbon dioxide and water vapor.
It also identifies the proportions of different isotopes in
those gases. Isotopes are variants of the same element
with different atomic weights, such as carbon-13 and
carbon-12, or oxygen-18 and oxygen-16. Ratios of
isotopes can be signatures of planetary processes,
such as how Mars might have lost much of its former
atmosphere.

Sample Analysis at Mars (SAM)
The Sample Analysis at Mars investigation, or SAM, will
use a suite of three analytical tools inside Curiosity to
study chemistry relevant to life. One key job is checking for carbon-based compounds that on Earth are
molecular building blocks of life. It will also examine the
chemical state of other elements important for life, and
it will assess ratios of different atomic weights of certain
elements for clues about planetary change and ongoing
processes.
SAM will examine gases from the Martian atmosphere
and gases that ovens and solvents pull from powdered
rock and soil samples. Curiosity’s robotic arm will deliver
the powdered samples to one of two inlet funnels on the
rover deck. Atmospheric samples enter through filtered
inlet ports on the side of the rover.

Mars Science Laboratory Landing

The suite’s third analytical tool, a gas chromatograph,
separates different gases from a mixture to aid identification. It detects organic compounds exiting a capillary
column, and then it feeds the separated fractions to the
mass spectrometer for a more definitive identification.
SAM also includes a sample manipulation system, and
a chemical separation and processing laboratory to support the analytical tools. The sample manipulation system maneuvers 74 sample cups, each about one-sixth
of a teaspoon (0.78 cubic centimeter) in volume. The
chemical separation and processing laboratory includes
pumps, tubing, carrier-gas reservoirs, pressure monitors,
ovens, temperature monitors and other components.
Fifty-two specially designed microvalves direct the flow of
gas through the system. Two soft-drink-can-size vacuum
pumps rotate 100,000 times per minute to allow all three
instruments to operate at their optimal pressures.
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SAM’s analysis of material from Martian rocks or soils
begins after powder collected and processed by tools
on the arm is dropped into one of SAM’s two solid-sample inlets while the inlet’s protective cover is open. The
inlet tubes are highly polished funnels that vibrate to get
the powder to fall into a reusable sample cup.
Fifty-nine of the instrument’s 74 cups are quartz that
can be heated to very high temperatures. The sample
manipulation system pushes the quartz cup holding
the powder into an oven that heats it to about 1,800
degrees Fahrenheit (about 1,000 degrees Celsius). That
process releases gas from the sample at various temperatures, depending on the chemistry of the sample.
The mass spectrometer measures the release continuously. Some of the gas goes to the tunable laser spectrometer for measurement of isotopes. Some goes to
a trap that concentrates any organics, then to the gas
chromatograph and mass spectrometer. After use, the
quartz cup can be baked to prepare it for re-use with
another sample.
Six of the cups hold calibration solids. SAM also carries
samples of gases for calibration.
Nine of the cups are for using a solvent method called
derivatization, rather than high temperature, to pull gases
from samples of Martian rocks and soils. If the mission finds a site rich in organics, this method could be
used to identify larger and more reactive organic molecules than is possible with the high-heat method. Each
derivatization cup contains a mixture of a solvent and a
chemical that, after it reacts with a compound of interest,
turns it into a more volatile compound that can be separated in the gas chromatograph. These chemicals are
entirely sealed in with a foil cover. For analysis of sample
powder from a Martian rock or soil by this method, the
sample manipulation system punctures the foil and adds
the powder to the liquid in the cup, and the oven heats
the sample to a modest temperature to let the reactions
proceed rapidly.
Curiosity’s “follow the carbon” investigation of organic
compounds begins as a check for whether any are present. Although organic molecules are not, in themselves,
evidence of life, life as we know it cannot exist without
them. Their presence would be important evidence
both about habitability and about the site’s capability for
preserving evidence of life. Meteorites bearing organic
compounds have pelted Mars, as well as Earth, for
billions of years. Uncertainty remains, however, about

Mars Science Laboratory Landing

whether any organics close enough to the surface for
Curiosity to reach them can persist in the harsh conditions there without the carbon in them transforming into
a more polymerized state.
NASA’s investigation of organics on Mars began with
the twin Viking landers in 1976. The original reports from
Viking came up negative for organics. SAM renews the
search with three advantages.
The first is Curiosity’s access. Mars is diverse, not
uniform. Copious information gained from Mars orbiters
in recent years has enabled the choice of a landing site
with favorable attributes, such as exposures of clay and
sulfate minerals good at entrapping organic chemicals.
Mobility helps too, especially with the aid of high-resolution geologic mapping generated from orbital observations. The stationary Viking landers could examine only
what their arms could reach. Curiosity can use mapped
geologic context as a guide in its mobile search for
organics and other clues about habitable environments.
Additionally, SAM will be able to analyze samples from
more protected interiors of rocks drilled into by Curiosity,
rather than being restricted to soil samples, as Viking
was.
Second, SAM has improved sensitivity, with a capability
to detect organic compounds at parts per billion levels
over a wider mass range of molecules and after heating
samples to a higher temperature.
Third, the derivatization method for assessing organics in some SAM samples can reveal a wider range of
organic compounds than was possible with the Viking
experiment. In doing so, it can also check a recent hypothesis that a reactive chemical recently discovered in
Martian soil — perchlorate — may have masked organics in soil samples baked during Viking tests.
If SAM does not detect any organics, that would be
useful information about the unfavorable conditions for
life near the Martian surface. Future missions might look
deeper.
If SAM does detect organics, one challenge will be
to confirm that these molecules are truly Martian, not
stowaways from Earth carried to Mars on Curiosity. The
rover carries five encapsulated bricks of organic check
material to enable control experiments. The check
material is a silicon-dioxide ceramic laced with small
amounts of synthetic fluorinated organic chemicals not

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found in nature on Earth and not expected on Mars.
The basic control experiment will collect a powdered
sample from an organic check brick with the same
drilling, processing and delivery system used for collecting samples from Martian rocks, and then will analyze the sample with SAM. If SAM finds any organics
other than the fluorine-containing markers, they will be
stowaway suspects. If only the markers are detected,
that would verify that organic-detection is working and
that the sample-acquisition and handling pathway has
passed a test of being clean of organic stowaways.
That control experiment can assess characteristics of
organic contamination at five different times during the
mission, using the five bricks of organic check material.
Researchers have a variety of tools at their disposal to
distinguish organic compounds present in Mars soils
and rocks from trace levels of organic compounds from
Earth that might make their way into these samples.
If organic chemicals are present in Martian samples,
SAM’s inventory of the types and mixtures may provide
clues to their origin. For example, organics delivered
by meteorites without involvement of biology come
with more random chemical structures than the patterns seen in mixtures of organic chemicals produced
by organisms. Patterns, such as a predominance of
molecules with an even number of carbon atoms, could
be suggestive of biological origin. The derivatization
process also allows searching for specific classes of
organics with known importance to life on Earth. For
example, it can identify amino acids, the chain links of
proteins. While these clues may not add up to a definitive case either for or against biological origin, they could
provide important direction for future missions.
Methane is one of the simplest organic molecules.
Observations from Mars orbit and from Earth in recent
years have suggested transient methane in Mars’ atmosphere, which would mean methane is being actively
added and then removed from the atmosphere of Mars.
With SAM’s tunable laser spectrometer, researchers will
check to confirm whether methane is present, monitor any changes in its concentration, and look for clues
about whether Mars methane is produced by biological
activity or by processes that do not require life.
The principal investigator for SAM is Paul Mahaffy,
a chemist at NASA’s Goddard Space Flight Center,
Greenbelt, Md. He is a veteran of using spacecraft
instruments to study planetary atmospheres. Mahaffy
has coordinated work of hundreds of people in several

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states and Europe to develop, build and test SAM after
NASA selected his team’s proposal for it in 2004.
NASA Goddard Space Flight Center built and tested
SAM. France’s space agency, Centre National d’Études
Spatiales, provided support to French researchers who
developed SAM’s gas chromatograph. NASA’s Jet
Propulsion Laboratory, Pasadena, Calif., provided the
tunable laser spectrometer. Honeybee Robotics, New
York, designed SAM’s sample manipulation system.
Rover Environmental Monitoring Station (REMS)
The Rover Environmental Monitoring Station, or REMS,
will record information about daily and seasonal changes in Martian weather.
This investigation will assess wind speed, wind direction,
air pressure, relative humidity, air temperature, ground
temperature and ultraviolet radiation. Operational plans
call for taking measurements for at least five minutes
every hour of the full-Martian-year (98-week) mission.
Spain provided this instrument for the Mars Science
Laboratory.
Information about wind, temperatures and humidity
comes from electronic sensors on two finger-like booms
extending horizontally from partway up the main vertical
mast holding the ChemCam laser and the Mastcam.
Each of the booms holds a sensor for recording air temperature and three sensors for detecting air movement
in three dimensions. Placement of the booms at an
angle of 120 degrees from each other enables calculating the velocity even when the main mast is blocking the
wind from one direction. The boom pointing toward the
front of the rover, Boom 2, also holds the humidity sensor inside a downward-tilted protective cylinder. Boom
1, pointing to the side and slightly toward the rear, holds
an infrared sensor for measuring ground temperature.
The pressure sensor sits inside the rover body, connected to the external atmosphere by a tube to a small,
dust-shielded opening on the deck. Electronics controlling REMS are also inside the rover body.
The ultraviolet sensor is on the rover deck. It measures
six different wavelength bands in the ultraviolet portion of the electromagnetic spectrum, including wavelengths also monitored from above by NASA’s Mars
Reconnaissance Orbiter. No previous mission to the

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surface of Mars has measured the full ultraviolet spectrum of radiation.
The REMS investigation will strengthen understanding
about the global atmosphere of Mars and contribute to
the mission’s evaluation of habitability.
The data will provide a way to verify and improve atmosphere modeling based mainly on observations from
Mars orbiters. For example, significant fractions of the
Martian atmosphere freeze onto the ground as a south
polar carbon-dioxide ice cap during southern winter and
as a north polar carbon-dioxide ice cap during northern
winter, returning to the atmosphere in each hemisphere’s
spring. At Curiosity’s landing site, far from either pole,
REMS will check whether seasonal patterns of changing
air pressure fit the existing models for effects of the coming and going of polar carbon-dioxide ice.
Monitoring ground temperature with the other weather
data could aid in assessment of whether conditions have
been favorable for microbial life. Even in the extremely
low-humidity conditions anticipated in the landing area,
the combination of ground temperature and humidity
information could provide insight about the interaction of
water vapor between the soil and the atmosphere. If the
environment supports, or ever supported, any underground microbes, that interaction could be crucial.
Ultraviolet radiation can also affect habitability. The ultraviolet measurements by REMS will allow scientists to
better predict the amount of ultraviolet light that reaches
Mars’ surface globally in the present and past. Ultraviolet
light is destructive to organic material and the reason
that sunscreen is worn on Earth.
The principal investigator for REMS is Javier GómezElvira, an aeronautical engineer with the Center for
Astrobiology (Centro de Astrobiología), Madrid, Spain.
The center is affiliated with the Spanish National
Research Council (Consejo Superior de Investigaciones
Científicas) and the National Institute for Aerospace
Technology (Instituto Nacional de Técnica Aerospacial).
Spain’s Ministry of Science and Innovation (Ministerio de
Ciencia e Innovación) and Spain’s Center for Industrial
Technology Development (Centro para el Desarrollo
Tecnológico Industrial) supplied REMS. The Finnish
Meterological Insitute developed the pressure sensor.
To develop the instrument and prepare for analyzing
the data it will provide, Spain has assembled a team of
about 40 researchers — engineers and scientists.
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The team plans to post daily weather reports from
Curiosity. Air temperature around the rover mast will
likely drop to about minus 130 degrees Fahrenheit
(about minus 90 degrees Celsius) on some winter nights
and climb to about minus 22 Fahrenheit (about minus
30 Celsius) during winter days. In warmer seasons,
afternoon air temperature could reach a balmy
32 Fahrenheit (0 degrees Celsius).
Radiation Assessment Detector (RAD)
The Radiation Assessment Detector, or RAD, investigation on Curiosity monitors high-energy atomic and
subatomic particles coming from the sun, from distant
supernovae and other sources. These particles constitute naturally occurring radiation that could be harmful
to any microbes near the surface of Mars or to astronauts on a future Mars mission.
RAD’s measurements will help fulfill the Mars Science
Laboratory mission’s key goals of assessing whether
Curiosity’s landing region has had conditions favorable for life and for preserving evidence about life. This
investigation also has an additional job. Unlike the rest
of the mission, RAD has a special task and funding from
the part of NASA that is planning human exploration
beyond Earth orbit. It will aid design of human missions
by reducing uncertainty about how much shielding
from radiation future astronauts will need. RAD is making measurements during the trip from Earth to Mars,
supplementing those it will make during Curiosity’s
roving on Mars, because radiation levels in interplanetary space are also important in the design of human
missions.
The 3.8-pound (1.7-kilogram) RAD instrument has a
wide-angle telescope looking upward from the hardware’s position inside the left-front area of the rover.
The telescope has detectors for charged particles with
masses up to that of an iron ion. RAD can also detect neutrons and gamma rays coming from the Mars
atmosphere above or the Mars surface material below
the rover.
Galactic cosmic rays make up one type of radiation that
RAD monitors. These are a variable shower of charged
particles coming from supernova explosions and other
events extremely far from our solar system.
The sun is the other main source of energetic particles
that this investigation detects and characterizes. The
sun spews electrons, protons and heavier ions in “solar
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particle events” fed by solar flares and ejections of matter from the sun’s corona. Astronauts might need to
move into havens with extra shielding on an interplanetary spacecraft or on Mars during solar-particle events.
Earth’s magnetic field and atmosphere provide effective
shielding against the possible deadly effects of galactic cosmic rays and solar particle events. Mars lacks
a global magnetic field and has only about 1 percent
as much atmosphere as Earth does. Just to find highenough radiation levels on Earth for checking and calibrating RAD, the instrument team needed to put it inside
major particle-accelerator research facilities in the United
States, Europe, Japan and South Africa.
The radiation environment at the surface of Mars has
never been fully characterized. NASA’s Mars Odyssey
orbiter, which reached Mars in 2001, assessed radiation
levels above the Martian atmosphere with an investigation named the Mars Radiation Environment Experiment.
Current estimates of the radiation environment at the
surface rely on modeling of how the thin atmosphere
affects the energetic particles, but uncertainty in the
modeling remains large. A single energetic particle hitting
the top of the atmosphere can break up into a cascade
of lower-energy particles that might be more damaging
than a single high-energy particle.
In addition to its precursor role for human exploration,
RAD will contribute to the mission’s assessment of
Mars’ habitability for microbes and search for organics.
Radiation levels probably make the surface of modern
Mars inhospitable for microbial life and would contribute to the breakdown of any near-surface organic
compounds. The measurements from RAD will feed
calculations of how deeply a possible future robot on a
life-detection mission might need to dig or drill to reach a
microbial safe zone. For assessing whether the surface
radiation environment could have been hospitable for
microbes in Mars’ distant past, researchers will combine
RAD’s measurements with estimates of how the activity
of the sun and the atmosphere of Mars have changed in
the past few billion years.
Radiation levels in interplanetary space vary on many
time scales, from much longer than a year to shorter
than an hour. Assessing the modern radiation environment on the surface will not come from a one-time set of
measurements. Operational planning for Curiosity anticipates that RAD will record measurements for 15 minutes
of every hour throughout the prime mission, on steady

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watch so that it can catch any rare but vitally important
solar particle events.
The first science data from the mission have come from
RAD’s measurements during the trip from Earth to Mars.
These en-route measurements are enabling correlations
with instruments on other spacecraft that monitor solar
particle events and galactic cosmic rays in Earth’s neighborhood and also are yielding data about the radiation
environment farther from Earth.
RAD’s principal investigator is physicist Don Hassler
of the Southwest Research Institute’s Boulder, Colo.,
branch. His international team of co-investigators
includes experts in instrument design, astronaut safety,
atmospheric science, geology and other fields.
Southwest Research Institute in Boulder and in San
Antonio, together with Christian Albrechts University in
Kiel, Germany, built RAD with funding from the NASA
Exploration Systems Mission Directorate and Germany’s
national aerospace research center, Deutsches Zentrum
für Luft- und Raumfahrt.
Measurements of ultraviolet radiation by Curiosity’s
Rover Environmental Monitoring Station will supplement
RAD’s measurements of other types of radiation.
Dynamic Albedo of Neutrons (DAN)
The Dynamic Albedo of Neutrons investigation, or DAN,
can detect water bound into shallow underground minerals along Curiosity’s path.
The DAN instrument shoots neutrons into the ground
and measures how they are scattered, giving it a high
sensitivity for finding any hydrogen to a depth of about
20 inches (50 centimeters) directly beneath the rover.
The Russian Federal Space Agency contributed DAN
to NASA as part of a broad collaboration between the
United States and Russia in the exploration of space.
The instrument can be used in reconnaissance to identify places for examination with Curiosity’s other tools.
Also, rock formations that Curiosity’s cameras view at
the surface may be traced underground by DAN, extending scientists’ understanding of the geology.
DAN will bring to the surface of Mars an enhancement
of nuclear technology that has already detected Martian

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water from orbit. “Albedo” in the investigation’s name
means reflectance — in this case, how high-energy
neutrons injected into the ground bounce off of atomic
nuclei in the ground. Neutrons that collide with hydrogen atoms bounce off with a characteristic decrease in
energy, like one billiard ball hitting another. By measuring
the energies of the reflected neutrons, DAN can detect
the fraction that was slowed in these collisions, and
therefore the amount of hydrogen.
Oil prospectors use this technology in instruments
lowered down exploration holes to detect the hydrogen
in petroleum. Space explorers have adapted it for missions to the moon and Mars, where most hydrogen is in
water ice or in water-derived hydroxyl ions.
DAN Principal Investigator Igor Mitrofanov of Space
Research Institute, Moscow, is also the principal investigator for a Russian instrument on NASA’s Mars
Odyssey orbiter, the high-energy neutron detector,
which measures high energy of neutrons coming
from Mars. In 2002, it and companion instruments on
Odyssey detected hydrogen interpreted as abundant
underground water ice close to the surface at high
latitudes.
The neutron detectors on Odyssey rely on galactic cosmic rays hitting Mars as a source of neutrons. DAN can
work in a passive mode relying on cosmic rays, but it
also has its own pulsing neutron generator for an active
mode of shooting high-energy neutrons into the ground.
In active mode, it is sensitive enough to detect water
content as low as one-tenth of 1 percent in the ground
beneath the rover.
The neutron generator is mounted on Curiosity’s right
hip, a pair of neutron detectors on the left hip. Pulses
last about 1 microsecond and repeat as frequently as
10 times per second. The detectors measure the flow of
moderated neutrons with different energy levels returning from the ground, and their delay times. Neutrons
that arrive later may indicate water buried beneath a
drier soil layer. The generator will be able to emit a total
of about 10 million pulses during the mission, with about
10 million neutrons at each pulse.
The most likely form of hydrogen in the ground of the
landing area is hydrated minerals. These are minerals
with water molecules or hydroxyl ions bound into the
crystalline structure of the mineral. They can tenaciously
retain water from a wetter past when all free water has
gone. DAN may also detect water that comes and
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goes with the Martian seasons, such as soil moisture
that varies with the atmospheric humidity. Together
with Curiosity’s cameras and weather station, DAN will
observe how the sparse water cycle on Mars works in
the present. DAN also could detect any water ice in the
shallow subsurface, a low probability at Curiosity’s Gale
Crater landing site.
Operational planning anticipates using DAN during short
pauses in drives and while the rover is parked. It will
check for any changes or trends in subsurface hydrogen content from place to place along the traverse.
Russia’s Space Research Institute developed the DAN
instrument in close cooperation with the N.L. Dukhov
All-Russia Research Institute of Automatics, Moscow,
and the Joint Institute of Nuclear Research, Dubna.
Mars Descent Imager (MARDI)
During the final few minutes of Curiosity’s flight to the
surface of Mars, the Mars Descent Imager, or MARDI,
will record a full-color video of the ground below. This
will provide the Mars Science Laboratory team with information about the landing site and its surroundings, to
aid interpretation of the rover’s ground-level views and
planning of initial drives. Hundreds of the images taken
by the camera will show features smaller than what can
be discerned in images taken from orbit.
The video will also give fans worldwide an unprecedented sense of riding a spacecraft to a landing on Mars.
MARDI will record the video on its own 8-gigabyte flash
memory at about four frames per second and close to
1,600 by 1,200 pixels per frame. Thumbnails and a few
samples of full-resolution frames will be transmitted to
Earth in the first few days after landing. The nested set
of images from higher altitude to ground level will enable
pinpointing of Curiosity’s location. The pace of sending
the rest of the frames for full-resolution video will depend on sharing priority with data from the rover’s other
investigations.
The full video — available first from the thumbnails in
YouTube-like resolution and later in full detail — will
begin with a glimpse of the heat shield falling away from
beneath the rover. The first views of the ground will
cover an area several kilometers (a few miles) across.
Successive frames taken as the vehicle descends will
close in and cover successively smaller areas. The video
will likely nod up and down to fairly large angles owing
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to parachute-induced oscillations. Its roll clockwise and
counterclockwise will be smaller, as thrusters on the
descent stage control that motion. When the parachute
is jettisoned, the video will show large angular motions
as the descent vehicle maneuvers to avoid re-contacting
the back shell and parachute. Rocket engine vibration
may also be seen. A few seconds before landing, the
rover will be lowered on tethers beneath the descent
stage, and the video will show the relatively slow approach to the surface. The final frames, after landing, will
cover a bath-towel-size patch of ground under the frontleft corner of the rover.
Besides the main objective of providing geologic context
for the observations and operations of the rover during
the early part of mission on Mars, MARDI will provide
insight about Mars’ atmosphere. Combining information from the descent images with information from the
spacecraft’s motion sensors will allow for calculating
wind speeds affecting the spacecraft on its way down,
an important atmospheric science measurement. The
descent data will later aid in designing and testing future
landing systems for Mars that could add more control for
hazard avoidance.
Throughout Curiosity’s mission on Mars, MARDI will offer
the capability to obtain images of ground beneath the
rover at resolutions down to 0.06 inch (1.5 millimeters)
per pixel, for precise tracking of its movements or for
geologic mapping. The science team will decide whether
or not to use that capability. Each day of operations on
Mars will require choices about how to budget power,
data and time.
Malin Space Science Systems, San Diego, provided
MARDI, as well as three other cameras on Curiosity:
the Mast Camera pair and the Mars Hand Lens Imager.
Michael Malin is the principal investigator for MARDI,
which shares a unified imaging-science team with the
other two instruments from his company.
MARDI consists of two parts: the wide-angle camera
mounted toward the front of the port side of Curiosity
and a digital electronics assembly inside the warm
electronics box of the rover’s chassis. The instrument’s
electronics, including the 1,600-pixel-by-1,200-pixel
charge-coupled device (CCD) in the camera, are the
same design as used in the Mast Camera and Mars
Hand Lens Imager.
The rectangular field of the CCD sits within a 90-degree
circular field of view of the camera lens, yielding a reMars Science Laboratory Landing

corded field of view of 70 degrees by 55 degrees. From
an altitude of 1.2 miles (2 kilometers) during descent that
will provide a resolution of about 5 feet (1.5 meters) per
pixel, though swinging and shaking of the spacecraft will
likely blur some frames despite a fast (1.3 millisecond)
exposure time.
Color information comes from a Bayer pattern filter array, as used in many commercial digital cameras. The
camera’s CCD is covered with a grid of green, red and
blue filters so that each exposure samples all of those
colors throughout the field of view. A piece of white
material on the inside surface of the heat shield will serve
as a white-balance target as the heat shield falls away at
the beginning of the recorded descent video.
Malin Space Science Systems also provided descent
imagers for NASA’s Mars Polar Lander, launched in
1999, and Phoenix Mars Lander, launched in 2007.
However, the former craft was lost during its landing and
the latter did not use its descent imager due to concern
about the spacecraft’s data-handling capabilities during
crucial moments just before landing.
Engineering Instruments
Some of the tools that primarily serve engineering
purposes on Mars Science Laboratory will also generate information useful to scientific understanding about
Mars. Most of these, including the engineering cameras
and the drill, are described in the spacecraft section
of this document. One set of instruments carried on
the heat shield of the spacecraft’s entry vehicle serves
specifically to gather data about the Martian atmosphere
and performance of the heat shield for use in designing future systems for descending through planetary
atmospheres.
MSL Entry, Descent and Landing Instrument
(MEDLI) Suite
A set of sensors attached to the heat shield of the Mars
Science Laboratory (MSL) is collectively named the MSL
Entry, Descent and Landing Instrument (MEDLI) Suite.
MEDLI will take measurements eight times per second
during the period from about 10 minutes before the vehicle enters the top of the Martian atmosphere until after
the parachute has opened, about four minutes after
entry. The measurements will be analyzed for information about atmospheric conditions and performance of
the entry vehicle.

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Due to the mass of the entry vehicle (5,359 pounds, or
2,431 kilograms, after jettison of the spacecraft’s cruise
stage), the diameter of its heat shield (14.8 feet, or 4.5
meters) and the speed at which the vehicle will enter
the atmosphere (about 13,200 mph, or 5,900 meters
per second), the heating and stress on the heat shield
will be the highest ever for an entry vehicle at Mars.
Experience gained with this mission will aid planning for
potential future missions that could be even heavier and
larger, such as would be necessary for a human mission
to Mars.
Models of the Martian atmosphere, heating environments, vehicle aerodynamics, and heat-shield performance, among other factors, were employed in
designing the Mars Science Laboratory entry vehicle.
Uncertainties in these parameters must also be modeled. To account for those uncertainties, the design
incorporates large margins for success. The margin
comes at a cost of additional mass. The goal of MEDLI
is to better quantify these atmospheric entry characteristics and possibly reduce unnecessary mass on future
Mars missions, by collecting data on the performance
of the Mars Science Laboratory entry vehicle during its
atmospheric entry and descent.

Mars Science Laboratory Landing

MEDLI consists of seven pressure sensors (Mars entry
atmospheric data system sensor, or MEADS), seven
plugs with multiple temperature sensors (Mars integrated sensor plug, or MISP) and a support electronics
box. Data from the entry vehicle’s inertial measurement
unit, which senses changes in velocity and direction,
will augment the MEDLI data. Each of the temperaturesensing plugs has thermocouples to measure temperatures at four different depths in the heat shield’s thermal
protection tiles, plus a sensor to measure the rate at
which heat shield material is removed due to atmospheric entry heating.
Analysis of data from the pressure sensors and inertial measurement unit will provide an altitude profile of
atmospheric density and winds, plus information about
pressure distribution on the heat shield surface, orientation of the entry vehicle and velocity. Data from the temperature sensors will be used to evaluate peak heating,
distribution of heating over the heat shield, turbulence
in the flow of gas along the entry vehicle’s surface, and
in-depth performance of the heat shield material.
NASA’s Exploration Systems Mission Directorate (which
has responsibility for planning human missions beyond Earth orbit) and Aeronautics Research Mission
Directorate (which invests in fundamental research
of atmospheric flight) have funded MEDLI. F. McNeil
Cheatwood of NASA’s Langley Research Center,
Hampton, Va., is the principal investigator for MEDLI.
Deputy principal investigator is Michael Wright of
NASA’s Ames Research Center, Moffett Field, Calif.

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Mission Overview
NASA’s Mars Science Laboratory mission will put a
mobile laboratory onto the surface inside Gale Crater on
Mars and use it to investigate the area’s past and present environments. The landing will use active guidance
for improved landing accuracy and a sky crane maneuver for the final descent to the surface. The mission’s
mobile laboratory is the Curiosity rover, equipped with
10 science investigations and a robotic arm that can drill
into rocks, scoop up soil and deliver samples to internal
analytical instruments. The mission will assess whether
the area has offered conditions favorable for life and
whether conditions were favorable for preserving a
rock record of evidence about whether life has existed
there. The Curiosity rover has the capability to drive for
12.4 miles (20 kilometers) or more during a mission lasting one Martian year (98 weeks).
Launch
A two-stage Atlas V 541 launch vehicle lofted the Mars
Science Laboratory spacecraft from Launch Complex
41 at Cape Canaveral Air Force Station, Fla. at 10:02
EST on Nov. 26, 2011. The rocket was produced by
United Launch Alliance, a joint venture of Boeing Co.
and Lockheed Martin Corp. The three numbers in the
541 designation signify a payload fairing, or nose cone,
approximately 5 meters (16.4 feet) in diameter; four
solid-rocket boosters fastened alongside the central
common core booster; and a one-engine Centaur upper stage. The launch was on the second day into a
launch period that went from Nov. 25 through Dec.18. It
was moved from Nov. 25 to allow time for removal and
replacement of a flight-termination system battery.
The launch successfully put the Mars Science Laboratory mission on its way toward Mars.
Curiosity’s Launch Period
As Earth and Mars race around the sun, with Earth
on the inside track, Earth laps Mars about once every
26 months. Launch opportunities to Mars occur at the
same frequency, when the planets are configured so
that a spacecraft launched from Earth will move outward and intersect with Mars in its orbit several months
later. This planetary clockwork, plus the launch vehicle’s
power, the spacecraft’s mass, and the desired geometry
and timing for the landing on Mars were all factors in
determining the range of possible launch dates.
Mars Science Laboratory Landing

One priority for choice of a launch period within the
range of possible dates was scheduling the landing to
occur when NASA orbiters at Mars are passing over the
landing site. Such scheduling aims to allow the orbiters
to receive radio transmissions from the Mars Science
Laboratory spacecraft during its descent through the
atmosphere and landing. If the landing is not successful,
this strategy will provide more information than would be
possible with the alternative of relying on transmissions
from the Mars Science Laboratory directly to Earth.
Landing on Mars is always difficult, with success uncertain. After an unsuccessful attempted Mars landing by
Mars Polar Lander in 1999 without definitive information
on the cause of the mishap, NASA set a high priority on
communication during subsequent Mars landings.
Interplanetary Cruise and Approach to Mars
The Mars Science Laboratory spacecraft is flying for
254 days to get from Earth to Mars. Most of this period
is the cruise phase of the mission. The final 45 days are
the approach phase.
Cruise Phase
Key activities during cruise included checkouts of the
spacecraft and its science instruments, tracking of
the spacecraft, attitude adjustments for changes in
pointing of the solar array and antennas, and planning
and execution of maneuvers to adjust its trajectory.
Opportunities for additional trajectory correction maneuvers, if needed, are scheduled during the approach
phase.
During cruise and approach phases, the spacecraft is
spin-stabilized at about two rotations per minute. The
attitude of the spacecraft’s axis of rotation relative to
Earth and the sun affects telecommunications, power
and thermal performance. The plane of the solar array
on the cruise stage is perpendicular to that axis, and the
two antennas used during cruise are pointed in line with
that axis, in the direction the array faces. The parachute
low-gain antenna, used during the first two months of
the trip when the angle between the sun and Earth was
relatively large, works at a wider range of pointing angles
than possible with the medium-gain antenna, which is
mounted on the cruise stage.

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Thrusters on the cruise stage are fired to adjust the
spacecraft’s flight path during trajectory correction maneuvers. The first two trajectory corrections, on Jan. 11
and March 26, removed most of the launch-day trajectory’s intentional offset. That intentional offset away from
Mars was a precaution to avoid the possibility of hitting
Mars with the launch vehicle’s upper stage. Prior to the
first maneuver, the Mars Science Laboratory spacecraft
was on a course that would have missed Mars by about
25,000 miles (about 40,000 kilometers) and sped past
the planet about 14 hours later than the targeted arrival
time.
The Jan. 11 trajectory correction used about 59 minutes
of thruster firings, changing the velocity of the spacecraft
by about 12.3 miles per hour (5.5 meters per second).

Schematic view of Mars Science Laboratory cruise phase
from Earth to Mars. Dates are given in Universal Time.

Mars Science Laboratory Landing

It removed most of the intentional offset, putting the
spacecraft on a course missing the target point in space
and time by about 3,000 miles (5,000 kilometers) and
20 minutes. The March 26 maneuver used about nine
minutes of thruster firings to achieve a velocity change
of 2 miles per hour (0.9 meters per second). It put the
spacecraft on a Mars-intersect course for the first time.
For the mission’s third scheduled opportunity for a
trajectory correction, on June 26, the navigation team
designed a maneuver to put the spacecraft on course
to reach the top of Mars’ atmosphere at the right place,
right angle and right time. This third trajectory correction
used 40 seconds of thruster firings to adjust the location
where the spacecraft will enter Mars’ atmosphere by
about 125 miles (about 200 kilometers) and to advance
the time of entry by about 70 seconds.

Six trajectory correction maneuvers (TCMs) are scheduled
during the voyage from Earth to Mars. Arrival at Mars will be
Aug. 6, 2012, Universal Time.
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Approach Phase

Entry, Descent and Landing

The final 45 days leading up to the Mars landing are the
approach phase. This phase includes opportunities for
up to three additional trajectory correction maneuvers.
These remaining opportunities are on July 29, Aug. 4
and Aug. 5, Universal Time (July 28, Aug 3 and Aug. 5,
Pacific Time), with an additional make-up time available
for the Aug. 4 maneuver if that opportunity is not used.
Factors that could lead to the need for final-week correction of trajectory predictions include calculations of
the effects of solar-radiation pressure and the effects of
thruster firings used to keep spacecraft antennas pointed toward Earth.

The intense period called the entry, descent and landing
(EDL) phase of the mission begins when the spacecraft
reaches the top of the Martian atmosphere, traveling at
about 13,200 miles per hour (5,900 meters per second). EDL ends about seven minutes later with the rover
stationary on the surface. From just before jettison of
the cruise stage, 10 minutes before entry, to the cutting
of the sky crane bridle, the spacecraft goes through six
different vehicle configurations and fires 76 pyrotechnic
devices, such as releases for parts to be separated or
deployed.

Trajectory correction maneuvers combine assessments
of the spacecraft’s trajectory with calculations of how to
use the eight thrusters on the cruise stage to alter the
trajectory. Navigators’ assessments of the spacecraft’s
trajectory use three types of tracking information from
ground antennas of NASA’s Deep Space Network in
California, Spain and Australia. One method is ranging,
which measures the distance to the spacecraft by timing
precisely how long it takes for a radio signal to travel to
the spacecraft and back. A second is Doppler, which
measures the spacecraft’s speed relative to Earth by
the amount of shift in the pitch of a radio signal from the
craft. A newer method, called delta differential one-way
range measurement, adds information about the location
of the spacecraft in directions perpendicular to the line
of sight. For this method, pairs of antennas on different continents simultaneously receive signals from the
spacecraft, and then the same antennas observe natural
radio waves from a known celestial reference point, such
as a quasar, which serves as a navigation reference
point.
Some activities during the final five days of the approach
phase will prepare the spacecraft for its atmospheric
entry, descent and landing. These activities include preheating of some components and enabling others. The
schedule includes four opportunities to update parameters for the autonomous software controlling events
during the entry, descent and landing. Some parameters
give the spacecraft’s onboard computer knowledge
about where the vehicle is relative to Mars. Other parameters may be updated based on observations by Mars
Reconnaissance Orbiter of the Red Planet’s variable atmospheric conditions in the week before landing. These
updates can fine-tune the spacecraft’s autonomous
controls for its descent through the atmosphere.

Mars Science Laboratory Landing

The top of Mars’ atmosphere is a gradual transition to
interplanetary space, not a sharp boundary. The atmospheric entry interface point — the navigators’ aim
point during the flight to Mars — is set at 2,188.6 miles
(3,522.2 kilometers) from the center of Mars. That altitude is 81.46 miles (131.1 kilometers) above the ground
elevation of the landing site at Gale Crater, though the
entry point is not directly above the landing site. While
descending from that altitude to the surface, the spacecraft will also be traveling eastward relative to the Mars
surface, covering a ground-track distance of about
390 miles (about 630 kilometers) between the atmospheric entry point and the touchdown target.
Ten minutes before the spacecraft enters the atmosphere, it sheds the cruise stage. The Mars Science
Laboratory Entry, Descent and Landing Instrument
(MEDLI) Suite begins taking measurements. The data
MEDLI provides about the atmosphere and about the
heat shield’s performance will aid in design of future
Mars landings.
A minute after cruise stage separation, nine minutes
before entry, small thrusters on the back shell halt the
two-rotation-per-minute spin that the spacecraft maintained during cruise and approach phases. Then, the
same thrusters on the back shell orient the spacecraft
so the heat shield faces forward, a maneuver called
“turn to entry.”
After the turn to entry, the back shell jettisons two solidtungsten weights, called the “cruise balance mass devices.” Ejecting these devices, which weigh about 165
pounds (75 kilograms) each, shifts the center of mass of
the spacecraft. During the cruise and approach phases,
the center of mass is on the axis of the spacecraft’s
stabilizing spin. Offsetting the center of mass for the period during which the spacecraft experiences dynamic
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pressure from interaction with the atmosphere gives
the Mars Science Laboratory the ability to generate lift,
essentially allowing it to fly through the atmosphere. The
ability to generate lift during entry increases this mission’s capability to land a heavier robot, compared to
previous Mars surface missions.
The spacecraft also manipulates that lift, using a technique called “guided entry,” to steer out unpredictable
variations in the density of the Mars atmosphere, improving the precision of landing on target.
During guided entry, small thrusters on the back shell
can adjust the angle and direction of lift, enabling the
spacecraft to control how far downrange it is flying. The
spacecraft also performs “S” turns, called bank reversals, to control how far to the left or right of the target
it is flying. These maneuvers allow the spacecraft to
correct position errors that may be caused by atmosphere effects, such as wind, or by spacecraft modeling
errors. These guided entry maneuvers are performed
autonomously, controlled by the spacecraft’s computer
in response to information that a gyroscope-containing
inertial measurement unit provides about deceleration
and direction, indirect indicators of atmospheric density
and winds.
During EDL, more than nine-tenths of the deceleration before landing results from friction with the Mars
atmosphere before the parachute opens. Peak heating
occurs about 75 seconds after atmospheric entry, when
the temperature at the external surface of the heat shield
will reach about 3,800 degrees Fahrenheit (about 2,100
degrees Celsius). Peak deceleration occurs about
10 seconds later. Deceleration could reach 15 g, but
a peak in the range of 10 g to 11 g is more likely.
After the spacecraft finishes its guided entry maneuvers,
a few seconds before the parachute is deployed, the
back shell jettisons another set of tungsten weights
to shift the center of mass back to the axis of symmetry.
This set of six weights, the “entry balance mass
devices,” each has a mass of about 55 pounds
(25 kilograms). Shedding them re-balances the
spacecraft for the parachute portion of the descent.
The parachute, which is 51 feet (almost 16 meters) in
diameter, deploys about 254 seconds after entry, at an
altitude of about 7 miles (11 kilometers) and a velocity of
about 900 miles per hour (about 405 meters per second). About 24 more seconds after parachute deployment, the heat shield separates and drops away when
Mars Science Laboratory Landing

the spacecraft is at an altitude of about 5 miles (about
8 kilometers) and traveling at a velocity of about 280
miles per hour (125 meters per second).
As the heat shield separates, the Mars Descent Imager
begins recording video, looking in the direction the
spacecraft is flying. The imager records continuously
from then through the landing. The rover, with its
descent-stage “rocket backpack,” is still attached to
the back shell on the parachute. The terminal descent
sensor, a radar system mounted on the descent stage,
begins collecting data about velocity and altitude.
The back shell, with parachute attached, separates
from the descent stage and rover about 85 seconds
after heat shield separation. At this point, the spacecraft is about 1 mile (1.6 kilometers) above the ground
and rushing toward it at about 180 miles per hour
(about 80 meters per second). All eight throttleable
retrorockets on the descent stage, called Mars landing
engines, begin firing for the powered descent phase.
After the engines have decelerated the descent to
about 1.7 miles per hour (0.75 meters per second), the
descent stage maintains that velocity until rover touchdown. Four of the eight engines shut off just before
nylon cords begin to spool out to lower the rover from
the descent stage in the “sky crane” maneuver. The
rover separates its hard attachment to the descent
stage, though still attached by the sky crane bridle and
a data “umbilical cord,” at an altitude of about 66 feet
(about 20 meters), with about 12 seconds to go before
touchdown.
The rover’s wheels and suspension system, which
double as the landing gear, pop into place just before touchdown. The bridle is fully spooled out as the
spacecraft continues to descend, so touchdown occurs at the descent speed of about 1.7 miles per hour
(0.75 meters per second). When the spacecraft senses
touchdown, the connecting cords are severed and
the descent stage flies out of the way, coming to the
surface at least 492 feet (150 meters) from the rover’s
position, probably more than double that distance.
Soon after landing, the rover’s computer switches from
entry, descent and landing mode to surface mode.
This initiates autonomous activities for the first Martian
day on the surface of Mars, Sol 0. The time of day at
the landing site is mid afternoon — about 3 p.m. local
mean solar time at Gale Crater.

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Rover Separation

Sky Crane Detail

Altitude: ~66 feet (~20 meters)
Velocity: ~1.7 mph (~0.75 meter/sec)
Time: Entry + ~400 sec

Cruise Stage Separation
Time: Entry - 10 min

Mobility
Deploy

Cruise Balance Devices Separation
Time: Entry - ~8 min

Touchdown

Entry Interface

Altitude: ~78 miles (~125 km)
Velocity: ~13,200 mph (~5,900 meters/sec)
Time: Entry + 0 sec

Heat Shield
Separation

Peak Heating

Altitude: 0
Velocity: ~1.7 mph
(~0.75 meter/sec)
Time: Entry + ~416 sec

Flyaway

Altitude: ~5 miles (~8 km)
Velocity: ~280 mph
(~125 meters/sec)
Time: Entry + ~278 sec

Peak
Deceleration

Back Shell Separation
Hypersonic
Aero-maneuvering

Altitude: ~1 mile (~1.6 km)
Velocity: ~180 mph
(~80 meters/sec)
Time: Entry + ~364 sec

Parachute Deploy

Altitude: ~7 miles (~11 km)
Velocity: ~900 mph
(~405 meters/sec)
Time: Entry + ~254 sec

Radar Data
Collection
Powered
Descent

Sky Crane
Flyaway

Profile of entry, descent and landing events, for one typical case. Exact timing will be determined by atmospheric conditions on
landing day.

Timing Uncertainties During Entry, Descent and
Landing
The span of time from atmospheric entry until touchdown is not predetermined. The exact timing and
altitude for key events depends on unpredictable factors
in atmospheric conditions on landing day. The guided
entry technique enables the spacecraft to respond
and adapt to the atmospheric conditions it encounters
more effectively than any previous Mars mission. The
span between the moment the spacecraft passes the
entry interface point and a successful touchdown in the
target area of Gale Crater could be as short as about
380 seconds or as long as about 460 seconds. Times
for the opening of the parachute could vary by 10 to
20 seconds for a successful landing. The largest variable during EDL is the length of time the spacecraft
spends on the opened parachute. Curiosity could be
hanging below a fully inflated chute as briefly as about
Mars Science Laboratory Landing

55 seconds or as long as about 170 seconds. Times
given in the above description and on the accompanying graphic are for a typical case, with touchdown
416 seconds after entry.
Mars Surface Operations
The planned operational life for the Mars Science
Laboratory is one Martian year on the surface. One
Martian year is 687 Earth days, or 669 Martian days,
which are called sols. Each sol is 24 hours, 39 minutes,
35.244 seconds long. The landing site is in an equatorial region, at 4.5 degrees south latitude. The season in
Mars’ southern hemisphere at the beginning and end of
the prime mission is late winter, about two thirds of the
way from winter solstice to spring equinox.
One Martian year is how long the scientists and engineers operating the rover will have to achieve the
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mission’s science goals. Adding to the challenge, some
periods of the mission will not be fully available for science tasks. These include an initial health checkout for
about 10 sols or more after landing and about 20 sols
in April 2013 when communications will be restricted
due to Mars’ position nearly behind the sun from Earth.
Strategies for maximizing the science accomplishments
in the time available include extensive preparations
before landing, efficiently coordinated use of the rover’s
capabilities and flexibility for responding to discoveries.
The structure of science activities is based on sending
a set of commands to the rover each Martian morning
for the activities to be performed during that sol. The
activity plan for a sol needs to fit within the constraints
of time, power and spacecraft-temperature factors, and
data downlink volume for that sol. During a communication relay opportunity when an orbiter passes overhead
in the Martian midafternoon, the rover transmits data
about the sol’s activities. Any of the sol’s results that will
influence the next sol’s planning need to be included in
this downlink, though additional data from the sol can
be transmitted during later relay opportunities.
With data from preceding sols, the rover team needs
to make decisions for each sol, such as what targets
to approach, what instruments to use, what observations to make and what downlink priority level to assign
for each set of data generated during the sol or stored
onboard from earlier sols. The rover team’s engineers
collaborate with scientists to determine what activities
are safe and feasible, and to develop and check the
sequences of commands for transmission to the rover.
For the first three months of Mars surface operations,
the team will work on a Mars time schedule to make
best use of the key hours between when one sol’s
downlink is received and when the next sol’s commands
must be ready, whatever time of day that is at the
operations center at NASA’s Jet Propulsion Laboratory,
Pasadena, Calif. Team members’ work shift will begin
about 40 minutes later each day than on the preceding
day because a Martian sol is that much longer than an
Earth day. After these three months, operations will transition to an Earth-day work schedule and will become
more geographically distributed as non-Pasadena team
members return to their home institutions and participate through teleconferencing.
The landing sol is designated as Sol 0, a change from
the practice of the Mars Exploration Rover missions,
which designated landing sols of Spirit and Opportunity
Mars Science Laboratory Landing

as Sol 1. On Curiosity’s Sol 0, if the landing has been
successful, the rover will check its health and measure
its tilt. It will fire all of its pyrotechnic devices for releasing post-landing deployments. Spring-loaded deployments, such as removal of dust covers from the HazardAvoidance cameras (Hazcams), occur immediately
when pyros are fired. Motor-driven deployments, such
as raising the high-gain antenna dish and raising the
camera mast, are scheduled for later sols.
Curiosity is also programmed to take images with its
front and rear Hazcams on Sol 0 both before and after
removal of the dust covers. It is possible but unlikely that
these images will reach Earth via orbiter relay on landing
night. The low volume of data that will fit into early relays
makes about 15 hours after landing a more likely time
for Earth to receive these first images from Curiosity’s
landing site. The first look at some color images taken
just before landing by the Mars Descent Imager may
come at about the same time. These may allow a determination of the rover’s precise location.
A commissioning phase during the first several weeks
of Mars surface operations prescribes steps to reach
full-pace science operations safely. This phase will begin
with about a month of characterization activities to learn
how all the subsystems and instruments on the Curiosity
rover are functioning after landing and within the environment and gravitational field of Mars.
The first drive will probably take place more than a week
after landing. First movements of the robotic arm and
sampling tools are scheduled to be part of the characterization activities following the first drive. Following
the characterization activities, special precautions will
continue to apply for each first-time activity. Collection of
science data by some instruments is scheduled to begin
on Sol 1, and science activities will ramp up during the
commissioning phase. For example, an analysis of the
composition of Mars’ atmosphere is a scientific priority
for early in the mission.
Priority activities for Sol 1 will not require commands
from Earth. They are built into command sequences
stored onboard from before landing. One priority is to
test motions of the rover’s high-gain antenna for direct
communications with Earth. Use of this antenna will be
the standard mode for sending commands from Earth
to Curiosity. The Sol 1 plan includes using the Mars
Hand Lens Imager (MAHLI) to take the first post-landing
color image. MAHLI is on the robotic arm, which will
be in its stowed position, with MAHLI looking off to the
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side of the rover, so what scene appears in the first
color image taken from Gale Crater will be determined
by the orientation of the rover when it touches down.
The Rover Environmental Monitoring Station and the
Radiation Assessment Detector are also in the Sol 1
plan for collecting data about environmental conditions
at the landing site. Weather information and the image
from MAHLI may be received on Earth the second day
after landing.
On Sol 2, if all is proceeding well, Curiosity will raise the
mast holding the Mast Camera (Mastcam), Chemistry
and Camera (ChemCam), and Navigation Camera
(Navcam). This is a priority so that Navcam can image
the sky. These early Navcam images will help the rover
determine the location of the sun and calculate the angle
toward Earth from that knowledge of the sun’s position.
This calculation will be used for pointing the high-gain
antenna toward Earth. Images taken by cameras on the
mast, showing calibration targets and the terrain around
the rover, may reach Earth during the first few days after
landing.
After completion of the commissioning phase, the pace
of driving and the frequency of multi-sol stops for acquiring and analyzing rock or soil samples will be determined by team decisions about science priorities. Some
possible destinations identified in advance from orbit
may be within several weeks of driving distance from the
landing site. With the time taken to investigate nearer
stopping points, other likely destinations might be more
than a year away.
Communications Strategy
Like all of NASA’s interplanetary missions, the Mars
Science Laboratory will rely on the agency’s Deep
Space Network to communicate with the spacecraft
and to track it during flight. The network has groups of
antennas at three locations: at Goldstone in California’s
Mojave Desert; near Madrid, Spain; and near Canberra,
Australia. These locations are about one-third of the
way around the world from each other. That assures,
whatever time of day it is on Earth, at least one of them
will have the spacecraft in view during its trip from Earth
through landing. At least one location will have Mars in
view at any time during the rover’s Mars-surface operations. Each complex is equipped with one antenna
230 feet (70 meters) in diameter, at least two antennas
112 feet (34 meters) in diameter, and smaller antennas.
All three complexes communicate directly with the con-

Mars Science Laboratory Landing

trol hub at NASA’s Jet Propulsion Laboratory, Pasadena,
Calif.
As the spacecraft travels from Earth to Mars during the
cruise and approach phases of the mission, it communicates directly with Earth in the X-band portion of the
radio spectrum (at 7 to 8 gigahertz). For this, the spacecraft uses a transponder and amplifier in the spacecraft’s
descent stage and two antennas. One of the antennas,
the parachute low-gain antenna, is on the aeroshell’s
parachute cone, which is exposed through the center of
the cruise stage. The other, the medium-gain antenna,
is mounted on the cruise stage. The parachute lowgain antenna provided communications during the early
weeks of the cruise to Mars, and will do so again starting
shortly before cruise-stage separation. For most of the
voyage, the job switched to the medium-gain antenna,
which provides higher data rates but requires more restrictive pointing toward Earth. The telecommunications
system provides position and velocity information for
navigation, as well carrying data and commands.
Communication during atmospheric entry, descent and
landing is a high priority. Landings on Mars are notoriously difficult. If this landing were not successful, maintaining communications during the entry, descent and
landing would provide critical diagnostic information that
could influence the design of future missions.
All three orbiters currently active at Mars — NASA’s
Mars Odyssey and Mars Reconnaissance Orbiter and
the European Space Agency’s Mars Express — will be
at positions where they can receive transmissions from
the Mars Science Laboratory spacecraft during its entry,
descent and landing. These transmissions to the orbiters use the ultra-high frequency (UHF) portion of the
radio spectrum (at about 400 megahertz) from three
different UHF antennas. The parachute UHF antenna,
mounted on the back shell, transmits information from
a few minutes before atmospheric entry until the rover
and descent stage separate from the back shell. At that
point, the descent UHF antenna on the descent stage
takes over. When the rover drops away from the descent
stage on its sky-crane bridle, the rover UHF antenna is
exposed to begin transmissions that continue through
landing.
The orbiters relay to Earth via X-band the information
they receive from the Mars Science Laboratory during
this critical period. Only Odyssey relays the information
immediately, however. The other two orbiters record

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data from the Mars Science Laboratory spacecraft, hold
it onboard, and send it to Earth hours later.
The Odyssey relay, called “bent pipe,” is what the flight
team and the public will rely upon on landing day for
step-by-step information about the latter part of the
descent and landing. Odyssey will not begin receiving
transmissions from Mars Science Laboratory until about
two minutes after atmospheric entry. After first acquisition of signal, the orbiter may lose and regain the signal
more than once as the descending spacecraft goes
through changes in configuration. Odyssey will be in
position to continue receiving and relaying information
from Curiosity for about half a minute to more than two
minutes after the rover lands. Then the orbiter will drop
below the horizon from the landing-site perspective.
Mission engineers are uncertain how soon after landing
the signal will be lost, because of uncertainty in duration of the entry, descent and landing process, and the
possibility that Curiosity could land where a hill or other
obstruction blocks the line of sight between the rover
and the orbiter.
The Mars Science Laboratory spacecraft will also
transmit in X-band during its entry, descent and landing process. This is the expected path for confirmation of the initial events in the process. Due to signal
strength constraints, these transmissions will be simple
tones, comparable to semaphore codes, rather than full
telemetry. The Deep Space Network will listen for these
direct-to-Earth transmissions. However, Earth will go out
of view of the spacecraft, “setting” below the Martian
horizon, partway through the descent, so the X-band
tones will not be available for confirming the final steps
in descent and landing. The X-band antenna in use
from cruise-stage separation until atmospheric entry is
the parachute low-gain antenna located on the back
shell. Then, transmissions are shifted to a tilted low-gain
antenna, also on the back shell. This tilted antenna will
transmit tones during the banking maneuvers of the
guided entry. About five minutes after the spacecraft enters the atmosphere, possibly shortly after the parachute
opens, Earth will set, ending receipt of X-band tones. By
then, the bent-pipe relay via Odyssey may have begun.
Radio transmissions travel at the speed of light. The
distance between Mars and Earth on Curiosity’s landing
day, 154 million miles (248 million kilometers), means the
signal takes 13.8 minutes to cross at light speed. The
whole process of entry, descent and landing takes about
seven minutes. By the time any transmissions could be

Mars Science Laboratory Landing

reaching Earth with confirmation of the first events of that
process, Curiosity will actually be on the surface of Mars
already, whether the landing was successful or not.
The communication links are not necessary for a successful landing. Under some scenarios of communication difficulties, the flight team on Earth could have
no confirmation of safe landing for a day or more
and still recover a successful mission after regaining
communication.
During Mars surface operations, the rover Curiosity has
multiple options available for receiving commands from
mission controllers on Earth and for returning rover science and engineering information.
Curiosity has the capability to communicate directly with
Earth via X-band links with the Deep Space Network.
This capability will be used routinely to deliver commands to the rover each morning on Mars. It can also
be used to return information to Earth, but only at
relatively low data rates — on the order of kilobits per
second — due to the rover’s limited power and antenna
size, and to the long distance between Earth and Mars.
Curiosity will return most information via UHF relay links,
using one of its two redundant Electra-Lite radios to
communicate with a Mars orbiter passing overhead. In
their trajectories around Mars, the Mars Reconnaissance
Orbiter and Mars Odyssey orbiter each fly over the
Curiosity landing site at least once each afternoon and
once each morning before dawn. While these contact
opportunities are short in duration, typically lasting only
about 10 minutes, the proximity of the orbiters allows
Curiosity to transmit at much higher data rates than the
rover can use for direct-to-Earth transmissions. The rover can transmit to Odyssey at up to about 0.25 megabit
per second and to the Mars Reconnaissance Orbiter at
up to about 2 megabits per second. The orbiters, with
their higher-power transmitters and larger antennas, then
take the job of relaying the information via X-band to the
Deep Space Network on Earth. Mission plans call for
the return of 250 megabits of Curiosity data per Martian
day over these relay links. The links can also be used for
delivering commands from Earth to Curiosity.
While not planned for routine operational use during Curiosity’s surface mission, the European Space
Agency’s Mars Express orbiter will be available as a
backup communications relay asset should NASA’s relay
orbiters become unavailable for any period of time.

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with alcohol and other solvents. Components tolerant of
high temperature were heated to reduce spore burden
according to NASA specification, at temperatures ranging from 230 to 295 degrees Fahrenheit (110 to 146
degrees Celsius) for durations up to 144 hours. The
planetary protection team carefully sampled the surfaces and performed microbiological tests to demonstrate
that the spacecraft meets requirements for biological
cleanliness.

Planetary Protection
When sending missions to Mars, precautions must be
taken to avoid introduction of microbes from Earth by
robotic spacecraft. This is consistent with United States
obligations under the 1967 Outer Space Treaty, the
international treaty stipulating that exploration must be
conducted in a manner that avoids harmful contamination of celestial bodies. “Planetary protection” is the
discipline responsible for the development of rules and
practices used to avoid biological contamination in the
process of exploration. NASA has a planetary protection
officer responsible for establishing and enforcing planetary protection regulations. Each spacecraft mission is
responsible for implementing measures to comply with
the regulations. In compliance with the treaty and NASA
regulations, the Mars Science Laboratory flight hardware
has been designed and built to meet planetary protection requirements.

The Mars Science Laboratory is also complying with a
requirement to avoid going to any site on Mars known
to have water or water-ice within 3.3 feet (1 meter) of
the surface. This is a precaution against any landing-day
accident that could introduce hardware not fully sterilized by dry heat into an environment where heat from
the mission’s radioisotope thermoelectric generator and
a Martian water source could provide conditions favorable for microbes from Earth to grow on Mars.
Another way of making sure the mission does not transport Earth life to Mars is to ensure that any hardware not
meeting cleanliness standards does not go to Mars accidentally. When the Atlas launch vehicle’s upper stage
Centaur separated from the spacecraft, the two objects
were traveling on nearly identical trajectories. To prevent
the possibility of the Centaur hitting Mars, that shared
flight path was deliberately set so that the spacecraft
would miss Mars if not for later maneuvers to adjust its
trajectory. By design, the Centaur was never aimed at
Mars.

NASA’s primary strategy for preventing contamination of Mars with Earth organisms is to be sure that all
hardware going to the planet is biologically clean. The
Mars Science Laboratory mission is allowed to carry up
to 500,000 bacterial spores on the entire flight system.
That’s about one tenth as many as in a typical teaspoon
of seawater. Spore-forming bacteria have been the
focus of planetary protection standards because these
bacteria can survive harsh conditions for many years as
inactive spores. One requirement for this mission is that
the exposed interior and exterior surfaces of the landed
system, which includes the rover, parachute and back
shell, must not carry a total number of bacterial spores
greater than 300,000, with the average spore density
not exceeding 300 spores per square meter (about 11
square feet). This ensures that the biological load is not
concentrated in one place. The heat shield and descent
stage will hit the ground hard enough that hardware
could break open. The number of spores inside this
hardware that could be exposed by the hard landings
of these components must be included in the 500,000
maximum number.

Portions of the flight hardware will impact the surface of
Mars as part of a normal landing event. This impact may
cause the hardware to split open and potentially release
spores trapped inside the hardware during manufacturing processes. To ensure MSL does not exceed the
spore allocation, studies were conducted on various
materials, including paint, propellants and adhesives, to
determine the number of spores in a given volume. In
many cases the parts of the spacecraft containing these
materials were treated with dry heat microbial reduction
to reduce the number of spores. For hardware expected to impact Mars, such as the cruise stage after its
separation from the aeroshell, a detailed thermal analysis was conducted to make sure that plunging through
Mars’ atmosphere creates enough heat that few to no
spores survive.

Two common methods used for reducing the number
of spores on the spacecraft are alcohol wipe cleaning and dry heat microbial reduction. Technicians and
engineers who assembled the spacecraft and prepared
it for launch routinely cleaned surfaces by wiping them

Mars Science Laboratory Landing

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Comparing Two Mars Rover Projects
Mars Science Laboratory

Mars Exploration Rovers

Rovers 1 (Curiosity) 2 (Spirit and Opportunity)
Launch vehicle

Atlas V Delta II

Heat shield diameter

14.8 feet (4.5 meters)

8.7 feet (2.65 meters)

Design mission life on Mars

1 Mars year (98 weeks)

90 Mars sols (13 weeks)

Science Payload
10 instruments, 165 pounds
5 instruments, 11 pounds
(75 kilograms) (5 kilograms)
Rover mass

1,982 pounds (899 kilograms)

374 pounds (170 kilograms)

Rover size (excluding arm)



Length 10 feet (3 meters);
width 9 feet (2.7 meters);
height 7 feet (2.2 meters)

Length 5.2 feet (1.6 meters);
width 7.5 feet (2.3 meters);
height 4.9 feet (1.5 meters)

Robotic arm
7 feet (2.1 meters) long,
2.5 feet (0.8 meter) long,
deploys two instruments, deploys three instruments,
collects powdered samples removes surfaces of rocks,

from rocks, scoops soil, prepares
brushes surfaces
and delivers samples for analytic
instruments, brushes surfaces
Entry, descent and landing

Guided entry, sky crane

Ballistic entry, air bags

Landing ellipse

(99-percent confidence area)

12 miles (20 kilometers) long

50 miles (80 kilometers) long

Power supply on Mars



Multi-mission radioisotope
thermoelectric generator
(about 2,700 watt hours per sol)

Solar photovoltaic panels
(less than 1,000 watt hours per sol)

Computer
Redundant pair, 200 megahertz,
Single, 20 megahertz,

250 MB of RAM, 2 GB of
128 MB of RAM, 256 MB of
flash memory flash memory

Mars Science Laboratory Landing

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Spacecraft
The Mars Science Laboratory spacecraft consists of
four major elements: rover, descent stage, aeroshell
and cruise stage. The rover, Curiosity, has the science
payload and systems that enable the rover to use the
payload effectively and send home the results. The
descent stage performs the final moments of delivering
the rover to the surface of Mars. The aeroshell, which
includes the heat shield and the back shell, provides
thermal protection and maneuverable lift during the initial
portion of descent through the Martian atmosphere, and
then a parachute ride for the next portion of the descent.
The cruise stage provides trajectory maneuvers, electrical power, communications and other functions during
the eight months from launch to landing.
Cruise Stage
The cruise stage is doughnut-shaped, about five times
wider than it is tall, with 10 radiators arranged around
the perimeter. The hole of the doughnut sits over a
cone holding the parachute on top of the aeroshell. One
surface of the cruise stage was attached to the launch
vehicle. That attachment was severed within the first
hour after launch. The other surface of the cruise stage
attaches to the top of the aeroshell. That attachment
will be severed 10 minutes before the spacecraft enters
Mars’ atmosphere. During the 254 days between those

two separation events, the cruise stage performs essential tasks of the flight, though it uses the computer
inside the rover.
The cruise stage primary structure is aluminum. An inner ring connects to the launch vehicle interface and the
back shell interface plate. A series of ribs connect other
components. The cruise propulsion system is used to
maintain the spacecraft’s spin rate, adjust the spacecraft’s orientation, and provide propulsion for trajectory
correction maneuvers during the trip between Earth
and Mars. Two clusters of thrusters each include four
thruster engines in different orientations enabling different directions of thrust. Each of the eight thrusters can
provide about 1.1 pounds (5 newtons) of force. They
use hydrazine, a monopropellant that does not require an oxygen source. Hydrazine is a corrosive liquid
compound of nitrogen and hydrogen that decomposes
explosively into expanding gases when exposed to a
catalyst in the thrusters. Two spherical propellant tanks
on the cruise stage, each 19 inches (48 centimeters) in
diameter, supply the pressurized propellant. Aerojet built
the thrusters at its Redmond, Wash., facility. On both
the cruise stage and descent stage, fuel tanks are from
ATK Space Systems, Inc., Commerce, Calif.; and pressurant tanks are from Arde, Inc., Carlstadt, N.J.

Cruise Stage
Back Shell
Interface Plate
Parachute Support
Structure
Back Shell
Parachute

Descent Stage
Bridle
Umbilical
Device

Entry
Vehicle
System

Rover

Heat Shield

Mars Science Laboratory flight system, expanded view
Mars Science Laboratory Landing

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The spacecraft spins at about two rotations per minute
for stability on its way to Mars. The cruise stage monitors the spin rate and the spacecraft’s attitude (orientation) with a star scanner and one of two sun sensor
assemblies. Each of the sun sensor assemblies, from
Adcole Corp., Marlborough, Mass., includes four sunsensor heads pointing in different directions. Based on
star tracking and sun sensing information, the cruise
stage uses its thrusters as necessary to maintain the
spin rate and attitude.
Most of the electrical power for the spacecraft during the
trip from Earth to Mars is provided by sunshine hitting
a ring-shaped array of photovoltaic cells on the upper
surface of the cruise stage. The multi-mission radioisotope thermoelectric generator on the rover supplements
the electricity provided by the cruise solar array on the
way to Mars. The solar array has six physical panels
totaling 138 square feet (12.8 square meters) of active
photovoltaic area. The photovoltaic cells from Emcore
Corp., Albuquerque, N.M., use layers of three different
materials to gain electricity from different portions of the
solar spectrum. The layers are gallium indium phosphorus, gallium arsenide and germanium. If operated at full
capacity at Earth, the array could produce about 2,500
watts, which would exceed the spacecraft’s needs.
The array and its operation are designed to satisfy the
mission’s requirements from launch day to the Mars approach. At its farthest from the sun, during the approach
to Mars, the array will produce 1,080 watts or more,
even when facing as much as 43 degrees away from
the sun.
Another important function for the cruise stage is to
maintain temperatures within designed ranges for the
parts of the spacecraft inside the aeroshell as well as
for the cruise stage itself. The 10 radiators of the heatrejection system are mounted as a ring around the
outer edge of the cruise stage. Fluid pumped through a
circulatory system disperses heat from the rover’s multimission radioisotope thermoelectric generator to warm
the electronics of the cruise stage and to be released
into space by the radiators.

friction with Mars’ atmosphere and provides other
functions.
The Mars Science Laboratory aeroshell is not only the
biggest ever built for a planetary mission, but also incorporates major innovations in attitude control for guided
entry and in thermal protection material. Lockheed
Martin Space Systems, Denver, built the aeroshell’s heat
shield and back shell.
The diameter of the heat shield is 14.8 feet (4.5 meters).
For comparison, heat shields of the Apollo capsules
that returned astronauts to Earth after visits to the moon
were just under 13 feet (4 meters) in diameter, and the
heat shields for the Mars Exploration Rovers, Spirit and
Opportunity, were 8.7 feet (2.65 meters).
This aeroshell, unlike any predecessor for an extraterrestrial mission, has a steering capability. This is a key
to the mission’s guided entry innovation for added
precision in landing. During a crucial portion of descent
through the upper atmosphere of Mars, before the back
shell deploys its parachute, the center of mass of the
spacecraft will be offset from the axis of symmetry (a
line through the center of the aeroshell). This offset puts
the aeroshell at an angle to its direction of movement,
creating lift as the spacecraft interacts with the atmosphere. With lift, the spacecraft can fly like a wing, rather
than dropping like a rock. A reaction control system with
small thrusters to adjust the orientation of the spacecraft
can steer banking turns. A series of turns can shorten
the net horizontal distance the spacecraft covers during
its descent. Performed in response to sensing how the
spacecraft is reacting to unpredictable variability in the
atmosphere, the maneuvers counteract the unpredictability and provide a more precise landing.

Aeroshell

The heat shield uses a different thermal protection
system than used on earlier Mars missions’ heat
shields, because the unique entry trajectory profile and
the mass and size of the vehicle could create external
temperatures up to 3,800 degrees Fahrenheit (about
2,100 degrees Celsius). The heat shield is covered with
tiles of phenolic impregnated carbon ablator (PICA)
material. NASA Ames Research Center, Moffett Field,
Calif., invented the PICA material; Fiber Materials Inc.,
Biddeford, Maine, made the tiles. PICA was first flown
as the thermal protection system on the heat shield of
NASA’s Stardust Sample Return Capsule.

The aeroshell that encapsulates the rover and descent
stage during the flight to Mars protects them from

The heat shield carries sensors for collecting data about
Mars’ atmosphere and the performance of the heat

The medium-gain antenna mounted on the cruise stage
serves in telecommunications with Earth during most of
the trip from Earth to Mars.

Mars Science Laboratory Landing

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shield. These are part of the Mars Science Laboratory
Entry, Descent and Landing Instrument (MEDLI) Suite,
which is described in the Mars Science Laboratory
Investigations section of this document.
The back shell, besides making up the upper portion of
the capsule protecting the rover during passage through
Mars’ atmosphere, includes several devices used during
the spacecraft’s atmospheric entry and descent.
The back shell carries two sets of detachable tungsten
weights for altering the spacecraft’s center of mass.
Eight small thrusters in the upper half of the back shell
are used for the guided entry maneuvers.
A conical structure at the top of the back shell holds
the parachute and its deployment mechanism. The
parachute is the largest ever built for an extraterrestrial
mission. It uses a configuration called disk-gap-band. It
has 80 suspension lines, measures 165 feet (50 meters)
in length, and opens to a diameter of 51 feet (nearly
16 meters). Most of the orange and white fabric is nylon,
though a small disk of heavier polyester is used near the
vent in the apex of the canopy due to higher stresses
there. The parachute is designed to survive deployment
at up to Mach 2.2 in the Martian atmosphere and drag
forces of up to 65,000 pounds. Pioneer Aerospace
Corp., South Windsor, Conn., made the parachute.
Mounted on the back shell are two antennas — the
parachute low-gain antenna and the tilted low-gain
antenna — for communicating directly with Earth using
X-band frequencies and another antenna — the parachute UHF antenna — for communicating with Mars
orbiters using an ultra-high frequency (UHF) band.
Descent Stage
The descent stage of the Mars Science Laboratory does
its main work during the final few minutes before touchdown on Mars. It provides rocket-powered deceleration
and two bands of telecommunications for a phase of the
arrival at Mars after the phases using the heat shield and
parachute. After reaching a constant vertical velocity, the
descent stage lowers the rover on a bridle and continues
descent until rover touchdown.
The descent stage uses eight rockets, called Mars lander engines (MLE), positioned around its perimeter in four
pairs. These are the first throttleable engines for a Mars
landing since the Mars Viking landings in 1976. They
Mars Science Laboratory Landing

were built by Aerojet, in Richmond, Wash., with throttle
valve assemblies from Moog Inc., East Aurora, N.Y. Each
can provide an adjustable amount of thrust up to about
742 pounds (3,300 newtons). The propulsion system
of the descent stage uses pressurized propellant. Three
spherical fuel tanks provide a usable propellant load of
about 853 pounds (about 387 kilograms) of hydrazine,
a propellant that does not require an oxygen source.
Two spherical tanks of pressurized helium provide pressure for propellant delivery, moderated by a mechanical
regulator.
While the rover is fastened to the descent stage, the two
components together are called the powered descent
vehicle. The fastenings are pyrotechnic bolts. Firing to
release these connections commences the spacecraft’s
sky crane maneuver.
To perform the sky crane maneuver of lowering the
rover on a bridle, the descent stage carries a device
called the bridle umbilical and descent rate limiter (BUD).
This cone-shaped device is about 2 feet (two-thirds of
a meter) long. Three tethers of the bridle, attached to
the rover at three points, are spooled around the BUD,
with enough length to lower the rover about 25 feet (7.5
meters) below the descent stage during the sky crane
maneuver. A slightly longer umbilical, with data and
power connections between the rover and the descent
stage, is also spooled around the BUD. A descent brake
in the device governs the rotation rate as the bridle unspools, hence the speed at which gravity pulls the rover
away from the descent stage. The descent brake, made
by the Starsys division of SpaceDev Inc. (now Sierra
Nevada Corp.), Poway, Calif., uses gear boxes and
banks of mechanical resistors engineered to prevent the
bridle from spooling out too quickly or too slowly. The
cords of the bridle are made of nylon. The BUD also includes springs for quickly retracting the loose bridle and
umbilical after they are severed at the rover end when
touchdown is detected.
Through the umbilical, the spacecraft’s main computer
inside the rover controls activities during the entry,
descent and landing. After the heat shield drops away,
crucial information for determining the timing of events
comes to that computer from the terminal descent
sensor, a radar system engineered and built specifically
for this mission. The radar, mounted on the descent
stage, has six disk-shaped antennas oriented at different
angles. It measures both vertical and horizontal velocity,
as well as altitude.

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The descent stage carries an X-band transponder and
amplifier and two telecommunication antennas: the descent low-gain antenna for communicating directly with
Earth via X-band transmissions and the descent UHF
antenna for sending information to Mars orbiters.
Rover
The Mars Science Laboratory rover, Curiosity, carries the
instruments of the mission’s 10 science investigations
plus multiple systems that enable the science payload
to do its job and send home the results. Key systems
include six-wheeled mobility, sample acquisition and
handling with a robotic arm, navigation using stereo imaging, a radioisotope power source, avionics, software,
telecommunications and thermal control.
The rover’s name was suggested by the winning entrant in a national naming contest conducted among
U.S. school students. More than 9,000 students,
ages 5 through 18, submitted entries in late 2008 and
early 2009. An essay by Clara Ma of Lenexa, Kans., a
12-year-old sixth-grader at the time, was selected by
NASA in May 2009.
Curiosity is 10 feet (3 meters) long (not counting its arm),
9 feet (2.7 meters) wide and 7 feet (2.2 meters) high
at the top of its mast, with a mass of 1,982 pounds
(899 kilograms), including 165 pounds (75 kilograms) of
science instruments. By comparison, each of the previous generation of Mars rovers, Spirit and Opportunity, is
5.2 feet (1.6 meters) long, 7.5 feet (2.3 meters) wide and
4.9 feet (1.5 meters) high, with a mass of 374 pounds
(170 kilograms), including about 20 pounds (9 kilograms)
of science instruments.
The science payload is described in the Mars Science
Laboratory Science Investigations section of this press
kit.
Curiosity’s mechanical structure provides the basis for
integrating all of the other rover subsystems and payload instruments. The chassis is the core of the rover.
With insulated surfaces, it forms the shell of the warm
electronics box containing the avionics. The mechanical subsystem provides deployments that bring the
rover to its full functionality, including deployments of the
remote-sensing mast, robotic arm, antennas and mobility system.

Mars Science Laboratory Landing

Rover Mobility
Curiosity’s mobility subsystem is a scaled-up version
of what was used on the three earlier Mars rovers:
Sojourner, Spirit and Opportunity. Six wheels all have
driver motors. The four corner wheels all have steering
motors. Each front and rear wheel can be independently
steered, allowing the vehicle to turn in place as well as to
drive in arcs. The suspension is a rocker-bogie system.
Combined with a differential connecting the left and right
sides of the mobility system, the rocker-bogie design enables a six-wheel vehicle to keep all its wheels in contact
with the ground even on uneven terrain, such as with a
wheel going over a rock as big as the wheel. On each
side, a bogie connects the middle and rear wheels and
provides a pivot point between those wheels. The rocker
connects the bogie pivot point to the front wheel. The
rocker’s pivot point connects to the differential across the
rover body to the rocker on the other side.
Curiosity’s wheels are aluminum, 20 inches (0.5 meter)
in diameter, which is twice the size of the wheels on
Spirit and Opportunity. They have cleats for traction
and for structural support. Curving titanium spokes
give springy support. The wheels were machined by
Tapemation, Scotts Valley, Calif. Titanium tubing for the
suspension system came from Litespeed Titanium,
Chattanooga, Tenn.
The drive actuators — each combining an electric motor and gearbox — are geared for torque, not speed.
Aeroflex Inc., Plainview, N.Y., built the cold-tolerant actuators for the wheels and other moving parts of Curiosity.
The rover has a top speed on flat, hard ground of about
1.5 inches (4 centimeters) per second. However, under
autonomous control with hazard avoidance, the vehicle
achieves an average speed of less than half that. The
rover was designed and built to be capable of driving
more than 12 miles (more than 20 kilometers) during the
prime mission. The actual odometry will depend on decisions the science team makes about allocating time for
driving and time for investigating sites along the way.
For Curiosity, unlike earlier Mars rovers, the mobility
system doubles as a landing system, directly absorbing
the force of impacting the Martian surface at touchdown.
As on the earlier rovers, the mobility system can also be
used for digging beneath the surface by rotating one corner wheel while keeping the other five wheels immobile.

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ChemCam

RUHF Antenna
MMRTG

Mastcam

RLGA
Antenna

REMS
High Gain
Antenna

DAN

RAD
MARDI

Turret
Robotic Arm
(CheMin, SAM inside the rover)

Mobility System

Curiosity Mars Rover
Locations of several science instruments and major subsystems on the NASA Mars rover Curiosity are indicated. These
include (clockwise from left): Rover Environmental Monitoring
Station (REMS); Mast Camera (Mastcam); Chemistry and
Camera (ChemCam); rover ultra high-frequency (RUHF)
antenna; multi-mission radioisotope thermoelectric generator
(MMRTG); rover low-gain (RLGA) antenna; high-gain antenna;

Dynamic Albedo of Neutrons (DAN); mobility system (wheels
and suspension); Radiation Assessment Detector (RAD);
Mars Descent Imager (MARDI); turret (see larger image for
tools on the turret at the end of the robotic arm); and robotic
arm. Two science instruments — Chemistry and Mineralogy
(CheMin) and Sample Analysis at Mars (SAM) — are inside
the body of the rover.

Rover Arm and Turret

rover body. The diameter of the turret, including the
tools mounted on it, is nearly 2 feet (60 centimeters).

The turret at the end of the Curiosity’s robotic arm holds
two science instruments and three other devices. The
arm places and holds turret-mounted tools on rock and
soil targets and manipulates the sample-processing
mechanisms on the turret. It is strong enough to hold
the 73-pound (33-kilogram) turret at full extension of the
arm. With the arm extended straight forward, the center
of the turret is 6.2 feet (1.9 meters) from the front of the

Mars Science Laboratory Landing

The arm has five degrees of freedom of movement
provided by rotary actuators known as the shoulder
azimuth joint, shoulder elevation joint, elbow joint,
wrist joint and turret joint. The Space Division of MDA
Information Systems Inc. built the arm in Pasadena,
Calif.

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APXS
Drill

CHIMRA

MAHLI
DRT

Turret of tools at the end of Curiosity’s robotic arm
Locations of tools on the turret that is mounted on Curiosity’s
arm are indicated. These include (clockwise from upper
left): the drill for acquiring powdered samples from interiors
of rocks; the Alpha Particle X-ray Spectrometer (APXS);
the sample processing subsystem named Collection and

Handling for In-Situ Martian Rock Analysis (CHIMRA),
which includes a scoop for acquiring soil samples; the Dust
Removal Tool (DRT) for brushing rock surfaces clean; and the
Mars Hand Lens Imager (MAHLI).

The science instruments on the arm’s turret are the
Mars Hand Lens Imager (MAHLI) and the Alpha Particle
X-ray Spectrometer (APXS). The other tools on the turret are components of the rover’s Sample Acquisition/
Sample Processing and Handling (SA/SPaH) subsystem: the Powder Acquisition Drill System (PADS),
the Dust Removal Tool (DRT), and the Collection and
Handling for In-situ Martian Rock Analysis (CHIMRA)
device.

of the drilled hole is 0.63 inch (1.6 centimeters). The drill
penetrates the rock and powders the sample to the
appropriate grain size for use in the two analytical instruments inside the rover: Sample Analysis at Mars (SAM),
and Chemistry and Mineralogy (CheMin). The powder
travels up an auger in the drill for transfer to sample
processing mechanisms. If the drill bit becomes stuck in
a rock, the drill can disengage from that bit and replace
it with a spare drill-bit assembly. The arm moves the drill
to engage and capture one of two spare bits in bit boxes
mounted to the front of the rover.

The Powder Acquisition Drill System is a rotary percussive drill to acquire samples of rock material for
analysis. It can collect a sample from up to 2 inches
(5 centimeters) beneath a rock’s surface. The diameter
Mars Science Laboratory Landing

The Dust Removal Tool, from Honeybee Robotics, N.Y.,
is a metal-bristle brushing device used to remove the
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dust layer from a rock surface or to clean the rover’s
observation tray.
One portion of the Collection and Handling for In-situ
Martian Rock Analysis device is a motorized, clamshellshaped scoop, 1.57 inches (4 centimeters) wide, to
collect soil samples from the Martian surface. The other
turret-mounted portion of this device has chambers
and labyrinths used for sorting, sieving and portioning
the samples collected by the drill and the scoop. These
functions are carried out by manipulating the orientation of the turret while a vibration device helps move
material through the chambers, passages and sieves.
Samples can be sieved to screen out particles more
than 0.04 inch (1 millimeter) across or to screen out
particles more than 0.006 inch (150 microns) across.
The vibration device also aids in creating the appropriate portion size and in the delivery action when the
device drops material into inlet ports of the analytical
instruments. Each of the inlet ports — two for Sample
Analysis at Mars and one for Chemistry and Mineralogy
— has a cover that can be opened and closed using a
motor.
An observation tray on the rover allows the Mars Hand
Lens Imager and the Alpha Particle X-ray Spectrometer
a place to examine collected and processed samples of
soil and powdered rock.
Rover Power
Rover power is provided by a multi-mission radioisotope
thermoelectric generator (MMRTG) supplied by the U.S.
Department of Energy. This generator is essentially a
nuclear battery that reliably converts heat into electricity. It consists of two major elements: a heat source that
contains plutonium-238 dioxide and a set of solid-state
thermocouples that convert the plutonium’s heat energy
to electricity. It contains 10.6 pounds (4.8 kilograms) of
plutonium dioxide as the source of the steady supply
of heat used to produce the onboard electricity and to
warm the rover’s systems during the frigid Martian night.
Radioisotope thermoelectric generators have enabled
NASA to explore the solar system for many years. The
Apollo missions to the moon, the Viking missions to
Mars, and the Pioneer, Voyager, Ulysses, Galileo, Cassini
and New Horizons missions to the outer solar system all
used radioisotope thermoelectric generators. The multimission radioisotope thermoelectric generator is a new
generation designed to operate on planetary bodies with
an atmosphere, such as Mars, as well as in the vacuum
Mars Science Laboratory Landing

of space. In addition, it is a more flexible modular
design capable of meeting the needs of a wider variety
of missions as it generates electrical power in smaller
increments, slightly more than 110 watts. The design
goals for the multi-mission radioisotope thermoelectric
generator include ensuring a high degree of safety,
optimizing power levels over a minimum lifetime of
14 years, and minimizing weight. It is about 25 inches
(64 centimeters) in diameter by 26 inches (66 centimeters) long and weighs about 99 pounds (45 kilograms).
Like previous generations of this type of generator, the
multi-mission radioisotope thermoelectric generator is
built with several layers of protective material designed
to contain its plutonium dioxide fuel in a wide range of
potential accidents, verified through impact testing. In
the unlikely event of a launch accident, it is unlikely that
any plutonium would have been released or that anyone would have been exposed to nuclear material. The
type of plutonium used in a radioisotope power system
is different from the material used in weapons and cannot explode like a bomb. It is manufactured in a ceramic
form that does not become a significant health hazard
unless it becomes broken into very fine pieces or vaporized and then inhaled or swallowed. If there had been
an accident at the launch of Mars Science Laboratory,
people who might have been exposed would have
received an average dose of 5 to 10 millirem, equal to
about a week of background radiation. The average
American receives 360 millirem of radiation each year
from natural sources, such as radon and cosmic rays.
The electrical output from the multi-mission radioisotope thermoelectric generator charges two lithium ion
rechargeable batteries. This enables the power subsystem to meet peak power demands of rover activities
when the demand temporarily exceeds the generator’s
steady output level. The batteries, each with a capacity of about 42 amp-hours, were made by Yardney
Technical Products, Pawcatuck, Conn. They are expected to go through multiple charge-discharge cycles
per Martian day.
Rover Telecommunication
Curiosity has three antennas for telecommunication.
Two are for communications directly with NASA’s Deep
Space Network antennas on Earth using a radio frequency in the X band (7 to 8 gigahertz). The third is for
communications with Mars orbiters, using the ultra-high
frequency (UHF) band (about 400 megahertz).

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X-band communications use a 15-watt, solid-state
power amplifier fed by the rover’s small deep space
transponder, manufactured by General Dynamics
Advanced Information Systems, Scottsdale, Ariz. Spain
provided the rover’s high-gain antenna, which is hexagonally shaped, nearly 1 foot (0.3 meter) in diameter
and mounted near the left edge of the rover deck. With
this antenna, the X-band subsystem is designed to
transmit at 160 bits per second or faster to the Deep
Space Network’s 112-foot-diameter (34-meter-diameter) antennas or at 800 bits per second or faster to the
Deep Space Network’s 230-foot-diameter (70-meterdiameter) antennas. The high-gain antenna, which
requires pointing, can be used for either transmitting or
receiving. The rover low-gain antenna, which does not
require pointing, is designed primarily for receiving communications from the Deep Space Network. X-band
reception through the high-gain antenna is anticipated
as the typical method for daily uplink of commands to
the rover.
The rover UHF antenna, a helix-pattern cylinder mounted high near the right-rear corner of Curiosity is fed by
a pair of redundant Electra-Lite radios, which were built
through a partnership between NASA’s Jet Propulsion
Laboratory and L-3 Cincinnati Electronics, Mason,
Ohio. These radios are software-defined, enabling them
to autonomously adjust their data rate to suit variations
in signal strength due to angles and transmission distance. They use standardized communication protocols
for interoperability with all the relay orbiters at Mars, and
are especially compatible with the adaptive Electra UHF
radio on NASA’s Mars Reconnaissance Orbiter. The primary method for the rover’s transmission of data is anticipated to be UHF relay to the Mars Reconnaissance
Orbiter or Mars Odyssey orbiter during two of the opportunities each Martian day when the orbiters pass in
the sky above the rover. The European Space Agency’s
Mars Express orbiter also has the capability to serve as
a backup relay.
Rover Computing
Curiosity has redundant main computers, or rover
compute elements. Of this “A” and “B” pair, it uses one
at a time, with the spare held in cold backup. Thus, at a
given time, the rover is operating from either its “A” side
or its “B” side. Most rover devices can be controlled by
either side; a few components, such as the navigation
camera, have side-specific redundancy themselves.
The computer inside the rover — whichever side is ac-

Mars Science Laboratory Landing

tive — also serves as the main computer for the rest of
the Mars Science Laboratory spacecraft during the flight
from Earth and arrival at Mars. In case the active computer resets for any reason during the critical minutes
of entry, descent and landing, a software feature called
“second chance” has been designed to enable the other
side to promptly take control, and in most cases, finish
the landing with a bare-bones version of entry, descent
and landing instructions.
Each rover compute element contains a radiation-hardened central processor with PowerPC 750 architecture:
a BAE RAD 750. This processor operates at up to 200
megahertz speed, compared with 20 megahertz speed
of the single RAD6000 central processor in each of the
Mars rovers Spirit and Opportunity. Each of Curiosity’s
redundant computers has 2 gigabytes of flash memory
(about eight times as much as Spirit or Opportunity),
256 megabytes of dynamic random access memory
and 256 kilobytes of electrically erasable programmable
read-only memory.
The Mars Science Laboratory flight software monitors
the status and health of the spacecraft during all phases
of the mission, checks for the presence of commands
to execute, performs communication functions and controls spacecraft activities. The spacecraft was launched
with software adequate to serve for the landing and for
operations on the surface of Mars, as well as during
the flight from Earth to Mars. The months after launch
were used, as planned, to develop and test improved
flight software versions. One upgraded version was
sent to the spacecraft in May 2012 and installed onto
its computers in May and June. This version includes
improvements for entry, descent and landing. Another
was sent to the spacecraft in June and will be installed
on the rover’s computers a few days after landing, with
improvements for driving the rover and using its robotic
arm.
Rover Navigation
Two sets of engineering cameras on the rover —
Navigation cameras (Navcams) up high and HazardAvoidance cameras (Hazcams) down low — will inform
operational decisions both by Curiosity’s onboard
autonomy software and by the rover team on Earth.
Information from these cameras is used for autonomous
navigation, engineers’ calculations for maneuvering the
robotic arm and scientists’ decisions about pointing the
remote-sensing science instruments.

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Curiosity’s Navcams and Hazcams generate grayscale
images that cover red wavelengths centered at about
650 nanometers. The cameras themselves are virtually identical to the engineering cameras on Spirit and
Opportunity, though Curiosity has redundant cameras
and slightly more powerful heaters for the cameras.
Curiosity has a total of 12 engineering cameras, each
weighing about 9 ounces (250 grams).
Curiosity’s Navcams, paired for stereo imaging, are
installed next to the science payload’s Mast Camera on
the remote-sensing mast. Curiosity carries two stereo
pairs of Navcams, one pair each connected to the
rover’s two redundant computers. The Navcams that
are controlled by and feed imagery to the “A” computer
are mounted directly above the ones linked to the “B”
computer. That puts the “A” pair about 6.5 feet (1.99
meters) above the ground when the rover is on hard,
flat terrain and the cameras are pointed straight out
(slightly lower when pointed downward), and the other
pair 2 inches (5 centimeters) lower. The left and right
cameras in each pair are about 16.5 inches (42 centimeters) apart, giving them approximately twice as long
a stereo baseline as the separation distance of navigation cameras on Spirit and Opportunity.
Each of the Navcams captures a square field of view
45 degrees wide and tall, comparable to the field of
view of a 37-millimeter-focal-length lens on a 35-millimeter, single-lens reflex camera. The lens focuses
the image onto a 1,024-pixel-by-1,024-pixel area of a
charge-coupled device (CCD) detector. This yields a
resolution of 0.82 milliradians per pixel — for example,
0.8 inch (2 centimeters) per pixel at a distance of
82 feet (25 meters), enough to resolve a golf ball at that
distance as a circle about two Navcam pixels wide.
The depth of field achieved by the fixed-aperture f/12
Navcams keeps anything in focus from a distance of
about 20 inches (0.5 meter) to infinity.
Curiosity has four pairs of Hazcams: two redundant
pairs on the front of the chassis and two redundant
pairs on the rear. The rover can drive backwards as
well as forward, so both the front and rear Hazcams
can be used for detecting potential obstacles in the
rover’s driving direction. The front Hazcams also provide
three-dimensional information for planning motions of
the rover’s robotic arm, such as positioning of the drill or
scoop for collecting samples.

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Each Hazcam has a fisheye lens providing a square field
of view 124 degrees wide and tall. The depth of field in
focus spans from about 4 inches (10 centimeters) to
infinity. Resolution of the Hazcams is 2.1 milliradians per
pixel on the same type of detector as in the Navcams.
At a distance of 33 feet (10 meters), the Hazcam resolution is 0.8 inch (2 centimeters) per pixel. A golf ball at
that distance would be approximately two Hazcam
pixels across.
The redundant pairs of Hazcams are mounted side by
side. On the front, each stereo pair has a baseline of
6.54 inches (16.6 centimeters) between the center of its
left eye and center of its right eye. Both the pair linked to
the rover’s “A” computer and the pair linked to the “B”
computer are mounted near the bottom center of the
front face of the chassis, about 27 inches (68 centimeters) above ground level. The rear stereo pairs each have
a baseline of 3.9 inches (10 centimeters), the same as
for both the front and rear hazard-identification cameras
on Spirit and Opportunity. The rear “A” pair on Curiosity
is toward the port side of the rear face of the vehicle (on
the left if a viewer were standing behind the rover and
looking toward it). The rear “B” pair is on the right, or
toward starboard. Both pairs are about 31 inches (78
centimeters) above ground level.
Curiosity’s Hazcams have one-time-removable lens covers to shield them from potential dust raised during the
rover’s landing. Pyrotechnic devices will remove the lens
caps after landing. The Navcams gain protection from
the stowed position of the remote-sensing mast during
the landing; they do not have lens covers.
Different navigation modes for rover drives use images from the engineering cameras in different ways.
Techniques include “blind” driving, hazard avoidance
and visual odometry. The set of commands developed
by rover planners for a single day’s drive may include a
combination of these modes.
When using the blind-drive mode, rover planners have
sufficient local imaging from the engineering cameras or
Mast Camera to determine that a safe path exists, free
of obstacles or hazards. They command the rover to
drive a certain distance in a certain direction. In a blind
drive, the rover’s computer calculates distance solely
from wheel rotation; one full turn of a wheel with no slippage is about 62 inches (157 centimeters) of driving. It
does not check imagery from the engineering cameras
to assess the slippage.

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When the rover planners cannot determine that a path
is free of obstacles, they can command driving that
uses hazard avoidance. Besides using this hazard
avoidance in rougher terrain, they might use it for an additional segment of driving beyond a blind drive on the
same day. Hazard avoidance requires the rover to stop
frequently to acquire new stereo imaging in the drive
direction with the engineering cameras and analyze the
images for potential hazards. The rover makes decisions
based on its analysis of the three-dimensional information provided by the stereo imaging. Rover planners set
variables such as how frequently to stop and check,
which cameras to use, and what type of decision the
rover makes in response to a hazard detection (whether
to choose a path around it or stop driving for the day).
Hazard avoidance can be supplemented with visual
odometry. Visual odometry uses Navcam images made
with the cameras pointed to the side of the route being
driven. By pausing at intervals during the drive to take
these images, the rover can compare the before-andafter situation for each segment of the drive. It can
recognize features in the images and calculate how far it
has actually traveled during the intervening drive segment. Any difference between that distance and the distance indicated from wheel rotation is an indication that
the wheels are slipping against the ground. In the day’s

set of driving commands, rover planners can set the
intervals at which the rover pauses for visual-odometry
checks, as suited to the type of terrain being traversed.
A slip limit can be set so that if the rover calculates that
it is slipping in excess of that amount, it will stop driving
for the day. The mode of using visual odometry checks
at intervals several times the rover’s own length is called
slip-check, to differentiate it from full-time visual odometry with sideways-looking stops as frequently as a fraction of the rover’s length.
Navigation modes differ significantly in the fraction of
time spent with wheels in motion versus stopped for
imaging and analysis of the images.
Curiosity can incorporate other safety features in each
drive, such as tilt limits. The rover’s inertial measurement unit, which incorporates gyroscopes, provides
information about changes in tilt. This and other information about the rover’s attitude, or orientation, serve
in use of the arm and the science instruments, and in
pointing the high-gain antenna, as well as in navigation.
Rover Thermal
Curiosity’s thermal control system was designed to
enable the rover to operate far from the equator so that

Rover size, compared with a 5-foot, 8-inch man

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the mission would have a choice of landing sites based
on science criteria. In a range of Mars surface temperatures from minus 207 degrees Fahrenheit (minus 133
degrees Celsius) to 81 degrees Fahrenheit (27 degrees
Celsius), the temperature-sensitive components inside
the rover can be maintained between minus 40 degrees Fahrenheit (minus 40 degrees Celsius) and 122
degrees Fahrenheit (50 degrees Celsius).

ing needs beyond the circulation of the heat rejection
system, the rover uses electrical heaters. These enable
flexibility in localizing and timing for the heat they provide. For example, a secondary warm electronics box
atop the remote sensing mast uses electrical heating to
maintain temperatures there above allowable minimums.

The rover’s heat rejection system has a pumpedfluid loop that can deliver heat from the multi-mission
radioisotope thermoelectric generator when the core
electronics need heating and take heat away from the
core if the rover is becoming too warm. Pacific Design
Technologies Inc., Goleta, Calif., built the pump.
The fluid loop runs through an avionics mounting plate
inside the insulated warm electronics box of the rover
chassis. The multi-mission radioisotope thermoelectric
generator cools passively with its radiator fins when its
heat is not needed for warming the rover. For heat-

Silicon chips mounted onto Curiosity’s deck bear the
names of people who participated in the “Send Your
Name to Mars” program online. Each chip is about the
size of a dime. More than 1.24 million names were submitted online. These names have been etched into silicon using an electron-beam machine used for fabricating microdevices at NASA’s Jet Propulsion Laboratory. In
addition, more than 20,000 visitors to JPL and NASA’s
Kennedy Space Center wrote their names on pages
that have been scanned and reproduced at microscopic
scale on another chip.

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‘Send Your Name to Mars’ Chips

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Curiosity’s Landing Site
The Mars Science Laboratory mission will place the
rover Curiosity at the foot of a mountain of sedimentary
strata, or layers, inside Gale Crater. The landing site at
4.6 degrees south latitude, 137.4 degrees east longitude will give the rover access to a field site with science
targets both on the crater floor beside the mountain and
in the lower layers of the mountain.
Gale Crater spans 96 miles (154 kilometers) in diameter,
giving it an area about the equivalent of Connecticut and
Rhode Island combined. It holds a mound, informally
named Mount Sharp, rising about 3 miles (5 kilometers)
above the crater floor, which is higher than Mt. Rainier
rises above Seattle. The slopes of Mount Sharp are
gentle enough for Curiosity to climb, though during the
prime mission of one Martian year (98 weeks), the rover
will probably not go beyond some particularly intriguing
layers near the base.
Gale sits at a low elevation relative to most of the surface
of Mars, suggesting that if Mars ever had much flow-

ing water, some of it would have pooled inside Gale.
Observations from orbit that add evidence of a wet
history include water-related clay and sulfate minerals
in the lower layers of the mound, and textures higher
on the mound where it appears that mineral-saturated
groundwater filled fractures and deposited minerals.
Stratification in the mound suggests it is the surviving
remnant of an extensive sequence of deposits that
were laid down after the impact that excavated the
crater more than 3 billion years ago. Each geological
layer, called a stratum, is formed after the layer beneath
it and before the one above it. The stack of layers that
forms Mount Sharp offers a history book of sequential
chapters recording environmental conditions when
each stratum was deposited. This is the same principle
of geology that makes the strata exposed in Arizona’s
Grand Canyon a record of environmental history on
Earth. For more than 150 years, geologists on Earth
have used stacks of strata from globally dispersed locations to piece together a record of Earth history.

Locations of landing sites for Curiosity and previous Mars rovers and landers
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Mount Sharp’s stack of layers is much taller than the
stack admired in the Grand Canyon. It is a closer
match to the amount of layering exposed in Mars’
Valles Marineris, the largest canyon in our solar system.
Therefore, Mount Sharp may offer one of the thickest
continuous sequences of strata in the solar system. On
Earth, the thickest sequences of strata that also contain
a diversity of materials are the best records of Earth’s history. Like the most complete copy of an ancient manuscript, they can be used to decode and tie together less
complete records from around the globe. It is hoped that
the record at Gale Crater will be just such a key reference
for deciphering Mars’ global history.
Gale Crater was named in 1991 for Australian astronomer and banker Walter F. Gale (1865–1945), who
discovered several comets and drew maps of Mars and
Jupiter. Coincidentally, the mound inside Gale, when
viewed from orbit, resembles the shape of Australia.
Curiosity’s Project Science Group chose the informal
name Mount Sharp in early 2012 as a tribute to geologist Robert P. Sharp (1911–2004). Sharp was a founder
of the field of planetary science, an influential teacher of
many current leaders in the field, and team member for
NASA’s first few Mars missions. He taught geology at the
California Institute of Technology (Caltech), in Pasadena,
from 1948 until past his retirement.
NASA’s choice of the landing site in Gale Crater in July
2011 followed a five-year process that considered about
60 sites and involved about 150 Mars scientists in a
series of public workshops. Four finalist sites identified in
2008 were mapped and examined so extensively from
orbit that they have become four of the best-studied
places on Mars. The detail in images taken by the High
Resolution Imaging Science Experiment camera on
NASA’s Mars Reconnaissance Orbiter, for example,
reveals virtually every individual boulder big enough
to spoil a landing. Mineral mapping by the Compact
Reconnaissance Imaging Spectrometer on the same
orbiter and the OMEGA spectrometer on the European
Space Agency’s Mars Express identified mineral evidence of wet histories at all four sites. All four finalist sites
qualified as safe for landing, so the selection could be
made based on the sites’ scientific appeal.
The guided entry technology enabling the Mars Science
Laboratory to land more precisely than previous Mars
missions, coupled with Curiosity’s driving capability,
meant that, for the first time, the main science destination for a Mars mission could be outside of the area that
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needed to qualify as safe for landing. The mission’s technologies for atmospheric entry, descent and landing give
the spacecraft about a 99-percent probability of landing
within an ellipse 12.4 miles (20 kilometers) by 15.5 miles
(25 kilometers), as calculated during the site-selection
process. That is about one-third the size of the landing
ellipses for Mars rovers that landed in 2004. Curiosity
was designed and built to be able to drive far enough to
get outside of its landing ellipse during its prime mission. While Curiosity was on its way from Earth to Mars,
continuing analysis of the entry, descent and landing
variables led to confidence in even higher precision.
This enabled shrinking the landing ellipse to about 4 by
12 miles (7 by 20 kilometers) and moving the center
target closer to Mount Sharp.
The slopes of Mount Sharp are too steep for the rover
to land safely on the mountain. The science targets
initially identified for the rover to investigate are in the
lower layers of the mountain, requiring the rover to drive
outside the landing ellipse to get to the science targets.
Subsequent observations and analysis have identified
additional science targets within the landing ellipse.
The pace at which Curiosity gets to the features of high
science interest inside and outside of the ellipse will
depend on findings and decisions made after landing,
including the possibility of identifying targets not yet
known. Getting to key destinations at lower layers of
Mount Sharp may take a large fraction of the 98-week
prime mission. The route may involve navigation through
some challenging terrains such as sand dunes, hills and
canyons.
In Curiosity’s field site — encompassing accessible areas inside and outside of the landing ellipse — features
that make Gale appealing to the science team include:
• An alluvial fan extending into the landing ellipse from
the crater wall to the north holds material shed from
the crater wall and likely carried by water.
• Down slope, or southward, from the alluvial fan lies
an exposure of hard, light-toned rock. The mineral composition of this area is unidentified so far.
Curiosity could investigate a hypothesis that this
exposure is sedimentary rock formed in interaction
with water, such as salts left by the drying of a lake.
Some relatively fresh, small craters in this part of the
crater floor may provide access to material that has
not experienced long exposure to the radiation environment affecting chemistry at the Martian surface.

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Landing ellipse in Gale Crater, in overhead view with north at the top

Curiosity’s landing area and surrounding terrain at Gale Crater, looking toward the southeast
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• Among the exposures in the lower portion of Mount
Sharp are packages of strata that contain clay minerals, strata that contain sulfate salts and strata that
contain both. Clays and sulfates both result from
wet environments. The differences in mineral composition from one package of strata to the next can
provide information about changes in environments
that may have been favorable for microbial life.
• Curiosity’s analysis of the exposed minerals will
provide confirmation of orbiter-based predictions for
the distribution and abundance of similar minerals
to be present over vast parts of Mars. In this regard,
Curiosity will provide important ground truth of hypotheses generated by previous missions.
• The sulfate salts retain trace amounts of water in
their mineral structure. Curiosity can monitor how
some of that water is released into the atmosphere
during warmer hours of the day and reabsorbed by
the salts during colder hours. These measurements
would provide information about the modern water
cycle on Mars.
• Canyons cut into the northern flank of Mount Sharp
resulted from flow of water long after the lower layers of the mountain had accumulated. The canyoncutting environment could have been a separate
habitable environment from the environment at
the time the clay-containing and sulfate-containing
layers formed. Analysis of material deposited at the
mouths of the canyons could provide information
about that later environment.

One important capability of Curiosity’s science payload
is to check for the presence of ingredients for life, including the carbon-based building blocks of biology called
organic compounds. Long-term preservation of organic
compounds requires special conditions.
Clays and sulfate-rich deposits such as the ones
Curiosity will investigate in Gale Crater can be good at
latching onto organic chemicals and protecting them
from oxidation. Another factor in long-term preservation
of organics on Mars is protection from natural radiation
that is more intense than what reaches Earth’s surface.
Radiation may gradually destroy organics inside rocks
at the surface, but Gale also offers rocks exposed by
relatively recent small-crater impacts.
Gale offers these attractive targets at which to check for
organic compounds. Finding organics is still a long shot,
but this chosen field site also offers records of multiple
periods in Mars history, grist for the mission’s investigation of environmental changes on Mars, with strong
prospects for identifying habitable environments.
Should Curiosity continue to be in working condition
following the prime mission, an extended mission could
continue the investigation by exploring higher, younger
layers of Mount Sharp.

• Extensive networks of fractures in the upper parts of
the sulfate-bearing strata are filled with minerals that
betray circulation of groundwater. These fracture
networks would represent yet a different, subsurface
habitable environment. The presence of minerals
lining these fractures indicates where Curiosity might
conduct analyses to look for organic compounds.

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