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The parachute is attached to the backshell and opens to about 15 meters (49 feet) in
diameter. The parachute design was tested under simulated martian conditions in a
large wind tunnel at NASA's Ames Research Center near Sunnyvale, Calif.
The backshell carries a deceleration meter used to determine the right moment for
deploying the parachute. Solid-fuel rockets mounted on the underside of the shell
Cruise stage
Back shell
Rover and
Heat shield
Flight system
reduce vertical velocity and any excessive horizontal velocity just before landing.
The airbags, based on Pathfinder's design, cushion the impact of the lander on the
surface. Each of the four faces of the folded-up lander is equipped with an envelope of
six airbags stitched together. Explosive gas generators rapidly inflate the airbags to a
pressure of about 6900 Pascal (one pound per square inch). Each airbag has double
bladders to support impact pressure and, to protect the bladders from sharp rocks, six
layers of a special cloth woven from polymer fiber that is five times stronger than steel.
The fiber material, Vectran, is used in the strings of archery bows and tennis racquets.
The lander, besides deploying the airbags, can set the rover right-side-up, if necessary,
and provides an adjustable platform from which the rover can roll onto Mars' surface.
It also carries a radar altimeter used for timing some descent events, as well as two
The lander's basic structure is four triangular petals made of graphite-epoxy composite
material. Three petals are each attached with a hinge to an edge of the central base
petal. The rover stays fastened to the base petal during the flight and landing. When
folded up, the lander's petals form a tetrahedral box around the stowed rover. Any of
the petals could end up on the bottom when the airbag-cushioned bundle rolls to a
stop after landing. Electric motors at the hinges have enough torque to push the lander
open, righting the rover, if it lands on one of the side petals.
Other motors retract the deflated airbags. An apron made out of the same type of
tough fabric as the airbags stretches over ribs and cables connected to the petals, pro-
viding a surface that the rover can drive over to get off the lander. The side petals can
also be adjusted up or down from the plane of the base petal to accommodate uneven
terrain and improve the rover's path for driving off of the lander.
Nearly 4 million people have a special connection to the Mars Exploration Rover pro-
ject by having their names recorded on each mission's lander. Each of the two landers
carries a digital versatile disc, or DVD, containing millions of names of people around
the world collected during a "Send Your Name to Mars" campaign, which ended in
November 2002.
At the heart of each Mars Exploration Rover spacecraft is its rover. This is the mobile
geological laboratory that will study the landing site and travel to examine selected
rocks up close.
The Mars Exploration Rovers differ in many ways from their only predecessor, Mars
Pathfinder's Sojourner rover. Sojourner was about 65 centimeters (2 feet) long and
Navigation cameras
Mini-thermal emission
spectrometer (at rear)
Low-gain antenna
Solar arrays antenna
Calibration target
High-gain antenna
Magnet array
Alpha particle
imager Mössbauer
Rocker-bogie mobility system
Rock abrasion tool
Mars Exploration Rover
weighed 10 kilograms (22 pounds). Each Mars Exploration Rover is 1.6 meter (5.2
feet) long and weighs 174 kilograms (384 pounds). Sojourner traveled a total distance
equal to the length of about one football field during its 12 weeks of activity on Mars.
Each Mars Exploration Rover is expected to travel six to 10 times that distance during
its three-month prime mission. Pathfinder's lander, not Sojourner, housed that mis-
sion's main telecommunications, camera and computer functions. The Mars
Exploration Rovers carry equipment for those functions onboard and do not interact
with their landers any further once they roll off.
On each Mars Exploration Rover, the core structure is made of composite honeycomb
material insulated with a high-tech material called aerogel. This core body, called the
warm electronics box, is topped with a triangular surface called the rover equipment
deck. The deck is populated with three antennas, a camera mast and a panel of solar
cells. Additional solar panels are connected by hinges to the edges of the triangle. The
solar panels fold up to fit inside the lander for the trip to Mars, and deploy to form a
total area of 1.3 square meters (14 square feet) of three-layer photovoltaic cells. Each
layer is of different materials: gallium indium phosphorus, gallium arsenide and germa-
nium. The array can produce nearly 900 watt-hours of energy per martian day, or sol.
However, by the end of the 90-sol mission, the energy generating capability is reduced
to about 600 watt-hours per sol because of accumulating dust and the change in sea-
son. The solar array repeatedly recharges two lithium-ion batteries inside the warm
electronics box.
Doing sport utility vehicles one better, each rover is equipped with six-wheel drive. A
rocker-bogie suspension system, which bends at its joints rather than using any
springs, allows rolling over rocks bigger than the wheel diameter of 26 centimeters (10
inches). The distribution of mass on the vehicle is arranged so that the center of mass
is near the pivot point of the rocker-bogie system. That enables the rover to tolerate a
tilt of up to 45 degrees in any direction without overturning, although onboard comput-
ers are programmed to prevent tilts of more than 30 degrees. Independent steering of
the front and rear wheels allows the rover to turn in place or drive in gradual arcs.
The rover has navigation software and hazard-avoiding capabilities it can use to make
its own way toward a destination identified to it in a daily set of commands. It can
move at up to 5 centimeters (2 inches) per second on flat hard ground, but under auto-
mated control with hazard avoidance, it travels at an average speed about one-fifth of
Two stereo pairs of hazard-identification cameras are mounted below the deck, one
pair at the front of the rover and the other at the rear. Besides supporting automated
navigation, the one on the front also provides imaging of what the rover's arm is doing.
Two other stereo camera pairs sit high on a mast rising from the deck: the panoramic
camera included as one of the science instruments, and a wider-angle, lower-resolu-
tion navigation camera pair. The mast also doubles as a periscope for another one of
the science instruments, the miniature thermal emission spectrometer.
The rest of the science instruments are at the end of an arm, called the "instrument
deployment device," which tucks under the front of the rover while the vehicle is travel-
ing. The arm extends forward when the rover is in position to examine a particular
rock or patch of soil.

The parachute is attached to the backshell and opens to about 15 meters (49 feet) in

diameter. The parachute design was tested under simulated martian conditions in a

large wind tunnel at NASA's Ames Research Center near Sunnyvale, Calif.

The backshell carries a deceleration meter used to determine the right moment for

deploying the parachute. Solid-fuel rockets mounted on the underside of the shell

Cruise stage

Back shell

Rover and

Heat shield

Flight system

reduce vertical velocity and any excessive horizontal velocity just before landing.

The airbags, based on Pathfinder's design, cushion the impact of the lander on the

surface. Each of the four faces of the folded-up lander is equipped with an envelope of

six airbags stitched together. Explosive gas generators rapidly inflate the airbags to a

pressure of about 6900 Pascal (one pound per square inch). Each airbag has double

bladders to support impact pressure and, to protect the bladders from sharp rocks, six

layers of a special cloth woven from polymer fiber that is five times stronger than steel.

The fiber material, Vectran, is used in the strings of archery bows and tennis racquets.

The lander, besides deploying the airbags, can set the rover right-side-up, if necessary,

and provides an adjustable platform from which the rover can roll onto Mars' surface.

It also carries a radar altimeter used for timing some descent events, as well as two

The lander's basic structure is four triangular petals made of graphite-epoxy composite

material. Three petals are each attached with a hinge to an edge of the central base

petal. The rover stays fastened to the base petal during the flight and landing. When

folded up, the lander's petals form a tetrahedral box around the stowed rover. Any of

the petals could end up on the bottom when the airbag-cushioned bundle rolls to a

stop after landing. Electric motors at the hinges have enough torque to push the lander

open, righting the rover, if it lands on one of the side petals.

Other motors retract the deflated airbags. An apron made out of the same type of

tough fabric as the airbags stretches over ribs and cables connected to the petals, pro-

viding a surface that the rover can drive over to get off the lander. The side petals can

also be adjusted up or down from the plane of the base petal to accommodate uneven

terrain and improve the rover's path for driving off of the lander.

Nearly 4 million people have a special connection to the Mars Exploration Rover pro-

ject by having their names recorded on each mission's lander. Each of the two landers

carries a digital versatile disc, or DVD, containing millions of names of people around

the world collected during a "Send Your Name to Mars" campaign, which ended in

November 2002.

At the heart of each Mars Exploration Rover spacecraft is its rover. This is the mobile

geological laboratory that will study the landing site and travel to examine selected

rocks up close.

The Mars Exploration Rovers differ in many ways from their only predecessor, Mars

Pathfinder's Sojourner rover. Sojourner was about 65 centimeters (2 feet) long and

Navigation cameras

Mini-thermal emission

spectrometer (at rear)

Low-gain antenna

Solar arrays antenna

Calibration target

High-gain antenna

Magnet array

Alpha particle

imager Mössbauer

Rocker-bogie mobility system

Rock abrasion tool

Mars Exploration Rover

weighed 10 kilograms (22 pounds). Each Mars Exploration Rover is 1.6 meter (5.2

feet) long and weighs 174 kilograms (384 pounds). Sojourner traveled a total distance

equal to the length of about one football field during its 12 weeks of activity on Mars.

Each Mars Exploration Rover is expected to travel six to 10 times that distance during

its three-month prime mission. Pathfinder's lander, not Sojourner, housed that mis-

sion's main telecommunications, camera and computer functions. The Mars

Exploration Rovers carry equipment for those functions onboard and do not interact

with their landers any further once they roll off.

On each Mars Exploration Rover, the core structure is made of composite honeycomb

material insulated with a high-tech material called aerogel. This core body, called the

warm electronics box, is topped with a triangular surface called the rover equipment

deck. The deck is populated with three antennas, a camera mast and a panel of solar

cells. Additional solar panels are connected by hinges to the edges of the triangle. The

solar panels fold up to fit inside the lander for the trip to Mars, and deploy to form a

total area of 1.3 square meters (14 square feet) of three-layer photovoltaic cells. Each

layer is of different materials: gallium indium phosphorus, gallium arsenide and germa-

nium. The array can produce nearly 900 watt-hours of energy per martian day, or sol.

However, by the end of the 90-sol mission, the energy generating capability is reduced

to about 600 watt-hours per sol because of accumulating dust and the change in sea-

son. The solar array repeatedly recharges two lithium-ion batteries inside the warm

electronics box.

Doing sport utility vehicles one better, each rover is equipped with six-wheel drive. A

rocker-bogie suspension system, which bends at its joints rather than using any

springs, allows rolling over rocks bigger than the wheel diameter of 26 centimeters (10

inches). The distribution of mass on the vehicle is arranged so that the center of mass

is near the pivot point of the rocker-bogie system. That enables the rover to tolerate a

tilt of up to 45 degrees in any direction without overturning, although onboard comput-

ers are programmed to prevent tilts of more than 30 degrees. Independent steering of

the front and rear wheels allows the rover to turn in place or drive in gradual arcs.

The rover has navigation software and hazard-avoiding capabilities it can use to make

its own way toward a destination identified to it in a daily set of commands. It can

move at up to 5 centimeters (2 inches) per second on flat hard ground, but under auto-

mated control with hazard avoidance, it travels at an average speed about one-fifth of

Two stereo pairs of hazard-identification cameras are mounted below the deck, one

pair at the front of the rover and the other at the rear. Besides supporting automated

navigation, the one on the front also provides imaging of what the rover's arm is doing.

Two other stereo camera pairs sit high on a mast rising from the deck: the panoramic

camera included as one of the science instruments, and a wider-angle, lower-resolu-

tion navigation camera pair. The mast also doubles as a periscope for another one of

the science instruments, the miniature thermal emission spectrometer.

The rest of the science instruments are at the end of an arm, called the "instrument

deployment device," which tucks under the front of the rover while the vehicle is travel-

ing. The arm extends forward when the rover is in position to examine a particular

rock or patch of soil.