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Rover   Sojourner   Rocky 7   Mars Exploration Rover (MER)

    Sojourner   Rocky 7   Mars Exploration Rover
Mass   11.5 kg
Size   60cm x 40cm x 35cm
  60cm x 40cm x 33cm   Height 157cm
Speed   0.007 m/sec (0.4 m/min)

      0.05 m/sec (3m/min)
One-Day Range   5m (Must stay within sight of the Lander)

100m (Does not depend on the Lander)

Total Range   Designed for 20m (Lasted 100m)       Designed for 1000m (Mission success defined at 600m)
Expected Lifetime   7 Days (Lasted 83)       90 Days (Could last longer)
Mission Description   During July 1997, explore the terrain of Mars within sight of the Pathfinder lander, conducting technology and science experiments.   On Earth, demonstrate new technology concepts for use in a long range (50km) traversal across Mars.  

Scientific goals are to search for, and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. Sites targeted appear to have been affected by liquid water in the past.

Mechanical System   Mobility configuration and general size are drawn from the Rocky 4 prototype.   Employs Sojourner flight spare wheels and steering struts, and is approximately the same size. All other mechanical designs are new.  

The design of the suspension system is similar to the Sojourner rover "rocker-bogie" system. However wheels and chassis design are new

Thermal System  

Employs aerogel insulator to stay above -40° C during Mars night.

Night temperatures on Mars can drop to -96°C (-140°F).

  Designed with fans to stay below 70°C during terrestrial desert testing.  

Rover's WEB operating range (-40° to +40° C). This is achived through the insulated walls of the rover body being gold-painted. Aerogel insulator used inside the WEB and limited use of Heaters.

Mobility System  

Six wheel rocker-bogey with four corner steering. Total of ten actuators.

Motor Control via Bang-Bang on/off motor actuation. based on motor's output shaft position. monitored by optical encoders. No variable rate motion is possible.


Modified six wheel rocker-bogey, with two tandem wheel pairs on one end and two steering wheels on other end. Total of eight actuators. Mechanical coupling of tandem wheels can reduce total actuators to six.

Accurate variable rate motion is accomplished with Proportional / Integral / Derivative (PID) motor servoing, Pulse Width Modulation (PWM) of motor currents, and optical encoder monitoring of output shaft position.


Six wheels, each with its own individual motor. The design of the suspension system is similar to the Sojourner rover rocker-bogie system.

Motor control is the same as used by Rocky 7


Control System  

Custom surface mount board set using radiation hardened components with 80C85 CPU, 100 KIPS


Employs duplicates of Sojourner flight accelerometers and quartz rate sensor. All computer components are commercial off the shelf (COTS). CPU is a Commercial 3U VME, 68060 CPU, 100 MIPS. Some other electronics are custom design, using COTS parts.


All computer components are commercial off the shelf (COTS). Some other electronics are custom design, using COTS parts.

On-board memory and processing capacity is roughly roughly 1000 more than Sojourner.

Navigation System  

Black and white CCD cameras, and five laser stripe projectors on front side of vehicle. Quartz rate gyro. Accelerometers (3). Wheel optical encoders. Bump detector switches.

Modified Behavior control navigation algorithm developed for Rocky 4. All other rover and ground station software is new.

Software written in C and assembly in a Unix development environment using a Silicon Graphics
Inventor® based operator interface.


Black and white CCD stereo camera pairs, three pairs total: front, back, and mast. Sun position sensor. Quartz rate gyro. Accelerometers (3). Wheel optical encoders.

Currently uses a version of the Sojourner navigation algorithm, modified to accommodate the different sensors and steering performance of Rocky 7. All other on and off-board software is newly developed.

Rocky 7 uses a Wind River® real-time operating system. Real Time Innovations
ControlShell®, Network Data Delivery System® and on-board stereo correlation software.

Written in C++, C, Lisp software on a Unix development. HTML/Java® based Rover operator interface.


Four B&W Hazcams (Hazard Avoidance Cameras): Mounted on the lower portion of the front and rear of the rover,

Two B&W Navcams (Navigation Cameras):
Mounted on the mast ,these black-and-white cameras use visible light to gather panoramic, three-dimensional (3D) imagery.

Two colour Pancams (Panoramic Cameras):
Stereo pair of cameras mounted on the Rover mast and delivers three-dimensional panoramas of the Martian surface.

One Microscopic Imager:
This monochromatic science camera is mounted on the robotic arm to take extreme close-up pictures of rocks and soil.

Power System  

GaAs solar panel. One primary, non-rechargeable battery.

Rover usage about 16W peak.


Rechargeable NiCad batteries, Six solar panels.

Rover usage about 35W average.


Rechargeable NiCad batteries, Solar array.

Rover usage about 100W average.

Scientific Payload   Alpha Particle X-Ray Spectrometer (APXS)
Irradiates rocks and soil and determines their chemical components from the backscatter signature.
  COTS Visible/Near-IR Reflectance Spectrometer
Pointed and calibrated by rover arm; sensitive from 350-850 nm.

COTS Color Filter Stereo Iimager
Mast mounted CCD cameras with RGB filters.

COTS Multispectral Close-up Imager
Close focus CCD camera with multi-spectral LED illumination.

Mossbauer Spectrometer
Flight qualified science instrument for measuring iron content in soils and rocks. Sometimes attached to rover in place of close-up imager.


Panoramic Camera

Microscopic Imager (MI)

Miniature Thermal Emission Spectrometer (Mini-TES)

Mossbauer Spectrometer (MB)

Alpha Particle X-Ray Spectrometer (APXS)

Rock Abrasion Tool (RAT)

Magnet Array

Manipulation System   A one DOF arm mechanism for deploying the one science instrument. (APXS)  

The shorter four degrees-of-freedom (DOF) arm stows against the side the chassis and can dig, dump, grasp rocks, carry one sample, and point an integrated optical spectrometer and its calibration target.

The longer three DOF mast stows in a slot in the solar panel, can raise a stereo camera pair and filter wheels to 1.4 meters above the ground, use these same cameras to visually inspect the entire vehicle, and deploy another 0.5 kg instrument canister to targets in a large area around the rover.


The robotic arm has flexibility through three joints (3 DOF). At the end of the arm is a turret, shaped like a cross. This turret, a hand-like structure, holds various tools that can spin through a 350-degree turning range. The four tools, or science instruments,
on the robotic arm are:
The Microscopic Imager
The Mossbauer Spectrometer

The Alpha Particle X-Ray Spectrometer
The Rock Abrasion Tool

The Pancam Mast Assembly stands 1.4 meters from the base of the rover wheel. The pancam mast assembly serves two purposes:
To act as a periscope for the Mini-TES science instrument, and to provide height and a better point of view for the Pancams and the NavCams.

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