Mars Exploration Rover

NASA's Mars Exploration Rover (MER) Mission (since 2003) is an unmanned Mars exploration mission that includes sending two Rovers (robots) to explore the Martian surface and geology. The mission was led by Project Manager Peter Theisinger of NASA's Jet Propulsion Laboratory and Principal Investigator Steven Squyres, professor of astronomy at Cornell University.

Rover design

Drive system

Each rover has six wheels mounted on a rocker bogie suspension system that ensures all six wheels will remain on the ground while driving over rough terrain. The rocker design ensures that the rover body only goes through half of the range of motion that the "legs" and wheels could potentially experience without this suspension system. The rover rocker-bogie design allows the rover to go over obstacles (such as rocks) or through holes that are more than a wheel diameter (250 mm or 10 in) in size. Each wheel also has cleats, providing grip for climbing in soft sand and scrambling over rocks. Each wheel has its own individual motor. The two front and two rear wheels also have individual steering motors (1 each). This steering capability allows the vehicle to turn in place, a full 360 degrees. The 4-wheel steering also allows the rover to swerve and curve, making arching turns. The rover is designed to withstand a tilt of 45 degrees in any direction without overturning. However, the rover is programmed through its "fault protection limits" in its hazard avoidance software to avoid exceeding tilts of 30 degrees during its traverses.

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Each rover has the ability to spin one of its front wheels in place to grind deep into the terrain. The rover is designed to remain motionless while the digging wheel is spinning.

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The rover has a top speed on flat hard ground of 50 mm/s (2 in/s). However, in order to ensure a safe drive, the rover is equipped with hazard avoidance software that causes the rover to stop and reassess its location every few seconds. So, over time, the vehicle achieves an average speed of 10 mm/s. The rover is programmed to drive for roughly 10 seconds, then stop to observe and understand the terrain it has driven into for 20 seconds, before moving safely onward for another 10 seconds.

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Power and electronic systems

When fully illuminated, the rover solar arrays generate about 140 watts for up to four hours per Martian day (sol). The rover needs about 100 watts to drive. The power system for the Mars Exploration Rover includes two rechargeable batteries that provide energy for the rover when the sun is not shining, especially at night. Over time, the batteries will degrade and will not be able to recharge to full power capacity. Also, by the end of the 90-sol mission, the capability of the solar arrays to generate power will likely be reduced to about 50 watts of power due to anticipated dust coverage on the solar arrays, as well as the change in season.

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The rovers run a VxWorks embedded operating system on a radiation-hardened 20 MHz RAD6000 CPU with 128 MB of DRAM with error detection and correction and 3 MB of EEPROM. Also, the rovers each have 256 MB of flash memory. To survive during all of the various mission phases, the rover's "vital organs" must not exceed extreme temperatures of -40 ºC to +40 ºC (-40 ºF to 104 ºF). At night the rovers are heated by eight RHUs which each continuously generate 1 W of thermal energy from the decay of radioisotopes, along with electrical heaters that operate only when necessary. A sputtered gold film and a layer of silica aerogel are used for insulation.

Related Topics:
VxWorks - Embedded operating system - Radiation-hardened - MHz - RAD6000 - CPU - MB - DRAM - EEPROM - Flash memory - W - Radioisotope - Gold - Silica - Aerogel

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Communication

The rover has both a low-gain and high-gain antenna. The low-gain antenna is omnidirectional, and transmits data at a low rate to Deep Space Network (DSN) antennas on Earth. The high-gain antenna is directional and steerable, and can transmit data at a much higher rate.

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The rovers are also able to uplink information to other spacecraft orbiting Mars, utilizing the Mars Odyssey and Mars Global Surveyor orbiters as messengers who can pass along news to Earth for the rovers. The orbiters can also send messages to the rovers. The benefits of using the orbiting spacecraft are that the orbiters are closer to the rovers than the Deep Space Network antennas on Earth and the orbiters have Earth in their field of view for much longer time periods than the rovers on the ground. The radio waves to and from the rover are sent through the orbiters using UHF antennas, which are shorter range than the low and high-gain antennas. One UHF antenna is on the rover and one is on a petal of the lander to aid in gaining information during the critical landing event.

Related Topics:
Mars Odyssey - Mars Global Surveyor

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The images are stored and sent to Earth using a software of ICER for all lossy image compression. All MER cameras produce 1024-pixel by 1024-pixel images at 12 bits per pixel. http://216.239.41.104/search?q=cache:qdeH3xRDiEEJ:tmo.jpl.nasa.gov/progress_report/42-155/155J.pdf+&hl=en&ie=UTF-8

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Navigation, thumbnail, and many other image types are compressed to approximately 1 bit/pixel, and lower bit rates (less than 0.5 bit/pixel) will be used for certain wavelengths of multi-color panoramic images.

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The MER mission, with a total of 18 cameras on two rovers, will rely heavily on ICER wavelet based image compression file format to enable delivery of image data back to Earth during its operations.

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The MER mission is significantly advancing the state of practice of image compression for deep-space missions by using image compressors that provide substantially more effective compression than that obtained by previous missions.

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The ICER image compressor was designed to meet the specialized needs of deep-space applications. ICER is wavelet-based and produces progressive compression, providing lossless and lossy compression, and incorporates an error-containment scheme to limit the effects of data loss on the deep-space channel. ICER noticeably outperforms the JPEG image compressor

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used by the MPF mission and provides significantly more effective lossless compression than the Rice compressor used by that mission.

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Scientific instrumentation

Located on the rover's Pancam Mast Assembly are:

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• Panoramic Camera (Pancam), for determining the mineralogy, texture, and structure of the local terrain.
• The mirror for the Miniature Thermal Emission Spectrometer (Mini-TES), from Arizona State University, for identifying promising rocks and soils for closer examination, and to determine the processes that formed Martian rocks. See the main Mini-TES article.

The mast-mounted cameras are mounted 1.5 metre high. One motor for the entire Pancam Mast Assembly head turns the cameras and Mini-TES 360º in the horizontal plane. A separate elevation motor can point the cameras 90º above the horizon and 90º below the horizon. A third motor for the Mini-TES mirror elevation, enables the Mini-TES to point up to 30º over the horizon and 50º below the horizon.

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The mast also carries two monochrome navigation cameras, and four monochrome hazard cameras are mounted on the rover's body (two in front and two to the rear).

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The rover arm (also called the instrument deployment device, or IDD) holds the following:

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• Mössbauer spectrometer (MB) MIMOS II, developed by Dr. Göstar Klingelhöfer at the Johannes Gutenberg University in Mainz, Germany, is used for close-up investigations of the mineralogy of iron-bearing rocks and soils.
• Alpha particle X-Ray Spectrometer (APXS), developed by the Max Planck Institute for Chemistry in Mainz, Germany, is used for close-up analysis of the abundances of elements that make up rocks and soils.
• Magnets, for collecting magnetic dust particles. The Mössbauer Spectrometer and the Alpha Particle X-ray Spectrometer will analyze the particles collected, and help determine the ratio of magnetic particles to non-magnetic particles and composition of magnetic minerals in airborne dust and rocks that have been ground by the Rock Abrasion Tool. There are also magnets on the front of the rover, which are studied extensively by the Mössbauer spectrometer.
• Microscopic Imager (MI), for obtaining close-up, high-resolution images of rocks and soils.
• Rock Abrasion Tool (RAT), for removing dusty and weathered rock surfaces and exposing fresh material for examination by instruments onboard.

The robotic arm will be able to place instruments directly up against rock and soil targets of interest.

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