Mars Exploration Rover

2007 Schools Wikipedia Selection. Related subjects: Space transport

Artist's Concept of Rover on Mars (credit: Maas Digital LLC)
Artist's Concept of Rover on Mars (credit: Maas Digital LLC)
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NASA's Mars Exploration Rover (MER) Mission is an ongoing unmanned Mars exploration mission, commenced in 2003, that sent two robotic rovers Spirit and Opportunity 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.

Primary among the mission's scientific goals is to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The Mars Exploration Rover mission is part of NASA's Mars Exploration Program which includes three previous successful landers: the two Viking landers in 1976 and Pathfinder in 1997.

The total cost of building, launching, landing and operating the rovers on the surface for the initial 90 day primary mission was about US $820 million. With the rovers still functioning over two years after landing, mission funding has been extended to at least September 2007.

In recognition of the vast amount of scientific information amassed by both rovers, two asteroids have been named in their honour: 37452 Spirit and 39382 Opportunity.

Brief timeline

The MER-A rover, Spirit, was launched on June 10, 2003 at 17:59 UTC, and MER-B, Opportunity, on July 7, 2003 at 15:18 UTC. Spirit landed in Gusev crater on January 4, 2004 at 04:35 Ground UTC. Opportunity landed in the Meridiani Planum on the opposite side of Mars from Spirit, on January 25, 2004 05:05 Ground UTC. In the week following Spirit's landing, NASA's website recorded 1.7 billion hits and 34.6 terabytes of data transferred, eclipsing records set by previous NASA missions.

NASA's Mars Exploration Rover Spirit casts a shadow over the trench that the rover is examining with tools on its robotic arm. Spirit took this image with its front hazard-avoidance camera on February 21, 2004, during the rover's 48th martian day, or sol 48.
NASA's Mars Exploration Rover Spirit casts a shadow over the trench that the rover is examining with tools on its robotic arm. Spirit took this image with its front hazard-avoidance camera on February 21, 2004, during the rover's 48th martian day, or sol 48.

On January 21, the Deep Space Network lost contact with the Spirit rover, for reasons originally thought to be related to a thunderstorm over Australia. The rover transmitted a message with no data on Wednesday the 21st, but the Spirit rover missed another communications session with the Mars Global Surveyor later that day. JPL succeeded on Thursday the 22nd in receiving a beep from the rover, indicating that it was in fault mode. On the 23rd, the flight team succeeded in getting the rover to send back data. As a consequence of the fault, believed to have been caused by an error in the rover's Flash memory subsystem, the rover was unable to perform any science for 10 days, while engineers updated its software and ran tests. The problem was corrected by reformatting Spirit's flash memory and upgrading the software with a patch to avoid memory overload, Opportunity was also upgraded with the same patch as a precaution. Spirit was returned to full scientific operations by 5 February. To date, this was the most serious anomaly in the mission.

On March 23, a news conference was held revealing what were announced to be "major discoveries", in the search for hints of past liquid water on the Martian surface. A delegation of the science team showed pictures and data revealing a stratification pattern and cross bedding within the rocks in the outcrop inside a crater in Meridiani Planum, landing site of the MER-B, Opportunity Rover, suggesting a history of flowing water in the region. The irregular distribution of chlorine and bromine also suggests that the rover sat in a place that once had been the shoreline of a salty sea, now evaporated.

On April 8, 2004, NASA announced that it was extending the mission life of the rovers from 3 months to 8 months. The extension provided an immediate additional US $15 million in funding through September, as well as $2.8 million per month for continuing operations.

On April 30, 2004, Opportunity arrived at Endurance crater, taking about 5 days to drive the 200 meters.

On September 22, 2004, NASA announced that it was extending the mission life of the rovers for another 6 months. Opportunity was to leave Endurance crater, visit its discarded heat shield, and then proceed to Victoria crater. Spirit was to attempt to climb to the top of the Columbia Hills.

On April 6, 2005, with the two rovers still functioning well, NASA announced an additional 18 month extension of the mission to September 2006. Opportunity was to visit the "Etched Terrain" and Spirit was to climb a rocky slope toward the top of Husband Hill.

Spirit's "postcard" view from the summit of Husband Hill: a windswept plateau strewn with rocks, small exposures of outcrop, and sand dunes.  The view is to the north, looking down upon the "Tennessee Valley".  This approximate true-color composite spans about 90 degrees and consists of 18 frames captured by the rover's panoramic camera.
Spirit's "postcard" view from the summit of Husband Hill: a windswept plateau strewn with rocks, small exposures of outcrop, and sand dunes. The view is to the north, looking down upon the "Tennessee Valley". This approximate true-colour composite spans about 90 degrees and consists of 18 frames captured by the rover's panoramic camera.

On August 21, 2005, Spirit summitted "Husband Hill" after 581 sols and a drive of 4.81 kilometers (2.99 mi).

Spirit celebrated its one Martian year anniversary (669 sols or 687 Earth days) on November 20, 2005. Opportunity celebrated its anniversary on December 12. Both rovers have lasted over seven times their original life expectancy. At the beginning of the mission, it was expected that Spirit and Opportunity would not survive much longer than ninety days. The Columbia Hills were "just a dream" according to rover driver Chris Leger.

On February 7, 2006, Spirit reached the semicircular rock formation known as Home Plate. It is a layered rock outcrop that puzzles, yet excites scientists. It is thought that Home Plate's rocks are explosive volcanic deposits, yet other possibilities exist, including impact deposits or wind/water borne sediment.

On March 13, 2006, Spirit's front right wheel ceased working while moving itself to McCool Hill. Her drivers attempted to drag the dead wheel behind Spirit, but this only worked until reaching an impassable sandy area on the lower slopes. Drivers directed Spirit to a smaller sloped feature, dubbed "Low Ridge Haven", where she is currently spending the long Martian winter, waiting for spring and increased solar power levels suitable for driving.

On September 26, 2006, Spaceflight Now reported that NASA has extended mission for the two rovers through September 2007.

On September 27, 2006, Opportunity reached the rim of Victoria crater.

Spirit has lasted over 1,000 Martian days exploring Gusev Crater as of October 25, 2006.

Spacecraft design

Delta II lifting off
Delta II lifting off

The Mars Exploration Rover is designed to be stowed in the nose of a Delta II rocket. Each spacecraft consists of several components. These are:

  • Rover - 185 kg (408 lb)
  • Lander - 348 kg (767 lb)
  • Backshell / Parachute - 209 kg (742 lb)
  • Heat Shield - 78 kg (172 lb)
  • Cruise Stage - 193 kg (425 lb)
  • Propellant - 50 kg (110 lb)

For a total mass of 1,063 kg (2,343 lb).

Cruise stage

MER cruise stage diagram (Courtesy NASA/JPL-Caltech)
MER cruise stage diagram (Courtesy NASA/JPL-Caltech)
Cruise stage of Opportunity rover
Cruise stage of Opportunity rover

The cruise stage is the component of the spacecraft used for travel from Earth to Mars. The cruise stage is very similar to the Mars Pathfinder design and is approximately 2.65 meters (8.7 feet) in diameter and 1.6 m (5.2 ft) tall including the entry vehicle (see below).

The primary structure is aluminium with an outer ring of ribs covered by the solar panels, which are about 2.65 m (8.7 ft) in diameter. Divided into five sections, the solar arrays can provide up to 600 watts of power near Earth and 300 W at Mars.

Heaters and multi-layer insulation keep the spacecraft electronics "warm." There is also a freon system used to remove heat from the flight computer and telecommunications hardware inside the rover so they don't get overheated. Cruise avionics systems allow the flight computer in the rover to interface with other electronics such as the sun sensors, the star scanner, and the heaters.

Cruise stage navigation components

Star scanner and sun sensor: The star scanner (with a backup system) and sun sensor allow the spacecraft to know its orientation in space by analyzing the position of the Sun and other stars in relation to itself. Sometimes the spacecraft can be slightly off course, a situation that is expected given the 320 million mile (500 Gm) journey the spacecraft will make. Navigators thus plan up to six trajectory correction maneuvers, along with health checks.

Propellant tanks: To ensure the spacecraft arrives at Mars in the right place for its planned landing, two light-weight, aluminium-lined tanks carry a maximum capacity of about 31 kg (about 68 lb) of hydrazine propellant. Along with cruise guidance and control systems, these tanks of propellant allow navigators to keep the spacecraft closely on course during cruise. Through burns and pulse firings, the propellant enables three different types of trajectory correction maneuvers:

  • An axial burn uses pairs of thrusters to change spacecraft velocity
  • A lateral burn uses two "thruster clusters" (four thrusters per cluster) to move the spacecraft "sideways" through seconds-long pulses
  • Pulse mode firing uses coupled thruster pairs for spacecraft precession maneuvers (turns)

Cruise stage communication components

The spacecraft uses a high-frequency X band radio wavelength that allows spacecraft communications with less power and smaller antennas than many older spacecraft, which used S band. Navigators send the commands through two X-band antennae on the cruise stage:

Cruise Low-gain Antenna: The cruise low-gain antenna is mounted inside the inner ring and the cruise medium-gain antenna is mounted in the outer ring. During flight, the spacecraft is spin-stabilized with a spin rate of 2 rpm. Periodic spin axis pointing updates will make sure the antenna stays pointed toward Earth and that the solar panels stay pointed toward the Sun. The spacecraft will use the low-gain antenna early in cruise when the spacecraft is close to Earth. The low-gain antenna is omni-directional, so the transmission power that reaches Earth falls off rapidly with increasing distance.

Cruise Medium-Gain Antenna: As the spacecraft moves farther from Earth and closer to Mars, the Sun comes into the same area of the sky as viewed from the spacecraft and not as much energy falls on the Earth alone. Therefore, the spacecraft switches to a medium-gain antenna, which can direct the same amount of transmission power into a tighter beam to reach Earth.


Overview of the Mars Exploration Rover aeroshell.
Overview of the Mars Exploration Rover aeroshell.

The aeroshell forms a protective covering for the lander during the seven month voyage to Mars. The aeroshell, together with the lander and the rover, constitute what engineers call the "entry vehicle." The aeroshell's main purpose is to protect the lander with the rover stowed safely inside from the intense heating of entry into the thin Martian atmosphere on landing day.

The aeroshell for the Mars Exploration Rovers is based on the Mars Pathfinder and Mars Viking designs.

Parts of the aeroshell

The aeroshell is made of two principal parts:

  • The heat shield (flat, brownish half)
  • The backshell (large, white-painted, cone-shaped half)

The heat shield protects the lander and rover from the intense heat from entry into the Martian atmosphere and acts as the first aerobrake for the spacecraft.

The backshell carries the parachute and several components used during later stages of entry, descent, and landing, including:

  • A parachute (stowed at the top of the backshell)
  • The backshell electronics and batteries that fire off pyrotechnic devices like separation nuts, rockets and the parachute mortar
  • A Litton LN-200 Inertial Measurement Unit (IMU), which monitors and reports the orientation of the backshell as it swings under the parachute
  • Three large solid rocket motors called RAD rockets (Rocket Assisted Descent), each providing about a ton of force (10 kilonewtons) for over 2 seconds
  • Three small solid rockets called TIRS (mounted so that they aim horizontally out the sides of the backshell) that provide a small horizontal kick to the backshell to help orient the backshell more vertically during the main RAD rocket burn


Built by the Lockheed Martin Astronautics Co. in Denver, Colorado, the aeroshell is made out of an aluminium honeycomb structure sandwiched between graphite-epoxy face sheets. The outside of the aeroshell is covered with a layer of phenolic honeycomb. This phenolic honeycomb is filled with an ablative material (also called an "ablator"), that dissipates heat generated by atmospheric friction.

The ablator itself is a unique blend of cork wood, binder and many tiny silica glass spheres. It was invented for the heat shields flown on the Viking Mars lander missions 25 years ago. A similar technology was used in the first US manned space missions Mercury, Gemini and Apollo. It is specially formulated to react chemically with the Martian atmosphere during entry and carry heat away, leaving a hot wake of gas behind the vehicle. The vehicle will slow from 19000 km/h (about 12000 mph) to about 1600 km/h (1000 mph) in about a minute, producing about 60 m/s² (6 g) of acceleration on the lander and rover.

Both the backshell and heat shield are made of the same materials, but the heat shield has a thicker 1/2 inch (12.7 mm) layer of the ablator. Also, instead of being painted, the backshell will be covered with a very thin aluminized PET film blanket to protect it from the cold of deep space. The blanket will vaporize during Mars atmospheric entry.


Mars Exploration Rover's parachute test
Mars Exploration Rover's parachute test

The parachute helped slow the spacecraft down during entry, descent, and landing. It is located in the backshell.

Parachute design

The 2003 parachute design is part of a long-term Mars parachute technology development effort and is based on the designs and experience of the Viking and Pathfinder missions. The parachute for this mission is 40% larger than Pathfinder's because the largest load for the Mars Exploration Rover is 80 to 85 kilonewtons (kN) or 18,000 to 19,000 lbf when the parachute fully inflates. By comparison, Pathfinder's inflation loads were approximately 35 kN (about 8,000 lbf). The parachute was designed and constructed in South Windsor, Connecticut by Pioneer Aerospace ( website), the company that also designed the parachute for the Stardust mission.

Parachute composition

The parachute is made out of two durable, lightweight fabrics: polyester and nylon. The parachute has a triple bridle (the tethers that connect the parachute to the backshell) made of Kevlar.

The amount of space available on the spacecraft for the parachute is so small that the parachute must be pressure packed. Before launch, a team must tightly fold together the 48 suspension lines, three bridle lines, and the parachute. The parachute team loads the parachute in a special structure that then applies a heavy weight to the parachute package several times. Before placing the parachute into the backshell, the parachute is heat set to sterilize it.

Parts that work in tandem with the parachute

Descent is halted by retrorockets and lander is dropped 10m (30 feet) to the surface.
Descent is halted by retrorockets and lander is dropped 10m (30 feet) to the surface.

Zylon Bridles: After the parachute is deployed at an altitude of about 10 km (6 miles) above the surface, the heatshield is released using 6 separation nuts and push-off springs. The lander then separates from the backshell and "rappels" down a metal tape on a centrifugal braking system built into one of the lander petals. The slow descent down the metal tape places the lander in position at the end of another bridle (tether), which is made of a nearly 20 m (65 ft) long braided Zylon.

Zylon is an advanced fibre material similar to Kevlar that is sewn in a webbing pattern (like shoelace material) to make it stronger. The Zylon bridle provides space for airbag deployment, distance from the solid rocket motor exhaust stream, and increased stability. The bridle incorporates an electrical harness that allows the firing of the solid rockets from the backshell as well as provides data from the backshell inertial measurement unit (which measures rate and tilt of the spacecraft) to the flight computer in the rover.

Rocket assisted descent (RAD): motors. Because the atmospheric density of Mars is less than 1% of Earth's, the parachute alone cannot slow down the Mars Exploration Rover enough to ensure a safe, low landing speed. The spacecraft descent is assisted by rockets that bring the spacecraft to a dead stop 10-15 m (30-50 ft) above the Martian surface.

Radar altimeter unit: A radar altimeter unit is used to determine the distance to the Martian surface. The radar's antenna is mounted at one of the lower corners of the lander tetrahedron. When the radar measurement shows the lander is the correct distance above the surface, the Zylon bridle will be cut, releasing the lander from the parachute and backshell so that it is free and clear for landing. The radar data will also enable the timing sequence on airbag inflation and backshell RAD rocket firing.


Artist's concept of inflated airbags
Artist's concept of inflated airbags

Airbags used in the Mars Exploration Rover mission are the same type that Mars Pathfinder used in 1997. Airbags must be strong enough to cushion the spacecraft if it lands on rocks or rough terrain and allow it to bounce across Mars' surface at freeway speeds after landing. To add to the complexity, the airbags must be inflated seconds before touchdown and deflated once safely on the ground.

The fabric used for the new Mars airbags is a synthetic material called Vectran that was also used on Mars Pathfinder. Vectran has almost twice the strength of other synthetic materials, such as Kevlar, and performs better at cold temperatures.

There were six 100 denier (10 mg/m) layers of the light but tough Vectran protecting one or two inner bladders of the same material in 200 denier (20 mg/m). Using the 100 denier (10 mg/m) means there is more actual fabric in the outer layers where it is needed, because there are more threads in the weave.

Each rover used four airbags with six lobes each, which were all connected. Connection is important, since it helps abate some of the landing forces by keeping the bag system flexible and responsive to ground pressure. The fabric of the airbags was not attached directly to the rover; ropes that crisscross the bags held the fabric to the rover. The ropes give the bags shape, which makes inflation easier. While in flight, the bags were stowed along with three gas generators that are used for inflation.


MER lander petals opening (Courtesy NASA/JPL-Caltech)
MER lander petals opening (Courtesy NASA/JPL-Caltech)

The spacecraft lander is a protective "shell" that houses the rover and protects it, along with the airbags, from the forces of impact.

The lander is a strong, lightweight structure, consisting of a base and three sides "petals" in the shape of a tetrahedron. The Lander structure consists of beams and sheets that are made from a composite material. The lander beams are made out of layers of graphite fibre woven into a fabric, creating a material that is lighter than aluminium and more rigid than steel. Titanium fittings are bonded (glued and fitted) onto the lander beams to allow it to be bolted together. The Rover is held inside the lander with bolts and special nuts that are released after landing with small explosives.

Turning the rover upright

The three petals are connected to the base of the tetrahedron with hinges. Each petal hinge has a powerful motor that is strong enough to lift the entire lander. The Rover plus Lander has a mass of about 533 kilograms (1175 pounds). The Rover alone weighs about 185 kg (408 lb). The gravity on Mars is about 38% of Earth's, so the motor does not need to be as powerful as it would on Earth. Having a motor on each petal ensures that the lander can place the rover in an upright position no matter which side the lander comes to rest on after the bouncing and rolling subsides on the surface of Mars.

The Rover contains accelerometers that can detect which way is down (toward the surface of Mars) by measuring the pull of gravity. The Rover computer, knowing which way is down, commands the correct lander petal to open to place the rover upright. Once the base petal is down and the rover is upright, the other two petals are opened.

The petals initially open to an equally flat position, so all sides of the lander are straight and level. The petal motors are strong enough so that if two of the petals come to rest on rocks, the base with the rover will be held in place like a bridge above the surface of Mars. The base will hold at a level even with the height of the petals resting on rocks, making a straight flat surface throughout the length of the open, flattened lander. The flight team on Earth may then send commands to the rover to adjust the petals to create a better pathway for the rover to drive off of the lander and safely move onto the Martian surface without dropping off a steep rock.

Moving the rover safely onto Martian surface

Spirit's lander on Mars
Spirit's lander on Mars

The process of the rover moving off of the lander is called the egress phase of the mission. The rover must be able to safely drive off of the lander without getting its wheels caught up in the airbag material or without dropping off a sharp incline.

To aid in the egress process, the lander petals contain a retraction system that will slowly drag the airbags toward the lander to get them out of the path of the rover (this step is performed before the Lander petals are opened.) Small ramps or "ramplets" are also connected to the petals, which fan out and create "driving surfaces" that fill in large spaces between the lander petals. These ramplets, nicknamed "Batwings," are made out of Vectran cloth. The "batwings" help cover dangerous, uneven terrain, rock obstacles, and leftover airbag material that could get entangled in the rover wheels. These Vectran cloth surfaces make a circular area from which the rover can roll off the lander, providing additional directions the rover can leave the lander. The ramplets also lower the height of the "step" that the rover must take off of the lander, preventing possible death of the rover. If the rover banged its belly on a rock or smashed into the ground as it was moving off the lander, the entire mission could be lost.

About 3 hours is allotted to retract the airbags and deploy the lander petals.

Rover design

Mars Exploration Rover vs. Sojourner rover (Courtesy NASA/JPL-Caltech)
Mars Exploration Rover vs. Sojourner rover (Courtesy NASA/JPL-Caltech)

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.

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.

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.

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 lithium ion batteries (weighing 16 pounds (7.15 kg) each), 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. For comparison, the future Mars Science Laboratory is expected to last approximately one Martian year using radioisotope thermoelectric generators to power its large suite of instruments. Solar panels are being considered for an MSL mission (or missions), but RTGs provide versatility to work in dark environments and high latitudes where solar energy is not an efficient method for power generation.

It was thought that by the end of the 90-sol mission, the capability of the solar arrays to generate power would likely be reduced to about 50 watts. This was due to anticipated dust coverage on the solar arrays, as well as the change in season. However, almost two Earth years later, the rover's power supplies hover between 300 watt-hours and 900 watt-hours per day, depending on dust coverage. Cleaning events (probably wind) have occurred more frequently than NASA originally anticipated, keeping the solar arrays relatively free of dust and extending the life of the mission.

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 °C to +40 °C (-40 °F to 104 °F). At night the rovers are heated by eight radioisotope heater units (RHU) 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.


The rover has both a low-gain and a 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 directly to Earth at a higher rate.

The rovers are also able to uplink information using the low-gain UHF antenna 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 relay through the Odyssey spacecraft is used for most of the data downlinked the Earth. 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.

All MER cameras (a total of 18 cameras on two rovers) produce 1024-pixel by 1024-pixel images at 12 bits per pixel. , although most images are truncated to 8 bits per pixel before compression.

The images are compressed using ICER before being stored and sent to Earth. 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-colour panoramic images.

ICER image compression provides substantially more effective compression than that obtained by previous missions. The image compressor was designed to meet the specialized needs of deep-space applications. ICER is wavelet-based and produces progressive compression, providing both lossless and lossy compression, and incorporates an error-containment scheme to limit the effects of data loss on the deep-space channel. ICER outperforms the JPEG image compressor used by the MPF mission and provides significantly more effective lossless compression than the Rice compressor used by that mission.

Scientific instrumentation

Located on the rover's Pancam Mast Assembly are:

  • Panoramic Camera (Pancam), for determining the texture, colour, mineralogy, and structure of the local terrain. The Panoramic-camera Mast Assembly (PMA) was built by Ball Aerospace & Technologies Corp., Boulder, Colorado.
  • Navigation Camera (Navcam), a lower resolution (but higher field of view) monochromatic camera for navigation and driving.
  • 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 meter high. One motor for the entire Pancam Mast Assembly head turns the cameras and Mini-TES 360° in the horizontal plane. A separate elevation motor can point the cameras 90° above the horizon and 90° below the horizon. A third motor for the Mini-TES mirror elevation, enables the Mini-TES to point up to 30° over the horizon and 50° below the horizon. The High-Gain Antenna Gimbal (HGAG) was also built by Ball Aerospace & Technologies Corp.

In addition, four monochromatic hazard cameras ( Hazcams) are mounted on the rover's body (two in front and two to the rear).

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

  • 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, developed by Jens Martin Knudsen and his group at the Niels Bohr Institute, Copenhagen. 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), development led by Ken Herkenhoff and his team at the USGS Astrogeology Research Program, for obtaining close-up, high-resolution images of rocks and soils.
  • Rock Abrasion Tool (RAT), developed by Honeybee Electronics, for removing dusty and weathered rock surfaces and exposing fresh material for examination by instruments onboard.

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

MER Panoramic Camera (Courtesy NASA/JPL-Caltech)
MER Panoramic Camera (Courtesy NASA/JPL-Caltech)
An image from Miniature Thermal Emission Spectrometer (Mini-TES), an instrument on the probe that is used for identifying rocks.
An image from Miniature Thermal Emission Spectrometer (Mini-TES), an instrument on the probe that is used for identifying rocks.
Alpha particle X-Ray Spectrometer (APXS) (Courtesy NASA/JPL-Caltech)
Alpha particle X-Ray Spectrometer ( APXS) (Courtesy NASA/JPL-Caltech)

Naming of Spirit and Opportunity

The Spirit and Opportunity rovers were named through a student essay competition. The winning entry was by Sofi Collis, a third grade Russian American student from Arizona.

I used to live in an Orphanage.
It was dark and cold and lonely.
At night, I looked up at the sparkly sky and felt better.
I dreamed I could fly there.
In America, I can make all my dreams come true.....
Thank-you for the "Spirit" and the "Opportunity"

— Sofi Collis, age 9

Prior to this, during the development and building of the rovers, they were known as MER-1 (Opportunity) and MER-2 (Spirit). Internally NASA also uses the mission designations MER-A (Spirit) and MER-B (Opportunity) based on the order of landing on Mars (Spirit first then Opportunity).


The NASA team uses a software application called SAP to view images collected from the rover, and to plan its daily activities. There is a version available to the public called Maestro. Maestro is written in Java so it will run on many different platforms including Microsoft Windows, Macintosh, Solaris, Linux, and Irix. The software, along with companion datasets, can be obtained from Maestro Headquarters.

Timestamps of Mars Exploration Rover images

It is possible to tell the time an image was taken by the Mars Exploration Rovers from the image's filename.

The images taken by Spirit and Opportunity have filenames with a built-in timestamp: characters 3–11 represent the number of (Earth) seconds since the J2000.0 epoch ( January 1, 2000 11:58:55.816 UTC) . Thus an image with a name like "1P132176262ESF05A6P2670R8M1.JPG" has a timestamp of 132176262 seconds, which corresponds to March 10, 2004 07:36:37.816 UTC.

Note: A leap second was added after December 31, 2005.


  • Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet by Steve Squyres (published August 2005; ISBN 1401301495)

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