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Mars Exploration Rover

2007 Schools Wikipedia Selection. Related subjects: Space transport

   Artist's Concept of Rover on Mars (credit: Maas Digital LLC)
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   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.
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   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.
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   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
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   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)
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   MER cruise stage diagram (Courtesy NASA/JPL-Caltech)
   Cruise stage of Opportunity rover
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   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.

Aeroshell

   Overview of the Mars Exploration Rover aeroshell.
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   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

Composition

   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.

Parachute

   Mars Exploration Rover's parachute test
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   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.
   Enlarge
   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.

Airbags

   Artist's concept of inflated airbags
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   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.

Lander

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

Communication

   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)
   Enlarge
   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.
   Enlarge
   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)
   Enlarge
   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).

Maestro

   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.

Books

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

   Retrieved from " http://en.wikipedia.org/wiki/Mars_Exploration_Rover"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
