Mars Polar Lander
Encyclopedia
The Mars Polar Lander, also referred to as the Mars Surveyor '98 Lander, was a 290-kilogram robotic spacecraft
lander
, launched by NASA
on January 3, 1999, to study the soil and climate
of Planum Australe
, a region near the south pole on Mars
, as part of the Mars Surveyor '98 mission
. However, on December 3, 1999, after the descent phase was expected to be complete, the lander failed to reestablish communication with Earth. It was determined the most likely cause of the mishap was an improperly ceased engine firing prior to the lander touching the surface, causing the lander to impact at a high velocity.
, a lander was sought as a way to gather climate data from the ground in conjunction with an orbiter. It was suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole. If that were true, then why does it differ from the Martian north pole, a region suspected to contain much less frozen water. In planning Mars Polar Lander, the potential water content in the Martian south pole was the strongest determining factor for choosing a landing location.
The primary objectives of the mission included:
enclosure housed the computer, power distribution electronics and batteries, telecommunication electronics, and the Capillary Pump Loop Heat Pipe (LHP) components which maintained operable temperature. Each these components included redundant units in the event that one may fail.
in Florida, aboard a Delta II 7425
launch vehicle. The complete burn sequence lasted for 47.7 minutes after a Thiokol Star 48
B solid-fuel third stage booster placed the spacecraft into an 11 month, Mars transfer trajectory at a final velocity of 6.884 kilometers per second with respect to Mars. During cruise, the spacecraft was stowed inside an aeroshell
capsule and was powered and communicated with Earth with the a segment known as the cruise stage.
oriented to absorb the intense, 1650 °C heat that would be generated as the descent capsule passed through the atmosphere. Traveling at 6.9 kilometers per second, the entry capsule entered the Martian atmosphere
at 20:10:00 UTC and was expected to land in the vicinity of 76°S 195°W in a region known as Planum Australe
. Communication was expected to be reestablished with the spacecraft at 20:39:00 UTC after having landed. However, no communication attempt was successful with the spacecraft.
The Phoenix
lander has subsequently completed most of the objectives of Mars Polar Lander, carrying several of the same or derivative instruments. Phoenix landed successfully on May 25, 2008.
, located on the bottom of the entry body, to aerobrake through 116 kilometers of the atmosphere. Three minutes after entry, the spacecraft had slowed to 496 meters per second signaling an 8.4-meter, polyester
parachute to deploy from a mortar
followed immediately by heat shield separation and MARDI being powered on, while 8.8 kilometers above the surface. The parachute further slowed the speed of the spacecraft to 85 meters per second when the ground radar began tracking surface features to detect the best possible landing location. When the spacecraft had slowed to 80 meters per second, one minute after parachute deployment, the lander separated from the backshell and began a powered descent while 1.3 kilometers aloft. The powered descent was expected to have lasted approximately one minute, bringing the spacecraft 12 meters above the surface. The engines were then shut off and the spacecraft would expectedly fall to the surface and land at 20:15:00 UTC near 76°S 195°W in Planum Australe.
Lander operations were to begin five minutes after touchdown, first unfolding the stowed solar arrays followed by orienting the medium-gain, Direct-To-Earth antenna to allow for the first communication with the Deep Space Network
. At 20:39:00 UTC, a 45-minute transmission was to be broadcast to Earth, transmitting the expected thirty landing images acquired by MARDI and signaling a successful landing. The lander would then power down for six hours to allow the batteries to charge. On the following days, the spacecraft instruments would be checked by operators and science experiments were to begin on December 7 and last for at least the following 90 Martian Sols, with the possibility of an extended mission.
, to photograph the area the lander was believed to be. An object was visible and believed to possibly be the lander; however, subsequent imaging performed by Mars Reconnaissance Orbiter
resulted in the identified object to be incorrect. Mars Polar Lander remains lost.
The cause of the communication loss is not known. However, the Failure Review Board concluded that the most likely cause of the mishap was a software error that incorrectly identified vibrations, caused by the deployment of the stowed legs, as surface touchdown. The resulting action by the spacecraft was the shutdown of the descent engines, while still likely 40 meters above the surface. Although it was known that leg deployment could create the false indication, the software's design instructions did not account for that eventuality.
In addition to the premature shutdown of the descent engines, the Failure Review Board also assessed other potential modes of failure. Lacking substantial evidence for the mode of failure, the following possibilies could not be excluded:
The failure of the Mars Polar Lander took place two and a half months after the loss of the Mars Climate Orbiter
. Inadequate funding and poor management have been cited as underlying causes of the failures. According to Thomas Young, chairman of the Mars Program Independent Assessment Team, the program "was under funded by at least 30%."
Robotic spacecraft
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
lander
Lander (spacecraft)
A lander is a spacecraft which descends toward and comes to rest on the surface of an astronomical body. For bodies with atmospheres, the landing is called atmospheric reentry and the lander descends as a re-entry vehicle...
, launched by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
on January 3, 1999, to study the soil and climate
Climate of Mars
The climate of Mars has been an issue of scientific curiosity for centuries, not least because Mars is the only terrestrial planet whose surface can be directly observed in detail from the Earth....
of Planum Australe
Planum Australe
Planum Australe is the southern polar plain on Mars. It extends southward of roughly 75°S and is centered at . The geology of this region was to be explored by the failed NASA mission Mars Polar Lander, which lost contact on entry into the Martian atmosphere.-Ice cap:Planum Australe is partially...
, a region near the south pole on Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, as part of the Mars Surveyor '98 mission
Mars Surveyor '98 program
The Mars Surveyor '98 program comprised two spacecraft launched separately, the Mars Climate Orbiter and the Mars Polar Lander ; on board the Mars Polar Lander spacecraft were two surface-penetrator probes...
. However, on December 3, 1999, after the descent phase was expected to be complete, the lander failed to reestablish communication with Earth. It was determined the most likely cause of the mishap was an improperly ceased engine firing prior to the lander touching the surface, causing the lander to impact at a high velocity.
History
As part of the intended goals of the Mars Surveyor '98 missionMars Surveyor '98 program
The Mars Surveyor '98 program comprised two spacecraft launched separately, the Mars Climate Orbiter and the Mars Polar Lander ; on board the Mars Polar Lander spacecraft were two surface-penetrator probes...
, a lander was sought as a way to gather climate data from the ground in conjunction with an orbiter. It was suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole. If that were true, then why does it differ from the Martian north pole, a region suspected to contain much less frozen water. In planning Mars Polar Lander, the potential water content in the Martian south pole was the strongest determining factor for choosing a landing location.
The primary objectives of the mission included:
- Land on the layered terrain in Mars south polar region.
- Search for evidence related to ancient climates and more recent periodic climate change.
- Give a picture of the current climate and seasonal change at high latitudes and, in particular, the exchange of water vapor between the atmosphere and ground.
- Search for near-surface ground ice in the polar regions, and analyze the soil for physically and chemically bound carbon dioxide and water.
- Study surface morphology (forms and structures), geology, topography and weather of the landing site.
Deep Space 2 Probes
Mars Polar Lander carried two, small, identical impactor probes known as Deep Space 2 A and B. The probes were intended to impact the surface with a high velocty at approximately 73°S 210°W, to penetrate the Martian soil and study the subsurface composition up to a meter in depth. However, after entering the Martian atmosphere, attempts to contact the probes failed.Spacecraft design
The spacecraft measured 3.6 meters wide and 1.06 meters tall with the legs and solar arrays fully deployed. The base was primarily constructed with an aluminum honeycomb deck, composite graphite epoxy sheets forming the edge, and three aluminum legs. During landing, the legs were to deploy from stowed position with compression springs and absorb the force of the landing with crushable, aluminum honeycomb inserts in each leg. On the deck of the lander, a small thermal, Faraday cageFaraday cage
A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields...
enclosure housed the computer, power distribution electronics and batteries, telecommunication electronics, and the Capillary Pump Loop Heat Pipe (LHP) components which maintained operable temperature. Each these components included redundant units in the event that one may fail.
Attitude control and propulsion
- While traveling to Mars, the Cruise Stage was three-axis stabilized with four hydrazineHydrazineHydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
monopropellantMonopropellant rocketA monopropellant rocket is a rocket that uses a single chemical as its propellant.-Chemical-reaction monopropellant rockets:...
reaction engine modules, each including a 22-newton trajectory correction maneuver thruster for propulsion and a 4-Newton reaction control system thruster for attitude control. Orientation of the spacecraft was obtained using redundant Sun sensors, star trackers, and inertial measurement units.
- During descent, the lander used three clusters of pulse modulated engines, each containing four 266-Newton hydrazine monopropellant thrusters. Altitude during landing was provided by a doppler radarDoppler radarA Doppler radar is a specialized radar that makes use of the Doppler effect to produce velocity data about objects at a distance. It does this by beaming a microwave signal towards a desired target and listening for its reflection, then analyzing how the frequency of the returned signal has been...
system and an Attitude and Articulation Control subsystem (AACS) controlled the attitude to ensure the spacecraft landed at the optimal azimuth to maximize solar collection and telecommunication with the lander.
- The lander was launched with two hydrazine tanks containing 64 kilograms of propellant and pressurized using heliumHeliumHelium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
. Each spherical tank was located the underside of the lander and provided propellant during the cruise and descent stages.
Communications
- During the cruise stage, communications with the spacecraft were conducted over the X bandX bandThe X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...
using a medium-gain, horn-shaped antenna and redundant solid state power amplifiers. For contingency measures, a low-gain omni-directional antenna was also included.
- The lander was originally intended to communicate data through the failed Mars Climate OrbiterMars Climate OrbiterThe Mars Climate Orbiter was a 338 kilogram robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander...
via the UHFUltra high frequencyUltra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
antenna. With the orbiter being lost on September 23, 1999, the lander would still be able to communicate directly to the Deep Space NetworkDeep Space NetworkThe Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
through the Direct-To-Earth (DTE) link, an X band, steerable, medium-gain, parabolic antenna located on the deck. Alternatively, Mars Global SurveyorMars Global SurveyorThe Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...
could be used as a relay using the UHF antenna at multiple times each Martian day; however the Deep Space Network could only receive data from and not send commands to the lander using this method. Communicating using the medium-gain antenna provided a 12.6-KBKilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
/s link and the UHF relay provided 128-KB/s uplink. Communications with the spacecraft would be limited to one-hour events, constrained by heat-buildup that would occur in the amplifiers; the number of communication events would also be constrained by power limitations.
Power
- During cruise, the Cruise Stage included two gallium arsenide solar arrays to power the radio system and maintain power to the batteries in the lander which kept certain electronics warm.
- After descending to the surface, the lander was to deploy two, 3.6-meter wide gallium arsenide solar arrays, located on either side of the spacecraft. Another two auxilary solar arrays are located on the side to provide additional power for a total of an expected 200 watts and approximately 8-9 hours of operating time per day.
- While the Sun would not have set below the horizon during the primary mission, too little light would have reached the solar arrays to remain warm enough for certain electronics to continue functioning. To avoid this problem, a 16-amp-hour nickel hydrogen batteryNickel hydrogen batteryA nickel–hydrogen battery is a rechargeable electrochemical power source based on nickel and hydrogen. It differs from a nickel–metal hydride battery by the use of hydrogen in a pressurized cell at up to 1200 psi pressure.The cathode is made up of a dry sintered porous nickel plaque, which...
was included to be recharged during the day and used to power the heater for the thermal enclosure at night. This solution also was expected to limit the life of the lander. As the Martian days would grow colder in late summer, too little power would be supplied to the heater to avoid freezing, resulting in the battery also freezing and signaling the end of the operating life for the lander.
Scientific instruments
| Mars Descent Imager (MARDI) | |
Mounted to the bottom of the lander, the camera was intended to capture thirty images as the spacecraft descended to the surface. The images acquired would be used to provide geographic and geologic context to the landing area. |
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| Stereo Surface Imager (SSI) | |
Using a pair of charge coupled devices (CCD), the stereo panoramic camera was mounted to a one-meter tall mast and would aid in the Thermal Evolved Gas Analyzer and determining areas of interest for the Robotic Arm. In addition, the camera would be used to estimate the column density of atmospheric dust, the optical depth of aerosols, and slant column abundances of water vapor using narrow-band imaging of the Sun. |
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| Light Detection and Ranging (LIDAR) | |
The laser sounding instrument was intended to detect and characterize aerosols in the atmosphere up to three kilometers above the lander. The instrument operated in two modes: active mode using an included laser diode and acoustic mode using the Sun as the light source for the sensor.
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| Robotic Arm (RA) | |
Located on the front of the lander, the Robotic Arm is a meter-long aluminum tube with an elbow joint and an articulated scoop attached to the end. The scoop was intended to be used to dig into the soil in direct vicinity of the lander. The soil could then be analyzed in the scoop with the Robotic Arm Camera or transferred into the Thermal Evolved Gas Analyzer. |
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| Robotic Arm Camera (RAC) | |
Located on the Robotic Arm, the charge coupled camera includes 2 red, 2 green, and 4 blue lamps to illuminate soil samples for analysis. |
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| Meteorological Package (MET) | |
Several instruments related to sensing and recording weather patterns, were included in the package. Wind, temperature, pressure and humidity sensors were located on the Robotic Arm and two deployable masts: a 1.2-meter 'main' mast, located on top of the lander and a 0.9-meter secondary 'submast' that would deploy downward to acquire measurements close to the ground. "Wind speed and direction is measured by a nine-element hot wire array wind sensor mounted on the main mast and a two-element wind sensor mounted on the submast. Three fast thermocouple assembly temperature sensors are mounted at different heights on the main mast. Two temperature sensors are also located on the submast and one on the elbow joint of the robotic arm. A soil temperature probe on a 15 cm fiberglass tube is mounted on the back of the robotic arm scoop and can be pushed into the ground by the arm. A barocap atmospheric pressure sensor is located inside the Payload Electronics Box. A tunable diode 2.656 and 2.729 micrometer laser is mounted on the main mast to measure the abundance of atmospheric water and carbon dioxide and to measure the isotopic ratios carbon-13/carbon-12 and oxygen-18/oxygen-16 in atmospheric carbon dioxide, and deuterium/hydrogen and oxygen-18/oxygen-16 in atmospheric water." |
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| Thermal and Evolved Gas Analyzer Thermal and Evolved Gas Analyzer The Thermal and Evolved Gas Analyzer is a scientific instrument aboard the Phoenix spacecraft. TEGA's design is based on experience gained from the failed Mars Polar Lander. Soil samples taken from the Martian surface by the robot arm are eventually delivered to the TEGA, where they are heated in... (TEGA) |
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The instrument was intended to measure abundances of water, water ice, adsorbed carbon dioxide, oxygen, and volatile-bearing minerals in surface and subsurface soil samples collected and transferred by the Robotic Arm. To do this, materials placed onto a grate inside one of the eight ovens, would be heated and vaporized at 1000 °C. The Evolved Gas Analyzer would then record measurements using a spectrometer Spectrometer A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization... and an electrochemical cell. For calibration, an empty oven would also be heated during this process for differential scanning calorimetry. The difference in the energy required to heat each oven would then indicate concentrations of water ice and other minerals containing water or carbon dioxide. |
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| Mars Microphone | |
The microphone was intended to be the first instrument to record sounds on another planet. Primarily composed of a microphone generally used with hearing aid Hearing aid A hearing aid is an electroacoustic device which typically fits in or behind the wearer's ear, and is designed to amplify and modulate sound for the wearer. Earlier devices, known as "ear trumpets" or "ear horns", were passive funnel-like amplification cones designed to gather sound energy and... s, the instrument was expected to record sounds of blowing dust, electrical discharges and the sounds of the operating spacecraft in either 2.6-second or 10.6-second, 12-bit samples. |
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Mission profile
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Launch and trajectory
Mars Polar Lander was launched on January 3, 1999, at 20:21:10 UTC by the National Aeronautics and Space Administration from Space Launch Complex 17B at the Cape Canaveral Air Force StationCape Canaveral Air Force Station
Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...
in Florida, aboard a Delta II 7425
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...
launch vehicle. The complete burn sequence lasted for 47.7 minutes after a Thiokol Star 48
Star 48
The Star 48 is a type of solid rocket motor used by many space propulsion and launch vehicle stages, including the Space Shuttle and the New Horizons probe. It is used almost exclusively as an upper stage...
B solid-fuel third stage booster placed the spacecraft into an 11 month, Mars transfer trajectory at a final velocity of 6.884 kilometers per second with respect to Mars. During cruise, the spacecraft was stowed inside an aeroshell
Aeroshell
An aeroshell is a rigid heat-shielded shell that protects a vehicle from pressure and heat created by drag during atmospheric entry , slows it down during entry, and may protect it from debris during spaceflight...
capsule and was powered and communicated with Earth with the a segment known as the cruise stage.
Landing encounter with Mars
On December 3, 1999, Mars Polar Lander encountered Mars while mission operators began preparing for landing operations. At 14:39:00 UTC, the cruise stage was jettisoned, beginning a planned communication dropout until the spacecraft had touched down on the surface. Six minutes prior to atmospheric entry, a programmed 80-second thruster firing turned the spacecraft to the proper entry orientation, with the heat shieldHeat shield
A heat shield is designed to shield a substance from absorbing excessive heat from an outside source by either dissipating, reflecting or simply absorbing the heat...
oriented to absorb the intense, 1650 °C heat that would be generated as the descent capsule passed through the atmosphere. Traveling at 6.9 kilometers per second, the entry capsule entered the Martian atmosphere
Atmosphere of Mars
The atmosphere of Mars is relatively thin and is composed mostly of carbon dioxide . There has been interest in studying its composition since the detection of trace amounts of methane, which may indicate the presence of life on Mars, but may also be produced by a geochemical process, volcanic or...
at 20:10:00 UTC and was expected to land in the vicinity of 76°S 195°W in a region known as Planum Australe
Planum Australe
Planum Australe is the southern polar plain on Mars. It extends southward of roughly 75°S and is centered at . The geology of this region was to be explored by the failed NASA mission Mars Polar Lander, which lost contact on entry into the Martian atmosphere.-Ice cap:Planum Australe is partially...
. Communication was expected to be reestablished with the spacecraft at 20:39:00 UTC after having landed. However, no communication attempt was successful with the spacecraft.
The Phoenix
Phoenix (spacecraft)
Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...
lander has subsequently completed most of the objectives of Mars Polar Lander, carrying several of the same or derivative instruments. Phoenix landed successfully on May 25, 2008.
Intended operations
Traveling at approximately 6.9 kilometers/second and 125 kilometers above the surface, the spacecraft entered the atmosphere and was initially decelerated by using a 2.4 meter ablation heat shieldHeat shield
A heat shield is designed to shield a substance from absorbing excessive heat from an outside source by either dissipating, reflecting or simply absorbing the heat...
, located on the bottom of the entry body, to aerobrake through 116 kilometers of the atmosphere. Three minutes after entry, the spacecraft had slowed to 496 meters per second signaling an 8.4-meter, polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
parachute to deploy from a mortar
Mortar
Mortar has several meanings:* Mortar , material used in masonry to fill the gaps between blocks and bind them together.* Mortar fires shells at a much lower velocity and higher ballistic arc than other ordnance....
followed immediately by heat shield separation and MARDI being powered on, while 8.8 kilometers above the surface. The parachute further slowed the speed of the spacecraft to 85 meters per second when the ground radar began tracking surface features to detect the best possible landing location. When the spacecraft had slowed to 80 meters per second, one minute after parachute deployment, the lander separated from the backshell and began a powered descent while 1.3 kilometers aloft. The powered descent was expected to have lasted approximately one minute, bringing the spacecraft 12 meters above the surface. The engines were then shut off and the spacecraft would expectedly fall to the surface and land at 20:15:00 UTC near 76°S 195°W in Planum Australe.
Lander operations were to begin five minutes after touchdown, first unfolding the stowed solar arrays followed by orienting the medium-gain, Direct-To-Earth antenna to allow for the first communication with the Deep Space Network
Deep Space Network
The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
. At 20:39:00 UTC, a 45-minute transmission was to be broadcast to Earth, transmitting the expected thirty landing images acquired by MARDI and signaling a successful landing. The lander would then power down for six hours to allow the batteries to charge. On the following days, the spacecraft instruments would be checked by operators and science experiments were to begin on December 7 and last for at least the following 90 Martian Sols, with the possibility of an extended mission.
Communications loss
On December 3, 1999, at 14:39:00 UTC, the last telemetry from Mars Polar Lander was sent, just prior to cruise stage separation and the subsequent atmospheric entry. No further signals were received from the spacecraft. Attempts were made by Mars Global SurveyorMars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...
, to photograph the area the lander was believed to be. An object was visible and believed to possibly be the lander; however, subsequent imaging performed by Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
resulted in the identified object to be incorrect. Mars Polar Lander remains lost.
The cause of the communication loss is not known. However, the Failure Review Board concluded that the most likely cause of the mishap was a software error that incorrectly identified vibrations, caused by the deployment of the stowed legs, as surface touchdown. The resulting action by the spacecraft was the shutdown of the descent engines, while still likely 40 meters above the surface. Although it was known that leg deployment could create the false indication, the software's design instructions did not account for that eventuality.
In addition to the premature shutdown of the descent engines, the Failure Review Board also assessed other potential modes of failure. Lacking substantial evidence for the mode of failure, the following possibilies could not be excluded:
- Surface conditions exceed landing design capabilities.
- Loss of control due to dynamic effects.
- Landing site not survivable.
- Backshell/parachute contacts lander.
- Loss of control due to center-of-mass offset.
- Heatshield fails due to micrometeoroid impact.
The failure of the Mars Polar Lander took place two and a half months after the loss of the Mars Climate Orbiter
Mars Climate Orbiter
The Mars Climate Orbiter was a 338 kilogram robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander...
. Inadequate funding and poor management have been cited as underlying causes of the failures. According to Thomas Young, chairman of the Mars Program Independent Assessment Team, the program "was under funded by at least 30%."
| Quoted from the report |
|---|
"A magnetic sensor is provided in each of the three landing legs to sense touchdown when the lander contacts the surface, initiating the shutdown of the descent engines. Data from MPL engineering development unit deployment tests, MPL flight unit deployment tests, and Mars 2001 deployment tests showed that a spurious touchdown indication occurs in the Hall Effect touchdown sensor during landing leg deployment (while the lander is connected to the parachute). The softwarelogic accepts this transient signal as a valid touchdown event if it persists for two consecutive readings of the sensor. The tests showed that most of the transient signals at leg deployment are indeed long enough to be accepted as valid events, therefore, it is almost a certainty that at least one of the three would have generated a spurious touchdown indication that the software accepted as valid. The software—intended to ignore touchdown indications prior to the enabling of the touchdown sensing logic—was not properly implemented, and the spurious touchdown indication was retained. The touchdown sensing logic is enabled at 40 meters altitude, and the software would have issued a descent engine thrust termination at this time in response to a (spurious) touchdown indication. At 40 meters altitude, the lander has a velocity of approximately 13 meters per second, which, in the absence of thrust, is accelerated by Mars gravity to a surface impact velocity of approximately 22 meters per second (the nominal touchdown velocity is 2.4 meters per second). At this impact velocity, the lander could not have survived." |
External links
- Mars Polar Lander site at Jet Propulsion LaboratoryJet Propulsion LaboratoryJet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
- Mars Polar Lander Mission at The NASA Solar System Exploration Home Page