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Mars polar explorer
Mars polar explorer -

Credit: NASA. 20,471 bytes. 341 x 260 pixels.

Class: Planetary. Type: Mars. Nation: USA. Manufacturer: Lockheed Martin Astronautics/Denver.

The Mars Polar Lander was part of the Mars Surveyor program, managed by the Jet Propulsion Lab in Pasadena. The MPL was built by Lockheed Martin Astronautics/Denver with the mission of studying Martian volatiles (frozen water and carbon dioxide) and climate history. The Martian polar regions were the best places to conduct these studies. The trajectory employed by only allowed a south polar landing. A target landing sector for the lander extended from 73 to 78 degrees south latitude, and 170 to 230 degrees west longitude. The final landing site would be selected in June of 1999, using new data obtained by the Mars Global Surveyor spacecraft. Attached to the cruise stage were two Deep Space 2 Mars Microprobes, penetrators which would seperate and bury themselves into the Martian surface a 100 km away from the main landing point. At the end of the scheduled mission, the lander would be frozen in place for more than one Earth year during the southern polar night season.

Total spacecraft mass was 615 kg. Mass of the Mars Polar Lander, less the penetrators was 576 kg, of which: Lander: 290 kg ; Propellant: 64 kg; Cruise Stage: 82 kg; Aeroshell & Heat Shield: 140 kg. Science payloads included: Mars Descent Imager (MARDI); Light Detection and Ranging (LIDAR) MVACS; Stereo Surface Imager (SSI); Robotic Arm (RA) / Robotic Arm Camera (RAC); Meteorological Package (MET); Thermal and Evolved Gas Analyser (TEGA). Mars landing was planned for December 3, 1999, with the end of the primary mission by February 29, 2000.

All contact with the spacecraft was lost at the point of separation of the lander and multiprobes. Subsequent investigations pointed to shortcomings in project management and preflight testing, with the result that future 'faster, better, cheaper' NASA missions would be not quite so 'cheap'.

Mission Profile

Three days before landing, one or two final trajectory correction manoeuvres would be performed to steer the lander as close as possible to its final landing site. The lander's error ellipse was expected to be 120 km long by 10 km wide. Ten minutes before landing, the lander's cruise stage would be jettisoned and the lander's heat shield would be oriented for atmospheric entry. For a successful landing, the lander had to intercept the atmosphere within 1 degree of its nominal entry angle. Too shallow an entry angle would cause the lander to skip off the atmosphere back into space. Too steep an entry angle would cause the lander to burn up in the atmosphere.

Prior to entry, two 3.5 kg penetrators provided by JPL's New Millennium Deep Space Project would be released. The probes would enter the atmosphere and impact the Martian surface approximately 100 km up-range of the lander. Each probe would consist of a forebody which would penetrate up to meter into the Martian soil, and an aftbody which would remain on the surface. The forebody contained acceleration sensors and a water experiment which would collect a small quantity of soil and heat it to release water. The aftbody contained electronics and an antenna to be used for one-way communication with the Mars Global Surveyor Orbiter. The probes were powered by non-rechargeable batteries and were expected to survive for two days.

Meanwhile, the lander would begin its encounter with the Martian atmosphere approximately 4 minutes and 33 seconds before landing. During this period, the lander would use the friction produced by the Martian atmosphere to decelerate rapidly from its initial velocity of 6.8 km per second. The temperature of the lander's heat shield would increase to 1650 C and it would experience peak G forces of 12 times Earth's gravity. Approximately two minutes before landing, the lander's parachute would be deployed. By this time, the lander would be travelling at a speed of 493 meters per second and would be 7.3 km above the Martian surface. Ten seconds after the parachute opens, the Mars Descent Imager (MARDI) would begin taking images. The first image would be acquired 0.3 seconds before the heat-shield is jettisoned. MARDI would take approximately 10 images of the Martian surface at increasing resolution as the lander descends. The fields of view of the MARDI images would decrease from 8 km across to 9 meters across just before landing. Approximately 100 seconds before landing, the lander legs would be extended and a landing radar would be activated to determine the distance to the Martian surface. 1.4 km above the surface, the lander's parachute and backshell would be separated and the lander would use a set of thrusters to perform a 35-second controlled descent to the Martian surface. Inertial gyros and accelerometers would be used to orient the lander during its final descent. The lander would land facing the best direction for its solar panels to generate power once it lands. The lander would not be in radio contact with the Earth at any point during the entry, descent and landing phase of the mission.

The lander would unfold its solar panels two minutes after landing and begin pointing its medium-gain radio antenna at Earth five minutes after landing; the MVACS Meteorology mast would be deployed a short time later. The lander would establish a two-way Earth-to-Mars radio link approximately 20 minutes after landing. During its first 20-minute communication session, it would transmit critical information on the spacecraft's health, initial meteorological data, and possibly some compressed images acquired by the MVACS SSI camera prior to deployment.

During the lander's first day on the Martian surface, it would also communicate with the Mars Climate Orbiter (MCO) via a UHF radio link that would be established when the orbiter passes over the landing site. MCO's polar orbit would enable approximately four orbiter passes each day in which lander data can be relayed to Earth and commands from Earth can be relayed to the lander. The MCO relay would be the lander's primary communications link during the mission. The Mars Global Surveyor Orbiter and the lander's medium gain antenna would also be available as backups.

During the lander's first day on the surface, it would begin relaying the MARDI descent images back to Earth and begin surveying its new environment. Some of the most anticipated data that would be acquired during the first days of the mission would be a scan of the horizon by the MVACS Surface Stereo Imager (SSI). The SSI was nearly identical to the IMP camera that flew on Mars Pathfinder, and would be capable of providing stereo colour panoramas of the landing site. Additionally, the SSI would acquire quantitative data relating to clouds and water vapour in the Martian atmosphere.

During the third day of the mission, the MVACS Robotic Arm would acquire its first samples of Martian soil. The robotic arm was about two meters long and has approximately the same strength as a human arm. The arm includes a probe to measure the temperature of surface and subsurface soil, and a Robotic Arm Camera which can take close-up images of the arm's workspace and soil samples.

Soil samples acquired by the Robotic Arm would be delivered to the MVACS Thermal And Evolved Gas Analyser (TEGA) for analysis. The TEGA sifted the soil into one of eight small ovens. As the samples were heated, the quantities of water vapour and carbon dioxide released were measured. The TEGA data could be used to determine the concentrations of water ice, adsorbed water and carbon dioxide, hydrated minerals and carbonates in the soil. These measurements would place valuable constraints on the understanding of the distribution and behaviour of volatiles on Mars, as well as give clues to Mars' climate history.

Robotic Arm Camera Image. The MVACS Robotic Arm Camera (RAC) would provide images of the Martian surface and the Mars Polar Lander from a unique perspective. At its closest focus, the RAC could obtain images with a resolution of 23 microns per pixel, which was higher resolution than the unaided human eye.

During its three month surface mission, the Mars Polar Lander instruments would measure both daily and seasonal variations in atmospheric properties. The LIDAR instrument would make the first such measurements of the Martian atmosphere. The MVACS Meteorology Package's Tuneable Diode Laser (TDL) Spectrometer would make the first accurate in situ measurements of the concentration of water vapour in the Martian atmosphere. The MVACS MET sensors would make the first measurements of temperature, pressure and winds in the Martian southern hemisphere.

The Mars Microphone would make the first recordings of the sounds of Mars. The microphone would be capable of detecting sounds generated by the lander and its instruments, as well as natural sound in the Martian environment. Microphone data would typically be acquired for 15 seconds each day, with the possibility of longer listening periods to search for unusual or intermittent sounds.

One of the major goals of the MVACS investigation was to search for Martian ground ice. Subsurface ice is common at high-latitudes on Earth. Models for the behaviour of water on Mars predict that ice could be stable throughout the year as close as 20 cm below the surface at the Mars Polar Lander's landing latitude. During the course of the mission, MVACS robotic arm would scoop up soil and dig a trench up to 50 cm deep. The trench walls would be examined by the Robotic Arm Camera and samples from inside the trench would be analysed for water ice content by the MVACS TEGA. The discovery of ground ice would be important for Mars science, as well for future human exploration of Mars.

The longevity of the Mars Polar Lander would be limited by its ability to withstand the rigors of the changing polar environment. The lander would arrive during the late Martian spring season in the southern hemisphere, when the sun would be above the horizon throughout the day, and surface temperatures would vary between -80 C and -20 C. Towards the end of the summer season, the sun would dip closer and closer to the horizon, making it colder, and more difficult for the lander to generate solar power. March 1, 2000, would mark the first true sunset at the Mars Polar Lander landing site. It was not expected that the lander would be able to collect much useful scientific data after this point. After it dies, the lander would spend the next year frozen in the Martian south seasonal carbon dioxide polar cap at a temperature of -125 C. There was a faint possibility that the lander would revive itself when the spring sun returns in 2001.


Total Length: 3.6 m. Total Mass: 576 kg.

Mars Polar Lander Chronology

03 January 1999 Mars Polar Lander Launch Site: Cape Canaveral . Launch Vehicle: Delta 7925. Mass: 576 kg.

The Mars Polar Lander was placed by the first burn of the second stage into a 157 x 245 km x 28.35 deg parking orbit. The second stage restarted at 20:55 GMT and shut down in a 226 x 740 km x 25.8 deg Earth orbit. The solid rocket third stage (a Star 48B with a Nutation Control System and a yo-yo despin device) then ignited and put the spacecraft into solar orbit, separating at 21:02 GMT. Mars Polar Lander was to land near the south pole of Mars on December 3, 1999, and conduct conduct a three month mission, trenching near its landing site and testing for the presense of frozen water and carbon dioxide. Attached were two Deep Space 2 Microprobes, penetrators which would impact the Martian surface separately from the lander and return data on subsurface conditions from widely spaced points.

When the spacecraft reached Mars on December 3, the lander separated from the cruise stage at 19:51 UTC and the two penetrators, Scott and Amundsen, were to separate about 20 seconds later. No further communications were ever received from the spacecraft. Landing had been expected at 20:01 UTC at 76.1S 195.3W, with the penetrators landing a few kilometres from each other at 75.0S 196.5W.

This failure resulted in a review and reassessment of NASA's 'faster, better, cheaper' approach to planetary missions.

03 December 1999 Contact lost with Mars Polar Lander

Mars landing was planned for December 3, 1999, with the end of the primary mission by February 29, 2000. All contact with the spacecraft was lost at the point of separation of the lander and multiprobes. Subsequent investigations pointed to shortcomings in project management and preflight testing, with the result that future 'faster, better, cheaper' NASA missions would be not quite so 'cheap'.


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Last update 12 March 2001.
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