The Mars Polar Lander, also known as the Mars Surveyor '98 Lander, was a 290-kilogram uncrewed 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. It formed part of the Mars Surveyor '98 mission. On December 3, 1999, however, after the descent phase was expected to be complete, the lander failed to reestablish communication with Earth. A post-mortem analysis determined the most likely cause of the mishap was premature termination of the engine firing prior to the lander touching the surface, causing it to strike the planet at a high velocity. The total cost of the Mars Polar Lander was US$165 million. Spacecraft development cost US$110 million, launch was estimated at US$45 million, and mission operations at US$10 million.
Mission background
History As part of the Mars Surveyor '98 mission, a lander was sought as a way to gather climate data from the ground in conjunction with an orbiter. NASA suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole. In planning the Mars Polar Lander, the potential water content in the Martian south pole was the strongest determining factor for choosing a landing location. A CD-ROM containing the names of one million children from around the world was placed on board the spacecraft as part of the "Send Your Name to Mars" program designed to encourage interest in the space program among children. The primary objectives of the mission were to:
Land on the layered terrain in the south polar region of Mars; 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; and Study surface morphology (forms and structures), geology, topography, and weather of the landing site.
Deep Space 2 probes
The Mars Polar Lander carried two small, identical impactor probes known as "Deep Space 2 A and B". The probes were intended to strike the surface with a high velocity 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. Deep Space 2 was funded by the New Millennium Program, and their development costs was US$28 million.
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 cage 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 of 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 hydrazine monopropellant 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). Orientation of the spacecraft was performed 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 measured by a Doppler radar 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 with helium. Each spherical tank was located at 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 band using a medium-gain, horn-shaped antenna and redundant solid state power amplifiers. For contingency measures, a low-gain omnidirectional antenna was also included. The lander was originally intended to communicate data through the failed Mars Climate Orbiter via the UHF antenna. With the orbiter lost on September 23, 1999, the lander would still be able to communicate directly to the NASA Deep Space Network through the Direct-To-Earth (DTE) link, an X band, steerable, medium-gain, parabolic antenna located on the deck. Alternatively, Mars Global Surveyor 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. The direct-to-Earth medium-gain antenna provided a 12.6-kbit/s return channel, and the UHF relay path provided a 128-kbit/s return channel. 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.
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