Mars Polar Lander Space Probe, USA

The Mars Surveyor '98 Programme was comprised of two spacecraft launched separately: the Mars Climate Orbiter (formerly the Mars Surveyor '98 Orbiter) launched in 1996, and the Mars Polar Lander (formerly the Mars Surveyor '98 Lander).

The two missions were designed to study the Martian weather, climate and water and carbon dioxide budget in order to understand the reservoirs, behaviour, and atmospheric role of volatiles and to search for evidence of long-term and episodic climate changes on Mars.

MARS MISSION OBJECTIVES

The project involved sending the Mars Climate Orbiter and Mars Polar Lander to Mars so as to analyse the planet's atmosphere and terrain. The mission cost $154 million, which includes the $65million cost of the craft.

The five primary objectives of the mission are:

• Record local meteorological conditions near the Martian south pole (temperature, pressure, humidity, wind, surface frost, ground ice evolution, ice fogs, haze, and suspended dust)
• Analyse samples of the polar deposits for volatiles, particularly water and carbon dioxide
• Dig trenches and image the interior to look for seasonal layers and analyze soil samples for water, ice, hydrates, and other aqueously deposited minerals
• Image the regional and immediate landing site surroundings for evidence of climate changes and seasonal cycles
• Obtain multi-spectral images of local regolith to determine soil types and composition

The project used a number of different instruments for the data collection. This includes a Mars Volatiles and Climate Surveyor (MVACS) instrument package - which included a robotic arm and attached camera, mast-mounted surface stereo imager and meteorology package, and a gas analyzer - and a Mars Descent Imager (MARDI) which planned to capture regional views from parachute deployment at about 8km altitude down to the landing. In addition, the Russian Space Agency provided a laser ranger (LIDAR) package for the lander, which would be used to measure dust and haze in the Martian atmosphere. As well as this a miniature microphone was also on board to record sounds on Mars.

A MARTIAN WEATHER STATION

The Mars Volatiles and Climate Surveyor's Meterological Package (MET) will function as a Martian weather station. The package consists of a collection of sensors at various heights on two masts, as well as a four pressure sensors that reside on the lander deck.

The MET is comprised of the MET mast, which has three temperature sensors on the 1.4m main mast, a wind sensor at the top of the mast which detects speed and direction, and a tunable diode laser (TDL) spectrometer on the mast, which measures water vapour in the atmosphere as well as other gases.

MISSION INSTRUMENTATION

Also included is the robotic arm atmospheric temperature sensor (RAATS), which acquires temperature measurements near the lander deck, and a MET pressure sensor which will measure the changes in the atmospheric pressure near the surface. This was provided by the Finnish Meteorological Institute Department of Geophysics (FMI/GEO). Furthermore, the MET is equipped with a soil temperature probe (STP), which can measure the temperature of the Martian soil.

A pair of small probes, known as the Deep Space 2 Mars Microprobes, were attached to the lander spacecraft. These were used to fall and penetrate beneath the Martian surface when the spacecraft reached Mars. The Lander weighs approximately 583kg, including 64kg of fuel, an 82kg cruise stage, a 140kg aeroshell/heatshield, and the two 3.5kg microprobes. The craft incorporates a thermally regulated interior component deck, which holds temperature sensitive electronic components and batteries and the thermal control system.

The robotic arm, the stereo imager and mast, a UHF antenna, the LIDAR, the MVACS electronics, the meteorology mast and the medium gain dish antenna are mounted on top of the base. The MARDI is found at the base of the lander, and the propellant tanks are affixed to the sides.

Star cameras and sun sensors, in conjunction with inert measurement units, provided three-axis stabilisation during cruise, while four hydrazine cruise reaction engine modules, each consisting of one 5-lbf trajectory correction maneuver thruster and one canted 1-lbf reaction control system thruster, provided attitude control. Control and knowledge for descent and landing is provided by a four-beam doppler radar system and an AACS subsystem.

MAINTAINING COMMUNICATION

Communication is maintained by two solid state power amplifiers and a fixed medium gain antenna using X-band. During surface operations communications (downlink and uplink) will be via the UHF antenna on the lander to the Mars Climate Surveyor orbiter, which functions as a relay to Earth.

Power, both during cruise and after landing is provided by two sets of gallium arsenide solar array wings. Power is stored in 16 amp-hr nickel-hydride common pressure vessel batteries for peak load operations and night time heating. The payload is allocated 25W of continuous power when operating.