Mission Profile
The 25 day launch window for the Mars Polar Lander opens on 3 January 1999. The launch vehicle will be a Med-Lite in a Delta II 7425 configuration. After an 11 month hyperbolic transfer cruise, on 3 December 1999 the Star 48 upper cruise stage will be jettisoned, and about 18 seconds later the microprobes will be dropped from the cruise stage into the martian atmosphere (also targeted at the southern polar layered terrain). The lander will then make a direct entry into Mars' atmosphere at about 7 km/s. Initial deceleration will be simple aerobraking using the 2.4 meter ablation heat shield. The inertial measurement unit will estimate the velocity throughout the entry and descent phase. At an altitude of about 8 km the parachute will be deployed by a mortar followed by heat shield separation. Just before heat shield separation, the descent imager (MARDI) will turn on. The landing legs will be deployed and the descent engines warmed up with short pulses. Then the parachute will be jettisoned and the descent engines fired, regulated by the spacecraft control system and the Doppler radar.
At 12 meters altitude the 2.4 m/s terminal descent phase will begin. Engine shutoff will occur when one of the landing legs touches the ground. The horizontal landing velocity will be less than 2.4 m/s vertical and 1 m/s horizontal. The orientation of the lander is controlled by the AACS subsystem to maximize solar array efficiency and minimize obstruction of the DTE antenna. The lander will touch down during the late southern spring season, during which the Sun will always be above the horizon at the landing site. Science experiments will begin and continue over the 90 day primary mission, with an extended mission to follow based on lander performance.
The Mars Surveyor '98 program development costs are capped at 183.9 million dollars. The Mars Polar Lander is part of NASA's 10-year Mars Surveyor Program, which will feature launches every 26 months when the Earth and Mars are favorably aligned.