The Mars Surveyor '98 program is comprised of two spacecraft launched separately, the MCO (Mars Climate Orbiter, formerly the Mars Surveyor
'98 Orbiter) and the MPL (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, behavior, and atmospheric role of
volatiles and to search for evidence of long-term and episodic climate changes. The last
telemetry from Mars Polar Lander was sent just prior to atmospheric entry on 3 December
1999. No further signals have been received from the lander, the cause of this loss of
communication is not known.
The Mars Polar Lander was to touch down on the southern polar layered terrain, between
73 S and 76 S, less than 1000 km from the south pole, near the edge of the carbon dioxide
ice cap in Mars' late southern spring. The terrain appears to be composed of alternating
layers of clean and dust-laden ice, and may represent a long-term record of the climate,
as well as an important volatile reservoir. The mission had as its primary science
objectives to:
- record local meteorological conditions near the Martian south pole, including
temperature, pressure, humidity, wind, surface frost, ground ice evolution, ice fogs, haze, and suspended dust,
- analyze 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, and
- obtain multi-spectral images of local regolith to determine soil types and composition.
These goals were to be accomplished using a number of scientific instruments, including
a Mars Volatiles and Climate Surveyor (MVACS) instrument package which was comprised of a
robotic arm and attached camera, mast-mounted surface stereo imager and meteorology
package, and a gas analyzer. In addition, a Mars Descent Imager (MARDI) was planned to
capture regional views from parachute deployment at about 8 km altitude down to the
landing. 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. A miniature
microphone was also be on board to record sounds on Mars. Attached to the lander
spacecraft were a pair of small probes, the Deep Space 2 Mars Microprobes, which were to
be deployed to fall and penetrate beneath the Martian surface when the spacecraft reached
Mars.
The Mars Polar Lander consists of a hexagonal base composed of aluminum honeycomb with
composite graphite epoxy face sheets supported on three aluminum landing legs. The lander
stands 1.06 m tall and approximately 3.6 m wide. The launch mass of the spacecraft is
approximately 583 kg, including 64 kg of fuel, an 82 kg cruise stage, a 140 kg
aeroshell/heatshield, and the two 3.5 kg microprobes. A thermally regulated interior
component deck holds temperature sensitive electronic components and batteries and the
thermal control system. Two solar panels extend out from opposite sides of the base.
Mounted on top of the base are 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.
The MARDI is mounted at the base of the lander, and the propellant tanks are affixed to
the sides. During cruise, the lander is attached to the cruise stage and enclosed in the
2.4 meter diameter aeroshell.
The spacecraft was three-axis stabilized during cruise using star cameras and sun
sensors in conjunction with inertial measurement units. 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. The descent
and landing propulsion system consists of three groups of four pulse modulated 266 N
hydrazine engines. Control and knowledge for descent and landing is provided by a 4 beam
Doppler radar system and an AACS subsystem. The hydrazine is stored in two diaphragm tanks
with a total capacity of 64 kg for both cruise and descent systems.
Communications between Earth and the spacecraft during cruise to Mars were via X-band
using two solid state power amplifiers and a fixed medium gain antenna mounted on the
cruise stage and backed up by a receive-only low gain antenna. During surface operations
communications (downlink and uplink) would be via the UHF antenna on the lander to the
Mars Climate Surveyor orbiter, which will function as a relay to Earth. Eight to ten relay
passes over the lander would have been available from the orbiter each day, but the number
of communications sessions would be limited by power demands. Uplink only communications
to Earth were to be provided by the medium gain DTE (direct to Earth) 2-axis articulated
antenna.
Power was provided during cruise phase by two gallium arsenide solar array wings with a
total area of 3.1 square meters attached to the cruise stage. After landing, two gallium
arsenide solar array wings with a total area of 2.9 square meters would have been
deployed. 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 25 W of continuous
power when operating.
Mars Polar Lander and the attached Deep Space 2 probes were
launched on a Delta-7425 which placed them
into a low-Earth parking orbit. The third stage fired for 88 seconds at 20:57 UT 3 January
1999 to put the spacecraft into a Mars transfer trajectory and the spacecraft and third
stage separated at 21:03 UT. Trajectory correction maneuvers were performed on 21 January,
15 March, 1 September, 30 October, and 30 November 1999.
After an 11 month hyperbolic transfer cruise, the Mars Polar Lander reached Mars on 3
December 1999. A final 30 minute tracking session begins at approximately 12:45 UT (7:45
a.m. EST) and was used to determine if a final thruster correction was necessary. Final
contact to retrieve data on the status of the propulsion system was made from
approximately 19:45 UT to 20:00 UT. At approximately 20:04, 6 minutes before atmospheric
entry, an 80 second thruster firing was to turn the craft to its entry orientation. The
Star 48 upper cruise stage was to be jettisoned at about 20:05 UT, and about 18 seconds
later the microprobes were to be dropped from the cruise stage into the Martian atmosphere
(also targeted at the southern polar layered terrain). The lander was to make a direct
entry into Mars' atmosphere at 6.8 km/s at about 20:10 UT (3:10 p.m. EST). Due to lack of
communication, it is not known at this time whether all these steps following final
contact were executed, nor whether any of the descent plan described below took place as
designed.
Initial deceleration would be simple aerobraking using the 2.4 meter ablation heat
shield. The maximum time from atmospheric entry to landing would be 4 minutes 33 seconds.
The inertial measurement unit would estimate the velocity throughout the entry and descent
phase and the thrusters would keep the craft aligned. At an altitude of about 7.3 km at
500 meters per second the parachute would be deployed by a mortar followed by heat shield
separation. Just before heat shield separation, the descent imager (MARDI) would turn on.
The landing legs would be deployed 70 to 100 seconds before landing and the descent
engines warmed up with short pulses. Then the parachute would be jettisoned and the
descent engines fired, regulated by the spacecraft control system and the Doppler radar.
The backshell would separate from the lander at about 1.4 km altitude at 80 m/s and the
descent engines turned on to slow the descent and turn the flight path to vertical.
At 12 meters altitude the 2.4 m/s terminal descent phase was to begin. Engine shutoff
would occur when one of the landing legs touched the ground. The horizontal landing
velocity would 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 would have touched down at approximately 20:15
UT Earth received time (3:15 p.m. EST) in the late southern spring season, during which
the Sun will always be above the horizon at the landing site. The other times listed above
are also Earth received times, light travel time from Mars at that point was approximately
14 minutes.
Immediately after landing the solar panels were to be deployed. The first signal from
the lander was to reach Earth at 20:39 UT (3:39 p.m. EST), but was never received. This
was to be the start of a 45 minute communications session. After this session the lander
was to recharge its batteries for about 6 hours. On 4 December at 04:30 UT (11:30 p.m. EST
December 3) a communications session was to begin which would have lasted about 2 1/4
hours. This session would have included images, including pictures from the Mars Descent
Imager, but again no transmission was received. The first sounds from the Mars Microphone
were to be released as early as 4 December and the first robot arm dig occur on 7
December. Science experiments would continue over the 90 day primary mission, with an
extended mission to follow based on lander performance.
The Mars Surveyor '98 program spacecraft development cost 193.1 million dollars. Launch
costs are estimated at 91.7 million dollars and mission operations at 42.8 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.