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 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 Mars
Climate Orbiter was destroyed when a navigation error caused it to miss its target
altitude
at Mars by 80 to 90 km, instead entering the Martian atmosphere at an altitude of 57 km
during the orbit insertion maneuver.
The Orbiter has as its primary science objectives to:
- monitor the daily weather and atmospheric conditions;
- record changes on the Martian surface due to wind and other atmospheric effects;
- determine temperature profiles of the atmosphere;
- monitor the water vapor and dust content of the atmosphere and
- look for evidence of past climate change.
Specifically it will observe and study dust storms, weather systems, clouds and dust
hazes, ozone, distribution and transport of dust and water, the effects of topography on
atmospheric circulation, atmospheric response to solar heating, and surface features, wind
streaks, erosion, and color changes. The orbiter will use two instruments to carry out
these investigations:
- The Mars Climate Orbiter Color Imager (MARCI) will acquire daily atmospheric weather
images and high resolution surface images and
- the Pressure Modulated Infrared Radiometer (PMIRR) will allow measurement of the
atmospheric temperature, water vapor abundance, and dust concentration.
The orbiter will also serve as a data relay satellite for the Mars Polar Lander and
other future NASA and international lander missions to Mars.
The Mars Climate Orbiter is a box shaped spacecraft about 2.1 m high, 1.6 m wide, and 2
m deep, consisting of stacked propulsion and equipment modules. The total spacecraft
launch mass of 629 kg includes 291 kg of propellant. An 11 square meter solar array wing,
measuring 5.5 m tip-to-tip, is attached by 2-axis gimbal to one side and a 1.3 m diameter
high-gain dish antenna is attached by 2-axis gimbal to a mast at the top of the propulsion
module. The MARCI and PMIRR instruments, as well as a UHF antenna and battery enclosure,
are mounted to the bottom of the equipment module.
Propulsion is achieved via a 640-N bi-propellant (hydrazine/nitrogen tetroxide) main
engine, mounted with the propellant tanks in the propulsion module, and hydrazine
thrusters. The orbiter is 3-axis stabilized. Attitude control and maneuvering capability
is provided by four 7-Nm thrusters (pitch/yaw) and four 0.3-Nm thrusters (roll) in
combination with reaction wheels. Attitude is determined using an inertial measurement
unit, a star tracker, and analog Sun sensors with knowledge of 25 mrad and stability of
1.5 mrad/(1 sec) and 3 mrad/(3 sec).
Spacecraft power is provided by 3 panels of GaAs/Ge solar cells on the 5.5 meter long
single-wing solar array which provide 1000 W of power at Earth and 500 W at Mars. Power is
stored in nickel hydride (NiH2) common pressure vessel batteries. Thermal control is
achieved through a combination of louvers, MLI, Kapton, paints, radiators and heater
circuits. Communications with Earth are in X-band using Cassini Deep Space Transponders
and 15 W RF solid state power amplifiers through the 1.3 m high gain antenna for both
uplink and downlink, a medium gain transmitting antenna, and a low-gain receiving antenna.
A 10 W UHF system is used for 2-way communications with the Mars Polar Lander. A RAD6000
processor is used for on-board command and data handling.
Mars Climate Orbiter was launched on a Delta-7425
. Launch was at 18:45:51 UT (1:45:51 p.m. EST) on 11 December 1998 from Pad A of Launch
Complex 17 at Cape Canaveral Air Station, Florida. After a brief cruise in Earth orbit,
the Delta II 3rd stage put the spacecraft into trans-Mars trajectory and about 15 days
after launch the largest trajectory correction maneuver (TCM) was executed using the
hydrazine thrusters. During cruise to Mars, three additional TCM's using the hydrazine
thrusters were performed on 4 March, 25 July, and 15 September 1999.
The spacecraft reached Mars and executed a 16 minute 23 second orbit insertion main
engine burn on 23 September 1999 at 09:01 UT (5:01 a.m. EDT) Earth received time (ERT,
signal travel time from Mars will be 10 minutes 55 seconds). The spacecraft passed behind
Mars at 09:06 UT ERT and was to re-emerge and establish radio contact with Earth at 09:27
UT ERT, 10 minutes after the burn was completed. However, contact was never re-established
and no signal was ever received from the spacecraft. Findings of the failure review board
indicate that a navigation error resulted from some spacecraft commands being sent in
English units instead of being converted to metric. This caused the spacecraft to miss its
intended 140 - 150 km altitude above Mars during orbit insertion, instead entering the
Martian atmosphere at about 57 km. The spacecraft would have been destroyed by atmospheric
stresses and friction at this low altitude.
The burn would have slowed the spacecraft and put it into a 14 hour elliptical (~150 x
21,000 km) capture orbit. The orbiter was to begin aerobraking, using the solar panel to
provide resistance and continue until a 90 × 405 km orbit was achieved, nominally on 22
November 1999, with periapsis at 89 N. The hydrazine thrusters would be used to change the
orbit to a 2-hour, 421 km near-circular polar science mapping orbit on 1 December 1999.
The orbit was to be nearly Sun-synchronous, crossing the daytime equator at about 4:30
p.m. local time. The first phase of the mission was to support the Mars Polar Lander from
its landing on Mars on 3 December 1999 to the end of the lander primary mission on 29
February 2000. The orbiter would pass over the lander site 10 times per Martian day for
5-6 minutes each time, communicating via the UHF 2-way relay link at 128 kbits/s. Mars
science operations and mapping, involving operation of the MARCI and PMIRR, would initiate
on 3 March 2000 and continue for one Martian year (687 days). At the end of the mapping
mission on 15 January 2002, the orbiter was to be placed in a stable orbit and function as
a UHF relay for the Mars 2001 mission.
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.
