Encyclopedia Astronautica
1998.12.11 - Mars Climate Orbiter

The Mars Climate Orbiter was the second flight of the Mars Surveyor Program. The probe was to enter a 160 km x 38600 km polar orbit around Mars on September 23,1999, and use aerobraking to reach a 373 km x 437 km x 92.9 degree sun-synchronous mapping orbit by November 23 1999. While the Mars Orbit Insertion burn began as planned on September 23, 1999 at 08:50 GMT, no signal was received after the spacecraft went behind the planet. Subsequent investigation showed that the spacecraft had plunged deep into the Martian atmosphere, with its closest approach to Mars being 57 km. It was concluded that the spacecraft burnt up in the atmosphere. It was later found that cutbacks in tracking, combined with incorrect values in a look-up table imbedded deep in the spacecraft software (use of pounds force instead of newtons) were to blame. This failure led to a shake-up of NASA's 'faster, better, cheaper' approach to unmanned spaceflight.

Launch had been as planned, with the Delta upper stage entered an initial 185 km x 198 km x 28.4 degree parking orbit. A second burn raised apogee to around 900 km. Then the Thiokol Star 48 third stage motor accelerated the spacecraft to a trans-Mars trajectory. The Delta stage was left in a 162 km x 857 km x 23.9 degree Earth orbit. Primary on-board propulsion for the orbit insertion manoeuvre at Mars was a 65 kgf Leros bi-propellant engine. Mars Climate Orbiter was equipped with a MARCI colour imager for mapping and weather studies; a PMIRR radiometer; and a UHF communications system which would also relay data from the (equally unsuccessful) Mars Polar Lander, scheduled for launch in January 1999. The science mission was to map the Martian surface at high resolution, and study the distribution of water vapour and ozone. It would study the transport of dust and water with latitude, the motions of weather systems and dust storms, and study the response to daily solar heating.

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