Mars Climate Orbiter (MCO)

Launch data: Designation  25571 / 98073A Launch date  11 Dec 1998 - 18:45:51 UT Launch site  CC, LC-17A Launch vehicle  Delta 7425-9.5 (#D264) Mission  Mars probe Satellite type

Mission details:

• The Mars Climate Orbiter was launched on a Boeing Delta 7425 on Dec 11, 1998. MCO is the second craft in the Mars Surveyor Program; the first was Mars Global Surveyor, currently aerobraking in orbit around Mars. MCO was built by Lockheed Martin Astronautics/Denver, consisting of an equipment module and a 640N Leros bipropellant orbit insertion engine. MCO carries the MARCI color imager for mapping and weather studies, the PMIRR radiometer, and a UHF communications system which will relay data from Mars Polar Lander, scheduled for launch in January 1999.
• The Delta upper stage entered an initial 185 km x 198 km x 28.4 degree parking orbit. A second Delta stage 2 burn raised apogee to around 900 km when the third Star 48 stage took over for the solar orbit insertion burn. An older Star 37E motor was used in the 1970s as the standard third stage, but was replaced by the much bigger Star 48 in the 1980s. The Star 48 and MCO are in solar orbit; the Delta stage 2 was left in a 162 x 857 km x 23.9 deg Earth orbit. Primary on-board propulsion for the orbit insertion manoeuvre at Mars was a 65 kgf Leros bi-propellant engine.
• Mars Climate Orbiter made its first orbit correction at 2133 UTC on Dec 21, 1998.
• Mars Climate Orbiter 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. 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.
• Mars Climate Orbiter began its Mars Orbit Insertion burn on Sep 23, 1999 at 08:50 UTC, but a navigation error meant that the closest approach to the surface of Mars was only 57 km, half the intended height. No signal was received after MCO went behind the planet, and it is feared that the spacecraft burnt up during the unintentional aerocapture maneuver. Closest approach to the planet was probably around 0900 UTC.
• The MCO MIB has determined that the root cause for the loss of the MCO spacecraft was the failure to use metric units in the coding of a ground software file, "Small Forces," used in trajectory models. Specifically, thruster performance data in English units instead of metric units was used in the software application code titled SM_FORCES (small forces). The output from the SM_FORCES application code as required by a MSOP Project Software Interface Specification (SIS) was to be in metric units of Newtonseconds (N-s). Instead, the data was reported in English units of pound-seconds (lbf-s). The Angular Momentum Desaturation (AMD) file contained the output data from the SM_FORCES software. The SIS, which was not followed, defines both the format and units of the AMD file generated by ground-based computers. Subsequent processing of the data from AMD file by the navigation software algorithm therefore, underestimated the effect on the spacecraft trajectory by a factor of 4.45, which is the required conversion factor from force in pounds to Newtons. An erroneous trajectory was computed using this incorrect data.
  It may never be clear whether MCO impacted Mars or remained in solar orbit.