Mars Climate Orbiter falls victim to disorganized ground crew

Technically, the MCO was fairly successful. The only unexpected problem arose because of the craft's asymmetrical solar array configuration, unlike that of Mars Global Surveyor. This meant that solar wind exerted forces off the center of mass of the spacecraft, which caused the craft to gain angular momentum. This momentum was imparted to the craft's reaction control wheels, which became saturated with momentum more often than had been predicted from data obtained by the earlier voyage of Mars Global Surveyor. Angular momentum desaturation (AMD) events had to take place, which caused small errors in the craft's trajectory. The actual trajectory of the craft and the trajectory the operations team thought it was on began to diverge by a factor of 4.45, the conversion factor from pounds to Newtons.

Anomalies in navigation and Doppler signatures of angular momentum desaturation (AMD) events were observed, but they were only informally report. As such, nobody realized the serious threat these anomalies were suggesting. Doppler solutions that consistently indicated a shallow flight path as MCO approached the planet and data collected after trajectory correction maneuver four (TCM-4) which showed a lower than expected periapse weren't addressed. Tracking data collected during the twenty four hours preceding orbital insertion also showed a declining periapse, which was by this time beginning to approach 80 km, the lowest considered survivable by MCO. A contingency trajectory correction maneuver, TMC-5, had been roughed out, but never fully planned. The use of TCM-5 was discussed but never executed because of concerns about its planning. Nevertheless, TCM-5 may have given MCO the periapse boost it needed to stay alive.

Mars Climate Orbiter was occulted by Mars at 09:04:59 UTC, forty nine seconds earlier than predicted. By that time, it was too late to save the craft from burning up in the atmosphere or skipping off into space.

The root cause was found to be the use of English units for thruster performance data generated by a ground based computer program. This data was used in the construction of trajectory models for the spacecraft, and the modellers assumed the data was in metric units as per the specifications.

The following is from the MCO Phase 1 Mishap Report.

Root cause:

• Failure to use metric units in the coding of a ground software file, "Small Forces," used in trajectory models

Contributing Causes:

1. Undetected mismodeling of spacecraft velocity changes
2. Navigation Team unfamiliar with spacecraft
3. Trajectory correction maneuver number 5 not performed
4. Systems engineering process did not adequately address transition from development to operations
5. Inadequate communications between project elements
6. Inadequate operations Navigation Team staffing
7. Inadequate training
8. Verification and validation process did not adequately address ground software

MPL Recommendations:

• Verify the consistent use of units throughout the MPL spacecraft design and operations
• Conduct software audit for specification compliance on all data transferred between JPL and Lockheed Martin Astronautics
• Compare prime MPL navigation projections with projections by alternate navigation methods
• Train Navigation Team in spacecraft design and operations
• Prepare for possibility of executing trajectory correction maneuver number 5
• Establish MPL systems organization to concentrate on trajectory correction maneuver number 5 and entry, descent and landing operations
• Take steps to improve communications
• Augment Operations Team staff with experienced people to support entry, descent and landing
• Train entire MPL Team and encourage use of Incident, Surprise, Anomaly process
• Develop and execute systems verification matrix for all requirements
• Conduct independent review on all mission critical events
• Construct a fault tree analysis for remainder of MPL mission
• Assign overall Mission Manager
• Perform thermal analysis of thrusters feedline heaters and consider use of pre-conditioning pulses
• Reexamine propulsion subsystem operations during entry, descent, and landing

It was not an unforeseen technical or mechanical failure on the orbiter that lead to its loss. Instead, it was a disorganized and informal ground crew that led to the demise of the Mars Climate Orbiter. The lessons learned from this mishap could not save the Mars Polar Lander mission, partly because the investigation of the MCO disaster left the operations team starved for expertise, and partly because of the proximity of the two missions in time.

Much of this information was found on the National Space Science Data Catalog (NSSDC) site, and in the Mars Climate Orbiter Mishap Investigation Report, Phase 1.