Space probe launched December 1998, crashed into Mars September 1999. Mission failed because Lockheed Martin used English units, and NASA used metric. Doh!

The mission was to collect data on the martian atmosphere over 1 martian year, and also to relay data from the Mars Polar Lander mission. Oh well, no worries, since the Lander's lost too ...

The Mars Climate Orbiter (MCO) fired its main engine at 09:01 UTC, September 23rd 1999, to begin orbital insertion into Mars orbit. Telemetry with the craft was lost five minutes later as it was occulted by Mars (went behind Mars as viewed from Earth), but communication was expected to be recovered twenty minutes later when it was supposed to reappear from behind Mars. No signal from Mars Climate Orbiter would ever be heard on Earth after 09:04:52 UTC, Thursday, September 23, 1999.

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 reported. 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, available at

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,

The Mars Climate Orbiter (MCO) spacecraft began as one half of a two part mission, the Mars Surveyor '98 program. It was originally called Mars Surveyor 98 Orbiter, or alternatively, Mars '98 Orbiter. The other half of the Mars Surveyor '98 program was the equally ill-fated Mars Polar Lander.

Mission Profile

MCO was lifted from Earth on December 11th 1998 at 18:45:51 UTC aboard a Delta II Lite launch vehicle equipped with four strap-on solid rocket boosters and a Star 48 (PAM-D) third stage. During the cruise, four trajectory correction maneuvers and a number of angular momentum desaturation events took place.

At 09:01 UTC, on September 23rd 1999, MCO began it's orbital insertion burn. This burn was to last 16 minutes and 23 seconds, during which time the craft would pass behind Mars. Telemetry was lost with MCO at 09:04:52 UTC as Mars occulted the craft, and MCO was never heard from again.

If the mission had gone as planned, then MCO would have found itself in a 14 hour elliptical capture orbit of approximately 150 by 21,000 km. Aerobraking by using the solar panel to provide drag would then have begun, and would have continued until the orbit had changed to about 90 by 405 km. This orbit would have ideally been obtained on the 22nd of November, 1999. On the 1st of December, thrusters would have been used to move the craft into a nearly circular orbit of 421 km.

The Mars Polar Lander (MPL) was expected to land on Mars on December 3rd 1999, and the first phase of the MCO was to serve as a communications relay between the lander and Earth until the end of the lander mission on the 29th of February 2000. MCO was to fly over the MPL landing site ten times a day for 5 or 6 minutes each time. Information between MPL and MCO would have been transmitted over a 2 way UHF link of 128 kbit/s.

Science and mapping operations were to begin on March 3rd 2000, and were scheduled to last a full Martian year, which is 687 days. After that, MCO was to be placed in a stable orbit and was destined to serve as a UHF relay station for the Mars 2001 mission.


The first objective of the Mars Climate Orbiter mission was to act as a relay station for the Mars Polar Lander mission, which was expected to arrive on the heels of MCO. After completing it's science objectives, MCO was to again serve as a relay station, this time for the Mars 2001 mission.

The science objectives of the MCO were, as the name implies, to study the Martian climate. Specifically, MCO was to examine daily weather and atmospheric conditions, find the dust and water content of the atmosphere, determine temperature profiles, and look for evidence of past climate change.


The Mars Climate Orbiter craft was basically a box, 2.1m high, 1.6m wide, and 2m deep. The interior consisted of stacked propulsion and equipment modules. It carried a 1.3 meter high gain dish antenna atop a mast above the propulsion module. This antenna was mounted on a 2 axis gimbal and was used to communicate with Earth on the X-band via the Cassini Deep Space Transponders.

Power was provided by a 5.5m long solar array which was attached to the side of the craft with a 2 axis gimbal. The solar array had a total surface area of 11 square meters, and consisted of three panels of GaAs/Ge solar cells, which could provide 1000 W at 1 AU. Power was stored in nickel hydride (NiH2) common pressure vessel batteries.

The propulsion system consisted of a bipropellent 640 N main engine, which used hydrazine and nitrogen trioxide as fuel. A total of eight smaller thrusters using a single propellant, hydrazine, were used for attitude control and maneuvering. Four of these thrusters were 7 N pitch/yaw thrusters, and the other four were 0.3 N roll thrusters.

Attitude was controlled by a combination of the mentioned thrusters and reaction control wheels. The spacecraft used an inertial measurement unit, and star tracker, and analog Sun sensors to find it's orientation in space.

Instruments on board the craft were the Mars Color Imager (MARCI), and the Pressure Modulator Infared Radiometer (PMIRR). MARCI was used to acquire approach images of Mars, and was supposed to be used to take pictures of the Martian atmosphere and surface. MARCI combined nadir pointed pushframe wide angle and medium angle cameras. The wide angle camera had a field of view of 140 degrees on seven spectral bands, two ultraviolet and seven visible. The medium angle camera had a 6 degrees field of view on ten spectral channels. PMIRR was a multispectral limb and nadir scanning atmospheric sounder. It had nine channels, and was supposed to provide vertical profiles of atmospheric temperature, dust, water vapor, and condensate clouds.

The instruments, UHF antenna, and battery enclosure were located at the bottom of the craft.

MCO had a launch mass of 625 kg, 291 kg of which was propellant.

Mars Climate Orbiter was part of NASA's Mars Surveyor Program. Development of the spacecraft cost about 192.1 million dollars, launch costs and mission operation costs were about 91.7 million and 42.8 million dollars respectively.

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