Oops! NASA Once Lost a $125 Million Spacecraft Because Engineers Forgot to Convert to Metric

Here’s what you’ll learn when you read this story:

• The Mars Climate Orbiter (MCO) launched in late 1998 and was predicted to reach Mars nine months later. But that never actually happened.

• As the MCO approached Mars, it ventured far too close and either burned up in the atmosphere or was lost to another orbit.

• NASA’s postmortem later found that the failure of the mission was a result of their contractor, Lockheed Martin, neglecting to convert to metric units in the software.

December 11, 1998—launch day for the Mars Climate Orbiter (MCO) and the accompanying Polar Lander, both of which were part of a larger NASA initiative known as Mars Surveyor ’98. NASA had commissioned Lockheed Martin to design and build the MCO, which was was destined to gather data on Martian weather while communicating with the Polar Lander.

There was just one problem: The orbiter would never reach Mars.

Superficially, everything seemed to be going according to plan. Lockheed Martin was at the design helm, and NASA’s Jet Propulsion Laboratory (JPL) was overseeing every aspect of the project. The MCO was equipped with eight thrusters intended to boost it into Mars orbit. It also had reaction wheels that could adjust its altitude and orientation, though they occasionally overdid the momentum, resulting in the MCO needing an angular momentum desaturation (AMD) event to reset itself. Once in orbit, the MCO was supposed to beam data back to specialized software on Earth, which would figure out its position and plan any necessary AMD events for the near future.

That communication was crucial, as it is for all active space missions. But soon after launch, software problems began to arise. During the journey, which was projected to last nine and a half months, the MCO’s software began acting up, requiring ground navigation data to be emailed to NASA for solutions. Even with corrections to the software, however, the MCO was still transmitting nonsensical data back to Earth.

In September of 1999, engineers computed and executed the final planned Trajectory Correction Maneuver (TCM-4) to refine the Mars Climate Orbiter’s approach to Mars. The intended trajectory would have produced a first periapsis (closest position to Mars) of about 140 miles (226 km) above the planet after orbit insertion. But navigators determined that the spacecraft’s predicted closest approach was lower than expected, revealing a serious trajectory error. The planet’s gravity was beginning to pull the orbiter in.

By the morning of September 23, 1999, the MCO had vanished with no way to reestablish communication. So…what happened?

According to NASA’s initial postmortem analysis, the spacecraft was only about 35 miles (57 km) from the ruddy surface of Mars when contact was lost. Engineers concluded that the orbiter either burned up in the Martian atmosphere or skipped off the atmosphere and was lost in space. When the agency investigated the following month and found a data issue, they noticed something suspicious about the small forces software that had been responsible for determining the MCO’s position and AMD: while everything else used metric units, this software was using Imperial units.

Lockheed Martin’s use of the wrong units in its software meant that the MCO was not even close to the trajectory it was supposed to be on. While NASA required Lockheed Martin to convert its measurements to metric units, the agency never verified which measurement system the company had employed before sending the MCO off to Mars, and there was reportedly no response from upper management when navigation staff voiced their concerns during the mission.

Investigators claimed that NASA was the party responsible for the failure of the mission, rather than Lockheed Martin. They stated that NASA officials had rushed everything to the detriment of the mission, neglecting to thoroughly test the small forces software as they should have, and that it was impossible to tell whether the systems engineering team had validated and verified the software to begin with.

Unfortunately, no matter whose fault it was, the Mars Polar Lander bore the brunt of the unit-conversion failure. Not long after this simple error pulled it disastrously away from its intended orbit, it was doomed to crash and burn.

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