Now You See It, Now You don't

NASA successfully launched the Mars Climate Orbiter Dec. 11, 1998, from a Delta II 7425 launch vehicle. As the orbitor began its nine-month jaunt to Mars, controllers at NASA’s Jet Propulsion Laboratory noticed small discrepancies between computer predictions and antenna signals indicating the spacecraft’s actual location. On Sept. 23, 1999, the craft ended its 286-day journey to Mars and began its Mars Orbit Insertion maneuver just as the craft passed behind the planet as predicted. Flight controllers eagerly waited the estimated 21 minutes for the return signal, but it never came.

Upon further review it was noted that the spacecraft had entered the Martian atmosphere 90 km (56 miles) lower than intended. The orbitor’s actual altitude was below the survivable altitude for such a spacecraft. Consequently atmospheric stresses and friction likely destroyed the $125 million Mars Climate Orbiter.

What was the cause of this $125 million mistake? The Mars Climate Orbiter Investigation Panel found the root cause to be “failure to use metric units in the coding of a ground software file used in trajectory models.” Lockheed Martin, the prime contractor for the mission, had measured the thrust firings in pounds of force as opposed to metric force units of Newtons as NASA had requested. NASA has used metric units for a number of years in compliance with the 1988 Omnibus Trade and Competitiveness Act and President Bush’s 1991 Executive Order 12770.