Mars Climate Orbiter lost

On this day in 1999, NASA lost contact with its Mars Climate Orbiter (MCO). An investigation soon revealed that the spacecraft had burned up in the Martian atmosphere because engineers had not converted English units to metric. Launched in December 1998, MCO was publicized as the first weather satellite for another planet. The spacecraft was supposed to observe weather patterns, measure distributions of water and ozone, and track dust storms. During its journey to the Red Planet MCO unexpectedly had to apply thrusters frequently to prevent the probe from spinning out of control. On 23 September 1999 mission control lost contact with MCO as it was inserting itself into orbit. The cause of the failure (and the excessive thruster maneuvers), investigators soon realized, was that thruster performance data were stored in English units, pounds. But other pieces of software used that data as if it were in metric units, Newtons. The unit confusion caused MCO to fly 170 kilometers closer to the Martian surface than planned, a trajectory that almost certainly tore the probe apart in the atmosphere.

Date in History: 23 September 1999