In 1999, a small unit mismatch sent NASA's Mars Climate Orbiter deep into the Martian atmosphere and led to the failure of the mission. The NASA Mars Climate Orbiter was lost on September 23, 1999, during its planned arrival at Mars. The spacecraft had travelled for nine months after launch and its onboard software was working with metric units. The failure came from a ground-software interface. Lockheed Martin software reported thruster impulse in pound-force-seconds, while the NASA navigation system expected newton-seconds. The navigation system therefore calculated only a fraction of the actual effect of repeated thruster firings. The error changed the spacecraft's path and caused it to pass far closer to Mars than planned.
