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

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 spacecraft received correct commands and survived its journey from Earth, but ground software used pound-force-seconds while navigation software expected newton-seconds. The resulting error changed the predicted trajectory and sent the spacecraft below its planned Mars orbit.