Which NASA orbiter was lost in 1999 because of a metric-unit conversion error?

Which NASA orbiter was lost in 1999 because of a metric-unit conversion error? Mars Climate Orbiter. The spacecraft was destroyed during its attempted arrival at Mars on September 23, 1999.

The failure resulted from a mismatch between units used by different parts of the mission. Ground software supplied impulse data in pound-seconds, a customary unit, while onboard navigation software expected the equivalent metric unit, newton-seconds. The discrepancy caused the navigation team to miscalculate the spacecraft’s trajectory.

Mars Climate Orbiter approached Mars too low. Instead of entering its planned orbit, it passed through the upper atmosphere at an unsafe altitude, where atmospheric drag likely destroyed or disabled it. The spacecraft had been designed to study Mars’s atmosphere, climate, dust, and water-related processes from orbit.

The incident is often simplified as “NASA forgot metric,” but the deeper problem was an interface and verification failure between teams and software systems. Mars Odyssey, Mars Reconnaissance Orbiter, and MAVEN are separate successful Mars missions, not the spacecraft lost in this accident.