ABSTRACT
The NASA Mars Climate Orbiter case is a monumental example of the signicance of units and conversions for practicing engineers. The Mars Climate Orbiter was set to land on the surface of Mars on September 23, 1999, to study the Martian climate, atmosphere, and surface. The orbiter trajectory was planned to be 226 km (140 miles) above the surface so that the gravitational acceleration of Mars could pull the Orbiter through the atmosphere at safe speeds. Instead, the trajectory was only 57 km (35 miles) and the orbiter was disintegrated by the atmospheric stresses. The magnitude of error was off by a factor of 4.45, the exact conversion from Newtons to lbforce. The trajectory was programmed for force inputs in metric Newtons; however, the crew at the controls was entering trajectory data in imperial units of lbforce. Fortunately, the Orbiter was unmanned; however,
the incident cost NASA well over $600 million.1 Despite the innite complexity in the engineering of the Orbiter, it was a simple conversion error that was ultimately the source of failure. This holds true for all engineers as it is easy to overlook such basic fundamentals.
