The Loss of Mars Climate Orbiter
The MCO spacecraft was launched on Dec 11, 1998, and headed to Mars for a multi-year mission to support its partner, the Mars Polar Lander, and to study the atmosphere and clouds of Mars. It spent months flying through space, finally reaching Mars in September, 1999. On Thursday, September 23, 1999, the spacecraft fired its rockets to alter its trajectory so that it would enter orbit around Mars. It passed behind the planet as it was firing ... and was never heard from again! cue spooky music
After several weeks of investigation, it was determined that the fundamental cause of the mishap was a mistake in a computer program used to control the spacecraft's thruster rockets. Engineers at Lockheed Martin wrote a computer program called "SM_FORCES", which calculated the thrust produced by the rockets for a given sort of firing. The output was supposed to be in metric units called "Newton-seconds." But the actual code produced thrust in English units called "pound-seconds".
1 Newton-second = 4.45 pound-seconds
The rockets were used a number of times during the long trip between the planets; each time, they caused the spacecraft to deviate a bit more from its proper path. The navigation team, at the Jet Propulsion Laboratory, didn't notice the error. By the time the MCO reached Mars, its actual position was significantly different from its expected position: the navigation team thought that it was about 110 km above the surface of Mars at closest approach ... whereas it was really only about 57 km above the surface. The aerodynamic forces of this improperly low altitude destroyed or disabled the spacecraft.
There were a number of reasons that no one caught the error.
For more information, see http://mars.jpl.nasa.gov/msp98/news/mco991110.html (or look at a local copy)
Copyright © Michael Richmond. This work is licensed under a Creative Commons License.