Mars Climate Orbiter

Mars Climate Orbiter was a spacecraft sent to Mars by NASA to study the weather there. It launched in 1998 but failed to reach Mars because it was sent to the wrong location due to a mistake in how it was programmed. The mistake was that NASA engineers used a measurement of force in one type of units, but the spacecraft was programmed to use a different type of units. This mistake caused it to fly off course and be lost in space.