The Mars Climate Orbiter space probe cost 327 million US dollars – and it crashed because of a mix-up between the metric and imperial systems.
NASA’s Mars Climate Orbiter launched in 1998. The intention of the mission was to send a space probe to circle Mars and examine the weather – something small, light, with lots of redundancies built in so that it would have a better chance of success.
Now, NASA uses the metric system. They have done so informally since 1990 and officially since 2007 – which makes sense, because all of the other space-going nations use metric. But in 1998, there was still some overlap between metric and imperial. And the orbiter fell right into that gap.
Lockheed Martin, one of the sub-contracting companies, had given NASA some software that produced impulse calculations in imperial units: pound force seconds. (I’ll spare you the “impulse power” jokes, Trekkers.) But NASA systems were expecting newton seconds, the metric unit.
This was a costly mistake: the difference between the measurements meant that the orbiter team miscalculated the position of the probe above Mars – thinking that it was much higher up than it actually was. The probe plunged into the Martian atmosphere and (probably) broke up.
NASA blamed themselves, in the most passive-aggressive way possible, for failing to double-check Lockheed Martin’s work.