Metric martians

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.

Mars Climate Orbiter
NASA/JPL/Corby Waste [Public domain], via Wikimedia Commons
Okay, I’ll admit it, I’m a bit obsessed with the metric system, with small mistakes that have big consequences, and space graveyards. This little story has all of these.

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.

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