When the spacecraft approached Mars, they needed an “orbital insertion” burn and that was handled by the spacecraft’s own on-board software which used SI units of Newton-seconds. That would have caused the craft to use only about 22% as much thrust as it needed. The error was somewhat counteracted by another error in the conversion from feet to meters…which is speculated to be why the error was not noticed in ground testing.
So the spacecraft ended up using only about 70% of the thrust it needed…and although its fate is uncertain - it must have hit the atmosphere very hard - and either burned up or bounced off of Mars’ atmosphere. Either way, contact was lost.
Ultimately, this does NOT appear to have been NASA’s fault. The “Systems Interface Standards” (SIS) documents that NASA provided to Lockheed Martin specified the use of metric/SI units - but Lockheed used US customary units instead. However there is an argument to be made that this kind of problem should have been detected when the various parts of the system were integrated prior to launch - and that is probably NASA’s fault.
Ultimately, NASA accepted responsibility…I don’t think they should have done so.
In all matters of science and engineering, SI units are the standard - and even if Lockheed hadn’t properly read the SIS document - they should have assumed SI units anyway.
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