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> A typical figure for a 15 year mission was a 75% chance of it making it the whole way, including launch. It's checked to an extreme degree. I've had people come back and correct an un-dotted 'i' symbol in a handwritten notebook. Really.

Can you break down this calculation? Where did 75% come from? I think your parent poster's point is this: no one really knows where these numbers are coming from.

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>...no one really knows where these numbers are coming from.

That was actually explained in the (excellent) comment. Snippet below, but please re read the comment or example how resistors are actually tested in batches to give real failure rates.

>Each resistor on a PCB, each explosive bolt, each screw and panel. All of it has a lifetime curve, typically a Bathtub plot, to an extreme degree

I'll admit, a lot of the time, you just can't get good enough vacuum on Earth. The best we could do was the nano-torr range, but space is much better. This does effect testing somewhat. Also, a lot of the time, it's the 'black swans' that really matter. Fun fact: the Hubble flies butt first, as they experimentally discovered that meteorites will affect the telescope less than flying it lenses first. I can't find the pic right now, but there is a softball sized hole in the computer (butt) section.

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