The other day I was watching a documentary about Mars rovers, and at one point a story was told about a computer on the rover that almost had to be completely thrown out because someone dropped a tool on a table next to it. Not on it, next to it. This same rover also was planned to land by a literal freefall; crash landing onto airbags. And that’s not even covering vibrations and G-forces experienced during the launch and reaching escape velocity.
I’ve heard similar anecdotes about the fragility of spacecraft. Apollo astronauts being nervous that a stray floating object or foot may unintentionally rip through the thin bulkheads of the lunar lander. The Hubble space telescope returning unclear and almost unusable pictures due to an imperfection in the mirror 1/50th the thickness of a human hair, etc.
How can NASA and other space agencies be confident that these occasionally microscopic imperfections that can result in catastrophic consequences will not happen during what must be extreme stresses experienced during launch, travel, or re-entry/landing?
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EDIT: Thank you for all the responses, but I think that some of you are misunderstanding the question. Im not asking why spacecraft parts are made out of lightweight materials and therefore are naturally more fragile than more durable ones. Im also not asking why they need to be 100% sure that the part remains operational.
I’m asking why they can be confident that parts which have such a low potential threshold for failure can be trusted to remain operational through the stresses of flight.
In: 3487
> I’m asking why they can be confident that parts which have such a low potential threshold for failure can be trusted to remain operational through the stresses of flight.
The parts are designed and tested to handle that specific condition.
They aren’t tested to handle other conditions. Particularly in combination. So while we can intuitively say “It’s probably fine”, the work to be *sure* it’s fine is significantly greater.
This is also why there tend to be so many duplicate copies of things. If you subject your thing to the simulated flight stress, you know it can survive that… once. You don’t want to use that part though, because you’re not sure it can survive it twice — you’ve not tested that.
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Incidentally, the same thing applies on the ground. I’ve done some work with lighting truss that was bolted together. If we dropped a bolt more than IIRC three feet onto the ground, it had to be thrown away. Obviously, the bolt is still probably-fine, but we’re talking about flying truss over people. The bolts aren’t tested and rated for being dropped and then used, so we don’t risk it.
… even if that means saying that a bolt that can handle 12,000lb of tension is incapable of surviving a four foot fall.
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