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
To keep it eli5, it’s the way stresses are applied. If you take a human and drop them on their head, they will sustain more damage than if you drop them on their feet. Why? Because of the way the forces are applied and transmitted through a structure. In test and development often components are not final torqued or fitted to their final structure, making them more susceptible to damage and appear fragile. Once they are in their final configuration they often are as robust as you are accustomed to. Another human body analogy, why are organs so weak and damagable when the human body is known to be very resilient? If a surgeon opens you up to “service” or “repair” you wouldn’t you be more susceptible to disease or injury? But once you are in your “flight configuration” i.e. closed up and recovered after post op medication your body is more resilient to the expected environment and stresses such as tripping and falling down, or scrapes.
The Apollo example is one that my above explanation doesn’t cover as well, but it is actually a very simple one. Because you can tell a human to not be a big dummy and kick the spacecraft. Why design for a situation when you can actually completely control whether that “load” of a foot gets applied or not? For the random object ripping through though, that is a probability game. You can look into MMOD probability curves to see how you can guesstimate chance of impact for a given area. This is well outside of an eli5 though. It boils down to humans think about what can go wrong and you can’t guarantee an outlier object moving fast enough won’t rip through your multi layer insulation.
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