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.
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>he 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.
Lets talk about where it is used and what happens if there is a flaw that needs fixed. If this is your home computer, it is actually pretty easy to get a technician there to fix it. If it goes to mars, there is no way to get a ‘fix’ to that device.
That is the first issue – we cannot simply fix it if it breaks. The second is cost.
Lets assume another situation – a one time available use on earth vs mars. Same issue of no-technician being able to fix it. I it costs $100 to get it there on earth, it may not be as big of an issue to send another. If it costs 2 billion and 8 months to get it another planet, it is no so easy to simply send another one to replace it.
So with Space hardware, the lack of servicability coupled to the extreme costs and time delays to get items to the location make it all the more important they are perfect or at least as perfect as we can make them.
The last part is we may design items to withstand specific forces, but we don’t want to expose them to these forces without reason. The windows on your home are impact resistant. We don’t regularly hit them with a hammer to check. Same idea here.
With that computer, it may cost $25,000 to replace it on earth with one that didn’t have that issue occur. On a 2 billion dollar mission where failure is extremely expensive, it can be worth it to replace the item rather than risk an extremely unlikely failure.
>I’ve heard similar anecdotes about the fragility of spacecraft.
This is also somewhat true.
Spacecraft have huge weight limits given the energy required to lift something into space. We simply cannot armor something like a battleship.
The second item is energy. We are used to thinking about impacts in earth terms, with wind resistance. In space, the speed differentials can be huge. We are talking about speeds in the thousands and tens of thousands of miles an hour. 200km is 17,000mph orbital velocity
Imagine a baseball sized object coming at your spacecraft with a differential speed of 2000 mph. It is this huge energy level based on speed that makes even small low mass items dangerous to spacecraft.
In earth terms, imaging dropping a bowling ball on a piece of plywood from waist height. Will it punch through? Now image a bullet from a gun. Will it punch through? In space, the bullet analogy is actually pretty good. A typical handgun shoots a bullet around 800mph. A hunting rifle – around 2000mph.
That is the power of speed.
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