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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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.
>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.
They perform an insane amount of engineering analysis, simulation and testing to validate that the systems will operate in the conditions they’re designed for, with very narrow safety margins. Which is why spaceflight is such a difficult and expensive endeavor, they must anticipate and account for ANY contingencies in the design or the mission will fail.
Keep in mind also that many things are extremely strong *in one specific way.* Bridge cables can hold up hundreds of tons but can be bent with a finger. Foils and plating can withstand thousands of degrees of heat but be soft enough to scrape with a fingernail. The list goes on.
And since spacecraft tend to spend their time… in space… you don’t have to design for generic atmospheric survivability as much.
They survive launch because they’re carefully packed and padded and not allowed to move. Fairings keep the wind and air from hitting them, bracing prevents knocks and shocks and sharp collisions.
People talking tolerances and certifications are more correct, but I think this answer will be more intuitive.
Grab two ends of a piece of paper. Without bending or twisting the paper, just keeping it as a flat plane, try to pull the paper apart. It’s very hard. Yet you can effortlessly roll the paper into a tube if you apply much less force to it just along a different direction.
A aluminum can can hold a great deal of pressure inside of it. You can tear the metal it’s made out of with your hands.
Being strong one way wont necessarily mean strength in another way.
> 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.
Strict auditing. The tool being dropped in your question probably made no difference. But if you’ve got a million pieces, each with a mistake that “probably” won’t make a difference, it becomes very likely that a few things are wrong. The best way to avoid it is by being very strict with processes.
The cost of remaking 10% of the pieces over silly mistakes is less than the cost of blowing 100% of it up.
Some good answers already, but worth remembering that things are designed for specific loads in specific directions during specific modes of operation.
For example: solar panels are designed to withstand large accelerations and vibrations when safely wrapped up during launch, but would be shredded by those same forces when deployed, or when being tested on Earth.
Generally speaking, spacecraft parts will be in an extremely well-defined environment – parts that need to be made strong can be made VERY strong in the direction where strength is important. Parts that can be made weak can be made VERY weak. Damage usually comes when it comes from an unexpected direction and weak parts are overpowered.
How many atmospheres can the ship withstand?
I get what you’re saying. I actually used to test rocket parts for a living for many years. I worked on dozens of launches. Maybe over a hundred.
You essentially design the part, build one for the rocket and one for testing. You test the one for the rocket in as close to operational conditions as you can and you test the other one to its design limits, which is far greater than what it has to do in space. We actually test them until they break usually.
It is insane how much care we take in handling parts for how much load these parts see in flight.
I don’t work there anymore, I just kind of take pictures now.
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