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Comment by sandworm101 | Hacker News Reader

If they have to go through all those checks, then that is a failure for several aspects of the program. The goal of reusability has been parts that don't need to be checked. The engines have been run over and over on test stands. They shouldn't have any faults after a single launch. If they do, then the test program wasn't accurate. If hardware needs to be redesigned to meet that goal, then it also needs to be re-tested and much of the program is back to day one. I'm sure they will do checks, but I am equally sure they dread finding something.

I;m reminded of the story of Shuttle's tires. They were designed to last four or five flights, but famously were replaced every time. SpaceX wants to end such things. Parts are to do what they are designed to do. A part designed to last multiple flights without the need to be x-rayed every time, isn't going to be x-rayed every time.

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It's not a failure. It would be sheer negligence to not have a full check for the _first time they've ever done this._

If they have cracks in things that are designed to go through multiple flights without cracks, and those cracks haven't appeared in testing, that's a failure. Any such finds in checks today means the necessity of checks again next time, and the hundreds of times after that. SpaceX needs to find nothing so that they can then decide at some later date to stop doing the checks. Not cracking open the fuel pumps after every flight is a necessary part of the planned cost reductions. If inspections suggest that the design needs to be checked every time, as with Shuttle, then new design is needed and the testing program hasn't met its goals.

> If they have cracks in things that are designed to go through multiple flights without cracks, and those cracks haven't appeared in testing, that's a failure.

No, it's real world engineering. You can't simulate everything when you're doing something totally new. You need to make tests on real hardware to confirm that your model is good.

Exact. It is not really any different than going from in-house to beta testing in software to get those real world bugs that always come up -- it is a known step of the design process before even starting.

Especially aerodynamics. Modeling fluids alone is very hard and intensive, and that's before you model surface interaction, possible ablation, temperature, shock, and all the other forces present in a dynamic situation.

Not doing any x-ray testing would be completely negligent.

"those cracks haven't appeared in testing" - this is the testing. You don't just simulate the stresses, you have got a bunch of devices that have experienced atmospheric reentry in different conditions, and now you could do the tests on them.

True, but if this additional testing reveals issues not revealed earlier, they'll just iterate again until they won't have to X-ray every plate after every flight, because that is clearly not the MO they have in mind. In the worst case scenario, they might need one extra vehicle generation (BFR?) to actually get there, but I'm quite certain they will eventually get there. Otherwise there's just no point to that company.

Even if you design a component to last for the life of the entire system, that doesn't mean there's no point checking it through that life. There will always be the pieces at the bottom end of the bell curve. You must catch them.

Look at the aviation industry for a good example. A pilot might check certain parts of the aircraft before starting it up each time. They'll likely check more things more closely for their first flight of the day. Then it'll get ever closer inspections every X days by maintenance personnel. These checks catch faults.

The idea of the program certainly is, that the rocket can be flown several times without requiring extensive checking/maintenance. However, as there are no experience with reusing the Falcon 9, it is the proper scientific/engineer approach to extremely carefully inspect the whole rocket to document its conditions to analyze possible failure reasons. The engines have been endurance tested on the ground, but not after reentry. So one has to learn about this. Ideally, all those inspections show that the rocket is just fine, but one can know only doing the proper science. With those experiences gained, it is possible determine the service intervals for standard use.

That's true, but it's not at all clear that scarygliders was talking only about these first few re-used rockets as it was a completely unqualified statement. I certainly read that post as talking about refurbishment generally, in which case sandworm101's reply seems to me to be perfectly reasonable and measured.

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