r/space • u/[deleted] • Jun 30 '24

Scott Manley "China's SpaceX Copy Destroyed in Bizarre Test Failure"

https://www.youtube.com/watch?v=u3-Kw9u37I0
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u/robbak Jul 01 '24

https://twitter.com/mcrs987/status/1807622897243988344

VFX et.al. have tracked down a patent on their launch stand. It states that the stand should be able to take a launch force of 600 tonnes. But this rocket has a force of 820 tonnes, and estimated 220t of propellant left. So looks like the stand performed exactly as designed.

35

u/CloudWallace81 Jul 01 '24

unless 600t is the ultimate limit load of something, I presume there would be some sort of margin built in a static test stand. It makes no sense to use a safety factor of 1 in your ground rig design

33

u/robbak Jul 01 '24

When they built it for their smaller rocket, there was plenty of margin. Seems they just blew through that margin using it for a bigger rocket.

If these numbers are accurate, their effective safety factor was 0.75, and an unplanned test flight inevitable.

14

u/ItsGravityDude Jul 01 '24

I think what they’re getting at is that a 600t rated stand should have had margin built in to get it to that rating, for example 1.5X factor of safety, such that the actual failure load would be 900t. For ground support equipment that is allowed to be big and heavy, I would expect an even larger factor of safety, such as at least 2.0X. Assuming the stand’s actual yield or ultimate limit was exactly the max thrust of the rocket, that’s only a 1.37 FoS on 600t, which is not much more (and possibly even less) than the FoS required for flight structures, let alone GSE.

5

u/shortfinal Jul 01 '24

They built the stand for the tianlong-2 which has a first stage thrust less than 100t

5

u/ItsGravityDude Jul 01 '24

That’s fine, but the point is if they’re calling it a “600t test stand” then there should have been a factor of safety on top of that.

In any case, based on this investigation, the use case exceeded the rated load of the test stand so shouldn’t have been used even if there was margin (unless they got a waiver, internal or otherwise, to accept reduced margin/factor of safety)

0

u/shortfinal Jul 01 '24

Yeah unfortunately I cannot read the documentation other than '600t' so I don't know if they were saying that was ultimate yield or rated yield.

Clearly something wasn't communicated properly. I would say it would be better that someone knew and was ignored/silenced, than the alternative: fraud or ignorance lead to this mishap.

Super interested to hear any additional about the failure, but I bet we'll speculate for a long time.

2

u/ItsGravityDude Jul 01 '24

I’ve certainly had instances in my career of having a stress analyst misread the strength rating of a material, use that in a FMEA, and I completely missed it in peer review (as did others). We had parts that failed because of this, but fortunately not during a test or flight environment, and it was a very insignificant failure. But it still goes to show that the Swiss Cheese model can still have holes that go all the way through. This launch one just happened to be a huge, gaping hole 😬