[AR] Re: fatigue life (was Re: Re: SpaceX F9 Launch/Update...)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Tue, 29 Dec 2015 22:32:51 -0500 (EST)
On Tue, 29 Dec 2015, Henry Vanderbilt wrote:
And for fatigue, even *flight* testing is always only an approximation,
because fatigue behavior can be quite sensitive to details...
You elided what I think is the most interesting part of my post, this modest
proposal:
"It might actually be easier, cheaper, and more effective to come up with a
boilerplate upper-stage mass&aerodynamics simulator, then instrument the hell
out of a first stage and fly it repeatedly till things start breaking."
Well, as witness the bit of my commentary I've excerpted above, even that
has its problems. :-) One particular snag is that it's kind of hard to
say just how representative that upper-stage simulator has to be, because
that can matter to things like the vibration environment. (The very large
difference in Saturn V vibration behavior between the Apollo 4 and 6
unmanned tests was mostly due to a more realistic fake LM on Apollo 6!)
So there are still issues with deciding which stresses matter enough to be
worth simulating.
It's not a ridiculous idea, but I'm not sure it's an obvious winner
either. One big advantage of fatigue testing on the ground is that if a
problem shows up suddenly, it's easier to collect the pieces for study!
Henry
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