On 12/27/2015 9:26 PM, Henry Spencer wrote:
On Sun, 27 Dec 2015, Henry Vanderbilt wrote:
Engines can to a considerable extent be life-tested on the ground. A
much larger unknown (as Bill has pointed out) is the fatigue lifetime
of the structure and tankage... The tricky thing is, whether (and
where, and how well hidden) F9 first stage might (or might not) have
its equivalent of the old Comet airliner's square-cornered windows - a
place where fatal fatigue builds up under flight cycles much faster
than expected.
That can also be tested on the ground, to some extent, if you understand
the flight loads halfway well: dedicate a fatigue-test airframe to
sitting in a hangar being flexed by hydraulic jacks, so that it builds
up cycles much faster than the flight vehicles. When that was done for
the Comet -- it wasn't a routine part of aircraft development then --
the window-corner fatigue failure was successfully duplicated.
Replicating some aspects of the rocket flight environment (notably the
vibration) admittedly might be difficult.