[net.columbia] Speculation II

piner@pur-phy.UUCP (Richard Piner) (02/04/86)

  It is now certain that the SRBs burned through. There have been near
misses in the past. NASA claims to have solved all problems with the SRBs.
But as I recall, the burn through problems were never duplicated in
static test on the ground. So while we are speculating, I thought
I might speculate on why the performance in flight might differ
from performance in static test.
   The difference between static test and flight conditions is
one of air flow. The SRB in flight is traveling at great speed
through cold air. This has got to cause some problems. Liquid
fueled engines are not exposed to such effects because they are
behind the craft and out of the air stream for the most part.
Static test of these engines should give reliable information.
But the SRB engine is a long tube packed with fuel. The fuel
burns from the core inside out. Cooling the skin might affect
the engine performance.
  There is also the problem of vibrations due to air flow over
the skin of the SRB. While these vibrations are no doubt small
in magnitude, it is conceivable that they could affect the burning
fuel inside. This is especially true if some sort of resonance 
is induced in the skin, fuel or plasma. Both of these effects
cannot be duplicated in static test. This is a case where only
a theoretical model could test the effects of high velocity cold
air flow over the skin. The complexity of the physics and chemistry
involved would make it a very difficult calculation to do, and it
is a second order effect to be sure. It would not surprise me
if NASA has not attempted to do this calculation. But a small
second order effect could explain why SRBs tend to come closer
to failure in flight than in static test. Perhaps the simple
thing to do, is just increase the engineering margin. I suspect
that that is what NASA has done. Anyway, any computer hackers
out there want to volunteer tackling this problem? It could keep
you busy and off the streets for years to come.
   Take note that NASA is looking for a problem in the manufacture
history of the SRB that failed. If they don't find one, then
new engineering studies will be required. That could take a
very long time.
   I still don't think that the SRBs were at fault in the
destruction of the Challenger. See my next posting.

					Richard Piner
					piner@pur-phy.UUCP

ems@amdahl.UUCP (ems) (02/10/86)

In article <1954@pur-phy.UUCP>, piner@pur-phy.UUCP (Richard Piner) writes:
> 
>   It is now certain that the SRBs burned through. There have been near
> misses in the past. NASA claims to have solved all problems with the SRBs.
> But as I recall, the burn through problems were never duplicated in
> static test on the ground. So while we are speculating, I thought
> I might speculate on why the performance in flight might differ
> from performance in static test.
(long discussion of cold and air flow ...)

I was surprised that you did not mention the G forces in flight.
It would seem to me that the effects of a couple of g's on stacked
fuel pellets and seals would be a critical area of interest?
(And would not show up in static tests)
-- 
E. Michael Smith  ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems

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