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From: gsh7w@astsun8.astro.Virginia.EDU (Greg S. Hennessy)
Newsgroups: sci.space.shuttle
Subject: Re: Columbia's Troubles
Message-ID: <1990Sep12.161535.20647@murdoch.acc.Virginia.EDU>
Date: 12 Sep 90 16:15:35 GMT
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Andrew Helyer writes:
#Was I tired and confused?  It seems kind of risky to launch a shuttle with a
#hydrogen leak lurking around.
#
#Does anyone have any further information?  I heard this at about 8:00am CST.

Since I just made arrangements for another trip to Marshall Space
flight center, I may be able to give you some further info.

First of all, no shuttle will launch with a large hydrogen leak
around. Since the hydrogen is so cold, it is impossible to build a
system with ZERO leaks in it. The important thing is to keep the leaks
low enough, which NASA has determined to be a level below 4 percent
hydrogen, the point where hydrogen becomes explosive.

In May the shuttle Columbia was set to launch with the ASTRO mission,
when hydrogen was detected the aft compartments of the shuttle.
Guesstimates indicated a leak of 24,000 cubic inches per second, and
finally the 17 inch disconnect valve was taken off and replaced with
the same part from Endeavour. When lab tested, the disconnect valve
was found to have scratches in the teflon seal, and 15,000 cis was
found to leak. Since the 24,000 cis figure was not very certain, the
launch was rescheduled for Sep 1. An interesting bit of debate was
whether or not to spend 6 days doing an additional tanking test. The
test would indicate if the shuttle was leaking. Since the launch
window was only going to be 12 days long, and passing of a tanking
test did not mean that the shuttle would not leak on the pad, and
since the thermal cycling of the tanking test would put a large strain
on the parts, and mostly since if there was a leak, it probably would
not be able to be fixed in time before the Discovery had to launch, it
was decided not to do a additional tanking test. At no point was the
shuttle in danger of violating safety rules. When the tanking for the
launch on Sep 5 was done, the shuttle was found to still leak. A fuel
pump was recently replaced, and a seal was found to be "crimped" in
the pump. This leak was probably there all along, just smaller than
the leak from the 17 inch disconnect valve leak.

Launch is currently scheduled for 1:25 AM or so, Tuesday Morning.


--
-Greg Hennessy, University of Virginia
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