daemon@decwrl.UUCP (11/09/83)
From: Ed Featherston HL01-1/P06 225-5241 <roll::featherston>
Begin Forwarded Message:
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Newsgroup : net.columbia
>From : DVINCI::FISHER
Organization : Digital Equipment Corp.
Subj: SRB failure recovery
Thinking about near-failures of an SRB and what might be done has led
me to some interesting questions which I wonder if someone out there
can answer.
Suppose only a single SRB lights up on the pad. Is the shuttle released
before SRB thrust is confirmed? If not, can the hold-down bolts and the
ET/orbiter structure withstand the thrust of a single SRB for 2+ minutes?
Now suppose a single SRB fails after the shuttle is in the air. From all
I have read, RTLS abort assumes that the SRB burn can proceed to completion
so that SRB sep and ET sep can occur. Can either the SRB or the SRB/ET
combination be separated while one or more SRBs are still burning? Are
any of the above SRB/ET configurations aerodynamically stable? Would the
orbiter get completely fried in the SRB exhaust? Would that be better than
umpteen million pounds of asymmetrical thrust? Would the SRB be likely to
collide with the orbiter? What happens to the SRB's steerable nozzle (and its
associate APU) when it gets no command input from the orbiter?
Have any analyses of the above questions been done, or is an SRB failure early
in the mission automatically fatal?
Thanks in advance for any answers,
Burns
Wed 9-Nov-1983 13:31 Eastern Daylight Time
Mail address : ...decvax!decwrl!rhea!dvinci!fisher
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End Forwarded Messageeder@ssc-vax.UUCP (Dani Eder) (11/11/83)
11 November 1983
If one SRB fails to light on the pad or, alternatively, the holddown
bolts on one side are not released, the results are catastrophic. In both
cases the External Tank is immediately sheared (ripped in half the long way).
The reason is there is a thrust beam inside the tank which crosses between
the SRB's. It connects the forward ends of the SRB's to each other and
to the skin of the ET. It is there to distribute any thrust imbalance
between the SRB's equally among the vehicle components. The nozzles of the
various engines are steerable to correct for this possibility.
The thrust beam is sized for about a 10% difference in thrust. If
one engine runs and the other doesn't, or one is freed from the pad and
the other not, the ET will be ruptured. The ET is .1 inch aluminum, while
the SRB's are more like 1 inch high strength steel. The tank goes first.
During flight there is no way to shut down an SRB intentionally or
accidentally short of destroying it. This is because the solid fuel
contains both fuel and oxidizer. Once ignited, the combustion is self-
sustaining. The combustion RATE is dependant on pressure. The only
way to slow it down is to lower the pressure by blowing the nozzle out
the rear end (which is not designed in), or by splitting the motor case
with an explosive charge (which is).
Pity the poor astronauts, since they will almost certainly die in
any of these accidents. If you go to see a launch in person, be aware
that the press and VIP viewing areas (3.5 mi from pad) are within
shrapnel range should the vehicle explode on the pad. They told us this
AFTER STS-1 (I was in the press area).
Dani Eder
Boeing Aerospace Company
ssc-vax!eder