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Date: Sat,  3 Mar 90 02:40:02 -0500 (EST)
Subject: SPACE Digest V11 #107

SPACE Digest                                     Volume 11 : Issue 107

Today's Topics:
		     Re: Ariane V36: Mission lost
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Date: 3 Mar 90 05:52:21 GMT
From: elroy.jpl.nasa.gov!jarthur!brutus.cs.uiuc.edu!samsung!cs.utexas.edu!jarvis.csri.toronto.edu!utgpu!utzoo!henry@decwrl.dec.com  (Henry Spencer)
Subject: Re: Ariane V36: Mission lost

In article <2074@kiwi.mpr.ca> fischer@dssmv2.UUCP (Roger Fischer) writes:
>>At H0+101 s, the high dynamic pressure attained created excessive
>>stresses on the structure and triggered the explosion...
>
>Do I understand this right? The Ariane did not explode, it disintegrated due
>to high dynamic pressure!?!

What's so remarkable about it?  That's what destroyed Challenger too.
A supersonic slipstream exerts *very* large forces.  In general, a
launcher (or a high-speed aircraft) is strong enough to stand those
forces only when they come more-or-less in the intended direction.
Flying forward is okay; flying sideways is not.  When Challenger's
external tank disintegrated and threw the orbiter violently out of
control, Challenger broke up.  Although the original report wasn't
quite detailed enough to be sure, it sounds to me like that's what
happened to Ariane V36:  the intact engines hit their gimbal limits
try to compensate for the misbehaving one, the still-unbalanced thrust
started to rotate the Ariane end over end, it exceeded its angle-
of-attack limit, and the aerodynamic forces tore it apart.  It does
not take a large angle to do this; at maximum speed (well, at maximum
dynamic pressure, the combination of speed and altitude that maximizes
aerodynamic forces), a *really tough* jet fighter might be rated for
a maximum angle of attack of ten degrees.  (Alas, I don't have numbers
for launchers -- anybody know?)
-- 
MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
an Operating System.          | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

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End of SPACE Digest V11 #107
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