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From: skip@ubvax.UUCP (Skip Addison Jr)
Newsgroups: net.space,net.columbia,net.aviation
Subject: Re: Shuttle sonic booms
Message-ID: <386@ubvax.UUCP>
Date: Thu, 12-Dec-85 11:30:04 EST
Article-I.D.: ubvax.386
Posted: Thu Dec 12 11:30:04 1985
Date-Received: Thu, 19-Dec-85 04:02:49 EST
References: <8512040306.AA22588@s1-b.arpa> <600@riccb.UUCP>
Reply-To: skip@ubvax.UUCP (Skip Addison)
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In article <600@riccb.UUCP> rjnoe@riccb.UUCP (Roger J. Noe) writes:
>> Why are there two sonic booms from the shuttle?
>
>It's because there are two "sonic cones" formed by the shuttle.  (There is
>very likely a more scientific term for this, but I don't know what it is.)
>With most supersonic aircraft, a cone-shaped shock wave expands from the
>nose of the craft outward.  Where and when this cone intersects the surface
>of the Earth determines who hears the sonic boom.  This cone usually expands
>at a wide enough angle to engulf the rest of the aircraft.  But the shuttle
>has a pretty unusual shape.  I think the vertical stabilizer (tail) rises
>above the cone-shaped shock wave formed by the nose.  This causes the tail
>to slam into the surrounding air the same way the nose does, and a second
>shock wave, also shaped like a cone, forms at the edge of the tail.  This
>is the explanation I have heard, anyway.  I don't think the two sonic booms
> ...
>--
>	Roger Noe			ihnp4!riccb!rjnoe

Sonic booms are created by major displacements of air or air rushing in to
fill a void.  A sonic boom is generated by the tail of the shuttle as a 
result of the drastic change in the shuttle cross-section there.  As the
shuttle moves it leaves behind a void which the surrounding air fills.
In fact, every exterior part of a super-sonic aircraft creates its own little
"boom" (shock-wave), but the only noticeable ones are usually generated by
the sudden intrusion of the nose and sudden abscense of the tail.  A more
streamlined aircraft has less of a boom.

Notice the two wakes left by some boats at high speeds.  Same principles.

-- Skip Addison
   {amdcad, amd, cae780}!ubvax!skip