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From: dsmith@HPLABSC (David Smith)
Newsgroups: net.space
Subject: Re:  Shuttle sonic booms
Message-ID: <8512041657.AA03985@hplabsc>
Date: Wed, 4-Dec-85 11:57:21 EST
Article-I.D.: hplabsc.8512041657.AA03985
Posted: Wed Dec  4 11:57:21 1985
Date-Received: Thu, 5-Dec-85 08:50:41 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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> Why are there two sonic booms from the shuttle?  (I'm told it goes "boom-boom"
> when it flies over before landing)

The shock waves from various protuberances coalesce (for reasons unknown
to me) around the bow and tail shocks.  As the bow shock passes the
observer, air pressure rises sharply.  Between bow and tail shocks, pressure
falls to below ambient.  The tail shock raises pressure sharply back to
ambient.  The two sharp pressure rises are heard as the two booms.  All
supersonic craft drag along an N-shaped wave heard as two booms.  How
well your ears can resolve them depends on the length and speed of the craft.
The shuttle is long, and as it approaches Edwards, it is slowing through Mach 1.

I have heard the shuttle's twin booms on the TV;  I have also heard twin
booms from aircraft I couldn't see in the vicinity of Beale AFB (home of
the SR-71).  The latter produced much more closely spaced booms.

			David Smith
			ucbvax!hplabs!dsmith