Asri-unix.1335
net.space
utzoo!decvax!cca!OAF@MIT-MC@sri-unix
Mon Apr 26 11:09:21 1982
Another Saturn V query - why the plume is up so high
From: Oded Anoaf Feingold <OAF MIT-MC AT>
The plume blossoms that high up because the fluid (exhaust gas)
comes out at much higher pressure than the surrounding atmosphere,
and expands outward.  The effect is of having a spherically
expanding shell of gas appearing behind the rocket.  The particular
angle through which the gas turns on expansion is in 3/4 powers of
tangents, called the NU function, and is tabulated for various Mach
numbers.

Effects of the plume going that high up (sometimes past the leading
edge of the rocket) are twofold (at least);
       1)      It changes the visual and radar signatures.  Important
       for you IFF and missile defense people.
       2)      It can deposit exhaust gases (or residues) on equipment
       in the vehicle's nose.  So you have to take account of that
       when designing your payload/instrumentation/whatever.

Sorry for the long answer to the short question.

Oded


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