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From: lcc.todd@LOCUS.UCLA.EDU (Todd Johnson)
Newsgroups: net.space
Subject: Specific Impulse (Metric)
Message-ID: <8603091946.AA24998@s1-b.arpa>
Date: Sun, 9-Mar-86 14:40:18 EST
Article-I.D.: s1-b.8603091946.AA24998
Posted: Sun Mar  9 14:40:18 1986
Date-Received: Wed, 12-Mar-86 06:16:03 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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The metric unit for specific impulse is SECONDS! I know, not only did I 
do all of my engineering degree in a country which has gone metric but I
am currently plowing through: Rocket Propulsion & Spaceflights Dynamics
by Cornelisse et al. Cornelisse is University of Delft, Holland. In any
system specific impulse is defined as:
	
	Isp = F dt / m go

Sorry about the subscripts. The "go" should be the standard acceleration
due to gravity at the equator which is near enought to 9.81 metres per
squared second to make no never mind. F is force in newtons, dt is time
in seconds, m is mass in kilograms. And the whole mess cancels out to 
seconds. 
	Specific impulse is a very useful RELATIVE measure of propellants.
The true use of specific impulse is for Earth oriented activities - e.g.:
getting to Earth orbit or dropping a ballistic missile on your nearest
enemy. It relates the expense of lifting the propellant to the capability
of the propellant to produce lift. 
	Now that we've got that straightened out, why doesn't someone tell
me how the NASA simulations of hypersonic flow through a De Laval nozzle
is progressing. I was given to believe that this fundamental work will
be applied towards figuring out how to sustain a flame at hypersonic 
speeds so that we may have scramjets. It is quite likely, however, that the
best of this information is classified. If it isn't, how about letting us
know?