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From: eder@ssc-vax.UUCP (Dani Eder)
Newsgroups: net.space
Subject: Re: Electromagnetic Launch
Message-ID: <540@ssc-vax.UUCP>
Date: Tue, 4-Feb-86 20:41:57 EST
Article-I.D.: ssc-vax.540
Posted: Tue Feb  4 20:41:57 1986
Date-Received: Fri, 7-Feb-86 20:41:25 EST
References: <8602010854.AA02457@s1-b.arpa>
Organization: Boeing Aerospace Co., Seattle, WA
Lines: 43

>      There have recently been several postings relating to
> electromagnetic launch from the Earth's surface.
> Why not use an accelerator boost for a next-generation shuttle?
> For an example, let's suppose this is Mount Kenya, a 5 Km
> tall mountain on the equator (the most efficient place to launch
> from, at least if you want equatorial orbits.)
> 
>                                     --Geoffrey A. Landis
>                                       Brown U.
[extensive calculations deleted from above article]

     The basic idea of electromagnetic accelerators to launch things off
the Earth is quite sound.  I have a few comments to make on your idea.  In
general, your launch facility will be expensive and you would want to
minimize it's cost and maximize the number of payloads you pump through
it so as to spread the cost around.

     This tends to drive you to as small a launcher as possible and as
small a payload size as possible, with a high launch rate.  At least for
the first launcher you build.  If your electrical efficiency is high, you
will want to do as much of the acceleration as possible electrically, and
minimize the chemical rocket part.  A limiting factor is atmospheric heating
as you leave the gun at high Mach numbers.  A last point I would like to 
make is you do not have to limit yourself to mountains.  With modern
structural materials one can build towers that literally extend out of
the atmosphere.  As an example, T300/934 Graphite/Epoxy composite, which
is used in airplanes, has a density of 0.057lb/in^3 and a compressive
strength of 215800 lb/in^2.  If we divide strength by density we get the
height of a column of graphite/epoxy that just barely can support it's
own weight.  It is 3.786 million inches or 59.7 miles.  If we taper the
tower, we can make it taller.  You also want to work at less than theoretical
strength, but the order of magnitude is correct.

     The cost driver on electromagnetic launchers seems to be the power
supplies.  You need a Gigawatt pulse on the order of seconds long.  Fortunately
the magnetic fusion folks are already developing such power suppllies for
their own experiments.  Thus, at present all the key technologies are in
hand or under intensive development.  It remains for some far sighted
individuals to do a convincing demonstration for the world.  It would give
people the idea that rockets are not the only way to get into space.

Reaching for the stars!/Dani Eder/Boeing/Advanced Space Transportation
ssc-vax!eder