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From: jtk@mordor.ARPA (Jordan Kare)
Newsgroups: sci.space
Subject: Re: Electromagnetic launchers
Message-ID: <16973@mordor.ARPA>
Date: Tue, 18-Nov-86 21:01:12 EST
Article-I.D.: mordor.16973
Posted: Tue Nov 18 21:01:12 1986
Date-Received: Tue, 18-Nov-86 23:40:49 EST
References: <8611132205.AA00902@s1-b.arpa> <869@hplabsc.UUCP>
Reply-To: jtk@mordor.UUCP (Jordan Kare)
Organization: S-1 Project, LLNL
Lines: 43

In article <869@hplabsc.UUCP> kempf@hplabsc.UUCP (Jim Kempf) writes:
>
>Re: offbeat launching schemes, sometime back I saw an article in
>a technical rocketry journal about using a space based laser to
>lift a vehicle using an electromagnetic field and MHD forces.
>Does anyone know what happened to this idea? 
>	Jim Kempf	hplabs!kempf

This may refer to Dr. Leik Myrabo's Apollo Lightcraft project.
Myrabo has designed (under contract to the Air Force) a series
of laser-propelled vehicles that use several different modes
of thrust generation, all powered by a laser beam incident from 
above.  One mode is an "MHD Fanjet", where the laser drives
a hydrogen-fuelled "rocket" (laser light passes thru a window and
is absorbed in hydrogen gas, which exits thru a nozzle), but the
rocket exhaust is used to generate electricity via an MHD system
(rather than providing direct thrust).  The electricity drives
an "electric fan" around the rim of the vehicle: arcs are established
between the vehicle rim and an outer shroud ring; blades between rim 
and shroud contain coils to generate a magnetic field; j x B forces
push the arc (and associated air) down and the vehicle up.  The advantage
is that one gets more thrust than a pure laser rocket per unit 
laser energy and per unit fuel mass, but can run at higher velocities
than any chemical-fuelled jet.

	Myrabo's systems are ingenious, but complex and untested, with
stiff requirements for the driving laser's properties.  I recommend
his book, "The Future of Flight" (with Dean Ing, Baen Books) for a
good collection of exotic propulsion techniques.  There are some even
more extreme suggestions around (e.g. using the photon pressure
of a laser beam in a resonant cavity formed between a vehicle and
the ground), but there are also some very simple (though not 
necessarily straightforward) versions of laser propulsion which
may be available quite soon.  For instance, a ground-based 
laser system capable of
launching a one ton payload into low earth orbit, at a maximum 
acceleration of six gees, EVERY 15 MINUTES (uh, lessee, four tons an 
hour, 96 tons a day, do maintenance on weekends, call it 30,000 tons
a year)... System cost less than the Space Transportation System ...
unit cost under $50/lb in orbit... When?  Maybe before the end of
the century.  Stay tuned...

		Jordin Kare	jtk@mordor.uucp  	jtk@s1-c.arpa