From: eder@hsvaic.boeing.com (Dani Eder)
Newsgroups: sci.space
Subject: Re: What about Saturn?/Future not Past
Date: 18 Aug 92 14:39:03 GMT
Distribution: na
Organization: Boeing AI Center, Huntsville, AL

wingo%cspara.decnet@Fedex.Msfc.Nasa.Gov writes:

[about the revival of the Saturn launch vehicle]

How about looking to the future instead of the past?

Dr. Robert Bussard is working under contract to DARPA to develop an
'electric fusion' machine.  The way it would work is to set up
a chamber bounded by current-carrying wires, such that a magnetic
field is set up that gets weaker towards the center, and strong
towards the periphery.  Into this chamber you inject electrons,
which are reflected by the magnetic fields at the edges, and thus
bounce radially from side to side.  The electrons are denser towards
the center of the chamber if they are all bouncing radially.

This setup creates a strong negative potential well in the middle,
caused by all the electrons in the central region.  Now the fun
part: drop deuterium & tritium ions into this chamber.  They are
attracted by the electron cloud, and accelerate towards the
center.  If the potential well is deep enough (tens of kilovolts),
the ions will be going fast enough at the center to fuse when they
run into each other.  The ones that miss or scatter will continue
to bounce around until they hit something.

The ones that fuse create particles with high energy - millions of
volts, which is enough to kick them entirely out of the central
region - to generating equipment outside of the chamber.  The trick
is that you use the electrons and geometry to create a trap for the
ions you want to fuse.  Electrons are much lighter than ions, and
thus are easier to control with magnetic fields - rather than
trying to contain a plasma directly with magnetic fields as the
Tokamak tries to do.

Bussard's calculations show it is possible to produce 2000 MW of
power in a 2 meter chamber.  The system weight would be on the
order of 3-4 tons.

Electric power generation is by direct climb of the charged particles
against a megavolt field set up by wires surrounding the chamber.
This produces megavolt output at some amperage with high
conversion efficiency.  The high voltage is then used to generate
thrust in this way:

You dump megavolt electron beams into a chamber (this is a souped
up TV tube, which uses 20 kilovolt electron beam to illuminate the
phosphors).  The beam energy is absorbed in a few tens of cm by
your propellant, getting it very hot, then it goes out a nozzle.

Specific implulse in the range of 2000 seconds is possible, before
the heat of the exhaust gas sets a limit.  This is somewhat better
than the NASP average specific impulse, and you don't have to
spend lots of time in the atmosphere, as NASP does, getting hot
and fighting drag.

This would make a dandy spaceplane engine.  Once in orbit, where
you have room to build a bigger magnetic nozzle (in the atmosphere
you have to stay within the aerodynamic lines for it to fly)
The specific impulse can be increased to 3000-5000 seconds.  This
is because the power can be spread over a larger area, and waste
heat melting your nozzle is the limiting factor.

This system is close to the 'Mr Fusion' we saw in 'Back to the
Future', and allows building real spacecraft, ones that don't
fall apart (stage) in flight.

Where they are is building a scaled prototype for DARPA, to
verify the calculations in the same way a wind tunnel model
is used in airplane design.  That completed, there should be
no stopping the full size machine from working.

This may seem futuristic to some, but no more so than cryogenic
rocket engines would have seemed in the 40's, and they were
actually built for the first time in the 50's.

Dani Eder


-- 
Dani Eder/Boeing/Advanced Civil Space/(205)464-2697(w)/232-7467(h)/
Rt.1, Box 188-2, Athens AL 35611/Member: Space Studies Institute
Physical Location: 34deg 37' N 86deg 43' W +100m alt.
***THE ABOVE IS NOT THE OPINION OF THE BOEING COMPANY OR ITS MANAGEMENT.***