Date: 20 Sep 87 05:29:51 GMT
From: ssc-vax!eder@beaver.cs.washington.edu  (Dani Eder)
Subject: Re: Ion engines

In article <480@esunix.UUCP>, bpendlet@esunix.UUCP (Bob Pendleton) writes:
> There are many missions that require something like ion propulsion.
> Unfortunatley, ion propulsion seems to be what is known as a HARD
> problem.  Give it time and don't give up.
> 
> Bob Pendleton @ Evans & Sutherland

Ion engines don't have to be hard to make.  Here at Boeing there is a
project to test a simple ion engine.  It consists of a welded case, a
perforated screen, about two dozen permanent magnets, a fuel feed line,
and a power supply with 26 components.  And that's it.  Part of the
difficulty in prior ion engine designs supported by NASA were (a) they
tried to squeeze the maximum performance out of them, and (b) they took
a lab power supply setup and tried to translate that to space use,
without first simplifying the circuit.  Thus you end up with an ion
engine with a 2000 component power supply. Dumb.

The real challenge for an ion engine is finding enough power to run
them.  You need a big photovoltaic array or a nuclear generator to feed
them.

For more information, contact Don Grim.  He's in charge of the
project.  He can be reached at (206)773-2569, or at:

Mail Stop 8E-22
Propulsion Systems
Engineering Technology Organization
Research and Engineering Division
Boeing Aerospace Company
POB 3999, Seattle,WA 98124

Dani Eder/Boeing/Advanced Space Transportation

Date: 26 Apr 91 12:51:59 GMT
From: agate!bionet!uwm.edu!zaphod.mps.ohio-state.edu!van-bc!rsoft!mindlink!a752@ucbvax.Berkeley.EDU  (Bruce Dunn)
Subject: Re: Buckyballs and ion engines

> dietz@cs.rochester.edu writes:
> I read with interest that some researchers are investigating
> "buckyballs" (buckminsterfullerenes, soccer-ball shaped molecules
> consisting of 60 carbon atoms) for use as reaction mass in ion
> engines.  Recently, a simple and potentially low cost means of making
> buckyballs was discovered; Smalley is projecting the cost should drop
> to a few dollars per pound.
> 
> 
> C60 has a mass of 720 AMU, vs. ~130 for cesium or xenon.  The
> advantage of C60 over other molecules would be that C60 appears to be
> very rugged, yet easily ionized, so it should be possible to ionize it
> without generating large numbers of low mass fragments, which would
> degrade engine efficiency (ion engines are most efficient when all the
> ions have about the same mass/charge ratio).  I read that buckyball
> ions accelerated to 15,000 mph have been observed to survive impact
> with metal surfaces, which illustrates how resilient they are.
> 
> 
>         Paul F. Dietz
>         dietz@cs.rochester.edu


     Sounds interesting!  Existing ion engine propellants all have their own
problems.  Mercury and cesium work well, but present spacecraft contamination
problems - some material emitted by ion engines doesn't get ionized, and the
metal vapor tends to come back and cause space craft problems (so I'm told).
Xenon works very well, giving efficiencies similar to that of mercury (thrust
system efficiency of about 0.7 at a specific impulse of 3000).  Xenon however
is a rare and expensive gas and even a modest program of ion engined craft
using it may well use more xenon than can be isolated each year.  Argon can be
used as a substitute for xenon, but the argon ions take more energy to create
than xenon ions and have a lower mass.  Thrust system efficiences with argon
are about 0.4 at a specific impulse of 3000.  Lower thrust system efficiency
does not mean lower specific impulse, but does mean that for a given thrust
level an argon ion engine requires about 60% more power than a xenon or mercury
engine.  This translates either into a bigger solar array or into a bigger
reactor and radiator system, depending on the source of thruster power.

Propellant     Mass     First Ionization Potential

Hg             200.6    10.43 volts
Cs             132.9     3.89 volts
Xe             131.3    12.13 volts
Ar              39.9    15.75 volts
Buckyballs     720      ????? volts
--
Bruce Dunn   Vancouver, Canada    a752@mindlink.UUCP