Posted to sci.astro:

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From: rgregoryclark@yahoo.com (Robert Clark)
Newsgroups: sci.astro,sci.physics,sci.space.policy,rec.arts.sf.science
Subject: Plasma propulsion for access to space?
NNTP-Posting-Host: 68.81.141.219

Copied below are some posts to sci.astro discussing a proposal for a
microwave powered space drive, either for access to LEO or as a
propulsion system for interplanetary travel.
The suggested proposal was to use microwave generated plasma as a
propellant. This would be analogous to what Leik Myrabo is doing with
lasers with his 'lightcraft'. Then to get the largest amount of
propulsive force you want a large generation of microwaves.
Some recent reports suggests ways of generating huge amounts of
microwaves:

E-BOMB
http://popularmechanics.com/science/military/2001/9/e-bomb/print.phtml

High-Power Microwaves
"The general public is familiar with the technology as it applies to
household microwave ovens that use this form of energy to penetrate
and cook food. Whereas a typical microwave oven generates less than
1,500 watts of power, the Division is working with equipment that can
generate millions of watts of power."
http://www.de.afrl.af.mil/Factsheets/HPM.html

The reports discusses high tech methods of generating the microwaves
as well as the low tech method of using high explosives.
Question: would you be better off just using the propulsive force
generated by the explosives rather than converting this energy into
microwaves?
There would be loss of efficiency in the conversion to microwaves but
chemical propulsion methods have an inherent inefficiency in that the
momenta of the expanding gasses move in all directions and only a
portion of this energy is directed out through the rocket nozzle. On
the other hand you can use all of the explosive force produced in all
directions in creation of the microwaves.
To evaluate this question you would also have to take into
consideration the efficiency of the fuel pellet used to generate the
plasma from the microwaves. In my proposal I discussed using grapes
only because that was used in the examples of plasma generation on the
web sites. I imagine there would be much more efficient materials to
use as a fuel pellet.

A separate possibility for a plasma drive for space access would be
to use Robert Winglee's idea of plasma propulsion:

Mini-Magnetospheric Plasma Propulsion (M2P2)
http://www.ess.washington.edu/Space/SpaceModel/M2P2/welcome.html

Winglee's proposed method is for an interplanetary drive that uses
the solar wind out in free space to provide a propulsive force against
the generated plasma.
Question: would it also work to use the Earth's magnetic field
against which the magnetic field generated by the ionized plasma would
be directed? You would also be using the force of the Earth's magnetic
field on the charged particles of the plasma.
Winglee discusses the fact that the force generated by the solar wind
is weak. You compensate for this by using a large scale plasma, on the
scale of kilometers.
The problem with using this drive as a launch system from Earth is
that you also have to operate against the force of gravity.
The Earth's magnetic field is rather weak, on the order of .5 gauss,
about one hundredth the strength of a common refrigerator magnet. In
order to overcome the force of gravity I imagine you would also need
kilometer scale plasma. The methods of generating large amounts of
microwaves could also be used in this case for generating the plasma.
An idea of the relative degree of force you could generate from the
Earth's magnetic field compared to the solar wind might be provided by
the fact that the Earth's field can move a compass needle but I don't
believe the solar wind would be able to visibly move a needle this
size. But then again you need much higher force generated to overcome
gravity. You might also be able to use a high density plasma to
generate sufficient force.

Bob Clark

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From: Robert Clark (rgclark@****.***)
Subject: Microwave powered ion drive.
Newsgroups: sci.astro, sci.physics, sci.space.policy
Date: 2000/07/30

Found this site while looking up info on microwaves:

Physics inside a Microwave Oven
http://home.earthlink.net/~marutgers/fun/microwave/microwave.html

One of the demonstrations on this page appears to show plasmas being
generated by heating grapes with a microwave oven. Nice Quicktime
movies here. It's also described on the page:

HOW THINGS WORK: Microwave Ovens
http://rabi.phys.virginia.edu/HTW//microwave_ovens.html

Would this provide a low energy means of creating the plasma required
for ion engines? One means of creating the required plasma is by
irradiating the propellent gas with intense laser or x-ray beams to
strip off the electrons of the atoms of the gas, producing an ionized
plasma. However, these are both high-frequency forms of EM radiation
and therefore require high energy to produce. Microwaves being longer
wavelengths require less energy to produce.
Another means that is actually used for the Deep Space 1 probe is to
use electrons emitted by a cathode to irradiate the gas, ionizing it.
How does the energy requirement for the heating element of a cathode
compare to the energy requirement for producing the microwaves?

If this can be exploited as a low energy means of producing plasmas
then this might be used not only for low thrust engines as on DS 1 but
also for lauching ships into space by beaming the microwaves into a
reaction chamber of a rocket lined with, er, grapes.

--
________________________________________________

"In order for a scientific revolution to occur,
most scientists have to be wrong"
-- Bob Clark
________________________________________________

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From: Robert Clark (rgclark@****.***)
Subject: Re: Microwave powered ion drive.
Newsgroups: sci.astro, sci.physics, sci.space.policy,
rec.arts.sf.science
Date: 2000/07/30

The Deep Space 1 ion engine is described at:

Innovative Engines
Glenn Ion Propulsion Research Tames the Challenges of 21st Century
Space Travel,
http://www.lerc.nasa.gov/WWW/PAO/PAIS/fs08grc.htm

The idea of the ground launched system is a little different from an
ion engine. Here the propulsion is provided by the rapidly expanding
plasma itself. Leik Myrabo of Rensselaer Polytechnic Institute is
researching such propulsion systems using high-energy lasers to create
the plasma:

Riding Laser Beams to Space,
http://www.space.com/businesstechnology/technology/laser_propulsion_000705.html

Highways of Light,
Scientific American, February 1999,
http://www.sciam.com/article.cfm?colID=1&articleID=00058731-ED4B-1CB8-B4A8809EC588EEDF

The Myrabo laser system uses a 10 kilowatt laser to lift a 2 oz.
Lightcraft about 100 ft. in the air. In the web page on the microwave
demonstrations, they use a standard 500 watt oven and the movies on
the
page show several plasma pulses being generated from one fuel cell
(the
grape). Would these pulses be able to lift a 2 oz weight?

Another recent story discusses the applications of using cold
plasmas:

Force Fields and 'Plasma' Shields Get Closer to Reality,
http://www.space.com/businesstechnology/technology/cold_plasma_000724.html

An advantage of the cold plasmas is the low power required to
generate
them. However the article mentions that hot plasmas can be generated
with higher densities. Perhaps the microwave plasma generation method
can match the efficiency of the cold generation system while allowing
the high densities of the hot plasmas.

--
________________________________________________

"In order for a scientific revolution to occur,
most scientists have to be wrong"
-- Bob Clark
________________________________________________

*********************************************************************

From: Robert Clark (rgclark@****.***)
Subject: Re: Microwave powered ion drive.
Newsgroups: sci.astro, sci.physics, sci.space.policy
Date: 2000-08-15 19:40:35 PST

In article <slrn8oe23i.m1d.ijk@force.stwing.upenn.edu>,
ijk@force.stwing.upenn.edu (Ian Kaplan) wrote:
> On Sun, 30 Jul 2000 08:34:04 GMT, Robert Clark <rgclark@my-deja.com> wrote:
> >
> > Would this provide a low energy means of creating the plasma required
> >for ion engines? One means of creating the required plasma is by
>
> This is essentially how the VASIMR drive being worked on at JSC's advanced
> space propulsion lab works. From the website, at
> http://spacsun.rice.edu/aspl/vasimr.htm:
>
> To operate the VASIMR, neutral gas (typically hydrogen) is injected at the
> forward end-cell and ionized. Then it is heated to the desired temperature and
> density in the central-cell, by the action of electromagnetic waves,
> similar to what happens in microwave ovens. After heating, the plasma
> enters a two-stage hybrid nozzle at the aft end-cell where it is exhausted
> to provide modulated thrust.
>
> I saw Franklin Chang-Diaz do a talk on it; he certainly appears (caveat: I
> know virtually no plasma physics just yet!) to know what he's about. I
> gather he has all the hard stuff working at this point, and is worrying
> now only about robustness and optimizing the nozzle and such. It certainly
> seems quite promising. Unfortunately, what with so few robotic missions
> coming up going any further away than Mars, there's no really strong
> demand for this sort of efficient propulsion, or even for DS1's ion
> drive! It could be a huge addition to a Galileo or Cassini-style probe, en
> route to becoming a routine element of long-distance human spaceflight. Ah
> well.
>
> --
> "Your pants are weak, old man." --Vader
>

I read of a plasma engine that Franklin-Diaz was working on for which
the power generation requirements were so large it was suggested that
nuclear powered engines might be required, especially for missions to
the outer solar system. I don't know if that is the same one as the
VASIMR drive.

Found another reference for a low power plasma drive:

Mini Microwave Thruster Has The Power
http://www.spacedaily.com/news/thruster-99b.html

This is a small thruster intended for satellite operations that only
uses 80 watts of power. Instead of the plasma itself providing the
propulsion, it is used to heat a propellant gas to high temperature.
It
would seem that using the plasma itself would provide a higher thrust.
Perhaps using another propellant preserves the plasma gas for a longer
time.

Dr. Michael Micci who is working on this drive pointed me to another
low power drive undergoing development announced at last months AIAA
Joint Propulsion Coference:

36th AIAA/ASME/SAE/ASEE Joint Propulsion
Conference and Exhibit
Technical Program as of 12 July 2000
Monday 17 July Conference Program
4:00 PM
AIAA-2000-3275
New Electrostatic Thruster for Small Satellite Application
S. Satori, Hokkaido Inst. of Technology, Sapporo Hokkaido, Hokkaido,
Japan; H. Okamoto, Astro Research Company, Fujsawa, Kanagawa, Japan;
M. Sugiki, Astro Research Company, Fujisawa, Kanagawa, Japan
http://pdf.aiaa.org/preview/2000/PV2000_3275.pdf
[abstract]

and

Successful Flight Demonstration of Plasma Thruster Under Microgravity
Tokyo - Feb. 27, 2001
http://www.spacedaily.com/news/japan-tech-01a.html

This thruster only uses 5 watts of power. This report can be ordered
from the AIAA. From the name this would appear to be an ion drive
(thrust provided by electromagnetically accelerating the ions) as
oppposed to a plasma drive, which would provide a higher thrust.

I still would like to find what be power vs. thrust efficiency of
my "grape" drive.

--
_______________________________________________

"In order for a scientific revolution to occur,
most scientists have to be wrong"
-- Bob Clark
_______________________________________________

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