Prelude to the "grape drive"? [was: NASA Successfully Tests Ion Engine.]

================================================== ==========
From: Robert Clark )
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...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
________________________________________________

================================================== ==========


Another recent story discusses the applications of using cold plasmas:

Force Fields and 'Plasma' Shields Get Closer to Reality,
http://www.space.com/businesstechnol...ma_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.


From: Robert Clark )
Subject: Plasma propulsion for access to space?
Newsgroups: sci.astro, sci.physics, sci.space.policy, rec.arts.sf.science
Date: 2002-11-05 21:21:09 PST
http://groups.google.com/groups?th=87680963df54e46c


Bob Clark

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(Ron Baalke) wrote in message ...
Dwayne Brown
Headquarters, Washington November 20, 2003
(Phone: 202/358-1726)

Lori J. Rachul
Glenn Research Center, Cleveland
(Phone: 216/433-8806)

RELEASE: 03-377

NASA SUCCESSFULLY TESTS ION ENGINE

NASA's Project Prometheus recently reached an important
milestone with the first successful test of an engine that
could lead to revolutionary propulsion capabilities for space
exploration missions throughout the solar system and beyond.

The test involved a High Power Electric Propulsion (HiPEP)
ion engine. The event marked the first in a series of
performance tests to demonstrate new high-velocity and high-
power thrust needed for use in nuclear electric propulsion
(NEP) applications.

"The initial test went extremely well," said Dr. John Foster,
the primary investigator of the HiPEP ion engine at NASA's
Glenn Research Center (GRC), Cleveland. "The test involved
the largest microwave ion thruster ever built. The use of
microwaves for ionization would enable very long-life
thrusters for probing the universe," he said.

The test was conducted in a vacuum chamber at GRC. The HiPEP
ion engine was operated at power levels up to 12 kilowatts
and over an equivalent range of exhaust velocities from
60,000 to 80,000 meters per second. The thruster is being
designed to provide seven-to-ten-year lifetimes at high fuel
efficiencies of more than 6,000-seconds specific impulse; a
measure of how much thrust is generated per pound of fuel.
This is a contrast to Space Shuttle main engines, which have
a specific impulse of 460 seconds.

The HiPEP thruster operates by ionizing xenon gas with
microwaves. At the rear of the engine is a pair of
rectangular metal grids that are charged with 6,000 volts of
electric potential. The force of this electric field exerts a
strong electrostatic pull on the xenon ions, accelerating
them and producing the thrust that propels the spacecraft.
The rectangular shape, a departure from the cylindrical ion
thrusters used before, was designed to allow for an increase
in engine power and performance by means of stretching the
engine. The use of microwaves should provide much longer life
and ion-production capability compared to current state-of-
the-art technologies.

This new class of NEP thrusters will offer substantial
performance advantages over the ion engine flown on Deep
Space 1 in 1999. Overall improvements include up to a factor
of 10 or more in power; a factor of two to three in fuel
efficiency; a factor of four to five in grid voltage; a
factor of five to eight in thruster lifetime; and a 30
percent improvement in overall thruster efficiency. GRC
engineers will continue testing and development of this
particular thruster model, culminating in performance tests
at full power levels of 25 kilowatts.

"This test represents a huge leap in demonstrating the
potential for advanced ion technologies, which could propel
flagship space exploration missions throughout the solar
system and beyond," said Alan Newhouse, Director, Project
Prometheus. "We commend the work of Glenn and the other NASA
Centers supporting this ambitious program."

HiPEP is one of several candidate propulsion technologies
under study by Project Prometheus for possible use on the
first proposed flight mission, the Jupiter Icy Moons Orbiter
(JIMO). Powered by a small nuclear reactor, electric
thrusters would propel the JIMO spacecraft as it conducts
close-range observations of Jupiter's three icy moons,
Ganymede, Callisto and Europa. The three moons could contain
water, and where there is water, there is the possibility of
life.

Development of the HiPEP ion engine is being carried out by a
team of engineers from GRC; Aerojet, Redmond, Wash.; Boeing
Electron Dynamic Devices, Torrance, Calif.; Ohio Aerospace
Institute, Cleveland; University of Michigan, Ann Arbor,
Mich.; Colorado State University, Fort Collins, Colo.; and
the University of Wisconsin, Madison, Wis.

For information about NASA on the Internet, visit:

http://www.nasa.gov

For more information about NASA's Glenn Research Center,
visit:

www.grc.nasa.gov

For more information about Project Prometheus on the
Internet, visit:

http://spacescience.nasa.gov/missions/prometheus.htm

Information about JIMO is available on the Internet at:

http://spacescience.nasa.gov/missions/JIMO.pdf


-end-

Robert Clark wrote:

================================================== ==========
From: Robert Clark )
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...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?
[snip]

No.

--
Uncle Al
http://www.mazepath.com/uncleal/qz.pdf
http://www.mazepath.com/uncleal/eotvos.htm
(Do something naughty to physics)

In article ,
Robert Clark 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
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.

There are already ion thrusters that use microwaves for ionization, and
also some that use lower-frequency radio waves. No actual thruster that
I'm aware of uses lasers or X-rays.

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?

Both are relatively efficient processes, in themselves. Unfortunately,
that doesn't imply that you get efficient ionization as a result. In
either case, much of the energy gets used unproductively.

To date, nobody has an *efficient* method of ionizing the plasma in an ion
thruster. The result is that ion thrusters have unimpressive efficiency
numbers, unless you run the exhaust velocity up to the point where the
efficient acceleration process dominates the inefficient ionization... but
most real-world applications optimize at quite low exhaust velocities, to
minimize the mass of the power source (higher exhaust velocities need lots
more power).

(Published numbers on efficiency need to be scrutinized very carefully,
because there is a lot of specsmanship -- often what is quoted is *not*
overall, end-to-end, low-voltage-DC-to-jet-power efficiency, but the
efficiency of some better-looking subset of the process.)

One reason for interest in Hall-effect thrusters and other plasma
thrusters, as alternatives to ion thrusters, is that they don't need high
ionization percentages and hence can avoid most of the efficiency penalty.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Robert Clark 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 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.

Microwaves being longer wavelengths have less energy *per* *photon*.
The energy it takes to ionize a gas is the same regardless of how you
do it. If you use microwaves, you nead more photons, but the same
number of watts.
--
Keith F. Lynch - - http://keithlynch.net/
I always welcome replies to my e-mail, postings, and web pages, but
unsolicited bulk e-mail (spam) is not acceptable. Please do not send me
HTML, "rich text," or attachments, as all such email is discarded unread.

(Henry Spencer) wrote in message ...
To date, nobody has an *efficient* method of ionizing the plasma in an ion
thruster. The result is that ion thrusters have unimpressive efficiency
numbers, unless you run the exhaust velocity up to the point where the
efficient acceleration process dominates the inefficient ionization... but
most real-world applications optimize at quite low exhaust velocities, to
minimize the mass of the power source (higher exhaust velocities need lots
more power).

Or more massive ions. Less massive ions increase the charge
density per thrust, increase the amount of overhead in
ionization per thrust, which leads to lower efficiency. We're
probably at the limit there atom-wise since Xenon is pretty
massive and pretty easy to handle (the only other good options
would be Radon, which is even rarer than Xenon, and Uuo, which
is even rarer than monkeys flying out of my ... well, anyway).
More massive molecules or "mesoscopic" particles (i.e. dust)
would lead to yet higher efficiencies but they're a lot more
difficult to use in an electric rocket without it getting all
gummed up in about two seconds. There's some research on
using C60, for example, in ion engines but it's still a
loooong way from workable. But if they ever get it to work
then it should lead to much higher efficiencies (since C60
is about 5.5x as heavy as Xe).


(Published numbers on efficiency need to be scrutinized very carefully,
because there is a lot of specsmanship -- often what is quoted is *not*
overall, end-to-end, low-voltage-DC-to-jet-power efficiency, but the
efficiency of some better-looking subset of the process.)

One reason for interest in Hall-effect thrusters and other plasma
thrusters, as alternatives to ion thrusters, is that they don't need high
ionization percentages and hence can avoid most of the efficiency penalty.

And run in a more useful range of power/thrust levels, at
present.

Dear Christopher M. Jones:

"Christopher M. Jones" wrote in message
...
....
Or more massive ions. Less massive ions increase the charge
density per thrust, increase the amount of overhead in
ionization per thrust, which leads to lower efficiency. We're
probably at the limit there atom-wise since Xenon is pretty
massive and pretty easy to handle (the only other good options
would be Radon, which is even rarer than Xenon, and Uuo, which
is even rarer than monkeys flying out of my ... well, anyway).
More massive molecules or "mesoscopic" particles (i.e. dust)
would lead to yet higher efficiencies but they're a lot more
difficult to use in an electric rocket without it getting all
gummed up in about two seconds. There's some research on
using C60, for example, in ion engines but it's still a
loooong way from workable. But if they ever get it to work
then it should lead to much higher efficiencies (since C60
is about 5.5x as heavy as Xe).

I'd worry about "selectively ionizing" a molecule for propulsion. Since
the number of electrons stripped off provides the handles for accelerating
the mass, the more electrons removed means the faster you can accelerate
the molecule. But the more electrons you remove the weaker (or smaller)
the molecule fractions become. So your C60 becomes just 60C, and you are
back to accelerating a bunch of light nucleii.

David A. Smith

On Fri, 28 Nov 2003 20:33:25 GMT, (Henry Spencer)
wrote:

In article ,
Robert Clark 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
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.

There are already ion thrusters that use microwaves for ionization, and
also some that use lower-frequency radio waves. No actual thruster that
I'm aware of uses lasers or X-rays.

How many use grapes?

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?

Both are relatively efficient processes, in themselves. Unfortunately,
that doesn't imply that you get efficient ionization as a result. In
either case, much of the energy gets used unproductively.

Can you get enough energy out of a grape that grapes are usable?
Would you grow grapes in space for long voyages? Can the spent grapes
be used to make wine with? Is there a market for space wine?

(Published numbers on efficiency need to be scrutinized very carefully,
because there is a lot of specsmanship -- often what is quoted is *not*
overall, end-to-end, low-voltage-DC-to-jet-power efficiency, but the
efficiency of some better-looking subset of the process.)

In this, as in many other areas, "figures don't lie, but liars
figure", I suppose.

One reason for interest in Hall-effect thrusters and other plasma
thrusters, as alternatives to ion thrusters, is that they don't need high
ionization percentages and hence can avoid most of the efficiency penalty.

--
Mary Shafer Retired aerospace research engineer

Dear Mary Shafer:

"Mary Shafer" wrote in message
...
On Fri, 28 Nov 2003 20:33:25 GMT, (Henry Spencer)
....
There are already ion thrusters that use microwaves for ionization, and
also some that use lower-frequency radio waves. No actual thruster
that
I'm aware of uses lasers or X-rays.

How many use grapes?

You probably already know this, and are being funny. The thread title
refers to how a (presumably wet) grape shoots out from between your fingers
when you try to squeeze it.

David A. Smith

On Sun, 30 Nov 2003 08:41:52 -0800, Mary Shafer
wrote:



Can you get enough energy out of a grape that grapes are usable?
Would you grow grapes in space for long voyages? Can the spent grapes
be used to make wine with? Is there a market for space wine?
--
Mary Shafer Retired aerospace research engineer

So, are you by any chance considering a new career as a writer of
satire? Or perhaps a TV ancherperson (or their scriptwriter).

:-)

On Sat, 29 Nov 2003 07:58:47 -0700
\(formerly\)" dlzc1.cox@net wrote:

I'd worry about "selectively ionizing" a molecule for propulsion. Since the number of electrons stripped off provides the handles for
accelerating the mass, the more electrons removed means the faster you
can accelerate the molecule. But the more electrons you remove the
weaker (or smaller) the molecule fractions become. So your C60
becomes just 60C, and you are back to accelerating a bunch of light
nucleii.

C_60 is pretty stable, though, and, like any molecule, will hold on tighter to its remaining electrons once it's already lost some. Some quick googling suggests C_60 can lose at least 3 electrons without breaking up, but will start shedding C_2 ions at some point after that. I don't know much about ion drives, but I'd think that'd be good enough.

What I'd be more worried about is carbon buildup on the grids. If even a small fraction of the molecules sticks to the charged surfaces (and those C_2 fragments are likely to be particularly sticky) the resulting soot buildup might well become a problem over time.

--
Ilmari Karonen
If replying by e-mail, please replace ".invalid" with ".net" in address.