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  Since this is for a propulsion system operating only in space I could make the pressure of the gas low by using a very large volume.
I am looking up references on this on the net. Some keywords to use if you want to look up some references are "non neutral plasma" and "Brillouin limit".
The Brillouin density limit is a limit on the number of ionized particles that can be contained on a magnetic trap based on the strength of the magnetic field.

     Bob Clark

Below is a post to sci.physics. It proposes just storing ionized gas for fuel for ion drive engines rather than using the power on board for ionizing the gas as well as accelerating the ions.
My question is what kind of power would you need to contain a fully ionized gas using magnetic or electric fields? If the gas was low density could you just use light weight permanent magnets?

      Bob Clark

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Newsgroups: sci.space.policy, sci.astro, sci.physics, sci.physics.relativity, sci.physics.fusion
From: Robert Clark
Date: Thu, 20 Sep 2007 13:47:28 -0700
Local: Thurs, Sep 20 2007 4:47 pm
Subject: Stored ionized gas for ion drives.

This page gives a formula for the exhaust speed of an ion engine in
terms of the charge on the ions and the voltage driving the ion flow:

Ion thruster.
http://en.wikipedia.org/wiki/Ion_thruster#Energy_usage

The exhaust speed increases with the charge on the ions and decreases
with their mass. You would think then that a light gas like hydrogen
would be ideal since heavier gases even when fully ionized would still
contain approximately equal numbers of neutrons as protons which would
not contribute to the charge but would approximately double the mass.
Yet it is the heavier gases like cesium and more recently xenon that
are used. The explanation is that of the energy it takes to ionize the
gas used as fuel. The figure on this page shows the energy to ionize a
light gas such as hydrogen is relatively high compared to the heavier
gases:

Ionization Energies.
http://hyperphysics.phy-astr.gsu.edu/hb … onize.html

The figure gives the energy per mole which is high in itself. It is
even worse when you consider this on a per mass basis since the mass
amount of hydrogen would be so small compared to the amount of energy
needed to ionize it.
So could we instead store the hydrogen or some other light gas
already in ionized form so we would not have to supply power to ionize
the gas, only to accelerate it?
If you used ionized hydrogen, so you would be accelerating protons,
then using 6 x 10^18 protons to make one 1 Coulomb, and a mass of 1.6
x 10^-27 kg for a proton, and V representing the voltage in volts, the
speed on the ions (protons) would be about (10^4)sqrt(2*V) in meters/
second.
If we made the voltage be 5,000 V we would get 1,000,000 m/s speed
much higher than any current ion drive. Also, there are power supplies
that convert low voltage high amperage power into high voltage, low
amperage power, even up to 500,000 V. The we could get 10,000,000 m/s
= 10,000 km/s exhaust speed.
The question is could we get light weight means of storing large
amounts of ionized gas? Note that is this for space based propulsion
not launch from Earth. You would have a possibly large energy
generating station that remained in low Earth orbit to supply the
power to ionize the gas once the spacecraft was placed in orbit. The
power generator would be left behind in orbit. Then the volume of the
gas container could be large to keep the density of the gas low. This
would allow very thin container walls. Note the low density would also
allow the electrostatic repulsion of the positively charged ions to be
more easily constrained.
A possible problem though is the charged ions contacting the walls
could lead to a loss of ionization. You might be able to use a low
level magnetic field to prevent the ions contacting the walls. Low
density of the gas would insure the strength of the magnetic field
required would be low. It might even be accomplished by thin permanent
magnets so you would not need to use extra power.
Some questions: what would be the electrostatic pressure produced by
a low density highly ionized gas? What strength magnetic field would
you need to contain it?
Note that with an exhaust speed of say 10,000 km/s, by the rocket
equation we could get the rocket itself up to relativistic speeds with
acceptable mass ratios.
Then this would provide a means of testing relativistic effects on
macroscopic bodies.

Bob Clark
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Michael, in that sci.astro thread I cited a reference you might want to consult for the different shapes the liquid would achieve during rotation in zero-g:

Fundamentals of Low Gravity Fluid Dynamics and Heat Transfer.
Antar, Basil and Vappu: Boca Raton: CRC Press Inc., 1993.

I don't remember though if it considered rotations aroung two different axes at once, which your original proposal would require.

   Bob Clark

The Atacama is the driest desert on Earth. Previous studies were able to find microbes in the wetter portions on the desert. However samples taken from the drier central region showed no detectable microbes.
This had been taken to explain the Viking "no life" results:

Mars-Like Atacama Desert Could Explain Viking No Life Results.
Moffett Field - Nov 10, 2003
http://www.marsdaily.com/reports/MarsLi … sults.html

Dry Limit of Life
"Extreme Life Summary (Jan 15, 2004): Among the triad of biological limits to life on Mars--cold, thin air and dryness--a new study in the driest place on Earth reveals a remarkably sterile crucible for testing instruments that might one day answer questions about microbial life on other planets. The Atacama desert in Chile, when probed with some of the same techniques used during the 1976 Viking mission, found no life on Earth, a finding that may help scientists understand the dry limits to life and the potential importance of site selection."
http://www.astrobio.net/news/modules.ph … le&sid=781

However, two separate studies have now found that microbes exist even in the driest parts of the Atacama:

Deliquescence in the Atacama.
Date Released: Monday, July 10, 2006
"While strolling through the salar, Wierzchos noticed a thin dirty gray layer along the edge of one of these salt rocks, a few millimeters (about one-quarter of an inch) below its surface. Intrigued, he broke off a piece of the rock and brought it back to the research station. He dissolved a bit of the material in water, placed a drop on a microscope slide, and took a look. He expected it to be some kind of mineral contamination.
"Instead, what he saw were living cells. There was life, thriving, inside dry salt rocks. He had discovered a previously unknown habitat for life on Earth. Microbes had been discovered living in rocks before. And they'd been found living in extremely salty - wet and salty - environments. But never inside dry salt rocks.
"In wet halite, okay,' says Wierzchos, citing the Dead Sea as an example of a wet, salty environment where microbes have been found. 'But this is dry halite. This is totally different stuff."
http://www.astrobiology.com/news/viewpr.html?pid=20309

A Preliminary Survey of Non-Lichenized Fungi Cultured from the Hyperarid Atacama Desert of Chile.
Date Released: Tuesday, August 22, 2006.
http://www.marstoday.com/news/viewsr.html?pid=21797 [abstract]

Bob Clark

Just saw this on Unmannedspaceflight.com:

Mineralogy of the light-toned outcrop at Meridiani Planum as seen by
the Miniature Thermal Emission Spectrometer and implications for its
formation.
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, E12S03,
doi:10.1029/2005JE002672, 2006
"Abstract
Analysis of Miniature Thermal Emission Spectrometer (Mini-TES) data has
led to the recovery of a pure end-member spectral shape related to the
light-toned outcrop observed at Meridiani Planum. Data from the MER
Mössbauer spectrometer, APXS, and previous Mini-TES measurements were
used to constrain a spectral library used to determine the mineralogy
of the outcrop from this spectral shape. Linear deconvolution of the
outcrop spectral shape suggests that it is composed primarily of
Al-rich opaline silica, Mg-, Ca-, and Fe-bearing sulfates, plagioclase
feldspar, nontronite, and hematite. Conversion of modeled mineralogy to
chemistry shows good agreement with the chemical composition of the
outcrops determined by APXS. Details of the analysis procedure and
implications for the formation of the outcrop are discussed along with
terrestrial analogs of the ancient environment at Meridiani."
http://www.gps.caltech.edu/~tglotch/2005JE002672.pdf

According to the authors the spectra of the Meridiani bedrock is best
matched by a composition that includes 10% nontronite clay.

    Bob Clark

 
  The energy for the lift force is coming from the same place as it does for subsonic airplanes and supersonic jets. The thrust for these cases is never enough to hold the airplane aloft. The weight is always several times the thrust provided by the engines. The force to raise the aircraft is provided by the lift.
The turn radius for the SR-71 Blackbird was about 150 km at Mach 3, which means a circle 300 km across. But remember all aircraft when turning use a banking maneuver. This allows some of the lift to keep the airplane aloft while some of the lifting force contributes to the turn.
I'm proposing having the wings be 90º to the horizontal. This means the entire lifting force is used for the turn. The thrust to keep the vehicle aloft could be taken by 1 g from the beamed propulsion thrust. Normally, an airplane won't bank at 90º because you want to make a level turn where you're not losing altitude. However, if you've seen aerobatics you'll observe these aircraft can make much tighter turns when they're banked at 90º. The control surfaces for these aerobatic craft are designed to be able to provide sufficient vertical upward direction to the craft to keep the craft aloft. It may be since you only need 1 g of upward thrust, control surface here as well could keep the craft aloft.
Also, I'm considering having the proportions of the craft change as you increase in Mach number. From the hypersonic waverider page you see the shape is for a much slimmer craft to achieve high L/D ratio at the higher Mach numbers. This would be analogous to the swept wings on the F-14 fighter/bomber. Then you might have a "bending body" as well as a lifting body where it curves in the middle so the entire body becomes a control surface.
The proposal is not to launch manned craft. The g forces are too high. Electronics such as on satellites can be hardened to survive thousands of g's, much more than the tens to hundreds of g's required here. This has been demonstrated by gun launched missiles and rockets.
The waverider shape is that of a flattened cone. There are not wings sticking out. This would make it much easier for the airframe to survive the g forces.
Some versions of beamed propulsion do use hydrogen as fuel. In these cases this could be used for cooling. The space shuttle survives the high temperatures of reentry at Mach 25 at least for a few minutes by using lift. This would also be used in this proposal. Thermal protection materials now are more advanced than when the shuttle was designed to extend the length of time these materials can withstand the high temperatures.
You would indeed reduce the power and cost for each transmitter if you had several of them strung out some distance apart. But this would involve a total cost more that just using a single transmitter.
The purpose of the proposal was to reduce the power and cost required for a transmitter for beamed propulsion, which is too high for a moderately sized satellite. I believed using this proposal, the megawatt sized lasers already in existance have sufficient power to launch medium sized satellites.

   Bob Clark

Thanks for the response. Any feedback helps me flesh out the idea.
The idea is indeed counter-intuitive because it seems to be saying you want there to be drag. This is indeed the case but the reason is because it's using the fact that the lift will be about 8 times this drag according to the data suggesting the hypersonic lift/drag ratio can be 8 to 1 for waveriders.
The nice thing about beamed propulsion is you can provide as much energy as you want (reasonably). For instance, if you need 10 megawatts to launch 360 kilos (not pounds) then you can have your own dedicated gas turbine electricity generator and run it as long as you wish, 18 minutes or whatever.  If the drag required 10 times as much energy you just run the generator for 180 minutes.
The cost of gas turbines is in the ten's of millions for megawatt class generators. The fuel cost to run the generator is actually less than what you would pay for electricity off the grid. Look at GE's web site for gas turbines for example. And remember the turbine will be used to provide the power to launch multiple payloads so can quickly pay for itself.
  You're calculations are correct for the drag at 25 km:

Drag (physics)
http://en.wikipedia.org/wiki/Drag_%28physics%29

The formula is one-half the coefficient of drag, times the area of the lifting surface, times the air density, times the square of velocity.

However, an altitude of 25km might be alright for a hypersonic scramjet, but you don't have to keep the craft at that low altitude for getting it up to speed when you're using beamed propulsion.
Let's look at the scenario I suggested where the craft is travelling in a circle. Here it is propelled by the beamed power to have thrust that would amount to an  acceleration of about 6 g's in the tangential direction and this is supposed to be a little above the drag. But this 6 g's can also be applied to propel the craft upward initially to high altitude. Here we're not trying to get the craft to high speed just high altitude. So we can make it move slowly upward if we wish to keep the drag low.
(You might also want to use a combination of the beamed thrust and the lifting force, especially since the L/D ratio is even better at low speeds. It's just that for the discussion here the calculation of the trajectory is more complicated when it's not moving in a circle.)
Let's move it to say 75,000m, 75 km. My reference gives the air density at that altitude as 3.5x10^-5 kg/m^3. So the drag force would be less than a thousandth of the amount at 25 km, around 100 newtons. You could then use 1 g of the beamed power or 1 g out of the lifting force to keep the craft at the high altitude while it is being accelerated in the circle.
Actually though you don't want to make the drag too low since that would also make the lifting force low and you wouldn't get enough force to keep the craft in a circle.

   Bob Clark