Using atmosphere as propellant

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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DeltaV
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Post by DeltaV »

GIThruster wrote:I think the study was run by Frank Meade and I'm sure I posted it over at NSF but blamed if I can find it. Was a whole computer ago and I lost a lot of stuff during my first and only crash.
This one?
http://www.stormingmedia.us/37/3796/A379644.html

GIThruster
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Post by GIThruster »

That looks like it! but I got my copy from Frank. It wasn't posted anywhere on the web before I put it up at NSF.

This looks like the same study save that the bulk of it was concerned with the various thrusts available based upon varied propellant dumped into the alpha stream and there's no mention of this in the abstract.

Still, looks like the same paper. Was a fun read. Anyone wants to look for it at NSF, it'll be in the Advanced Concepts folder.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

GIThruster
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Post by GIThruster »

Nope, sorry, this is a different paper, but here it is anyway:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD ... tTRDoc.pdf
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

GIThruster
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Post by GIThruster »

Here's another, again not the one I had posted at NSF but this one does cover many of the same issues, including explaining the trimodal approach, p.541 bottom:

http://adl.serveftp.org/papers/Advancem ... ulsion.pdf
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

DeltaV
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Post by DeltaV »

GIThruster wrote:If you don't have the flow rate, perhaps a pulse detonation version? That's even closer to a lighting strike. . .
Image

Here I'm assuming a UHVDC power source that stores enough energy between pulses to make the arc worthwhile. Or, sequencing through several engines to approximate a continuous load.

Direct charging of the electrodes by alphas is also a possibility (Charge accumulation timing issues? Sync with POPS subfrequency?). No "plasma windows" needed: sealed, insulated conductors through Polywell's vacuum chamber wall.

Otherwise, the above scheme requires only direct conversion (different from just letting alphas hit a conductor, since DC tries to reclaim almost all the kinetic energy). No down-conversion.

The exhaust might impinge tangentially on a linear aerospike nozzle (not shown). This engine is mostly hollow, so several could be combined without a huge mass penalty. Engines probably electrically sequenced, so that the load on the reactor is more even, in step with the air injection cycles.

Electrode wear is a likely issue. Maybe a plasma sheath around each electrode to distribute the current? Or let them be consumables.

The elliptical chamber might also be useful for continuous air heating via a REB. Atmospheric-cruise and orbit-boost engines sharing the same elliptical chamber? Ionization laser from one end, REB from the other, depending on flight mode. The higher average-power REB might need magnetic shielding (bulk HTS?) or active cooling for the chamber walls. You can't set up a reverse-flow vortex like Orbitec's VCCW in a non-circular geometry like this.

DeltaV
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Post by DeltaV »

GIThruster wrote:Yes well, the best study I've seen of this portion of the issue was a study done at AFRL on fusion drives. IIRC, what they were proposing was a trimodal operation where one uses the alphas in all three modes.
How did they transition the alphas from vacuum chamber to engine chamber? Or am I in error thinking DPF needs a vacuum too?

zapkitty
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Post by zapkitty »

DeltaV wrote:
GIThruster wrote:Yes well, the best study I've seen of this portion of the issue was a study done at AFRL on fusion drives. IIRC, what they were proposing was a trimodal operation where one uses the alphas in all three modes.
How did they transition the alphas from vacuum chamber to engine chamber? Or am I in error thinking DPF needs a vacuum too?
Well technically a very, very thin atmosphere of decaborane at a few torr... ... with a chance of lightning and occasional gusts of helium... :)

Yeah, it's a vacuum. I'd presume a plasma window or similar machination for the rocket versions. What papers on DPF spacecraft there are don't go into that much detail.

DeltaV
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Post by DeltaV »

Figure 7 from
M. Frantz, "A Focusing Property of the Ellipse", American Mathematical Monthly, 101 (1994), p 250-258
Image
Everything tends to end up on the line containing the foci. Flatter ellipses concentrate wavefronts faster. The paper assumes photons and a perfect reflecting surface. Shock waves in a gas are probably more prone to dispersal, but the general effect could be similar.

zapkitty
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Post by zapkitty »

It all depends on your parameters, of course, but is an arc the best way of transfering MWe to MWt to kN?

I'd wonder if, given the known efficiency of impellers in converting MWe to kN, if it might be more efficient to accept the downconversion mass penalty and just use blades until you're going fast enough to switch to a microwave heated fanjet and then later on to ramjet mode... all the while using MHD techniques when and where appropriate... both the impellers and the jet should operate at as high a voltage as you can afford to save downconverter mass....

And of course once you run out of air you switch modes to microwave electrothermal thruster...

.... still say it'll be simpler and cheaper to use polywell to build an SSTO that hauls your ass to orbit in 10 minutes and leave the mucking about in atmosphere to craft specialized for that purpose... :)

WizWom
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Post by WizWom »

As an engineer, of course the obvious thing to do is BUILD the thing, and test it. Especially if its something as simple as an elliptical arcjet.
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DeltaV
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Post by DeltaV »

I'd guess that REB is more efficient than pulsed arc, but REB might be heavier.

I'd like at least a 2-D simulation before bending metal or winding composite. 3-D sim would be better to explore various end cap shapes, skewed elliptic cylinders with exit slots near one end, inlet locations, etc.

Fans are cool for VTOL and low speed flight, but currently need down conversion. E-APE might fill a gap between fans and QED-ARC REB initiation around M2.5. Too early to say.

Here's a screwball idea for high-voltage lift fans:
Hollow fan blades with slotted trailing edges, E-APE interiors (fed by air from the hub, which also provides HV and commutates the ionization laser) and airfoil exteriors. Conductive outer duct or a connected, rotating conductive ring to complete the circuit across a small gap to ground. It would need large blades (the best ones have a 'wavy' outer surface), so limited to low speeds.

kunkmiester
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Post by kunkmiester »

You could also just build something so freaking big the mass penalty for down conversion is negligible. :twisted: :roll:

Anyone ever build a DC motor to run at a million volts? What would be the mass penalty of that sort of thing?
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DeltaV
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Post by DeltaV »

It has to fit in my backyard, or there's no point.

GIThruster
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Post by GIThruster »

"It has to fit in my backyard, or there's no point."

ROFL!!!

A man after my own heart.

Truthfully, USAFL is looking at systems that can fit in your back yard.

Starfighters, without the included hyperdrive.

For hyperdrive, you need the ability to generate large amounts of negative mass with negative inertia.

The only person who knows how to do this is Jim Woodward.

That's the truth.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

DeltaV
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Post by DeltaV »

For now, I'd be happy with access to and from LEO. The zero g will help my back. In case I spot a nice island from orbit, I'd want to be able to visit it without needing an Act of Congress. Refueling needs won't be a concern with Polywell, at least for trips of a week or less. Regarding hyperdrive, I can do without that for now. Who needs the hassle of Klingons, Romulans, Ferengi, Wraith, Replicators, Orai, 14 ft tall silicon-based insects with molecular acid blood, etc. Maybe later, if I get bored.

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