Using atmosphere as propellant

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

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rjaypeters
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Postby rjaypeters » Mon Sep 20, 2010 9:29 pm

93143 wrote:For all-rocket SSTO, yeah, it does need to be pretty light. Not necessarily quite that light, but if the engine performance I assumed can't be achieved due to ionization effects, that ~250-tonne structure+payload mass drops substantially. And you can forget about a powered descent...

I'm thinking airbreathing SSTO will work out a bit better. 100 MW is still useless, of course...
Might we consider using the (pB11 please) Bussard to power a zero stage lifter for any given orbiter? The fuel should be pretty cheap and reaction mass cheaper. Please let us avoid cryogenics if we can.

In that vein, I think it was GW Johnson who pointed out heavier aircraft act like waterballoons on toothpicks on the ground. Could a zero stage land and takeoff from the water (with all the dis/advantages thereto)?
"Aqaba! By Land!" T. E. Lawrence

R. Peters

Nydoc
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Postby Nydoc » Fri Apr 22, 2011 8:21 pm

DeltaV wrote:It's VTOL electric lift fans, transitioning to electric turbines up to ~M2.5, transitioning to REB from there to orbit. See Bussard's papers on hypersonic propulsion. I'm feeding air to the REB until the atmosphere thins out, only then blending in onboard reaction mass.


Would this be feasible to do with just the electric turbines and without the VTOL electric lift fans so as to decrease the weight of the vehicle and increase payload mass?

Also, would it be possible to power the REB using SAFE-400 reactors?

DeltaV
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Postby DeltaV » Sat Apr 23, 2011 2:06 pm

Nydoc wrote: Would this be feasible to do with just the electric turbines and without the VTOL electric lift fans so as to decrease the weight of the vehicle and increase payload mass?

It would, but far more power is required to get to orbit from the M2.5 regime, so why not include VTOL in my "dream" vehicle (remember, it has to land and take off from my back yard). The fuel mass penalty for a Polywell (small amounts of hydrogen and Boron 11) is negligible, unlike chemical propulsion (e.g., Shuttle fuel/oxidizer tank). No big mass penalty for letting the reactor run all day (as when cruising in the atmosphere before/after orbit).

Assuming efficient, hubless, rim-drive electric motors such as NASA studied, lightweight composite and/or metallic glass fan blades and maybe room-temp superconductors, the VTOL penalty may be more severe in volume than in mass.

All-electric propulsion allows for some interesting possibilities, such as multiple motor-fan modules in rotatable, spherical housings (similar to a ball valve) which can be either aligned along a propulsion duct or turned orthogonal to the duct for VTOL. CFD experts are needed to find blade designs useful from VTOL to M2.5 (REB initiation speed per Bussard). Nice thing about the "ball valve" arrangement is that the VTOL inlets/outlets are sealed for higher speeds simply by rotating the motor-fan modules into alignment with the main duct.

The big question with regard to using Polywell as a subsonic flight power source is how do you convert >1MV to a lower voltage without a huge mass penalty. Low-voltage motors have advanced far, and are probably the best choice for slower speeds IF the low voltage is available. The REB is happy with high voltage.

Nydoc wrote: Also, would it be possible to power the REB using SAFE-400 reactors?

SAFE-400 produces about 0.1 MW or 0.0001 GW. Reaching orbit with a REB requires power in the multi-GW range. 93143 once posted a model that assumed ~6 GW Polywell output. He assumed a high mass penalty due to radiation shielding (gammas being the worst). Things improve with lower gamma emission. We need some real Polywell data to know what the gamma situation will actually be.

Nydoc
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Postby Nydoc » Mon May 02, 2011 2:31 am

DeltaV wrote:Efficient, superconducting, high power density electric fans would be great for VTVL, and electric turbines for low-medium speed forward flight. The problem is that they require low voltage, which requires extra mass to down-convert Polywell's ~1.5MV to a usable range. Maybe this can be done lightly with high-frequency converters, but I haven't been able to get any of the EEs on this forum to provide mass estimates.

Maybe the VTVL fans could be run off a waste-heat loop? Or maybe you could use the heat from a plasma chamber to get them spinning? I think the best solution would be to just nix the fans. No hefty down-converter needed and you save the engineering and maintenance costs of the fans. Of course, then you'd never know if VTVL works on Mars :wink:

DeltaV
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Postby DeltaV » Mon May 02, 2011 3:57 pm

Nydoc wrote:Maybe the VTVL fans could be run off a waste-heat loop? Or maybe you could use the heat from a plasma chamber to get them spinning?
I'll leave thermodynamics questions to someone like 93143.

Nydoc wrote:I think the best solution would be to just nix the fans. No hefty down-converter needed and you save the engineering and maintenance costs of the fans.
The integrated motors/fans are (mostly) already-known technology. Engineering those is trivial compared to the fusion power system. What maintenance costs? Frictionless magnetic bearings, no grease/oil/fuel/filters, noncorrosive materials, firmware control loops, rugged sensors, long-life EM actuators. As long as you don't hit a flock of geese...

You could fly VTOL/subsonic with high-voltage-only using a REB, or my EAPE above, but ozone, noise and heat are worse. If a low-mass, low-voltage power source can be attained, something like my ducted ball-valve idea* is probably better for near-ground operation over existing airports.

(* I'm thinking of at least two aft-exiting propulsion ducts, with at least four rotatable motor/fan ball modules per duct. Maybe some composite flow straighteners between modules to reduce turbulence seen by downstream fans during forward flight. The modules have a 180 deg range of motion about axes roughly parallel to the vehicle's pitch axis, allowing forward and reverse** thrust, and a few deg of motion about axes roughly parallel to the roll axis during VTOL mode.)

(** HTOL optional for heavier payloads.)

Nydoc wrote:Of course, then you'd never know if VTVL works on Mars :wink:
For now I just want to focus on earth to orbit. Once there, you are halfway to anywhere.

Nik
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Or let some-one else do the hard work ??

Postby Nik » Tue May 03, 2011 5:51 pm

"The SKYLON payload bay is 4.6m diameter and 12.3m long. It has been designed to be compatible with expendable launcher payloads but in addition to accept standard aero transport containers which are 8 foot square in cross section and 10, 20, 30 or 40 feet long. It is anticipated that cargo containerisation will be an important step forward in space transport operations, enabling the "clean" payload bay to be dispensed with.

The vehicle can deliver 12 tonnes to a 300km equatorial orbit, 10.5 tonnes to a 460km equatorial spacestation or 9.5 tonnes to a 460km x 28.5 deg spacestation when operating from an equatorial site."

Given a Polywell as ground-based power source, the Skylon's hydrogen and oxygen cryo-fuel are cheap. Assemble the Polywell-powered rocket in orbit and let it do the sexy interplanetary stuff...

DeltaV
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Postby DeltaV » Wed May 04, 2011 3:52 am

Skylon can't land in or take off from my back yard.

[Edit]
Skylon takeoff rotation speed: 590 km/hr or 367 mi/hr.
Can you say "infrastructure"?
Last edited by DeltaV on Fri May 13, 2011 2:47 pm, edited 1 time in total.

mvanwink5
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Postby mvanwink5 » Wed May 04, 2011 5:25 pm

What about using a polywell powered heavy lift vehicle to launch material and supplies, and a different vehicle for the human payload? A "Reaver" rocket, to use a Firefly movie reference, without the radiation shielding, for the heavy lifting. A vehicle to go to mars could use distance from the reactor, rather than heavy shielding for reducing radiation exposure. Just some other thoughts.
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

Nydoc
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Postby Nydoc » Wed May 11, 2011 11:07 pm

DeltaV wrote:I keep seeing that Blended Wing-Body airframe morphing into a flatter, wider variant of the X-33 shape for SSTO, with a Polywell in the middle and embedded, sealable VTOL fans (nice and fluffy for reentry with metallic TPS, if radiation shield and down converter mass can be kept low enough). The boundary-layer ingesting upper surface propulsors might then get it to M2-3, REB zone, without that somewhat bulbous BWB forward section and the long wings. Nice thing about that location for the propulsors is that they don't see much reentry heating.

NASA's X-48B is scaled down from a conceptual 240 ft wide design. This gives it nearly the wingspan of an A380. With that huge of a wingspan, the VTOL would certainly help you find a place to land it. As far as reentry heating goes, I wonder if having a conventional tube body could allow for feathered reentry.

DeltaV
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Postby DeltaV » Thu May 12, 2011 2:51 pm

Nydoc wrote:NASA's X-48B is scaled down from a conceptual 240 ft wide design. This gives it nearly the wingspan of an A380. With that huge of a wingspan, the VTOL would certainly help you find a place to land it.
I was referring to general shape, not size (note also my comment about deleting the bulbous nose and long wings). As a first approximation, maybe something like LoFlyte or NorGrum's hypersonic bomber: http://www.aerospaceweb.org/design/wave ... ples.shtml

Lots of planform area for propulsion ducts having embedded, semi-spherical, rotatable motor/fan modules (M 0-2.5). Integration with REB duct(s) (> M 2.5) to be determined (talking here about the low-speed ducts' forward/aft inlets/outlets being blended into the REB duct(s) inlet(s)/outlet(s), not that I'd expect those connections to be open above M 2.5).

In forward flight (VTOL inlets/exhausts closed, all motor-fan modules aligned with ducts), I think having a few semi-spherical bumps or semi-conical depressions here and there on the aeroshell surface (well, 16 at least - 8 dorsal and 8 ventral, towards - but not too close to - the leading edges, bilateral symmetry) would be acceptable drag-wise and hopefully heat-wise.

I'm currently leaning away from the aft-dorsal, boundary-layer-ingesting propulsors for M < 2.5. They would work, as long as AoA is kept low (feasible prior to REB boost to orbit), but require separate VTOL hardware. Better to use the same propulsors for VTOL and sub-M2.5 forward flight.

Nydoc wrote:As far as reentry heating goes, I wonder if having a conventional tube body could allow for feathered reentry.

The peak reentry speed of Rutan's suborbiters is about 1/5 that of a vehicle returning from orbit. Significantly different heat loads. I'd rather keep the rotating parts/joints on the smallish side, within the overall aeroshell envelope.

DeltaV
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Postby DeltaV » Thu May 26, 2011 2:43 pm

Fuel-Sipper - the Turbo-Electric Flying Wing

Image

45,000,000 We / 90,000 lbf = 500 We/lbf with superconducting motors.
{About twice as efficient as the F-35B lift fan's (mechanical power in)/(lift force out)}.

So, using this thrust efficiency for a very rough estimate (ignoring fan, motor and duct efficiency differences between VTOL hover using rotating motor-fan ball modules and take-off using an aft-dorsal, linear propulsor array) a vehicle weighing about 1,000,000 lb (747-8 class) with superconducting motors would require

(1,000,000 lb)(500 We/lbf) = 0.5 GWe

to hover in VTOL mode.

An order of magnitude less electrical power than needed by the REB for boost into orbit.
Hence my "hover or cruise all day before and after orbit" philosophy.

[EDIT - fixed dead link, added picture and F-35B comment]
[EDIT - Picture link above gone behind paywall -- uploaded below and added link to NASA paper]

https://www.aiaa.org/uploadedFiles/About-AIAA/Press-Room/Key_Speeches-Reports-and-Presentations/2012/Hathaway-EPP-SFW-GEPC1-5-AIAAjan2012.pdf
Attachments
DistributedTurbo-ElectricPropulsion.png
DistributedTurbo-ElectricPropulsion.png (204.99 KiB) Viewed 1825 times
Last edited by DeltaV on Sat Jan 10, 2015 4:44 pm, edited 4 times in total.

ladajo
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Postby ladajo » Thu May 26, 2011 9:00 pm

The peak reentry speed of Rutan's suborbiters is about 1/5 that of a vehicle returning from orbit. Significantly different heat loads. I'd rather keep the rotating parts/joints on the smallish side, within the overall aeroshell envelope.


Key point. Nice.

DeltaV
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Postby DeltaV » Sat May 28, 2011 2:06 pm

DeltaV wrote:(1,000,000 lb)(500 We/lbf) = 0.5 GWe

to hover in VTOL mode.

Coincidentally, this is the total output of a coal-fired power plant I used to live near.

One coal plant for hover. Ten coal plants for orbit.

Which is why this will only work with fusion, or something better.

WizWom
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Postby WizWom » Tue Jul 19, 2011 9:00 pm

DeltaV wrote:
DeltaV wrote:(1,000,000 lb)(500 We/lbf) = 0.5 GWe

to hover in VTOL mode.

Coincidentally, this is the total output of a coal-fired power plant I used to live near.

One coal plant for hover. Ten coal plants for orbit.

Which is why this will only work with fusion, or something better.



http://ntrs.nasa.gov/archive/nasa/casi. ... 009270.pdf
Optimal specific mass characteristics were found to be dependent on overall power plant scale with 3 kg/kWe being potentially achievable at a net electrical power output of 1-MWe.

So, 3000 kg/MW using fission, ready for space. 500 MW would be 1,500,000 kg, that is, 1500 tons. So your VTOL idea is out.

However, the total output of the 747-8's engines is 66500 lbf, 99,750 kg mass to replace - each. Call the total 400,000 kg. That is about twice the fuel mass (188,000 kg). Of course, since there is an airstream, we could use that for heat rejection, which would lighten the system vis-a-vis a space nuclear plant.

In other words, today, we could make a fission-electric supersonic plane that could fly for years at over the speed of sound.
Last edited by WizWom on Thu Jul 21, 2011 8:09 pm, edited 1 time in total.
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KitemanSA
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Postby KitemanSA » Tue Jul 19, 2011 9:59 pm

WizWom wrote: So, 3000 kg/MW using fission, ...
Source?


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