Using atmosphere as propellant

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

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WizWom
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Postby WizWom » Tue Jul 27, 2010 10:36 pm

Wandering Kernel of Happiness

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Postby DeltaV » Wed Jul 28, 2010 7:15 am

I'd need more than 6 seconds to make it worthwhile.

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Postby IntLibber » Sun Aug 15, 2010 12:22 am


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Add Lightness and Simplicate

Postby rjaypeters » Wed Sep 01, 2010 6:57 pm

What a great thread!

I'm pretty sure this thread's posters know the design of SSTO vehicles is a long-time goal of the aerospace industry which has failed for lack of a good power source (and other things, e.g. money and good light-weight materials are also high on the list).

Aside from the over-concentration on the rotary theme, I think the most innovative attempt was the Rotary Rocket Roton. See here:



By most innovative, I mean there was no messing with wings (too heavy to be useful for long enough to be worth the weight) or runways.

The helicopter phase solves a last-mile problem. How to land and take off while not building too much speed at low altitude or tearing up the backyard real estate.

Some of us have proposed up to four propulsion systems (did I read that right? turbojet + ramjet + scamjet + reaction drive?) for the Polywell-powered SSTO. Two is the maximum we should permit. So:

1. A helicopter phase powered by the very high voltage DC motors (which are yet to be invented) or stepped-down voltage motor (I know - weight penalty). The advantage here is the motors are kept inside the body of the vehicle and we don't attempt to carry ducts into space. Although I don't much like counter-rotating rotors for this application, they might be the simpler way to counter rotor torque. Else we could use retractable anti-torque fans.

Lift the Polywell SSTO high enough so the reaction drive won't bother the neighbors by making too much noise or tearing up the landing pad.

2. The Polywell-powered reaction drive phase (which could use air as reaction mass but there I go adding complexity). The reaction drive must also provide the bulk of the reentry thermal protection in two ways: reducing the speed of reentry and pushing the stagnation shock boundary away from the bottom of the vehicle (which must have a TPS to protect from the energy of the reaction drive anyway).

When reentry is achieved and speed is slow enough, spin up the rotors for landing.

I really like the concepts of the elliptical arc-pulse engines and REBs, but the point of SSTO is to put mass into orbit and bring it back down again. Extended cruise through the atmosphere? Build a Polywell-powered REB screamer if you must (please - I'd love to ride that puppy!), but don't tack on the requirement to reach orbit.
"Aqaba! By Land!" T. E. Lawrence

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Re: Add Lightness and Simplicate

Postby Stoney3K » Wed Sep 01, 2010 7:30 pm

Because we can.

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Add Lightness and Simplicate

Postby rjaypeters » Thu Sep 02, 2010 12:53 am

Stoney3K: I should have written counter-rotating _coaxial_ rotors at the top of the vehicle. The modified tilt-rotors shown in "Avatar" have their place in a primarily atmospheric vehicle. Note the size of those rotors relative to the size of the remainder of the vehicle.

For interacting with the surrounding medium, the greatest efficiencies are found by accelerating the greatest amount of mass by the least change in velocity, consistent with the other constraints on your technology. External rotors are the best at low speeds near liftoff and landing.

Also note, these external rotors would fold against the body of the vehicle for high speed flight. Another reason not to like counter-rotating is one must arrange for stowage of two sets of rotors...

"...scramjet has already been used on the SR71..." No, sir. The SR-71 used a very heavily augmented turbojet. We haven't built operational scramjets, yet. That I know about...

Certainly the Polywell will reject heat to the environment. The problems come in when attempting to use the waste heat.
"Aqaba! By Land!" T. E. Lawrence

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Postby kunkmiester » Thu Sep 02, 2010 3:21 am

Evil is evil, no matter how small

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Postby DeltaV » Thu Sep 02, 2010 6:46 am

I'm thinking embedded, ducted, electric lift fans for VTOL. Better for redundancy. Say, 8 fans embedded in a large-planform vehicle. The lift fans can be mounted in semi-spherical gimbals for thrust vectoring. Mechanically simpler than external rotors that must be stowed. Separate, embedded, electric turbines for higher speeds up to REB start (~M2.5), the turbines sharing inlets/exhausts with the REB (used for orbit boost). Sliding doors to seal where necessary for boost/reentry. Metallic TPS, doable with a "fluffy", large-planform vehicle. That's my baseline. Modify as appropriate for elliptical arc pulse engines or whatever...

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Postby rjaypeters » Thu Sep 02, 2010 9:56 am

kunkmiester wrote: "Mass is the important part in countering torque. A proper set of counterweights can be held inside the vehicle, and will do just as much, though with a higher mass penalty."

Yes, since we must counter torque, I'd like to get some lift out of in the bargain and avoid higher mass.

DeltaV: Although you certainly want to build a sexy vehicle, I don't think we are going to agree, but here goes...

Please tell me how eight fans closing inlet doors distributed around the vehicle are simpler and lighter than one or two helicopter hubs at the top of a conical or pyramidal shell.

Large platform = mass. IMO, the better SSTO efforts (including the Clipper demonstrator) showed the way with smaller platforms and planforms to minimize structure.

I can't tell from my fuzzy memory this morning, are you proposing to lift this large planform straight up through the atmosphere? If so, please include the drag penalty in your trajectory calculations.
"Aqaba! By Land!" T. E. Lawrence

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Postby Stoney3K » Thu Sep 02, 2010 3:26 pm

Because we can.

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Postby rjaypeters » Thu Sep 02, 2010 11:20 pm

"Aqaba! By Land!" T. E. Lawrence

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Postby zapkitty » Fri Sep 03, 2010 2:57 am


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Postby DeltaV » Fri Sep 03, 2010 3:32 am


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Postby rjaypeters » Fri Sep 03, 2010 11:03 am

"Aqaba! By Land!" T. E. Lawrence

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Postby DeltaV » Sat Sep 04, 2010 4:51 am



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