Talk-Polywell.org

May 27, 2010 USAF vehicle breaks record for hypersonic flight (AP)


In this image provided by the U.S. Air Foce an X-51A Waverider rides under the wing of a B-52 Stratofortress Dec. 9, 2008. A similar X-51A successfully launched from a B-52 Stratofortress, Wednesday May 26, 2010. The Rocketdyne-built air breathing scramjet engine accelerated the vehicle to Mach 6. It was the longest supersonic combustion ramjet-powered hypersonic flight to date. (AP Photo/US Air Force - Mike Cassidy)



An experimental aircraft has set a record for hypersonic flight, flying more than 3 minutes at Mach 6 - six times the speed of sound.



http://www.physorg.com/news194161305.html

Yeah the news is all over the usual suspect sites
I have read meanwhile though, that they "only" reached Mach 5, before they lost telemetry.

Yeah, they can now burn the engine for 200 seconds. I think the first test flight was a less than 1 second burn. The old strategy was to simply let the test vehicle crash into the sea, and not even bother recovering it. The engine is toast. I gather they still do that.

I'm not going for a ride on one yet, but a lot of people did not think they could get one to burn for minutes.

This does make Dr. Bussard's idea for a Polywell-powered aerospace plane, essentially a scramjet with REB-heated air rather than hydrogen-combustion-heated, a trifle less of a fantasy.

REB-heated air

Tom:

Would you mind to explain the acronym "REB", in this context? I gather it is something to do with using the radiation/products from the Polywell fusion to heat the air, but do you have some more detail on how Bussard envisaged to do this I'd be interested, thnx.

Actually never mind I found Bussard's paper, relativistic electron beam (REB)

http://www.askmar.com/Fusion_files/QED% ... ulsion.pdf

One of the schemes Dr. Bussard proposed for coupling the output of a Polywell to gas to produce a rocket, or in this case a jet, engine is to fire a Relativistic Electron Beam (REB) into the gas, which should heat the gas very efficiently. He proposed it for the high thrust, lower specific impulse, end of his proposed spectrum of Polywell-powered spacecraft. I have characterized it as "the arc-jet from Hell."

In the case of his air-breathing SSTO, an electron beam would substitute for hydrogen combustion in a a scramjet similar to the X-51 configuration for the portion of flight where sufficient atmosphere exists to make usable thrust. I think this could extend as high as about 70 miles.

Obviously, to be economical the craft would have to be reusable. The practical design will have to last orders of magnitude longer than 200 seconds.

The papers on these proposed engines are in the repository maintained by Askmar.com. Dr. Bussard's career started out in nuclear rocketry, and he literally "wrote the book" on the subject.

http://www.askmar.com/Fusion.html

Bussard, R. W.; DeLauer, R.D. (1958), Nuclear Rocket Propulsion, McGraw-Hill
Bussard, R.W.; DeLauer, R. D. (1965), Fundamentals of Nuclear Flight, McGraw-Hill



There has been a lot of press on the VASMIR approach. There is nothing wrong with the Variable Specific Impulse Magnetoplasma Rocket drive, but the proposals so far have been unrealistic as to how to power them. Compact fission power sources have been proposed, but a close look throws some doubt that a good power to weight ratio is actually possible. VASMIR and Polywell would be a good fit.

Tom Ligon wrote:Yeah, they can now burn the engine for 200 seconds. I think the first test flight was a less than 1 second burn. The old strategy was to simply let the test vehicle crash into the sea, and not even bother recovering it. The engine is toast. I gather they still do that.

I'm not going for a ride on one yet, but a lot of people did not think they could get one to burn for minutes.

This does make Dr. Bussard's idea for a Polywell-powered aerospace plane, essentially a scramjet with REB-heated air rather than hydrogen-combustion-heated, a trifle less of a fantasy.

I would point out (from my understanding) that the biggest issue with the scramjet design was to develop a configuration that would combust fuel at supersonic speeds. (In other words, the fast moving air blows the candle out. )

This ought not to be any sort of a problem for a heat exchanger design, such as would be the case with a polywell reactor. Since you aren't having an issue with fuel burning, I dare say a reactor powered system need only have a sufficiently large heat exchanger, and it will just work.

Simple.

Tom Ligon wrote:One of the schemes Dr. Bussard proposed for coupling the output of a Polywell to gas to produce a rocket, or in this case a jet, engine is to fire a Relativistic Electron Beam (REB) into the gas, which should heat the gas very efficiently. He proposed it for the high thrust, lower specific impulse, end of his proposed spectrum of Polywell-powered spacecraft. I have characterized it as "the arc-jet from Hell."

In the case of his air-breathing SSTO, an electron beam would substitute for hydrogen combustion in a a scramjet similar to the X-51 configuration for the portion of flight where sufficient atmosphere exists to make usable thrust. I think this could extend as high as about 70 miles.

Obviously, to be economical the craft would have to be reusable. The practical design will have to last orders of magnitude longer than 200 seconds.

The papers on these proposed engines are in the repository maintained by Askmar.com. Dr. Bussard's career started out in nuclear rocketry, and he literally "wrote the book" on the subject.

http://www.askmar.com/Fusion.html

Bussard, R. W.; DeLauer, R.D. (1958), Nuclear Rocket Propulsion, McGraw-Hill
Bussard, R.W.; DeLauer, R. D. (1965), Fundamentals of Nuclear Flight, McGraw-Hill



There has been a lot of press on the VASMIR approach. There is nothing wrong with the Variable Specific Impulse Magnetoplasma Rocket drive, but the proposals so far have been unrealistic as to how to power them. Compact fission power sources have been proposed, but a close look throws some doubt that a good power to weight ratio is actually possible. VASMIR and Polywell would be a good fit.

I assume the design required the use of a plasma window? I can't think of an alternative method at the moment.

If you mean how to separate the e-gun from the gas chamber, Dr. Bussard admited that was going to be an interesting engineering problem (code for "I don't know"). He thought a thin metal membrane might be involved, but I suspect it would be tricky to make it work.

It could be hard to get a heat exchanger to work at supersonic flow conditions, but I'd bet an electric arc would heat the gas about as fast as anything can.

Evidently it is hard to get hydrogen to stay lit above Mach 7.

Tom Ligon wrote:If you mean how to separate the e-gun from the gas chamber, Dr. Bussard admited that was going to be an interesting engineering problem (code for "I don't know"). He thought a thin metal membrane might be involved, but I suspect it would be tricky to make it work.

"an interesting engineering problem" is a pretty good answer.

Tom Ligon wrote: It could be hard to get a heat exchanger to work at supersonic flow conditions,

I thought about that. Make the tube(s) longer! Also, you can use electrostatic charges to force the air into more intimate contact with the heat exchanger surface.

Tom Ligon wrote: but I'd bet an electric arc would heat the gas about as fast as anything can.

That seems like the easiest way, except for cooling off the electrodes of course. That's one of the advantages of using an electron beam. You don't have to worry about an electrode overheating. You just shoot it down the bore of the engine, and you can even make sure the engine has no obstruction by turning the beam with a magnet. Might even be able to reduce thermal loading on the walls by charging them more negatively.

Tom Ligon wrote: Evidently it is hard to get hydrogen to stay lit above Mach 7.

If you got a long enough tube, enough heat and enough oxygen, it all ought to work at some point. BURNING hydrogen as fuel would yield an even greater thrust. I thought the idea was to just heat the incoming air.

I remember bringing up the point about the e-gun needing to be in a high vacuum because we were having fits getting dispenser cathodes to work well. The bright discharges that sometimes occurred in our machines tended to kill cathode activity, so we were sensitized to the problems of deactivation and poisoning.

But at the same time we were looking at alternatives. Among these are diamond films and the ends of Buckytubes, both of which can be coaxed into emitting copious electrons, and they may resist deactivaton.

We also found tungsten filaments to be relatively robust, and I think they are the preferred emitters at EMC2 today. What I saw on my visit was nearly identical to some I made, possibly just copies of my design. I used halogen bulbs from a common model of car headlight, because they were readily adapted and I knew I could get more.

Tom Ligon wrote:I remember bringing up the point about the e-gun needing to be in a high vacuum because we were having fits getting dispenser cathodes to work well. The bright discharges that sometimes occurred in our machines tended to kill cathode activity, so we were sensitized to the problems of deactivation and poisoning.

But at the same time we were looking at alternatives. Among these are diamond films and the ends of Buckytubes, both of which can be coaxed into emitting copious electrons, and they may resist deactivaton.

We also found tungsten filaments to be relatively robust, and I think they are the preferred emitters at EMC2 today. What I saw on my visit was nearly identical to some I made, possibly just copies of my design. I used halogen bulbs from a common model of car headlight, because they were readily adapted and I knew I could get more.

I don't think commercial electron beam welders use a super hard vacuum. Presumably one for a scram jet engine wouldn't need a super hard vacuum either. The polywell would, but I don't think the beam emitter would. I had always envisioned the concept as having a reactor and a beam emitter. Are you suggesting that the reactor be a combination reactor and beam emitter?

Tesla had come up with ways to do an open ended vacuum tube before the '30s, for his "death beam." I can't see the system being much harder here. The simplest system was simply an airflow over the opening, which created suction. You already have a massive airflow, you'd just have to get the geometry right.

Would the ionization of air from compression heating in a scramjet be enough for microwave heating to work?

As for the Tesla 'death beam', his poor documentation gives us little idea of what he really came up with, or whether it would have really worked.

Tom Ligon wrote: There has been a lot of press on the VASMIR approach. There is nothing wrong with the Variable Specific Impulse Magnetoplasma Rocket drive, but the proposals so far have been unrealistic as to how to power them. Compact fission power sources have been proposed, but a close look throws some doubt that a good power to weight ratio is actually possible. VASMIR and Polywell would be a good fit.

actually, most times I read something about VASIMR, someone usually mentions Polywell as being VASIMR´s perfect fit.

AcesHigh wrote:

Tom Ligon wrote: There has been a lot of press on the VASMIR approach. There is nothing wrong with the Variable Specific Impulse Magnetoplasma Rocket drive, but the proposals so far have been unrealistic as to how to power them. Compact fission power sources have been proposed, but a close look throws some doubt that a good power to weight ratio is actually possible. VASMIR and Polywell would be a good fit.

actually, most times I read something about VASIMR, someone usually mentions Polywell as being VASIMR´s perfect fit.

A power source like polywell would be an excellent fit for VASIMR, but I'm not certain that VASIMR is a perfect fit for polywell, at least not in the atmosphere. If I recall properly, VASIMR relies on the microwave heating of hydrogen. There is a conversion loss from converting electricity into microwave energy. I think heating air directly with an electron beam might be the most efficient way of applying the energy to the reaction mass, at least while you're in the atmosphere.