Rockets!

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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Zixinus
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Rockets!

Postby Zixinus » Fri Jul 06, 2007 8:10 am

What are the possibilities of using Polywell as a rocket? What can be done? Relativistic electron beams are mentioned. What of this?

MisterX
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Ion Engines

Postby MisterX » Sat Jul 07, 2007 10:47 pm

There are many designs for electric spacecraft engines. You can read about them here: http://en.wikipedia.org/wiki/Electric_propulsion

All of them are waiting for a suitable power source. Batteries won't do, and people don't like the idea of spaceships with powerful fission reactors flying about.

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Postby Zixinus » Sun Jul 08, 2007 11:32 am

I know. People interested are hoping that solar power would solve it. Of course they never heard of inverse-square law.

Could Polywell be used for fusion directly?

The list on Wikipedia is also quite small. I find these ones to be better:

http://www.projectrho.com/rocket/rocket3c2.html
http://www.daviddarling.info/encycloped ... cprop.html

I'm especially curious about this idea that Tom Ligon calls "Arcjet from hell", something about using relativistic electron beams. It's one of Dr.Bussard's ideas as well. Does anybody have a source?

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Postby MisterX » Sun Jul 08, 2007 2:12 pm

I'm betting some (if not all) of solar electric ion propulsion advocates have heard of the inverse square law.

http://nmp.nasa.gov/ds1/tech/sep.html

According to this page, using solar powered ion engines they could slowly build speed while in range of the sun. It made an overall velocity change of 4.3 kilometers per second, and it could have gone faster.

Could Polywell be used for fusion directly?


Hasn't the polywell already been used for fusion? What's this directly nonsense?

Zixinus
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Postby Zixinus » Sun Jul 08, 2007 9:37 pm

According to this page, using solar powered ion engines they could slowly build speed while in range of the sun. It made an overall velocity change of 4.3 kilometers per second, and it could have gone faster.


For small scale applications and around Mars, solar power is fine. However, for larger applications, like a manned mission some people are proposing, or for missions for Jovian planets, solar power is not enough, and RTGs or even fission reactors would be needed. RTGs have been used for quite a long time now.
Also, Nuclear power can support much bigger crafts then what would be practical with solar power.

EDIT: Oh, and another thing: the ion engines are partly chosen because they have fairly ow-electric energy consummation. There are several other ideas that would outperform ion engines, yet are not used due to power constraints.
Magnetoplasmadynamic engines for example can deliver stunningly high ISP and quite a good bit of thrust compared to other electric engines. There is also VASIMR, whith its amusing ability to switch gears, giving quite a bit of adaptability.

Hasn't the polywell already been used for fusion? What's this directly nonsense?


Sorry, bad wording.

I mean to use the fusion products directly as an exhaust. Making a reactor/engine that would somehow give thrust. Of course it would be powered by a seperate reactor. Or not? That's the part I haven't figured out.

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Postby JoeStrout » Sun Jul 08, 2007 11:16 pm

Yes, the fusion products can be used directly as reaction mass. I think this is what Dr. Bussard refers to as the "QED engine systems," referred to in the 2006 IAC paper, but I haven't yet followed the references.

However, the performance of this approach sounds impressive. It's tunable — you can exchange thrust for specific impulse (Isp), depending on how you do it. But he claims, "Their potential performance exceeded that of all other rational alternatives by a factor of the order of 1000x; that is the engine systems provided Isp 1000x higher at the same thrust/mass ratio, or thrust/mass ratios 1000x higher than others at the same Isp."

When Jim Benson was on The Space Show, he said that he'd spoken to Dr. Bussard about polywell fusion at length, and was quite excited about the applications for space travel: "We would be to the Moon in hours; we would be to Mars in days; we would be to all the other planets in the solar system in weeks."

Definitely a game-changing technology, if it can be made to work.
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Zixinus
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Postby Zixinus » Sun Jul 08, 2007 11:58 pm

Yes, that's the one. Can you supply more details? The Space Show's audio quality is very bad (either that, or the USA has horrible phone line service).

djolds1
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Re: Rockets!

Postby djolds1 » Fri Jul 13, 2007 8:12 am

Zixinus wrote:What are the possibilities of using Polywell as a rocket? What can be done? Relativistic electron beams are mentioned. What of this?


Its called "Quiet Electric Discharge"

Documents at Askmar:

http://tinyurl.com/273g2s
http://tinyurl.com/2huubw
http://tinyurl.com/yup9m3
Vae Victis

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Postby ANTIcarrot » Thu Aug 16, 2007 10:33 am

Conversation continued from here at site admin's request.

Polywell space technology applications powerpoint presentation:
http://isdc2.xisp.net/%7Ekmiller/isdc_a ... ile_id=422

JoeStrout wrote:No, not by orders of magnitude. According to Jim Benson: "to the Moon in hours, to Mars in days, anywhere in the solar system in weeks." Nothing else even comes close.


Yes, and concord was faster than a 747. Speed is not the most important thing in the world. It didn't make concord competitive.

Yes a Isp of 4k-5k would be very nice - but the only place I've been able to find that claim for polywell derived engines is in your statements here and elsewhere. Even the optimistic predictions for QED/DFP engines don't have high thrust and high Isp because there are usually fundamental problems with that.

Right, there's always a trade-off between thrust and Isp.


Plus other pesky things. Like cost. Safety. Engineering experience. Ease of maintenance. Reliability. The last three simply cannot be pulled out of a hat. They require lots and lots of time. All the maths and power point presentations and even ground tests in the world won't change that. It's the same reason why carbon fibre has taken 30 years to get into civil aircraft in significant quantities. They simply didn't have the experience to trust it.

Why do you say that? I'd expect a polywell rocket to get you into orbit very handily


Because despite what Mr Bussard may believe or claim, aneutronic means LOW radiation, not NO radiations. Even if the intended main reactions do not produce neutrons, the unintended side reactions inevitably do. And there are truly severe problems flying anything in our atmosphere that's 'only a little bit' radioactive. The large 'super plane' SSTO has also been considered before, and rejected, for logistical reasons that have nothing to do with Isp.

The 'arc jet from hell' high thrust engine is also vapourware. Even with practically unlimited energy on earth, I have found no evidence that anyone is claiming to produce a engine of this type and class.

As I said at the start, an Isp of 5000 would be nice, but that's the very limit of open-cycle Gas Core Nuclear Rocket technology, which is pretty much the best 'conventional' design we could build today. Beyond that designs require either unobtanium for either the fuel (like antimatter) or the reactor walls (to contain the heat). I would personally need a little more explanation and some reasonably hard numbers (engine weight for example) before I accepted this as a reasonable prospect.
Last edited by ANTIcarrot on Thu Aug 16, 2007 11:01 pm, edited 1 time in total.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

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Postby MSimon » Thu Aug 16, 2007 11:49 am

Yes, and concord was faster than a 747. Speed is not the most important thing in the world. It didn't make concord competitive.


A factor of an hour or two in a six hour trip is not significant.

Cutting a couple of years off a Mars trip is significant.

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Postby Zixinus » Thu Aug 16, 2007 2:06 pm

Even the optimistic predictions for QED/DFP engines don't have high thrust and high Isp because there are usually fundamental problems with that.


I recall that QED engines in particular were relatively high Isp and had enough thrust to get to LEO, and then some.

Yes a Isp of 4k-5k would be very nice - but the only place I've been able to find that claim for polywell derived engines is in your statements here and elsewhere.


Look up, there are papers regarding ideas of Polywell and space engines. They contain much more serious science then what the powerpoint presentation says.

Because despite what Mr Bussard may believe or claim, aneutronic means LOW radiation, not NO radiations.


And thus little required shielding. Perhaps it would not have to carry shadow shield mass measured in tens of tons, like most fission schemes.

The 'arc jet from hell' high thrust engine is also vapourware. Even with practically unlimited energy on earth, I have found no evidence that anyone is claiming to produce a engine of this type and class.


Of course not, it would require aneutronic, low-mass fusion technology. Aneutronic equals "wacked" among fusion researchers, and low-mass is impossible with most magnetic confinement schemes

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Polywell rocket engines

Postby JoeStrout » Thu Aug 16, 2007 7:37 pm

ANTIcarrot wrote:Yes, and concord was faster than a 747. Speed is not the most important thing in the world. It didn't make concord competitive.


The concord was slightly faster than a 747 — barely more than a factor of 2. A QED (i.e. polywell) engine would be dramatically faster than chemical rockets, by a factor of 100 to 1000. The two situations are not even remotely comparable.

And yes, speed isn't all that matters; thrust/weight ratio is important too, and there too the QED engine is expected to far outperform chemical rockets.

You can propose other advanced systems, like nuclear thermal, and they will come a bit closer, but I don't think anything else seriously explored performs nearly as well as QED.

ANTIcarrot wrote:Yes a Isp of 4k-5k would be very nice - but the only place I've been able to find that claim for polywell derived engines is in your statements here and elsewhere.

So, if you haven't even done cursory research into the topic, one wonders why you're speaking with such an air of authority. :) Start with the 2006 Valencia paper, and then follow the references. Of particular use are The QED Engine: Fusion-Electric Propulsion for Cis-Oort/Quasi-Interstellar (QIS) Flight, and The QED engine spectrum - Fusion-electric propulsion for air-breathing to interstellar flight.

And BTW, 4k-5k is modest. The QIS paper mentions Isp up to 70k sec for electric propulsion, or over a million seconds for a direct-heating engine.

ANTIcarrot wrote:Plus other pesky things. Like cost. Safety. Engineering experience. Ease of maintenance. Reliability. The last three simply cannot be pulled out of a hat. They require lots and lots of time.

Yes... so? I never claimed we'd be zipping to Mars tomorrow. But I do claim that polywell-based engines, if they work, will revolutionize spaceflight like no other technology (which would also have to go through a development period) can.

ANTIcarrot wrote:As I said at the start, an Isp of 5000 would be nice, but that's the very limit of open-cycle Gas Core Nuclear Rocket technology, which is pretty much the best 'conventional' design we could build today. Beyond that designs require either unobtanium for either the fuel (like antimatter) or the reactor walls (to contain the heat). I would personally need a little more explanation and some reasonably hard numbers (engine weight for example) before I accepted this as a reasonable prospect.

Since you seem to be in direct disagreement with Dr. Bussard, I encourage you to read his papers (the space applications were not covered by the embargo) and point out where he has gone wrong.
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Re: Polywell rocket engines

Postby ANTIcarrot » Fri Aug 17, 2007 1:54 am

JoeStrout wrote:The concord was slightly faster than a 747 — barely more than a factor of 2. A QED (i.e. polywell) engine would be dramatically faster than chemical rockets, by a factor of 100 to 1000. The two situations are not even remotely comparable.


I still stand by my point. There are other considerations. In this case the most important is that Mr Bussard's work has (the last time I checked) not been peer reviewed. Until then, let us not forget, however appealing these designs they remain theoretical. And real engineering beats theory nine times out of ten.

Everyone who has publically talked about arc-jets has considered them in low thrust applications. Even with 10MW sources available on the ground, no one has even considered, even in theory, high thrust designs. It would not of course be the first time Mr Bussard has thought of something no one else has. But it would also not be the first time that one of his apparently really good ideas turned out to be less workable in practice than he had initially believed.

You can propose other advanced systems, like nuclear thermal, and they will come a bit closer, but I don't think anything else seriously explored performs nearly as well as QED.


The Daedalus interstellar probe I believe had comparable performance. But then again so does pixie dust. We don't know how to build either, but we do know they'd work really well if we could build them. Paper designs always work better than real designs.

So, if you haven't even done cursory research into the topic, one wonders why you're speaking with such an air of authority. :)


I know a little about rocket design, and I've been following pollywell since the Google video came out. However I'll admit that I haven't been doing so over the last few months, since the first four or five reports were basically identical. It seems I have some reading ahead of me.

http://www.askmar.com/ConferenceNotes/2 ... 0Paper.pdf
NB: This paper was just updated as I was checking the references. Reference 20 is still missing, but the blurred graphics are now crisper and more colourful. I've seen the text before though. Sadly (from a space point of view) it remains an extended advert for the Polywell concept itself, and only makes a few arbitrary claims of space application at the start.

I woudl like to follow the references, but none of the (space) relevant ones seem to be available online for viewing or sale. Hence they do not convince me. :)

http://www.askmar.com/Fusion_files/The%20QED%20Engine.pdf

Okay, this is new; and I hope you'll understand when I say reading this might take a while. Still, that's a strange abstract. Why use [Isp] in the last sentence when Isp woudl have been much clearer? It looks very much like handwavium as it is. Or just the authors playing silly-buggers.

http://adsabs.harvard.edu/abs/1993jpmc.confQT...B
What a lovely and completely uninformative library index card. I've come across sites like this before but can't get the actual articles out of them for love nor money. Would you happen to know where I can find the library that goes with this index? Without that, I can't read or buy it, and hence I am not convinced by it.

And BTW, 4k-5k is modest. The QIS paper mentions Isp up to 70k sec for electric propulsion, or over a million seconds for a direct-heating engine.


The paper also seems to repeat the flawed claim that the reactor produces no neutrons.

The QED file talks about a 10GW polywell. This would (conservatively) produce around 10MW of neutrons during operation; equal to a 12.5MW D-T fusion engine; comparable to Europe's JET reactor.

An average person standing 50m away receives 7kJ of neutrons or 104 grays, or 1000 sieverts per second, which (the US military believes, so I'm told) would kill them instantly.
30 day limit: 5.8e-7 sieverts per second
Annual limit: 9.5e-8 sieverts per second
Both represent current limits for space workers.

I admit I've only skimmed through the article, but I cannot seem to find the section where they address this, or say they are deliberately not address the issue of shielding. This is a significant and practical issue for manned or unmanned payloads alike. It might be so obvious they thought it didn't need saying (Nuclear reactors make radiation you say? Who'd have thunked it?) but the lack of information leaves me skeptical, and wondering what else they've not mentioned.

NB: I will be reading it in detail over the next few days. The above comment is subject to revision.

Yes... so? I never claimed we'd be zipping to Mars tomorrow. But I do claim that polywell-based engines, if they work, will revolutionize spaceflight like no other technology (which would also have to go through a development period) can.


That we can both agree on.

Since you seem to be in direct disagreement with Dr. Bussard, I encourage you to read his papers (the space applications were not covered by the embargo) and point out where he has gone wrong.


1) Missing out on significant practical issues; without even saying he was leaving them as 'minor engineering problems for the student'.
2) Even with the best engineering, aircraft fall out of the sky on a regular basis. With a large fleet of polywell driven SSTOs you would disintegrating radioactive fusion cores falling over farmland, cities, oceans and playgrounds (Think of the children!).
3) Mr Bussard has been wrong before. The complete history of the ram-jet design makes for interesting reading.
4) He comits the cardinal sin of not including any pretty pictures of what his spaceship might look like.
5) I'm a nasty suspicious b*****d, and don't take anything at face value.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

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Postby MSimon » Fri Aug 17, 2007 2:02 pm

Anti- carrot,

What the heck does peer review have to do with Bussard's machine working?

Climate science is supposedly peer reviewed. It is looking shoddier by the day.

Peer review often falls into the consensus trap.

Peer reviewers don't exhaustively study a paper. They just give it the once over.

Let me quote:
real engineering beats theory nine times out of ten.


The neutron problem is not hard to solve. You use water as reaction mass. You use the reaction mass as shielding. It doesn't take much water to absorb most of the neutron energy. The water would act as a reflector as well.

There is no point in working out al the details until we know what a working reactor actually looks like and its performance (neutrons/Joule) etc.

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Postby Zixinus » Fri Aug 17, 2007 8:30 pm

1) Missing out on significant practical issues; without even saying he was leaving them as 'minor engineering problems for the student'.


An attitude contributable to the fact that the man definitely won't see the ground tests of the thing, let alone someone building a rocket out of it.
If it is possible, then it will be done, no matter how crazy it seems. That does not mean it will be easy, just that that its possible.

Besides, the man isn't one tasked with building the rockets. It isn't his main profession.
Perhaps he knows a surprising lot, as he was born in a period when such authors like Heinlein and Asimov were alive, and science in science-fiction was considered obvious, and authors actually designed their spaceships to some realistic extant.

2) Even with the best engineering, aircraft fall out of the sky on a regular basis. With a large fleet of polywell driven SSTOs you would disintegrating radioactive fusion cores falling over farmland, cities, oceans and playgrounds (Think of the children!).


You know what pisses me off? Emotional appeal. If you say "think of the children" then you are appealing to emotion, not reason.

So, fusion cores may burn up in million ton atmosphere.

We can design RTGs to survive re-entry and hard fall. We can design a fusion core to not release any radioactive material.

Furthermore, unlike a fission core, the radioactive material would be much, much smaller, less deadly and long-lived. We are talking about involounterly transmutated material, reactor components, that most likely will fairly quickly transmutate into stable materials.

3) Mr Bussard has been wrong before. The complete history of the ram-jet design makes for interesting reading.


And has been right before too. He studied nuclear engineering for the single purpose to figure out how to use the heat generated by a fission (that's fission, not fusion) core as a rocket engine. His Nuclear Thermal Rocket design, called KIWI design was out on paper before Sputnik was lunched, and efforts were made by NASA to do it. No NTR rocket was ever lunched, but for reasons unrelated to the technical feasibility of the idea.

Furthermore, the ramjet idea does work, although not with H-H fusion obviously. The basic idea was not discredited however, in fact, it has been much improved.

4) He comits the cardinal sin of not including any pretty pictures of what his spaceship might look like.


Dude, HE'S A frick NUCLEAR ENGINEER AND PHYSICIST, not an artist. The papers were on budget too, so I don't think they could have afforded an artist. Furthermore, they are trying to make a science paper afterall, not a article in "popular mechanics".

5) I'm a nasty suspicious b*****d, and don't take anything at face value.


It's good to be sceptical, I'm one too (not very active one though), but do make more research.

The paper also seems to repeat the flawed claim that the reactor produces no neutrons.


And for all practical purposes, there will be no neutrons.

Shielding is included for the rocket and reactor design, the paper specifically deals with the engine and its characteristics.


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