polywell reactor for booster rocket applications?

Discuss how polywell fusion works; share theoretical questions and answers.

Moderators: tonybarry, MSimon

ohiovr
Posts: 409
Joined: Mon Mar 02, 2009 6:36 pm
Contact:

polywell reactor for booster rocket applications?

Post by ohiovr »

Hello Polywell thinkers,

I'm curious about the power scalability of the polywell. I've read that the power output scales to the 7th power of its size or something to that effect. And that a gigawatt reactor could take up as little space as 10 meters across. I don't really understand the math to find this out on my own. Where do we start with? How does a detection of 9 neutrons with such and such size reactor mean that one a few times bigger can output the same energy as a single commercial fission reactor? Could I have and equation please :D

I've been following the focus fusion crowd too and their claims are not nearly as profound saying their hopes are for reactors the size of garages that produce 10 or 20 megawatts of electricity. That's fantastic if true even still. But gigawatts and beyond well that could be useful for rocketry. Maybe even electric booster rockets. But seriously just one or two gigawatts isn't even close to the power output of one saturn V F-1 booster engine which:

"Through 10 Fuel suction lines, 1350 gallons (about 4ton) of RP-1 are supplied to the F1 engine per 1 second in flight"

[url - http://apollomaniacs.web.infoseek.co.jp ... v_s1ce.htm

1350 gallons of kerosene per second! Each gallon of kerosene contains about 142,200,000 joules of energy and each second a single f-1 engine gobbles down 53.33 megawatt hours worth of chemical energy.

If Bussard was right, how big of a reactor would be needed to compete with that kind of energy output? Are electric booster rockets pure unadulterated fantasy that could never ever happen? - /url]

ohiovr
Posts: 409
Joined: Mon Mar 02, 2009 6:36 pm
Contact:

Post by ohiovr »

aahhh where did my message go????

Betruger
Posts: 2310
Joined: Tue May 06, 2008 11:54 am

Re: polywell reactor for booster rocket applications?

Post by Betruger »

That's funny, I tried to quote your first post and the text showed up in the text editor, but once posted it just disappears. Let's try it again without the quote tags.

<<

Hello Polywell thinkers,

I'm curious about the power scalability of the polywell. I've read that the power output scales to the 7th power of its size or something to that effect. And that a gigawatt reactor could take up as little space as 10 meters across. I don't really understand the math to find this out on my own. Where do we start with? How does a detection of 9 neutrons with such and such size reactor mean that one a few times bigger can output the same energy as a single commercial fission reactor? Could I have and equation please :D

I've been following the focus fusion crowd too and their claims are not nearly as profound saying their hopes are for reactors the size of garages that produce 10 or 20 megawatts of electricity. That's fantastic if true even still. But gigawatts and beyond well that could be useful for rocketry. Maybe even electric booster rockets. But seriously just one or two gigawatts isn't even close to the power output of one saturn V F-1 booster engine which:

"Through 10 Fuel suction lines, 1350 gallons (about 4ton) of RP-1 are supplied to the F1 engine per 1 second in flight"

http://apollomaniacs.web.infoseek.co.jp ... v_s1ce.htm

1350 gallons of kerosene per second! Each gallon of kerosene contains about 142,200,000 joules of energy and each second a single f-1 engine gobbles down 53.33 megawatt hours worth of chemical energy.

If Bussard was right, how big of a reactor would be needed to compete with that kind of energy output? Are electric booster rockets pure unadulterated fantasy that could never ever happen?


>>

edit - You had a misplaced URL tag, that's the only oddity I found.

MSimon
Posts: 14332
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

ohiovr,

Your url tags were messing things up - I took out one of the brackets on each opening and closing tag and added an "-" after each tag. Of course I could have just deleted the tag but I wanted you to see what you did wrong.
Engineering is the art of making what you want from what you can get at a profit.

MSimon
Posts: 14332
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

I don't think you have to go the full Saturn I route.

I did some BOE and with LH2 reaction mass and a maglev slingshot I think a 6 GW LH2 cooled Pollywell could get you SSTO. I think I figured the Polywell and supporting eqpt at 50 tons and the payload at 100 tons and about 700 tons of reaction mass heated to Space Shuttle ME exhaust temps.

I could be off though. It has been over a year since I did the calcs and the spread sheet is not immediately handy. But it does give you a sort of feel for what is possible.
Engineering is the art of making what you want from what you can get at a profit.

ohiovr
Posts: 409
Joined: Mon Mar 02, 2009 6:36 pm
Contact:

Post by ohiovr »

Thanks for the replies and the heads up on my url tag. BTW I use Open Office.org for my spread sheets. Its free and does everything I need it to do (which I don't have a big enough imagination to find something it cannot do or that I care that it lacks).

But doesn't the space shuttle main engines have a thrust to weight ratio (shuttle and full tank included) less than 1?

I don't see any advantages of an electrically heated propellant if exhaust velocities aren't much better than H2 LOX. Nerva had specific impulses in the 900s which really isn't all that incredible. Thousands would be nice :)

I guess my dream ship would:

1. Be reusable over and over without a total tear down refit like the shuttle on each launch.
2. Allow powered landings without wings
3. Be able to reach the outer planets in human time scales
4. Be large enough for centrifugal artificial gravity
5. Have significant mass fractions for payload
6. Be a Single stage.

I know of a technology that can do this but there's a few problems with it. Firstly it kills people and destroys satellites. And treaties forbid it. And the ride is a little bumpy. That it kills people can be solved but requires some technology that is not quite there yet (which puts it in the same boat as Polywell). The satellite problem, that alone would ground it.. Thinking of the billions invested in the sky we have. I doubt most satellites are hardened for thermonuclear detonations even in the kiloton range. Yes that is possible and without any fission material.

So basically I want a revolutionary propulsion system that doesn't require a dues ex machina to make it political possibility.

I guess I want a miracle that can open the skies to all mankind. Some kind of answer to the unholy grail of propulsion: project orion.

MSimon
Posts: 14332
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

But doesn't the space shuttle main engines have a thrust to weight ratio (shuttle and full tank included) less than 1?
Not having to carry all that LOX (got a bagel and some onions?) is a big help.
Engineering is the art of making what you want from what you can get at a profit.

TallDave
Posts: 3114
Joined: Wed Jul 25, 2007 7:12 pm
Contact:

Post by TallDave »

I remember seeing some rough calcs. They seemed to indicate costs could be comparable to a space elevator.

It's a lot of power density and very high specific impulse. It should be far, far more efficient at getting out of a gravity well than chemical rockets.

Skipjack
Posts: 6104
Joined: Sun Sep 28, 2008 2:29 pm

Post by Skipjack »

I saw a nice study for a Nuclear Lightbulb (fission)reactor (NERVA derivate) based SSTO vehicle a while ago. The thing would be gigantic, but it would be very reusable also.
If you managed to do the same with a Polywell instead, I guess you would get rid of the biggest disadvantages and design problems that thing had.
This is one of the reasons why I am on this forum. I think that even if a polywell failed as a commercial powerplant, it would still be very usable for space applications.

Nik
Posts: 181
Joined: Thu Mar 12, 2009 8:14 pm
Location: UK

Nuclear Bomber studies...

Post by Nik »

Even if you're not going for runway take-off/landing, the US work on 'nuclear bombers' might apply. eg...
http://en.wikipedia.org/wiki/Convair_X-6

IIRC, they considered both direct & indirect cycles, former being a flow-through 'light bulb', latter using a heat-transfer liquid eg sodium.

A lot of the mass distribution, plumbing and shielding may mirror polywell installation...

Um, what would you use as reaction mass ?? I suppose the simplest may be water, giving a super-heated steam rocket...

FWIW, I suspect Alan Bond's Sabre engine would have the edge trans-atmospheric, but there's no contest beyond low orbit. A polywell reactor looks like the fast-track to Moon, Mars and beyond...

Anyone looked at the Nerva nuclear engine series recently ?? IIRC, they reached the stage of being ground-run...

djolds1
Posts: 1296
Joined: Fri Jul 13, 2007 8:03 am

Post by djolds1 »

Skipjack wrote:I saw a nice study for a Nuclear Lightbulb (fission)reactor (NERVA derivate) based SSTO vehicle a while ago. The thing would be gigantic, but it would be very reusable also.
The "Liberty Ship?"

IIRC the T/W for an NLB is not promising for Earth to orbit. Nice Isp, questionable thrust.

Unlike NERVA, the DUMBO design solid core nuclear rocket can get you SSTO. T/W >1. Not as dirty as Orion, but not entirely "clean" either.
Skipjack wrote:If you managed to do the same with a Polywell instead, I guess you would get rid of the biggest disadvantages and design problems that thing had.
This is one of the reasons why I am on this forum. I think that even if a polywell failed as a commercial powerplant, it would still be very usable for space applications.
No. For space applications, Polywell is basically a huge battery. Except for DFP its all indirect - electricity heats propellant. If polywell doesn't give you net power to use, its a waste of mass and you might as well use a fission reactor.
Nik wrote:FWIW, I suspect Alan Bond's Sabre engine would have the edge trans-atmospheric, but there's no contest beyond low orbit. A polywell reactor looks like the fast-track to Moon, Mars and beyond...
LACE engines like SABRE max at approx 700 seconds Isp. Assuming polywell works the ARC cycle (for SSTO/Moon/Mars) rocket maxes at approx 1500 seconds Isp.

Edit - Error - ARC maxes at ~2500s Isp.
Nik wrote:Anyone looked at the Nerva nuclear engine series recently ?? IIRC, they reached the stage of being ground-run...
There were a few studies on a variant called "MITEE" done a couple of years ago for the now defunct NASA Institute of Advanced Concepts.

Duane
Last edited by djolds1 on Tue Mar 17, 2009 12:51 pm, edited 1 time in total.
Vae Victis

MSimon
Posts: 14332
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

I like LH2 for reaction mass 3X the ISP vs water for the same operating temp. The cooling will also be very helpful.
Engineering is the art of making what you want from what you can get at a profit.

Skipjack
Posts: 6104
Joined: Sun Sep 28, 2008 2:29 pm

Post by Skipjack »

Yeah, I think it was the liberty ship. I can not quite remember anymore.
Of course the polywell would have to generate net power. Read what I said! I said "even if a polywell failed as a commercial powerplant".
That meant "even it does not make commercial sense" and that could have many reasons. E.g. it could be to expensive to maintain (frequent material replacements, or something like that), combined with not THAT high net power that it can compete with coal (remember compete with coal price wise, yes?). All that could still make it a good heat source for a NERVA type engine.

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Post by 93143 »

If Polywell is that high-maintenance you'd be better off with Sea Dragon for cheap orbital access and nuclear electric for deep space. Shuttle is the classic example of how not to do this sort of thing. It needs to be reusable and reliable, and there's too much of a feasibility gap between 100 MW and 6000 MW for a spacelaunch application to be a better idea than a commercial power plant. IMO...

Skipjack
Posts: 6104
Joined: Sun Sep 28, 2008 2:29 pm

Post by Skipjack »

Uhm, nuclear electricity is also not price competitive with coal... at least not yet. It is also much more maintenance intensive than coal. It is also much more complicated than coal. So I stand by what I said. A polywell, even if not price competitive with coal (and therefore not interesting as a commercial powerplant), could still make lots of sense for space applications.

Post Reply