I had a crazy idea...

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weed_eater_guy

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I just joined a Design-Build-Fly team at my college that competes radio controled craft (built from scratch) against other colleges around the nation. I had an idea though:

In order to test the concept that I've had, a NERVA-like reactor powering a space-plane, why not build a miniturized version? A small nuke reactor built into a carbon-fiber and aluminum plane running on a tank of LH2. It'd be expensive and need very delicate workmanship (a nuke reactor!), but if it worked, the university would have one hell of a product on their hands: a working model of a Nuclear Thermal Rocket space plane.

I have no idea of a nuke reactor can be built of such a small size and still maintain it's efficiency, let alone if test flights would have to be conducted in the middle of a nuclear test site or not, due to a lack of shielding that can be fit in the plane. Just wondering what yall think.
 
weed_eater_guy said:
I just joined a Design-Build-Fly team at my college that competes radio controled craft (built from scratch) against other colleges around the nation. I had an idea though:

In order to test the concept that I've had, a NERVA-like reactor powering a space-plane, why not build a miniturized version? A small nuke reactor built into a carbon-fiber and aluminum plane running on a tank of LH2. It'd be expensive and need very delicate workmanship (a nuke reactor!), but if it worked, the university would have one hell of a product on their hands: a working model of a Nuclear Thermal Rocket space plane.

I have no idea of a nuke reactor can be built of such a small size and still maintain it's efficiency, let alone if test flights would have to be conducted in the middle of a nuclear test site or not, due to a lack of shielding that can be fit in the plane. Just wondering what yall think.
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I have to say it's a sweet idea, but you've no real grasp of the things you're up against. :) One is a severe power-to-weight ratio problem. Another is the material - it's illegal for you to attempt to even get it. And if you did, you'd likely die of radiation poisoning in a fairly short time. (Very ugly time, too - before it's over you'd be wishing someone would shoot you!)
 
What if it crashed in a city? It wouldn't be very cost effective either. Not a good idea.
 
okay, if the ship were full-sized, I'd think the reactor shielding would include a thick platting of steel or titanium or something to keep the reactor from spilling everywhere.

Light, i think you're right, the power to weight ratio for a small plane would probably not work, economy of scale, you need proportionately more material per fuel or engine component weight as a vehicle becomes smaller. A reactor that small would still need sufficient metal to contain the hot blast of hydrogen that would fire out of it. But assuming the components could be made small enough, and that it could be built safely in a nuclear test site somewhere, and that if it was radioactive we could get ahold of the proper gear to handle it, then it might just be possible.

as for the material, this college has a nuclear reactor running in it for educational purposes, so I'm told, I've never actually seen it, but if the college could do that, they could get approval for a micro-sized reactor.
 
Hang on, is this for in atmosphere or in space use? If in atmosphere, the anecdotal story is that both the USSR and the USA looked at nuclear planes in the cold war. The USA couldnt get past the need for shielding. Then after the cold war they chatted to the russians, who said "Shielding? What shielding?"

Then theres the simple problem of the propellant. You need to either accelerate somethign very light very fast, like an ion engine, or something very heavy not so fast. So ideally you use heavy metals. Something that would not be popular on earth and would be expensive even in space.
 
NERVA engines are good for space because they have a very high specific impulse (allowing you to accelerate a lot with a small amount of fuel), but they have very poor thrust/mass ratios. The bad thrust/mass ratio doesn't matter in space where there's no drag and you can afford to wait a long time for a small acceleration to accumulate into a large velocity change. For an aircraft, however, I imagine that you would need a much better thrust/mass ratio.
 
I was assuming that a small RC rocket-plane would be adequate only for atmospheric test flights, both in the capabilities such a small craft would have and the fact that the FAA or Space Command (whoever authorizes spaceflights) would laugh their asses off at the proposal.

If the plane is RC, it doesn't nessecarily have to have very extensive shielding, as long as the reactor in the plane was operated from a good distance away (i'm assuming this operation would be conducted in the desert somewhere, like a nuke test site or something), and/or those involved were wearing radiation suits. If it could support the weight of it's own shielding, that'd be great, but if not, there's no human pilot that's going to get lit up like a christmas tree. I think that was the problem with NERVA rockets, I think they focused on shielding for their engines, which of those sizes would need a hell of alot, and would probably still be radioactive somewhat.

As for fuel, I was thinking, like NERVA, that LH2 could be used. This would, yes, mean that a refrigerant unit would also have to be packed in this rocketplane. Too much weight? I have no idea, i still can't find what the world's smallest nuclear reactor size has been, and if it's anywhere near my dream-size of a coke can or a little bit larger.
 
Speaking of totally crazy ideas, I had an idea for a fuck-powered generator.
When people fuck, they produce body heat, right? Heat + Water = Steam. Steam is fed through tube to spin turbine, generating electric power.
The only stumbling block would be the amount of fuckers and fuckees to generate that amount of heat. :p
 
The problem with reducing the size of a reactor is that the smaller the chunk of uranium the less heat it will produce.

Ideally you would what a air breathing system, much like a jet but instead of introducing fuel to heat and expand the air you would use the heat from the uranium. You would want to heat the air by about 1000c so the core would have to be much hotter then that. It would be very difficult to get that much heat out of a few grams of pure uranium. You might be better of using plutonium, but you will never get permission to get your hands (opps.. robot manipulators) onto that.

Nether could you use conventional control rods , as this would reduce the density of the core reducing heat output. You could control the engine output with a control rod made of uranium. Inserting the rod would increase the output and retracting it would reduce output.

Heat transfer would also be a major problem. Existing nuclear rockets pass fuel through the reactor core. This is not an option for a small reactor because you are trying to keep the core density at its highest. The easiest would be to use a coolant to transfer energy from the core to the incoming air.

Some math now. 1gramsof Uranium has an energy content of around 80MWatts. With natural decay this energy would be reduced to about 1KW in around 20billion years, outputting an average of around 0.00004Watts
We would want at least 100watts to power our craft. With a efficiency of say 20% the core would have to provide 500watts. We will say that your craft cant fly below 50watt output.
So in a perfect universe your craft should be able to fly non stop for around 800 years on one gram of Uranium.
You would of course have to increase the reaction of the uranium 12.5million times.

So the question is how much energy will one gram of pure uranium output?. I don’t know but my semi educated guess is that it will be below 500Watts.


By the way.. I love RC aircraft. I have just finished my first home built RC aircraft. Its a twin electric with control attained by turning of the left engine to turn left when in climb and turning on the left engine to turn right in glide mode and visa versa. As yet it has not had a powered flight. A few indoor glides proved it could fly and when the right weather condition come round I’m out to the local park for its first test run( and most likely its last).
 
Nice to know the plane's reactor would not need to be refueled in my lifetime :). I agree, heat transfer would be a hell of a problem, which is why the reactor wouldn't heat incoming air directly, or with a coolant system (doesn't seem efficient, lots of places it can break appart, complexity is something I avoid if I can). I was thinking it would use LH2, like a coolant system, only that LH2 would not need to transfer it's heat to ambient air with radiators and all. It's the thrust itself, all it's heat is used to expand the gas very fast and thus it is a rocket. But an added bonus would come if it were an airbreathing system, then the sizzling-hot H2 could be blasted into a channel of flowing ambient air, in which it'd burn like a traditional chemical rocket. This way, you've got the energy of the reactor, plus the energy of traditional H2-O2 burning. I'd assume many computer simulations and test engines would have to be built to perfectly shape the air channel to make best use of the H2 blast angles, combustion rates, shock waves, moving components to shape the air channel according to speed, all the stuff that... yeah... this sounds more like a project for JPL than University of Illinois, lol

btw... RC aircraft are awesome, never had the chance to fly them (damn German regulations), but I'm on the DesignBuildFly team here, and I really want to have some fun with this. A shame that your plane has not been freed yet, best of luck to you!
 
guthrie said:
Hang on, is this for in atmosphere or in space use? If in atmosphere, the anecdotal story is that both the USSR and the USA looked at nuclear planes in the cold war. The USA couldnt get past the need for shielding. Then after the cold war they chatted to the russians, who said "Shielding? What shielding?"
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Thats not the story at all, the US and the USSR were in a race to build planes powered by nuclear reactors. the Russians built planes without sheilding and filmed videos with the planes in the air, and let the videos get captured by US intelligence, who thought the USSR had built manufacturable, safe planes powered by nuclear energy. The US admitted the USSR having technological superiority over them (was a public release on TV). So an extra 30 billion were dumped into the us research program to get the US back into the race, only to find out 5 years later that the Russians dumped their program and bluffed to have working nuclear powered planes which were safe to fly. Neither the US nor the USSR managed to build a plane that could take off due to the imense amounts of sheilding needed to absorb the radioactivity. I think the last of the programs were dumped by 1971.

And dont bullshit again, anyone who does physics knows that radioactivity needs to be absorbed. Russian physicists would certainly know that.
 
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what if a full-scale nuclear-thermal-rocket spaceplane were launched and landed in a "safe" location, like antarctica, or a designated plot of desert somewhere? that way you'd only have to put shielding between the engine and the cockpit and/or cargohold, rather than wrapping the whole engine in shielding.
 
They did that in the 1959-71 era or nuclear powered flight, the amount of sheilding needed to keep the pilots safe prohibited the plane from functioning effectively.

The radiation emerging from the engine would creat radioactive isotopes in the air it passes through. Although, im not sure, your welcome to try landing it in antarctica if you think its benificial and worth the hastle ;) .

Besides, the US airforce has already made a robotic plane powered by a different kind of nuclear reactor, one that dosnt polute as much and on which is sufficiently light.
 
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I'm not a nuclear engineer, but it seems to me that there should be size limit for mini reactors. You know that chain reaction/critical mass thing. There should be plenty of uranium for reaction to proceed.
 
The AFRL has new ideas to solve that problem. Instead of a conventional fission reactor, it is working on a type of power generator called a "quantum nucleonic reactor". This obtains energy by using X-rays to encourage particles in the nuclei of radioactive hafnium-178 to jump down several energy levels, creating energy in the form of gamma rays. A nuclear UAV would generate thrust by using the energy of these gamma rays to produce a jet of heated air.
 
so far quantum nucleonic reactor still needs alot of work. for example, the synchrotron in Hyogo Japan, while being run by the University of Texas at Dallas, was able to make the hafnium release energy from the nuclear isomer configuration, but a similar test conducted by Argonne Consortium showed completely negative results, and refutes the very ability of the University of Texas to make Hafnium do what it needs to do to work in this reactor. Not only that, but I'm not sure how one goes about acquiring large ammounts of Hafnium, and not just any hafnium, but hafnium-178, to be made into fuel elements for the world's future air and spacecraft!

I hope to god I'm wrong and that this works. It'd be a beautiful thing...
 
Odin'Izm said:
And dont bullshit again, anyone who does physics knows that radioactivity needs to be absorbed. Russian physicists would certainly know that.
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Pardon? I was refering to the need for shielding to stop the pilot glowing in the dark.
And do you have any back up links for your entirely plausible tale?
 
back up links for a knowledge of nuclear radiation? I didn't know there was such a thing anymore, if that's what you mean.
 
I seem to recall that there are plenty of websites talking about nuclear physics, some of them are even correct. I dont understand what Odin'Izm is talking about radiation needing to be absorbed. Sure, after a while (a year or two probably) there would likely be embrittlement of the plane's structure, but if you only want to make an unmanned craft you can get away with far less shielding than if you want a crew on board as well.
 
guthrie said:
Pardon? I was refering to the need for shielding to stop the pilot glowing in the dark.
And do you have any back up links for your entirely plausible tale?
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I called you a bullshitter because of your phrase "sheilding, what sheilding?" which you directed it towards soviet aeronautics of the 1960's era.

Aha... sheilding to stop the pilot glowing in the dark... right...

Quote from "Aircraft Nuclear Propulsion program." Metal Progress, 76 (December, 1959) 93 find an E-book if you want further proof.

It should be noted that the United States was not the only country working on atomic aircraft in the early years. The Soviet Union had a few projects of their own. One aircraft, a flying boat, prototyped in 1950 would have a flying weight of 1,000 tons had it not been rejected due to price. It was planned to equip the giant airplane with four atomic turbo-prop engines. The wing span was more than 130 meters, and the total power of the engines exceeded one-half million horsepower. This airplane was supposed to carry 1,000 passengers and up to 90 tons of load at a speed of 900 kilometers per hour.

It was planned to surround the reactor with five layers of shielding. The layers were supposed to be as follows: first layer - beryllium oxide reflector; second layer - liquid sodium for removing heat from the walls; third layer - cadmium, for absorbing slow neutrons; forth layer - paraffin wax, for slowing down fast neutrons; fifth layer - a steel shell, for absorbing slow neutrons and gamma-rays. Such multilayer 'armor' permits decreasing the weight and size of the necessary shielding. The coolant was liquid lead.
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As far as my story goes, it was named the "nuclear bomber gap" it followed the "bomber gap" of june 1955. You might find it in a history encyclopedia, but as the program was quite secret it might be easier to look for it in a military history encyclopedia. There was also a Discovery program about it I beleive.
There is a nice exerpt in the "Hutchinson encyclopedia of world history."
 
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