I am a big fan of sci-fi, and most sci-fi shows/movies have their own version of the "Soda-can-sized Nuclear Reactor", and I have tried googling for more information on the fiesability of such a device, but I cant find anything... what do you guys think?

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Windows 98 is like that drunk uncle that thinks he knows everything and always tries to convince you he was a CIA operative, and when you argue, he gets violent and then passes out.

First we need a mission that can use nuclear power in order to develop the technology..

oh. wait. we did. It was called JIMO. Well, then I modify my argument:

Fisrt we need to stop cancelling missions that help develop new technology. Or, as NASA puts is so eloquently, "deferring the mission"...

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~ cogito cogito ergo cogito sum ~

Nothing in life is good nor bad; thinking makes it so.

Weren't the Voyager and Pioneer probes powered by nuclear reactors?

NASA's Project Prometheus is currently working on ways to use nuclear technology for space exploration.

RTG, they're called: radioisotope thermal generators. Prometheus is developing, to put it simply, a second generation of these apparati.

What I was sarcastically referring to was how JIMO has been deferred. It is the mission that could have really taken advantage of this technology. With it being deferred, so too will be the progress on Prometheus.

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~ cogito cogito ergo cogito sum ~

Nothing in life is good nor bad; thinking makes it so.

The 'Cassini' prob is and is not. does, but doesent. It has a cell of 'Hot' mater ie;radium or whatever, Nuclear fuel. It does not have a reactor. It generates energy by useing the heat to produce electrical charge. It will last about 25 years, or untill the fuel cools down. easy, safe. and the Cassini prob is not the first to use this form of energy transfer.
As for your question re small reactors, yes the reactor of some smaller dimensions is possible. DO NOT try this at home. If you were to power your car., and have an accident. The ambalance crew wont come near you......

lol, I don't think I could even get my hands on sufficient grade material to make one anyway but yah, I did some reading on RTGs and they seem pretty safe, (atleast compared to fission reactors). so thanks everyone, that answers my question.

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Windows 98 is like that drunk uncle that thinks he knows everything and always tries to convince you he was a CIA operative, and when you argue, he gets violent and then passes out.

The smallest currently available nuclear reactors are Naval reactors used to power submarines. The plan for Promethius and JIMO was to take that technology and shrink it down even farther, but it would still be bigger than a soda can, probably bigger than your car.

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...and we'll be saying a big hello to all intelligent life forms everywhere; and to everyone else out there, the secret is to bang the rocks together, guys...

The smallest reactors are currently on subs, the Los Angeles class Fast attack subs. Here's a bit of info I've collected for anyone who's interested (sorry for the lack of detail, the US Navy is surprisingly sparce on info when it comes to their nuclear reactors ):

It's called the S6G nuclear reactor, if you want to further research it.

The reactors produce 26,100 kw of power. In the sub it uses turbines & gearing to power a shaft/propellor. In space, the energy would most likely be used to power an ion engine (no moving parts)

The reactor fits in a space about 10m long, 10m wide, and 12m tall, in a space behind the crew quarters and infront of the machinery.
See this cutaway for a visualization:
http://americanhistory.si.edu/subs/const/a...ges/cutaway.jpg

...and this for a comparison with people:
http://www.teachersparadise.com/ency/en/me..._arp_750pix.jpg

For the life of me I can't find wieghts, but you can see just by the dimensions, this wouldn't be practical to get into space, despite the possiblities it creates with such a high output.

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~ cogito cogito ergo cogito sum ~

Nothing in life is good nor bad; thinking makes it so.

All of the obove facts dont change the ever improving abilaty of science to overcome the problems of size.
There is no reason why a much smaller reactor couldent be built. It probebly has been. They arent going to tell anyone are they.
Keeping it cool and safe are the real objectives. Useing plazma fields to contain a fusion core reactors heat seems a little beond us today. Given time and techno., we will crack it.

For sure, astromark, by no means am I saying it won't be done. Just trying to give alittle information to anyone who is interested in the topic.

Of course, given the time, we'll learn to make anything better (in this case smaller and safer). If I thought reactors could only ever be as small as they are now, my world might look a little more like this:

The Home Computer

laughing out loud

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~ cogito cogito ergo cogito sum ~

Nothing in life is good nor bad; thinking makes it so.

Haha, nice pic aeolus... that steering-wheel thing really gave me a good laugh.

But yah, I think that within the next 15-25 years, we will start to see nuclear reactors in space, though I think reactors considerably smaller do exist, it is probably to great of a risk to put them on subs, risking the enemy getting their hands on one.

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Windows 98 is like that drunk uncle that thinks he knows everything and always tries to convince you he was a CIA operative, and when you argue, he gets violent and then passes out.

This is not the smallest reactor out there. The smallest I know of has a core about the size of a trash can and fits into a cylinder about 12ft in diameter and 10 ft feet long (for the whole primary plant, there is about 35 ft at 12 ft diameter used for support equipment). The reactor is used on board the submarine NR-1, google it if you want to know what it's for. I believe the core is rated around 3MW.

As for the LA class submarines, I don't know where you got 26100KW for their rating, but the actual rating is from 150-165MW, depending on which model you're looking at. Also, when you talk about the machinery it sits forward of, that machinery is just as important as the reactor itself, that's where all the turbines and support equipment is, without that stuff you have a radioactive chunk of metal in a can. and the space it occupies is 11m in diameter and about 12m long, though there is a lot of empty space in there (a lot).

Oh, and if you were curious, the reactor core of an S6G plant (just the vessel that holds the fuel and the fuel itself) weighs about 110 +/-3 tons. After you add in the rest of its systems you are looking at at least 1000tons of machinery. Not to mention at least 20000 gallons of water to keep the reactor full of water and make steam with.

Any other nuclear questions, email me, I operate LA class reactors for a living.

BTW, I highly doubt you will see a reactor in space in the next 50 years. The NRC (nuclear regulatory commission) would have a heart attack if anyone tried.

In a more proactive age, we were testing nuclear rocket engines. If we want to go to mars, we'll have to go back to looking at them to reduce propellant mass and power energy intensive life support.

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There have already been numerous nuclear reactors in space. While the U.S. has flown only one space nuclear reactor (Snap-10a in 1965), the former Soviet Union launched over 30.

A more recent U.S. design called SP-100 would produce about 100 kilowatts electric power and is about the size of a small trash can.

Space nuclear reactors are probably the smallest ones, much smaller than those powering submarines.

Overview: http://www.world-nuclear.org/info/inf82.html

Civilian Uses of Nuclear Reactors in Space (1.5MB pdf): http://www.princeton.edu/~globsec/pu...1_1-2Rosen.pdf

Remember Mr. Fusion. Just throw in the banana peels and other trash.

I've seen a nuclear battery the size of a buttom. The nuclear material excited a phospher coating which powered the photovoltaic.

Wouldn't want it as a watch battery (though that's about the size it was) as it was still radioactive...

"Hey, stranger! Say, that's quite a tan you have on your wrist..."

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

True...

Then again, space craft don't need enough power to propel an 18,750 ton (37.5 Million lb) craft under the water at velocities up to, um, er... I'll have to stop, there, I'm afraid.

And with enough power left over to desalinate drinking and showering water for a 155-man crew, cook their food, scrub their air, power all those computers, etc... Essentially enough leftover power for a small town.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

The S6G is rated at about 130 megawatts thermal power. The electric output is probably around 26,100 kilowatts (equivalent to 26 megawatts or 35,000 horsepower).

Space-based nuclear reactors are much smaller and lighter, and produce much less power. The U.S. space-based reactor design SP-100 was targeted at 100 kilowatts (electrical) output, but the design was scalable from 10s of kilowatts to about 1 megawatt (electrical).

This paper described a version of the SP-100 producing 300 kilowatts (electrical), and weighing 8,300 kg (18,300 lbs): (5MB .pdf): http://hdl.handle.net/2060/19870016405

The OP asked what's the lower limit (size, mass, output) of a nuclear fission reactor. Unknown but the earlier U.S. Snap-10A reactor and Soviet space-based reactors were small enough to be orbited by then-existing rockets.

http://www.eoearth.org/article/Nucle...tors_for_space

The reason the JIMO was deferred was that the cost estimate for the mission went over US$30 billion, with no reason to think it was going to get cheaper. As far as I know the compact reactor was the expensive part, and it was only going to generate 25-100KWatts.

I have a lot of hope for compact reactors in the future for space probes, but we don't quite have the technology down yet.

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Forming opinions as we speak

For those of you who need (like me) to wrap their heads around a more intuitive frame of reference, 130 MW is 174,333 HP, and 26.1 MW is 35,001 HP.

By comparison, the Nimitz class aircraft carriers use to A4W nuclear reactors and the steam generators are capable of providing 140,000 shaft horsepower.

Each.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

I used to do that, too. Not LA class, though. Now I work on bigger reactors.

Cool. I used to work with nukes, though not the ones that release their energy gradually...

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

Wikipedia has a great article on atomic batteries. Check it out.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

You mean like those things they kept in the sixteen large tubes I walked past on my way to work?

Yeah, except mine (I use that term loosely, as I really didn't own them - the taxpayers did) were kept on a Common Strategic Rotary Launcher (CSRL).

Without putting too fine a point on it, I was a member of the first crew to test the AGM-86 on the CSRL.

There.

Throw that in the fire and see what happens.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

The problem with a soda can size nuclear reactor is that if it breaks you've got a serious problem! Even if you could make them as safe as normal reactors, I assume because of their size they would be incredibly useful across nearly every industry and work their way into a lot of consumer appliances. So the sheer number of them out there would make even today's failure rate unacceptable.

I remember seeing a 1950s design for a nuclear powered car once , I almost wish they had built a prototype before people realized how dangerous reactors could be.

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"Bessie Braddock to Churchill "Winston, your drunk!"
Churchill: "Bessie, you're ugly, and tomorrow morning I shall be sober""
the solar system

Not really. You go in there, pick up the peices, put them in a lead container and ship them back to the manufacturer. Maybe put a big yellow sticker on it - "no not flush contents down drain, do not eat, do not sleep next to when unsheilded, may cause cancer in the State of California".

Same as when any other industrial hardware breaks.

The above was partially tongue-in-cheek, but if it's a battery using passive alpha-beta decay, it probably wouldn't even be dangerous for brief periods of unsheilded exposure. I've heard of nuclear pacemaker batteries being used before - the risks of continual surgery to replace the batteries outweigh any possible risks of radiation damage by orders of magnitude, so they are used inside human bodies.

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