Aside from the obvious political issue that the anti-nuclear folks would raise holy hell, I’m wondering if there are any technical issues with using a US Navy nuclear reactor in space. I was reading about the VASIMR engine and it’s requirements for large amounts of power, and they were talking about how we could get that sort of energy production, and they mentioned nuclear but said something like we’d need to do a lot more testing of this new energy source before we could entertain a nuclear reactor in space. I was thinking, however, that the US Navy has been doing nuclear reactors for decades…it’s not new at all. When I was in the Navy I wasn’t a nuclear tech, so I figured I’d ask here…what are or would be the technical issues (leaving aside the fear and resistance of the anti-nuclear crew)? Could we basically take a US Navy nuclear reactor from, say, an attack boat or boomer or other capital ship, crate it up and use that to power our electrical propulsion rocket engines?
You’d need to add a big ass generator to the reactor to produce electricity. As was pointed out to me in another thread that the nuclear reactors in the subs power the propellers directly through a steam turbine, so you’d need that generator as well. I believe the Navy has some reactors used mainly for electrical generation so the generators should be available. The reactors designed for submarines should be as compact as possible already making them very suitable for launch into space.
And cooling would be a huge issue.
The two biggest issues I see are cooling it & what happens if/when the launch vehicle goes BOOM.
I have no idea what a nuclear reactor weights, but it might be considerable, depending on how much it can be shipped up in pieces and assembled in space.
Why? My understanding is that the natural circulation systems in some of the newer systems are used to reduce noise, but that wouldn’t be an issue in this. I assume you think it’s got something to do with the zero G environment, but I’m not seeing it as a major issue. Can you explain?
You’d almost certainly send up the fuel and reactor separately, so, again, not seeing a major issue here…this is more an issue on the fear side than on the technical side. Do you think the fuel/reactor are going to explode like a nuclear weapon or something?
Can you guys go into some details about the cooling issue? I know the Navy uses various cooling methods in their reactors, and an see how some of them might have issues, but my guess is those wouldn’t be chosen. Maybe I’m missing something here, however…as I said, I wasn’t a nuke guy in my time in the Navy.
Yeah, cooling is by far the largest issue. Space is “cold” in that it has a low absolute temperature, but since there’s not really much, y’know, stuff up there heat doesn’t dissipate particularly well because there’s nothing to impart your heat onto. Basically, it’s cold but it doesn’t cool things down the way Antarctica or an ice bath might.
The way current nuclear power works, AFAIK, is it’s a glorified steam plant. It runs really hot and just boils water and uses the steam to move a turbine, then condenses that steam back into water and sends it off for cooling, cycling in new cool water. The two primary issues in space would be:
- Getting enough water up there (let alone the other components)
- Cooling the hot water
Cooling is legitimately a huge issue, like, we have trouble in space preventing tiny computer chips less powerful than your phone from overheating, cooling tons of water to keep a nuclear reaction from running away would be a monumental task. In space, you can’t take air cooling for granted, the only way anything dissipates heat is relying on radiation or manual hit sinks, neither of which are likely to be sufficient.
US Navy nuclear reactors are closed systems (they don’t all use water for coolant either), so, again, not seeing the issue. I’m not sure what you think, but afaik the reactors on subs don’t dissipate their excess heat into the surrounding ocean or pull in water from the ocean either, and most of the reactors are rated for decades between refueling or putting in new coolant (not sure about the last part…not a nuclear tech). You don’t need to radiate the excess heat into space, which I know isn’t very easy.
Unless I’m wrong about that. This being GQ, feel free to bring in some cites as I’m really curious about this and would like to see some data. I did some quick Google searches on
For your VASIMR engine, you’d be using the nuke to generate electricity. This means operating it as a heat engine, which takes heat from a high-temperature sink (in this case, the reactor fuel), extracts some quantity of useful work from it, and dumps the rest of that heat to a low-temperature sink. The laws of thermodynamics dictate the minimum percentage of heat that has to get dumped to the low-temp sink based on the temperatures involved; for power plants, it’s going to be on the order of 40-50%. Land-based nukes use cooling towers to dump their waste heat to atmosphere, or else they use convenient rivers or ponds. Rest assured, the Navy’s nukes, just like land-based nukes, are dumping their waste heat somewhere. It’s almost certainly the ocean; I don’t recall seeing any Navy vessels fitted with cooling towers.
So if you’re generating electrical power in space with a heat engine, you have that same need to dump large amounts of waste heat. Except now you can only cool via thermal radiation, or by evaporation. The latter method is going to be limited by how much evaporative coolant you can bring with you, since you’ll be pissing away the vapor into space over time. The former method is challenging because you need very large surface areas, or very high temps (or some combination of the two), to dump heat into space at a useful rate.
I found this thread on dumping waste heat, so I presume that’s what I’m missing. I thought since the reactors were closed systems they wouldn’t need to dump waste heat, especially since that would also (I thought) increase ways to detect the things. Seems several of my assumptions on how Navy reactors worked were wrong.
Ok, so the waste heat would be a potential issue that would take some serious engineering to get around.
Well, there’s also the matter of various treaties that we have signed. I believe that we made a promise to keep nuclear devices out of space.
I suppose we could argue that this is not a nuclear weapon but an electrical generator. But others might not believe us. (We didn’t believe Iran when they claimed that about their nuclear facilities.) So others might start sending their own ‘peaceful’ nuclear devices into space, too, hanging just above us.
That’s the kind of proliferation that these treaties were designed to avoid. So it’s probably not a smart idea to be the first ones to break (or even ‘bend’) these treaties.
Columbia had an approx. 250 mile debris field. How safe scattering radioactive material over that distance, or even further if it’s wind blown? If the booster rocket goes, the payload goes with it.
I doubt they are just going to velcro the fuel rods to the side of the ship and hope for the best. I’ve seen fuel containment vessels for shipping get hit by trains at high speed, so I don’t think it would be a serious engineering challenge to ensure that the rods were contained in the event of a booster mishap. Not saying it wouldn’t be any issue at all, just don’t think it would be a show stopper (except politically).
Don’t some of the spacecraft we’ve sent out have small nuclear reactors on them already? 
They do, which means I highly doubt that that’s prohibited by treaties. Notably, though, the nuclear-powered spacecraft we’ve sent up before use a very different kind of technology, which doesn’t scale up very well.
Not reactors, but radioisotope thermoelectric generators. They don’t work by fission like nuclear reactors, but simply utilize the heat generated by a radioactive material as it decays. These are indeed launched in containers designed to contain the radioactive material in the event of a failure of the launch vehicle.
Are you saying that those reactors are ok by treaty but regular fission reactors aren’t? If so, do you have a cite for that?
The upside of RTGs is that they work using literally anything that’s hot. You could power an RTG with a burrito. We could stick some non-fissile material inside and have something which couldn’t be used for a weapon any more than any other satellite could be. Not that that would stop the whining, lying, and conspiracy-mongering.
The downside is that they’re inefficient: The RTGs based on thermocouples have efficiency in the 5% range. Other designs have efficiencies in the 20% range.
Unless things changed, I beleive Navy ship/sub reactors are also all manually controlled. Every valve and switch.
The russians have the most experience with reactors in space.