Space Submarine

Now bear with me. I am not as dumb as the thread title suggests. Well, perhaps I am, but this is still damn interesting to me.

I was reading about Magnetoplasmadynamic Thrusters and the 200 Newton thrust level caught my eye, but it requires a lot of power. So I decided to investigate what’s the smallest fission reactor built. I didn’t find a definitive answer, but I did find a Navy nuclear research sub NR1, which weighs only 400 tons (apparently), can house 9 crewmembers, stay submerged for almost a year, and withstand great pressures (thick walls?).

Since this sub only weighs 4x as much as a space shuttle, delivering it to orbit in a few pieces might be expensive, but not infeasible. However, what would you do with a sub in orbit, might you ask? And here in lies the question.

What are the practical issues (considering we figure out a way to send reactor + fuel into orbit safely without causing every Greenpeace member on earth to collectively explode) of retrofitting a nuclear submarine to be interplanetary space-faring ship? Will the reactor work in ZeroG? Could you replace the propellers with electric thrusters of similar size or would they have to be much bigger? Do you need a giant radiator to radiate away the heat since there’s no sea water? Etc.

I mean, I know the whole thing is silly and it’s probably much easier and cheaper to design a nuclear space ship from scratch, but it’s a fun exercise in futility, if anything.

Regards, Groman

Reactors of one sort are already being used in space to power space craft. Every one of the probes we’ve sent to the outer planets has had a nuclear power supply. Admittedly, it’s not identical to a sub’s, but it’s still a nuke reactor (though more like a “battery” than what we think of as a reactor).

And the hardest part will always be in dealing with the folks who dislike nuclear energy. (We’ve been safely launching nuke powered space craft since the 60s.)

I always assumed that when the word “reactor” is used, a critical-mass controlled chain-reaction is implied and that RTG’s and such are “nuclear generators” not “nuclear reactors”.

You’re right, but IIRC, many of the new safe reactors, like pebblebeds and CANDUs operate on principles similar to the RTGs.

Delivering it in pieces is infeasible with current or near-future technology. We haven’t yet learned how to do real construction in space, like welding. Even on earth it’s no simple matter to cut a submarine in 4 pieces and then put it back together.

Even if that were possible, necessary modifications include (but are not limited to):
[li]Alternative cooling mechanism for the reactor. Cooling things is (relatively) easy when you’re sitting in water; it can be much more difficult when you’re sitting in vacuum.[/li][li]Redesigned thermal control of the entire vehicle, e.g. how to handle the heat on the sunlit side and the cold on the dark side.[/li][li]New oxygen and water supply or generation system. Modern submarines generate these from seawater, I believe. That won’t work in space.[/li][li]Modifying all plumbing and moving parts to work in zero-G.[/li][li]Navigation system requirements are completely different. Replace sonar with radar, get rid of ballast tanks and install thrusters, etc.[/li][li]Docking system needs to be added.[/li][li]Submarines aren’t 100% airtight, or even 100% airtight. They have bilge pumps to remove water that leaks in. Air leaking out of a space capsule is harder to deal with (needs to be replenished as fast as it escapes).[/li][/ul]

Besides, a submarine hull is complete overkill for a spacecraft. A spacecraft only needs to withstand an outward pressure of 1 atmosphere, or even 1/3 atmosphere if you use a pure oxygen environment. Submarine hulls are designed to withstand inward pressure of tens of atmospheres.

Unless we add mechanisms to snap or screw it together. :slight_smile:

One big problem I see is a nuke power plant can’t be used to propel a spaceship by turning screws. You need to (given our current level of tech) expel reaction mass, which means you must push against mass that you are providing (and hence loosing).

See the link in my OP. Electric thruster, such as plasma or ion.

I seem to remember (several years ago) some concerns over a nuclear-powered Soviet satellite whose orbit had decayed. No one knew where it would eventually crash and there was a lot of concern over the release of radioactive material if it hit land. If I remember correctly, it landed in the ocean, but a crash in or near a populated area would probably not have been considered “safe” by the locals.

I read that Wikipedia article, and all I can say is this:

Sht!! The Soviets are ahead of us! We gotta get crackin’!!*

Honestly, I just wanted to bring up one point. An article in the Smithsonian’s Air & Space magazine once detailed a plan for a nuclear powered cruise missile. It was some years back (early '90s), but it went into how a nuclear reactor would create thrust by the fission of material in it’s core. I don’t have back issues laying around, but I’ll see what I can do to track that article down.

But, I’d need to read up on ionic thrusters to make a comment on the OP. I took an orbital mechanics class in school and IIRC, an impulse of 10k for something like that is darn impressive.

Those damned Communists!

Could you be possibly talking about Project Orion and NERVA ?

Point of clarification: The satellite (Cosmos 954 ) Crashed near the Great Slave Lake in Canada’s Northwest Province.
from Here :

The other nuclear-powered that fell to earth was Cosmos-1402. This was the one I referred to in my previous post.

I think I am, but the article was specific in the intent on bombing the bajeezus out of the Soviets with a cruise missile: not only was the warhead a fusion bomb, but the thrust ‘reactants’ were basically fallout from the reactor of the missile.

Dang, I can’t believe I remember that article from 10 years ago. Now I have to find it!! :smiley:

I’m all about bombing those damned Soviets.

I did. electric thrusters work by expelling mass using electricity (as opposed to chemical energy). Again if you run out of reaction mass you are dead in the water, but at least you have electricity for the next 500 years or so.

Also nuke power can be used in place of chemical rockets. Basically the reactor heats the propellent instead of combustion, which accelerates the mass so it can be expelled out the back.

Well so it’s a two-fuel system, essentially. One fuel being the fissionable material used for electricity generation, the other whatever it is the ion/plasma thruster is expelling. That doesn’t necessarily cause a problem since your thrust is proportional to the speed you can accerate your material, not only its mass.

Just to clear things up on the CANDU reactor, it works as follows. A large tank (“calandria”) has a whole bunch of parallel tubes passing through it. In the tubes are bundles of rods of fuel – usually unenriched uranium oxide. The tank is filled with ‘heavy water’ (contains deuterium in place of regular hydrogen). The fission in the fuel produces high-energy neutrons, which lose energy to the deuterium moderator. The neutrons go on to catalyse more fission events, the energy is used to boil a second, isolated cycle of water, which can turn steam turbines and make electricity.

Far as I know, no CANDU reactor has been built on a mobile platform – they’re all at hydro generating stations or research labs. Also, the CANDU design isn’t really ‘new’; the first one went into service in 1962, I believe.

Atomic Energy of Canada Limited

It was a nuclear-powered ramjet missile known as SLAM, or Project Pluto. It would deliver nuclear warheads to it’s targets, and then fly around the enemy country spewing fallout to add insult to injury.

In regards to the OP - I do not believe that a PWR (Pressurized Water Reactor), such as that used on NR-01, can be adapted to freefall.

Without getting into big details, the problem is that even though the coolant going through the core is supposed to remain a liquid at all times, a PWR uses a vessel called a Pressurizer to ensure that operating pressure for the reactor coolant is always far above saturation presure for the plant’s operating pressure. The way this is done is that the environment in the pressurizer is actually at saturation temperature for the plant’s operating pressure. Usually several hundred degrees warmer than the temperature in the plant’s core. Because the water in the Pressurizer is connected to the rest of the coolant system, it exerts that pressure through the whole system, without actually mixing with the coolant going through the core. In effect a PWR plant has two general temperature environments: The circulating loop, at an average operating temperature; and the pressurizer at a higher temperature, to ensure that the core never reaches saturation conditions to allow boiling.
In a gravity field, or even in a simulated gravity field, when any liquid is heated to a gas, the newly formed gas bubbles will rise to the top of the vessel it is in - in the pressurizer vessel, this means that there is a bubble of steam at the top of this vessel, that actually provides the pressure to keep the rest of the coolant well above saturation pressure.

In freefall, however, there is no reason for the less dense steam to move away from the heating elements. So what is more likely to happen is that the steam bubble will form around the heating elements, which would effectively insulate the elements from the heaters. The effect of this would be to mean that once a bubble is formed in the pressurizer it wouldn’t be able to raise the temperature of the surrounding water very easily… until the bubble collapsed again, allowing water into direct contact the heating elements. Which would remove one of the most important safety features of a PWR - the certainty that a properly operating plant won’t allow boiling in the core. Even here in our one-g field, it’s a bad thing for a PWR to experience boiling in the core. (In general - there are technical considerations I don’t think I can get into without having to hunt anyone who reads this thread down to kill 'em and eat their brains. I don’t believe they’re a secret to anyone with knowledge of thermodynamics, but I have to balance things out with my own oath to hold certain knowledge secret whether I think it’s useful, or not.) Because the channels going through the core in a PWR are so thin, it is devastating to have that insulating effect of steam bubbles keeping the core from transferring it’s heat into the coolant. It is relatively easy for these channels to get blocked by steam bubbles, and once that happens, the heat of fission being produced in the core can’t be removed from the core - and causes the temperature of the core materials to rise… until eventually, something fails.

And having your power plant fail - especially something in the core fail - is a bad thing[sup]tm[/sup].

This isn’t to say that there aren’t reactors that work in freefall, just that the Navy’s PWRs are not the sort of reactor for that environment.

I would also like to point out: there’s no real reason to insist than all the components in a space vessel are all in the same hull. In a submarine, because of the incredible pressures involved, it doesn’t make sense, to most naval designers, to have more than one pressure vessel. In short it’s cheaper to make one larger vessel that can withstand hundreds (perhaps even thousands) of pounds pressure per square inch, than to make several. Economies of scale. However, that sort of stress just doesn’t exist with vacuum work - there’s some concern about containing the internal pressure of the astronauts’ environment, but it’s not the same magnitude of concern. So, instead of having huge concerns about building the most powerful pressure hull possible for x amount of money, the biggest concern is going to be: what is the maximum mass we can lift in any single given launch? And while space borne construction is still a virgin field, I suspect that making a rigid frame that can withstand a moderate constant thrust is going to be easier to do than actually trying to connect seperate modules into a single pressure hull in orbit.

Nitpick: The Northwest Territories is not a province, it is a territory (yes the name is plural, the “state” isn’t). The difference lies in the fact that provinces have a great deal more power to self-govern than the territories do. The federal government wields more power in the territories.

'Nother nitpick. Nuclear power stations do not generate hydroelectricity (electricity from water), that is what hydroelectric dams are for. Many folks up here erroneously refer to all electricity as hydro because that is where a great deal of our electricity comes from (especially out west). Nuclear power plants are generally separate facilities from the hydroelectric plants.


I remember some talk of having a great “ice ship” mission to Jupiter: essentially, a submarine is assembled in orbit and covered meters-thick in water ice. This protects the crew from the sun’s and Jupiter’s radiation, micro-meteorite strikes, and provides the bulk mass for a nuclear rocket.

More ice is picked up from the jovian moons for the return trip.