how are “nuclear powered” submarines and space probes powered?

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In other words, where do “nuclear powered” vehicles get their power from?

I imagine it’s not from fusion or fission, nor can it involve getting water to turn to steam, an in many other types of power generation.

So how does it work?

EDIT: it seems that nuclear submarines actually do use fission, so I’m switching my question to only focus on space vehicle power generation.

In: 3

They are powered by small nuclear fission reactors. That’s why they’re called nuclear powered submarines. It’s exactly what it says on the label.

> I imagine it’s not from fusion or fission

I’m not sure why you think that, but nuclear submarines do in fact have a compact yet fully-fledged fission reactor that boils water into steam to drive a turbine. Nuclear-powered space probes typically don’t have a reactor, but they have a device called an RTG (Radioisotope Thermoelectric Generator) that uses thermocouples to generate electricity directly from the heat of radioactive decay. RTGs supply only a trickle of power, but they are compact and long-lived and have no moving parts. There have been a handful of experimental nuclear fission reactors operated in space, typically using molten NaK metal instead of water as coolant, but none have flown since the late 1980s.

They have thermoelectric piles. These would be like the peltier coolers you can buy on ebay/amazon.On those, if you connect power, it moves heat so one side gets hot and the other gets cold. It’s a pretty big difference too. They work the same in reverse too, so if one side is hot and the other cold, it’ll output power.

edit – this is for the satellites…
edit 2 – it is radioactive fission, the radioactive decay of elements makes them hot, and that heat is put through the thermopiles.

Nuclear submarines are powered by a standard nuclear fission reactor that creates heat and turns a steam turbine.

Nuclear spacecraft are powered by something called a Thermo Electric Generator which is a device that uses a gradient in heat to create electrical power with no moving parts (sorta like a solar panel, except it uses heat instead of light) and a lump of naturally decaying radioactive material provides the heat

Some space probes use heat from natural radioactive decay [of a radioactive material] to produce electricity via thermocouples and something called the Seeback effect. This does not require any sort of reactor and does not require moving parts. However the power output is relatively low. Basically the heat from the emitted radiation from the material is turned into electricity for powering components.

A short answer to the question would be that some nuclear powered submarines can be powered by a reactor that either charges internal batteries or it could generate steam to power a turbine.

in space there are nuclear powered satellites that use decaying elements ( like plutonium, etc.) that create heat and then power to charge batteries as well but there are also solar powered satellites that continuously charge batteries that keep the unit in operation using solar arrays.

Submarines do have a fission reactor that generates steam that drives a turbine. The same for nuclear-powered surface ships. Some use reactors with very high U-235 content so a small reactor can operate for a very long time. We talk about over 93% for US nuclear submarines. This is U-235 levels that usually only exist in nuclear weapons.

Space probes are different they use [ Radioisotope_thermoelectric_generator](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator) The have a radioactive element as a heat source. They thermocouples to produce electricity from the temperature difference between the radioactive material and radiators on the outside. This is not a nuclear reactor, it use uses radioactive material as a heat source.

The same idea is used on a [heat-powered electric stove fan](https://www.youtube.com/watch?v=cyAEDiQJrSY) The heat is from the fuel that you burn in the stove and not radioactive material.

These two things are totally different.

Nuclear submarines have a small nuclear reactor inside a submarine, it makes electric power with a steam turbine, and everything runs on electricity.

A space probe uses a radioactive thermal generator. The radioactive stuff generates heat and the heat is converted into electricity using the Thermoelectric effect. No moving parts.

These are two different questions, really. The mechanism used in a submarine is different from what’s in a space probe.

The only thing they share in common is this: Nuclear effects make something hotter than the stuff around it. When there’s a hot thing and a cold thing near each other, you can convert that temperature difference into other forms of energy.

In the case of a submarine the nuclear effect going on is that there’s nuclear fission, which makes the uranium rods really hot. This heat is used to make a steam engine turn. In some designs this steam engine drives both a generator for the boat’s electricity AND the propeller shaft for the boat. In other designs it drives just the generator only and then a separate electric motor uses that electricity to drive the propeller shaft itself.

This is a bit different from in a space probe, where nuclear material is used in something called an RTG (Radioisotope Thermoelectric Generator). In this design, heat is still invovled, but this time its just the normal waste heat that comes from letting the nuclear material decay on its own at a natural pace. When an isotope material decays it does put out some amount of heat. An RTG uses that difference in heat between the hot isotope and the cold vastness of space to create a battery. If you make a “thermocouple” between two types of metal and make one hotter than the other, they generate electrical current flowing between them.

The big, big differences between the two approaches are:

1 – Moving parts: Submarine nuclear reactors have them (It’s a steam engine). Space Probe RTG’s do not (It’s just “this metal plate is hotter than that one so that makes a current”).

2 – Sprint vs Marathon: Nuclear reactors put out a LOT more power than an RTG but doing so causes the fuel to decay faster, so they have to return to port occasionally to swap fuel rods. Space Probe RTGs are much lower power by comparison, BUT they last and last and last because the decay happens at its natural rate.

3- Size: It’s hard to make a nuclear reactor that’s small. There’s a minimum size of ‘stuff’ needed to be to sustain the reaction. If you’re going to be driving a big giant boat with it, that’s fine. But if you’re going to be driving something smaller, it’s not fine. RTG’s can work on a very tiny scale, to power a small thing without costing a lot of mass to do it (and keeping mass low is everything when it comes to designing a space probe that has to be launched by rocket.)