Eli5: How does nuclear submarine/space rockets works? Could this be use for interplanetary travel?


Eli5: How does nuclear submarine/space rockets works? Could this be use for interplanetary travel?

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Nuclear submarines move like any other type of submarine it’s just they use a nuclear reactor to generate electricity to turn the propeller. So that wouldn’t work for space travel.

Yes, there have been concepts and practical applications of nuclear fission powering rockets.


In a submarine you have a small nuclear reactor creating a lot of electricity to power the submarine, including creating oxygen and powering the electric motors.

For rockets, power is very important and the sun isn’t always a reliable provider through panels. So there are RTGs, essentially very small nuclear reactors, that produce a constant small amount of power. Rovers or the Voyager probes are powered by these.

To propel rockets with nuclear power there are multiple concepts. The most ridiculous one was the Orion project, which wanted to detonate nuclear bombs to shoot rockets forward. This was scrapped for obvious reasons.

The more practical approach are nuclear thermal rockets, where nuclear fission heats up gas in a chamber, similar to water in a nuclear reactor, but instead of letting the steam power a turbine, the gas then gets released to push the rocket forward.

Unfortunately, this still needs a good chunk of highly radioactive material, which could get dispersed during a failure.

There is no way a nuclear rocket could take off from earth. Any method that might have the power to do it would irradiate a large area and a lot of the upper atmosphere. There are a few ways they could work in space:

[Blowing up bombs behind the vehicle](https://en.m.wikipedia.org/wiki/Nuclear_pulse_propulsion)

[Boiling the non nuclear fuel and squirting it out the back](https://en.m.wikipedia.org/wiki/Nuclear_thermal_rocket)

[Flinging very hot nuclear fuel out](https://en.m.wikipedia.org/wiki/Fission-fragment_rocket)

[To power an ion engine](https://en.m.wikipedia.org/wiki/Nuclear_electric_rocket)

In some cases nuclear decay is the method of generating the power/heat, rather than a nuclear reactor.

There’s more but I’m not sure what the differences are. As far as I know none have been tried in space, though there is radioactive decay generators powering some rovers/exploration craft. [There is other similar types of generator, but this sort of thing. ](https://en.m.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)

How does which part of it work? Are you asking specifically about the nuclear reactor?

There have been some spacecraft with fullblown nuclear reactors, as well as many that use an RTG, which generates electricity from the heat produced by radioactive decay (you can think of these as being a bit like a “nuclear battery”). It’s usually more straightforward to use solar panels to keep spacecraft powered though. For long-distance travel, a particularly promising idea is the “solar sail”, a large, lightweight structure facing the Sun – the spacecraft would be propelled by the force of sunlight hitting the sail.

> Could this be use for interplanetary travel?

Interplanetary travel is just very, very hard. There have been several extremely tentative proposals to send an unmanned spacecraft to do a flyby of Proxima Centauri, the nearest solar system. But it would take many decades to get there, and the risk of something going wrong over that length of time is very high. It’s also not really clear how interesting the results would be – especially since by the time the probe arrives, there will probably have been all kinds of developments in telescopes and theoretical modelling and we might already have learned many of the things it can tell us.