Why do we not use nuclear energy to roam about in space and go the distance if it lasts long and needs minimum refueling?
In: 4
Fun fact: We do!
It’s just really, really slow because of the *other* problems with using nuclear power in space. Nuclear power as we mostly use it requires the earth-like environment we live in.
We can’t really do “nuclear fuel in -> electricity out.” Earthside nuclear power plants make electricity surprisingly primitively. We put the nuclear fuel close enough together to react with each other but not have a runaway chain reaction. As the neutrons are flying around and and bumping into the atoms of the fuel and causing them to break apart in a burst of energy and neutrons it heats up the fuel rods. We then take this heat and use it boil water. The resulting steam is forced through a steam turbine which spins really hard and that’s how we get the electricity.
Fundamentally a nuclear power plant generates electricity the same way that the earliest of coal- or wood-fired power plants did. Boil water, make steam, spin thing, get electricity. Spin thing, get electricity is actually how most power plants work.
So the problem with nuclear power in space is all that water is *heavy* and you get useful work from temperature through temperature *differences.* And vacuum is a fantastic insulator.
So once the nuclear reactor heats up the water and boils it, what next? Do you vent the steam into space? If so, you’d be better off doing that in the first place as your thrust (look up the hypothetical ‘nuclear salt-water rocket’), but then you lose water. But if you *don’t* do that then how do you turn it back into water? You’d have to wait for it to cool down which will take a long, *long* time in space.
And if you’re not venting it into space then how do you turn electricity into vroom? We can’t actually do that yet. The closest we get are “ion engines” which effectively take individual particles and accelerate them to extremely high speeds before throwing them out the back. They turn electricity and very very small amounts of propellant into vroom.
Which is how we use nuclear energy to roam about in space right now. There’s a thing called an “RTG,” a radioisotope thermoelectric generator. You can turn heat directly into electricity with a temperature differential, it’s just not very scalable. The most common piece of hardware for doing this is a “peltier.” I’ve got one right next to me right now, actually. It’s the cooling force behind my 6-can soda fridge that’s sitting on my desk. You put electricity into it and one side gets hot while the other side gets cool. You can do it in reverse, where if you make it so one side is hot and the other side is cool then you get electricity out of it.
So you get a lump of highly radioactive metal which, as noted above, gets warm as it reacts, and use that as the “hot” side of a thermocouple. The cold side is a bunch of radiators. And boom, hot side + cold side = small amounts of electricity.
Which can, very, very slowly, drive an ion engine, as well as power the rest of the electronics on the probe.
Latest Answers