Why do people use rocket fuel instead of nuclear power for spacecraft?
In: Technology
Rocket fuel boom = big boom
Nuclear fuel boom = big boom + radiation everywhere
So people choose to go with the lower risk choice, aka rocket fuel
Most rockets are a lot more powerful then nuclear reactors. To put it into perspective the ill fated Fukushima Daiichi unit 1 nuclear reactor is just twice as powerful as the combined fuel pumps in the Saturn V first stage. And that is just to pump the fuel and oxidizer into the actual engine where most of the power comes from. The designs for nuclear powered launchers have not used nuclear reactors for power but rather nuclear bombs, and in plural. This was one of the first projects to be scraped with the growing concerns of health issues due to nuclear testing. Something about a rocket leaving a trail of nuclear explosions across half the country did not sit too well with the public relations managers.
However if you start talking about nuclear reactors in the spaceships themselves and not the launchers and landers it is a very realistic idea. In fact both the US and the USSR have launched fully functional nuclear reactors into orbit in order to power the electronics on satellites. This was in the days when nuclear test projects had more support. Power efficient electronics means that current satellites and spacecrafts are able to utilize solar panels or if the mission includes operation in areas with little sunlight they have been using the decay heat from an isotope of plutonium to generate electricity.
But there is currently a new project with the goal of designing nuclear reactors for space missions again. And there is two reasons for this. Firstly the plutonium needed can only be generated in breeder reactors which is used to make isotopes for nuclear weapons. Most of these reactors have shut down due to the nuclear weapons agreements meaning that the plutonium is in limited supply. Secondly there have been a lot of advancements in electrical thrusters. Modern satellite designs will often use ion thrusters all around in order to increase the lifetime of the satellite before it runs out of fuel. The fuel is still used for propulsion but much less. Satellites with only station keeping duties are able to use its solar panels to power its thrusters but we might design missions to the outer planets where there is far less sunlight so we need the power of a nuclear reactor to power these thrusters.
I vaguely remember watching the old “Cosmos” television series, where Carl Sagan said something about how there was some sort of treaty that disallowed use of nuclear devices in space. He also mentioned that this was a pity, because space exploration is intended to be for peaceful purposes.
Nuclear reactors make heat. Heat isn’t particularly useful in and of itself. Heat can be turned into electricity through a number of types of cycles, that’s how spacecraft use it, as well as the nuclear plant down the street. Electricity isn’t that useful in propulsion, as electrons have very small mass.
To move a rocket, you shoot **stuff** out the nozzle at high speed. There is a relationship between the mass of the stuff and the speed of the stuff that determines the thrust of the rocket.
To make a nuclear powered rocket, you need the nuclear reactor **plus** stuff to shoot out. With a chemical rocket, the combusted fuel used to make the energy **is the stuff** shot out. there is no energy transfer (or 100% efficient energy transfer if you prefer) which gives very high efficiency. The nuclear solution has to transfer the energy to the stuff, which is less efficient.
TL;DR: High weight (for safety) and low efficiency makes nuclear energy a bad rocket choice.
I believe it mainly comes done to a risk vs reward. If a ship fails at launch it could release a large amount of nuclear radiation. Im no professional on the matter however. I do know the mars rover uses a Radioisotope Thermoelectric Generator to provide power.
In order to get your rocket to go one way, you have to throw something in the opposite direction. While I guess you could use nuclear power to boil water or something, it just doesn’t create the thrust necessary, as it only creates energy.
Rocket fuel creates an explosion that provides trust in a given direction.
Nuclear reactors generate heat which is transferred to water then steam which is used to turn a turbine to make electricity. (Generalizing)
You could use nuclear power to power things such as a electric motor but that motor doesn’t provide trust. Motors make mechanic motion but that would be the equivalent of sticking a boat motor outside your rocket.
Tldr: Rocket Fuel goes boom in right direction. Nuclear power keeps lights on.
Because nuclear reactors are heavy and you cant use nuclear power the same way as rocket fuel, nuclear power isnt what you think it is, you dont get power straight from a reactor, nuclear poweplants still have to use water to use the nuclear power which creates heat, transforming water into high pressure steam that spins the generator. So if you would go that way you would have to carry some liquid on the rocket that youre gonna vaporize using a nuclear reactor so why not then remove the reactor and use just the liquid fuel that reacts with itself, and not have to eject the expensive nuclear reactor with the first or second stage that will just get destroyed when it falls.
And if you think about setting of nuclear explosions, do i even have to say what a bad idea that would be considering rockets can have failures and can explode over populated areas.
There is always a non-zero chance that a rocket will explode when launched. The early ~~Saturn V~~ pre-Mercury rockets, the Space Shuttle, and new SpaceX rockets all have had numerous explosions during launch or re-entry.
If a nuclear powered rocket were to explode, it would spread nuclear material over a very large area – an incredibly large area if that explosion happens high in the atmosphere. This would be a catastrophic event, and even at low probability of occurrence it is a significant enough danger to make nuclear propulsion a bad idea.
Nuclear power generates heat which is not possible to cool in the vacuum of space since there are no air molecules for conduction and convection of heat to take place.
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