Why can’t we build nuclear powered rockets in order to reach the moon or mars and the beyond?
We have nuclear powered subs, aircraft carriers etc.
I read the US tried in the early years of the Cold War but cancelled the program.
What gives?
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We can and have. Nuclear power has been used in space.
It has some huge drawbacks tho. It’s just big and heavy and produces a ton of heat that’s hard to get rid of. Solar is often better.
If you are asking about the rocket engine itself being nuclear, there are a host more issues. It is still big and heavy, and has much lower thrust than a chemical rocket, but much lower efficiency than electric rockets, so it occupies an awkward middle ground. Add to that the risks of trying to keep a running nuclear reactor at high power output in space, keeping it all tiny and light, and you’ve got yourself a bad combo.
Nuclear powered means steam powered, generally speaking and water is tremendously dense. Think of having one piece of coal instead of shoveling it in.
Also since we haven’t bothered investing in it, it’s not really viable from a weight-to-power aspect. The system is too heavy to break atmosphere.
Once we get to spaceships that don’t enter atmosphere, we can handle those with current nuclear power technology.
Edit: Oops I lied and googled it. The primary reason we don’t use it is safety. If a rocket fails, it becomes a nuclear device.
Spacecraft accidents happen WAY more often than ocean going ships. Think of the Challenger of Columbia shuttles exploding on launch or reentering atmosphere. Now make it radioactive. The other issue is turning the energy into usable thrust. Ships like submarines or aircraft carriers do this easily by simply utilizing their reactors to power a steam engine. It works essentially the same as a coal powered ship of yesteryear, but uses the heat from the reactor instead of burning coal. Using that energy to spin a propeller is easy. Using it to exit a gravity well, less so.
All that said we DO use nuclear power in space, to power long range probes. All of our long range space probes use a small radioactive “battery” to generate power over the long mission lengths these probes have.
Largely, it’s political considerations.
We can’t even get the political will to build nuclear power plants in the US right now for a variety of reasons, chief among them being people being scared of nuclear power and picturing Chernobyl every time they hear the word “Nuclear”. Now try telling everyone you’re putting a nuclear reactor on a rocket – Imagine the headlines and the people panicking!
Okay so the other answers answered about nuclear power supplying electricity to ships. Which does happen in some situations, though it’s a cost benefit of “how badly do we need this nuclear power vs the chance of the rocket raining nuclear material down if it fails.”
The other thing about the Cold War nuclear rockets is that they were absolutely terrible for life in every iteration.
Rockets use gas to propel them. Using electricity from nuclear power isn’t directly convertible in an easy way in space like it could be in atmosphere. You can use electricity to spin a turbine for propulsion in atmosphere(or fluid, like water) but not in vacuum.
Though reactor shielding is heavy. Literally lead. Which doesn’t work well for weight on an aircraft while keeping the crew from turning to goop or shielding it if it crashed.
You could use other forms of power though. Like the thermal energy.
Which was a concept. A gas goes into the reactor, gets heated up by the reactor, and is expelled out faster on the other side. Project Pluto tended to also irradiate the air that was heated. So all the throughput of the engine, was turned into radioactive air. Which is bad. That was scrapped because a nuclear fallout air freshener was an issue.
In space you could use the thermal power to expand a gas and push like a rocket but that’s expensive, heavy, and also has the same issues as launching any other radioactive material. They absolutely could not be used in atmosphere because they would literally be dumping radiation as exhaust. They are more efficient though. So possibly are being looked at for Mars.
There’s the project Orion, which used nuclear bombs to push a ship forward. Literally detonate the bomb behind a shield and use it to push the ship. This was more theory than practice since it needed to withstand a nuclear detonation and the shockwave. This one seems self explanatory why there are issues.
Edit: there are electric drives but they produce low thrust to weight but can be very very efficient. So longer burn times. Deep space probes like people mentioned but not great for manned “get there before life support runs out” missions.
Nuclear powered subs and other ships use a nuclear-powered steam turbine to drive a propeller.
Propellers don’t work in space.
What you could do is bring a bunch of water and use a steam jet for propulsion, but water is really heavy so it’d be really inefficient. You could also explode a bunch of nuclear bombs behind you and ride the shockwave forward, which has obvious downsides as well
The previous designs are known as solid core nuclear thermal reactors. You take a mixture of uranium and graphite and push it through something like a pasta maker to make long fuel rods with holes through them for the hydrogen fuel to travel through.
Hydrogen is a wonderful fuel because its atoms are very light and therefore the rockets that use it have a high fuel efficiency – known as “specific impulse” – about double that of chemical rockets.
That’s the upside. There are a bunch of downsides:
* The temperature of the core is limited by the materials in the core; they have to stay cool enough so they don’t melt. In the NERVA tests, they generally ran at about 2400 K, while chemical rockets run at about 3500 K.
* The nuclear core is heavy and the shielding to protect the rocket from radiation is also heavy. That makes the thrust/weight for the engine pretty poor, and therefore the engine performance is worse.
* Hydrogen is very non-dense and therefore requires bigger and heavier tanks.
* As soon as you turn on the engine, it becomes very radioactive. For the NERVA tests all of the testing had to be controlled remotely and there was a special building required so they engines could be disassembled without irradiating the workers.
* You need significantly enriched uranium, at least 20% on up to 90% depending on the engine design. This is highly controlled because you can make weapons from 20% enriched.
With most of the designs, the resulting performance you get isn’t really much better than what you get with chemical rockets for most scenarios.
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