propulsion - Is nuclear fusion a viable means of powering spacecraft?

Current experimental fusion reactors are still decades away from generating a net energy output. The test reactor at the National Ignition Facility made a crucial breakthrough last year when they first managed to get more energy out of their fusion chamber than they put into it. But keep in mind that:

• The energy output was only positive when you measure the input energy as the energy of the laser beams entering the fusion chamber. But the process to create these laser-beams is only 1% effective. Also, there is no method yet to extract the energy from the fusion chamber and turn it into electricity. You can't assume that such a method would be 100% effective either. So the energy efficiency of the whole facility is still magnitudes away from being positive.


• The positive output was merely for 150 PICOseconds


• That test reactor currently has the size of a factory complex.

It will still take decades until we have a fusion facility capable of completely(!) powering itself. It will take even longer until the technology is feasible for economic use and even longer until the technology is miniaturized enough to be considered for use in space.

I will try to update my answer when this has happened. But I am not sure I will still be alive then.

There is, however, another method with which we successfully managed to create a fusion reaction with positive output: The fusion bomb. Unfortunately the only way to use their energy is in form of a single, huge explosion, larger than a common nuclear fission bomb (because a fission bomb is used to ignite the fusion reaction). Propelling a spacecraft through shockwaves produced by nuclear bombs is obviously crazy. But not so crazy that nobody ever though about it. There is a theoretical concept called Project Orion which is exactly that. In theory it doesn't even look bad. It might in fact currently be the only viable method for manned interstellar travel within our technical capabilities. But it never got above theoretical planning, because:

1. It would need to be huge to be efficient and thus insanely expensive.


2. Putting nuclear weapons into orbit would be a violation of the Outer Space Treaty of 1967.