Perhaps a more achievable way to use fusion power is to control detonation of a miniature fusion bomb to power a craft.
One design, being pursued at the University of Washington, works by dropping a pellet of two hydrogen isotopes, surrounded by metal rings made of lithium, into a combustion chamber.
At the right moment, a huge magnetic field slams the metal rings closed around the pellet, compressing the fuel to incredible pressures, leading to fusion. It’s a bit like how your car engine uses controlled explosions of gasoline.
A grain of sand of this fusion material would the same energy content as four litres of rocket fuel. But a major problem with this research is that actually testing one would likely violate nuclear test ban treaties.