Gun type fusion was heavily investigated in the 60s. Unfortunately the velocities this company is looking to achieve even with their next iteration (20 km/s) is

Gun type fusion was heavily investigated in the 60s. Unfortunately the velocities this company is looking to achieve even with their next iteration (20 km/s) is nowhere near what is needed (~150-300 km/s) to achieve ignition. The generally agreed upon strategy that you would use to achieve such speeds is a long series of rail guns with each stage accelerating the projectile a few km/s. The stages would have identical power supplies, just the rails would vary in length, so you don't have lots of one off parts; and with a large number of stages the amount of power in any one set of rails (and thus the amount of wear) can be kept manageable. The limiting factor turns out to be the projectile's ability to hold itself together, which puts the minimum size of such a system at around 300 meters - big but not absurd. You run into most of the same issues as with other inertial confinement fusion proposals - you need to mass produce extremely precise fuel capsules extremely quickly and you need very high power drivers which can fire in rapid succession. Railguns may be preferable to lasers, but not by a huge margin. At the time it was viewed as a technically possible but likely uneconomical method of power generation. https://archive.org/details/proceedingsofimp00impa/page/n3/mode/2up https://archive.org/details/proceedingsofimp00impa/page/n3/m...