MC Fusion: It's Not Just a British Rapper Anymore

So I was thinking of using magnetic-confinement fusion rockets, for my book—the humans use them for in-system travel, saving the big beast inertial-confinement proton-chain rockets for their starships (which have to get to the edge of the system as fast as possible, thus they like the proton-chain rocket's ∆_v of 15%c, or 7.5% for normal purposes). But MC fusion engines have such a low thrust! Remember my example of basing the mass ratio and engine mass on the Blackbird, how you'd get a ∆_v of 1%c, but only at 1/3 g? Yeah, well, I tried it with the Reaction Engines LLC Skylon. It has a mass ratio of (345/53=)6.5, and with the MC-fusion's exhaust velocity, you get a ∆_v of 5% c (again, 2.5% if you're into stopping).

As for the engine mass, well, I had to find it myself, based on the thrust-to-weight ratio, but each SABRE engine a Skylon has, has a mass of 9829.6 kg. Which would come to an MC fusion engine (massing 19,659.2 kg) with a thrust of 1,638,269,990 newtons. Which would move a ship massing 345 tons at...484 gs! I guess we call it the Raspberry Jam Express! Even with the artificial-gravity based inertia protections, that seems like a lot.

Fortunately, a ship with an MC-fusion rocket would be unlikely to be as small as a Skylon, since you have to contain the reaction within the ship itself. Let's say our system-ship is four times the size of a Skylon, which by the square-cube law gives us 22,080 tons. This translates to a nice, comfy acceleration of 3.8 gs—mere roller coasters do that, they might not even need artificial gravity! Also, at a rate of 2.5%c, the ships do 1 AU in 5h32m, and, assuming comparable payload to the Skylon, they can carry 960 tons each, or approximately as much as an oil barge.

Incidentally, you can probably use smaller ships with IC fusion, since the fusion reaction actually happens outside them. I'm not 100% sure, but I think the 1000 ton minimum size listed for IC fusion, on Project Rho, is a mistake. I think so because 1000 tons was used in that Friedwardt Winterberg paper I mentioned, but that was the mass of the whole spacecraft. Really an IC fusion system would only have the same mass as listed for Project Orion—indeed, there isn't really a lot of difference between an IC fusion rocket, and an Orion ship with hydrogen bombs. And the minimum mass for that is 8 tons.