Reply to post: Re: Fusion rocket engines - the gist

Re: Fusion rocket engines - the gist

Right, the basic idea is that you need to accelerate the mass you have at as high a velocity as you can get, meaning that the "burn" temperature will probably need to exceed the melting point of the engines for it to become efficient. The F1 (as I recall) burns kerosene+O2 which is heavier/denser than the H2+O2 used by the other stages. Granted the kerosene produces heavier exhaust and lower burn temp, but it's still hot enough to melt the engine. And so "a way" to keep from melting the nozzles needs to be there.

My assumption, in essence, is to blast water into a layer at the sides of the engine, then light off the fusion reaction in the middle near the focal point of a parabola (also surrounded by cooling liquid so that it does not melt either). The resulting temperature of the liquid would give you the 'v' part of the 'mv' impulse, and the overall energy of the reaction would increase the K.E. of the liquid to get you as high a 'v' as you can possibly get (thereby minimizing the mass of liquid needed to get thrust).

There were several fission based rocket engines tested in the 1950's and 1960's that were test-fired but never flew. It used nuclear fuel to heat liquid H2, but I think using water would have been a better design.

https://en.wikipedia.org/wiki/Nuclear_thermal_rocket

In short it's a way to get a bit more velocity by applying heat more efficiently to the "impulse fluid", and at much higher temperatures than you could get with a chemical burn. I expect fusion to be similar.

yeah no doubt better engines exist now than the F1 used in Apollo, but the design principles of fusion or fission exclude combustion kinds of things. Heating needs to be done differently, and gamma capture by the "impulse fluid" would be extremely effective (and not melt engine parts so easily)

years ago I figured out that a dense fluid that was heated and accelerated directly by fusion gamma and neutron radiation would give you the best fuel utilization efficiency, being as a heavy fluid does not need such a large tank to store it in...

[to double thrust you must either double exhaust velocity or double the mass flow rate. doubling mass flow rate takes twice the energy. doubling velocity takes 4 times the energy. doing the math, yeah)