Nuclear powered rockets

7-13:23: Update of post of July 12, 2023:

What about that fission fragment engine? The idea is to embed fissonable material within the aerogel. The fission material would get hit with neutrons, and the fission would cause the fragments to escape the aerogel. The fragments are then directed out a "nozzle" at very high velocity. The mass of the fragments times the velocity squared would be the thrust ( I think). If the velocity is 1/10th light speed, then that would be a lot of thrust from a small mass. ( E=mc squared)

Based upon recollection, the best results were with the fissonable material close to the surface of the aerogel. That makes sense because the fission fragments have to work their way out of the aerogel. The same is true with the neutrons.

Control may be an issue. How to keep the fissionable material from fissioning? Once it starts, it is a chain reaction, as it emits more neutrons than it absorbs. There would have to be some control device. That may be a problem. It may be necessary to let the reactions run to completion, then discard what's remaining of the aerogel.

What if the aerogel were in thin slices, with a moderator between slices? The moderator would stop neutrons, which would stop the reaction. There'd be a stack of aerogel impregnated with fissionable uranium. Bombard it with neutrons, and let the reaction proceed until complete, then discard the aerogel. Each aerogel slice would come off the stack until the fuel is exhausted.

Would this work? Only thing I know is that NASA may be funding research into such a device. It may not be as I speculated here. There were few details from what I saw.

the original post of 7-12-23 below:

So the Angry Astronaut says he will go to the UK and be a part of the nuclear powered rocket that is being developed. It's an interesting subject, and project too. There was a nuclear thermal rocket developed during the Apollo Era, which was called NERVA. It was at a high state of technical readiness, but was scrapped.

It's not a new idea. But what is new here is to use the nuclear power to generate power that would enable fusion, and to use the fusion product as reaction mass. I mentioned a person withe the "handle" of QuatumG. This morning, I googled the name, and found his blog. The blog is still there, but he doesn't post much anymore. He seems to lost interest. Funny, in a way. Maybe the concept is one that he may have thought up himself. Now someone else is doing it.

As mentioned yesterday, what will be done with all the heat generated by the reactor? Some electricity can be generated that way, and the electricity can be used to enable fusion. The fusion products will be going at a fraction of the speed of light. Since the fusion products have mass and velocity, there will be thrust. But not very much, really.

Nuclear thermal rockets need lots of lots of thermal energy. The NERVA program was dealing with 1 gigawatt reactors. This indicates another problem with this concept. In order to get usable amounts of thrust, you will need massive reactors. Massive reactors will generate massive amounts of heat. A gigawatt of thermal energy might generate a third of that in electrical energy. Further losses will occur from the generation of electricity. The whole mess needs to be cooled down.

Is it possible to make a thermal rocket design that will do this job, and do it efficiently? I think there will be a problem. The ratio between thrust and thermal power was something like 50 lbs of thrust for every megawatt. The kind of reactors involved here are not likely to be a megawatt. Maybe half a megawatt. This means only 25 pounds of thrust. The ISP will be 30-45k, but the thrust won't amount to much. It would have to run all the time in order to get going.

In the end, it will still be a nuclear thermal engine. Waste heat could be used to generate electricity, which could be used to gain addition thrust. This is only a marginal improvement. This method isn't likely to be efficient at all.

I'd prefer the fission fragment concept I posted about previously. The reaction doesn't thermalize, so heat wouldn't be an issue. The generation of heat is a low tech way of going about generating thrust. There's still the problem of thrust. Generally speaking, there will be a trade off between thrust and ISP. It's like automobiles. If you need a race car, you need a lot of power. Power means fuel consumption. A low ISP rocket engine is like an economy automobile. It can get good gas mileage, but it won't go that fast. Rockets need to go fast. High ISP rocket engines aren't good for getting out of deep gravity wells. The fission fragment design wouldn't be any "hot rod", but it would be about as efficient as it gets.

a ted talk about anti matter propulsion, which is a different subject, but the same guy who has a concept nasa is studying regarding fission fragments--Ryan Weed