Project Orion (nuclear propulsion) sizes of vehicles
One of the problems of space propulsion is the limits of chemically powered rockets. This causes a nightmare of having to build super large rockets that can only propel a spacecraft to limited objectives. So, the question is this: can nuclear power be used effectively? It so happens that a lot of research was done in this area in the fifties, but ended due to policy decisions.
Elon Musk's rockets are pushing the boundaries of chemically powered rockets to their maximum. Thanks to his work, it appears that the task of getting a payload to Earth orbit could remove launch costs to the point to where useful spinoffs could be contemplated. One of these may be to use nuclear power in deep space. Since it is deemed a problem to use this on the ground, perhaps the objection would be less if this was done in space. Perhaps.
The 50's research reveals that the bombs seemed quite small. Even smaller than the "suitcase nukes" that are mentioned from time to time. Peeling around the mysterious of jargon here, a small nuke, if feasible, could yield just 30 tons. You are almost getting in the region of a large conventional bomb here.
The advantage would be in the amount of yield in relation to the mass expended. This is why the use of chemical rockets are so limited. Musk needs a 400 ft tall rocket to get to orbit. True, it carries a large payload, but it is rather huge. Once it is in orbit, it has a lot of extraneous mass that gets in its own way. He will need to refuel multiple times in order to get to the moon for the Artemis project. The Apollo project utilized a mass shedding strategy that left only a 30k pound lunar lander. More than one way to skin the cat. But back to the nuclear option...
Reading down into the linked article, each bomb may weigh less than 500 pounds. It gives an explosive yield of 30 tons or more. The article isn't clear on that, though. If the numbers are meaningful, then it is a ratio of 12 to 1 in terms of yield. It is probably more than that, though. The amount of energy in a nuclear explosion is a factor of 1 million times greater. If it is only 12, that is too low. In any case, there is much more yield per pound expended, which would translate into a much more powerful rocket.
The article gets a little vague, so not much more can be gleaned than that.
Previously on the blog, it was proposed, and may actually be studied right now, is to use a fission fragment device. It wouldn't be an explosion, but it would use fission fragment as the reaction mass. Such seems to be rather elaborate. Why not just blow the damned thing up like Project Orion? Could the explosions be minaturized so much that they wouldn't be so much different than chemical power?
That is to say, what if a fissionable mass was embedded into this aerogel mixture, and was caused to explode? The aerogel weighs almost nothing. Could a means of detonating the thing be set up in much the same way as the Orion project? The explosion could propel the spacecraft towards its destination. Perhaps a yield even smaller than 60 tons could be achieved. Perhaps it could be quite small. The advantages would be in a high thrust and high ISP nuclear propelled rocket.
Did the decision makers give up too soon?
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