Nuclear propulsion

I’ve been designing a Mars mission with a nuclear rocket. Admittedly this might be a bit much for a one man operation. It grew out of desire to render a NERVA II rocket engine with blender. Although I’m not known to be detail oriented the things that I try to model should look at least a little bit like they might look if they were actually made some day, so I used “existing” hardware to estimate weight of a spaceship and then plug the numbers in to the rocket equation. After some tuning I came up with a two stage space tug that has about 1.5 Gg of mass at low earth orbit. This contraption should be able to transfer five BA 330 modules and 200 Mg of cargo to Mars orbit.

The propulsion unit for my design. It needs six.
A propulsion unit for my design, it needs six.

Before anyone gives harsh critique on the numbers: this is a very notional design: I’d be happy if the numbers are within an order of magnitude of the correct ones. And did I mention that much of the stuff is sort of vaporware or less real.

Close up of the NERVA II. To show the scale, the big cube is 10^3 m3, the green speck is 0.1^3 m3. The Hydrogen tank is almost 47 m long.
Close up of the NERVA II. To show the scale, the big cube is 10^3 m3, the green speck is 0.1^3 m3. The Hydrogen tank is almost 47 m long.

I like physics, I like rockets and almost anything space related, so for me this type of thinking by doing is fun. What is more surprising is that some quite serious people have thought that this could actually be done. Nuclear rocket engines have been proposed and tested ( “direct” nuclear jet engines too).

“Steady progress was made in engine efficiency and controllability, and in lowering the release of radioactivity” [from here]. Just to make it clear these beasts were no sissy nuclear electrics, the idea was to spray a hot reactor core with hydrogen. Several designs were tested in the atmosphere. The word that surely comes to mind when thinking about this sort of engine test is erosion. One would expect that active parts of the core would be spewed out of the hot end even in normal operation.

There is always the possibility of the not so unlikely turbopump failure. While my limited knowledge suggests that because there is no need for an oxidizer it is a bit easier to design one, the eventual pump failure could still lead to a loss of coolant. Not to worry, they tested (KIWI TNT) what happens if you stop the coolant. Boom.

While my design sketch is a space tug, i.e. it would never be used in the atmosphere thus limiting the release of radioactive substances to the biosphere, these engines were also suggested as upper stages for chemical rockets to boost performance. Then there is of course Project Orion, which from the current viewpoint boggles the mind.

No point, just some perspective.