Nostr Web Client

What about Europa? Sure, Jupiter is long way out, but Europe has a ready supply of water, and Jupiter's moon system probably has useful in-situ resources we could use to manufacture fuel. Then you have a gas station on the way to the outer solar system.

Realistically, the Moon is probably the first place to go, since it's close enough to allow easy resupply from Earth. If we embrace nuclear propulsion we should be able to make fairly regular trips between Earth and Mars.

Daniel Wigton 1y ago

Nuclear isn't as attractive as I would wish. Efficiency is driven by exhaust velocity which is in turn a function of exhaust particle mass and temperature. Temperature is limited by material science, you can't melt your engines, so the only dial you can turn is particle mass. With nuclear you can use pure hydrogen (H2) instead of H2O for a chemical hydrolox engine. So atomic mass of ≈ 2 instead of 18.

That is a factor of 9. But temperature is kinetic energy so solving e=1/2 m*v^2 for velocity is v is going to result in a square root of mass. Sqrt(9) = 3. So the best nuclear can do is 3 times more efficient than chemical. Actually it isn't even that good because we don't burn hydrolox engines at stoichiometric fuel ratios. We burn fuel rich to lower the average atomic mass of the fuel. I.E. we expell unburnt H2. So the actual nuclear benefit is about 2x in theory.

Reply to this note

Please Login to reply.

Discussion

Daniel Wigton 1y ago

This is ignoring that nuclear will invariably have a worse mass fraction and thrust to weight ratio making the comparison even worse.

It all annoys me, we need better materials.

MichaelJ 1y ago

That may be true for nuclear rockets, but what about nuclear pulse propulsion?

I suppose many of the proposals I've seen for really effective nuclear rockets use some sort of magnetic containment to skirt the materials limitations. That's probably a shaky thing to deal with, if nuclear fusion attempts are any indication.

Daniel Wigton 1y ago

Yes. Nuclear pulse is better. Magnetic confinement might work for fusion but it would be tricky for fission. You'd have to let your nuclear fuel melt or even vaporize to get hot enough. That'd be a bear to regulate without control rods.

You can do nuclear electric with ion engines, but those are such low thrust that they'd still be slower than chemical in the inner solar system. Could be very attractive for missions to the outer planets though.

MichaelJ 1y ago

Nuclear pulse would be the way to bootstrap ourselves into the solar system, IMO. Powerful and efficient. Long-term you want fusion, but you can figure that out later.

Low Information Voter 1y ago

Electrostatic dusty plasma, muh man. Proven in lab, never flown.