3 ms·

The paper doesn't seem to go into the reaction mass issue much. What are they using for reaction mass? And how do you aim the exhaust? With fission nuclear pro

The paper doesn't seem to go into the reaction mass issue much. What are they using for reaction mass? And how do you aim the exhaust? With fission nuclear propulsion you run out of reaction mass long before you're out of energy. It's a few times better than chemical fuels, but not 10x better.

peterburkimsher 2y ago
The antimatter exhaust could be aimed by putting matter behind it, but it would erode the matter. Better to have it in an electromagnetic field (torus + magnetic monopole) so it doesn't touch the matter. Those electromagnets would need power too, so I guess a battery or RNG (nuclear) solution could be used. What concerns me most is the radiation risk of travelling close to light speed. Surely we'd pass by some ionising radiation, or weakly-interacting neutrinos. I suppose the only way to be sure is to build a prototype and try it.
- Animats 2y ago
  > I suppose the only way to be sure is to build a prototype and try it. Not in our planet's back yard. Maybe behind the moon.
- kelnos 2y ago
  > What concerns me most is the radiation risk of travelling close to light speed. Surely we'd pass by some ionising radiation, or weakly-interacting neutrinos. It's much worse than that. At those speeds, the cosmic background radiation would get blue-shifted to the point that you'd be constantly bathed in x-rays and gamma rays.
ianburrell 2y ago
It is possible to use antimatter directly but it sounds like that only uses the pions with magnetic nozzle. The main use of antimatter is to heat reaction mass. The advantage over nuclear rocket is that the "temperature" of antimatter is really high so the specific impulse can also be high. One advantage is that can change the amount of reaction mass to get more thrust or better efficiency.
- mr_toad 2y ago
  The pions coming out of the reaction are moving at relativistic velocities and provide far more specific impulse.

peterburkimsher 2y ago

The antimatter exhaust could be aimed by putting matter behind it, but it would erode the matter. Better to have it in an electromagnetic field (torus + magnetic monopole) so it doesn't touch the matter. Those electromagnets would need power too, so I guess a battery or RNG (nuclear) solution could be used. What concerns me most is the radiation risk of travelling close to light speed. Surely we'd pass by some ionising radiation, or weakly-interacting neutrinos. I suppose the only way to be sure is to build a prototype and try it.

Animats 2y ago
> I suppose the only way to be sure is to build a prototype and try it. Not in our planet's back yard. Maybe behind the moon.
kelnos 2y ago
> What concerns me most is the radiation risk of travelling close to light speed. Surely we'd pass by some ionising radiation, or weakly-interacting neutrinos. It's much worse than that. At those speeds, the cosmic background radiation would get blue-shifted to the point that you'd be constantly bathed in x-rays and gamma rays.

ianburrell 2y ago

It is possible to use antimatter directly but it sounds like that only uses the pions with magnetic nozzle. The main use of antimatter is to heat reaction mass. The advantage over nuclear rocket is that the "temperature" of antimatter is really high so the specific impulse can also be high. One advantage is that can change the amount of reaction mass to get more thrust or better efficiency.

mr_toad 2y ago
The pions coming out of the reaction are moving at relativistic velocities and provide far more specific impulse.