Re:Voyager 2 is back online after eight months of radio silence
by Retric on Tuesday November 03, 2020 @12:35PM
(#24981830)
Nuclear ION reactors are orders of magnitude more efficient. I think you’re being confused by not actually modeling what’s going on.
Smaller nuclear detonations are less efficient in that they directly liberate less energy from their fuel. A nuclear explosion in space also radiates most of it’s energy as X-Rays which on earth you heat the atmosphere but in space mostly just do nothing. So their directly turning less nuclear energy into motion. Further, a smaller percentage of that force is then collected by the pusher plate compared to the Bell nozzle at the bottom of a traditional rocket. https://en.wikipedia.org/wiki/Bell_nozzle
Now as nuclear is so much more energy dense than chemical energy on paper they look better. But compare ISP’s and you see just how much energy is lost.
All of that can be simplified by just looking at ION thrusters ISP and vs the ISP of hypothetical Orion rockets. At that point it’s just a question of what percentage of mass is reaction mass vs the reactor + fuel and it turns out you can get reaction mass well over 80% making at least 60% more efficient before considering the pusher plate assembly’s mass vs physical ION engine’s mass.
PS: And that’s when looking at existing ION engine designs. Hypothetically, you could eject matter at a large fraction of C using energy giving orders of magnitude higher ISP, at the cost of lower energy efficiency etc.
Smaller nuclear detonations are less efficient in that they directly liberate less energy from their fuel. A nuclear explosion in space also radiates most of it’s energy as X-Rays which on earth you heat the atmosphere but in space mostly just do nothing. So their directly turning less nuclear energy into motion. Further, a smaller percentage of that force is then collected by the pusher plate compared to the Bell nozzle at the bottom of a traditional rocket. https://en.wikipedia.org/wiki/Bell_nozzle
Now as nuclear is so much more energy dense than chemical energy on paper they look better. But compare ISP’s and you see just how much energy is lost.
All of that can be simplified by just looking at ION thrusters ISP and vs the ISP of hypothetical Orion rockets. At that point it’s just a question of what percentage of mass is reaction mass vs the reactor + fuel and it turns out you can get reaction mass well over 80% making at least 60% more efficient before considering the pusher plate assembly’s mass vs physical ION engine’s mass.
PS: And that’s when looking at existing ION engine designs. Hypothetically, you could eject matter at a large fraction of C using energy giving orders of magnitude higher ISP, at the cost of lower energy efficiency etc.