6 ms·

ionized particle moving in your frame can be recovered as energy while the particle itself can be used as reaction mass (He) or even as fusion fuel (H).

by trhway 5y ago

ncmncm 5y ago
First, you have to ionize it all.
- trhway 5y ago
  required ionization energy is dwarfed by the particle kinetic energy to be collected which is in MeV.
  - ncmncm 5y ago
    Fine. But how would you achieve it?
ClumsyPilot 5y ago
"ionized particle moving in your frame can be recovered as energy" You also recover it's momentum, which means you slow down. Really you are recovering your own kinetic energy, you are breaking against the interstellar medium, probably very violently and destructively. That's like saying "a building was moving in the frame of reference of the plane, so it didn't crash - it recovered energy." A more advanced version of this concept is known as Buzzard ramjet, and it was calculated to be energy negative https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
- trhway 5y ago
  following your logic we wouldn't be making aerodynamic shapes and would be driving/flying brick shaped vessels instead.
  - ben_w 5y ago
    Making something aerodynamic minimises your losses, it doesn’t “recover” energy. If you have a more precise idea and that was an analogy, I recommend giving that idea in a more precise way — I’ve seen my own “what if” ideas wildly misunderstood by my own poor analogies.
    - trhway 5y ago
      >Making something aerodynamic minimises your losses, it doesn’t “recover” energy. not necessarily. For some parts aerodynamic design means loss minimization, while some parts (like [ram]jet engine inlets or pretty much whole body of a scramjet plane/missile) are designed for ram effect, ie. to recover some of the kinetic energy of the incoming air as the air has velocity in the hull's frame of reference. The same thing for interstellar medium - the "aerodynamic" design would mean either coming up with some means of smoothly redirecting the incoming medium around the ship (probably by ionization and EM field) and/or recovering the energy and collecting the mass, whereis GGP limits the consideration only to the "breaking against the interstellar medium, probably very violently and destructively."
      - ben_w 5y ago
        “ram effect” isn’t something I can Google (I get pages about farming); the closest I’m familiar with given the context would be ram compression of air intakes in engines, but that’s for increasing the mass flow though the engine, not energy recovery. The only engine I’ve heard of that attempts to use the ISM as a source of fusion fuel is the Bussard ramjet referenced by @ClumsyPilot (which uses an EM field), and as they point out, it’s been demonstrated to be a net-loss not a net-gain. An easy way to intuit this result is that the energy per particle of a fusion reaction is similar to the 14 MeV per particle (0.82-22.4 MeV for the most promising reactions) which I used as a starting point in my calculation. You’d actually have to decelerate the ISM from the frame of reference of the ship in order to increase the rate of fusion to its maximum, but even then most nucleon impacts do not cause fusion and instead bounce, slowing you instead of helping you even if you can solve the problem of efficiently using the energy of any particles you decelerated at the front of your ship to accelerate them again at the back.

ionized particle moving in your frame can be recovered as energy while the particle itself can be used as reaction mass (He) or even as fusion fuel (H).

by trhway 5y ago

ionized particle moving in your frame can be recovered as energy while the particle itself can be used as reaction mass (He) or even as fusion fuel (H).

ncmncm 5y ago

First, you have to ionize it all.

trhway 5y ago
required ionization energy is dwarfed by the particle kinetic energy to be collected which is in MeV.
- ncmncm 5y ago
  Fine. But how would you achieve it?

ClumsyPilot 5y ago

"ionized particle moving in your frame can be recovered as energy" You also recover it's momentum, which means you slow down. Really you are recovering your own kinetic energy, you are breaking against the interstellar medium, probably very violently and destructively. That's like saying "a building was moving in the frame of reference of the plane, so it didn't crash - it recovered energy." A more advanced version of this concept is known as Buzzard ramjet, and it was calculated to be energy negative https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet

trhway 5y ago
following your logic we wouldn't be making aerodynamic shapes and would be driving/flying brick shaped vessels instead.
- ben_w 5y ago
  Making something aerodynamic minimises your losses, it doesn’t “recover” energy. If you have a more precise idea and that was an analogy, I recommend giving that idea in a more precise way — I’ve seen my own “what if” ideas wildly misunderstood by my own poor analogies.
  - trhway 5y ago
    >Making something aerodynamic minimises your losses, it doesn’t “recover” energy. not necessarily. For some parts aerodynamic design means loss minimization, while some parts (like [ram]jet engine inlets or pretty much whole body of a scramjet plane/missile) are designed for ram effect, ie. to recover some of the kinetic energy of the incoming air as the air has velocity in the hull's frame of reference. The same thing for interstellar medium - the "aerodynamic" design would mean either coming up with some means of smoothly redirecting the incoming medium around the ship (probably by ionization and EM field) and/or recovering the energy and collecting the mass, whereis GGP limits the consideration only to the "breaking against the interstellar medium, probably very violently and destructively."
    - ben_w 5y ago
      “ram effect” isn’t something I can Google (I get pages about farming); the closest I’m familiar with given the context would be ram compression of air intakes in engines, but that’s for increasing the mass flow though the engine, not energy recovery. The only engine I’ve heard of that attempts to use the ISM as a source of fusion fuel is the Bussard ramjet referenced by @ClumsyPilot (which uses an EM field), and as they point out, it’s been demonstrated to be a net-loss not a net-gain. An easy way to intuit this result is that the energy per particle of a fusion reaction is similar to the 14 MeV per particle (0.82-22.4 MeV for the most promising reactions) which I used as a starting point in my calculation. You’d actually have to decelerate the ISM from the frame of reference of the ship in order to increase the rate of fusion to its maximum, but even then most nucleon impacts do not cause fusion and instead bounce, slowing you instead of helping you even if you can solve the problem of efficiently using the energy of any particles you decelerated at the front of your ship to accelerate them again at the back.