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Interesting concept. Why couldn't we do this with matter? Instead of firing light off at black holes, why not fire some material around a gravity well and allo

Interesting concept. Why couldn't we do this with matter? Instead of firing light off at black holes, why not fire some material around a gravity well and allow it to strike the spacecraft in a way that it A) imparts the inertia it has gathered from whatever body you shot it around and B) is captured to be fired again at a new angle according to your new position? I know there are a ton of logistics to wade through with this, but it should be at least hypothetically possible. It's the same concept as in the article, save for the fact that we are now firing matter around objects we actually can reach in our lifetimes rather than light around black holes that would take an exceedingly long time to propagate.

ajkjk 8y ago
So: shoot ourselves, catch the bullet, shoot again? I think the logistic issues of catching a bullet are probably the limiting factor here. Light at least _wants_ to be absorbed. Matter just wants to go through you.
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lodi 8y ago
You're proposing to fire some material around a planet in such a way that it comes back to a mothership with more momentum than it started with. Now imagine that instead of going "there and back", you find a trajectory that sends it from planet A, to planet B, then back to the mothership. You're coming back even faster now! Why stop at two planets? Find a trajectory so you can do planet A, planet B, planet C, perhaps planet A again... and so on. Now just delete the mothership from this picture; the 'material' is the spacecraft itself. This is a gravity assist, and by stacking enough of them you can basically pick up as much extra delta-V as you want (at least until you reach Solar escape velocity). https://en.wikipedia.org/wiki/Interplanetary_Transport_Network https://en.wikipedia.org/wiki/Interplanetary_Transport_Netwo... The main drawback is that it can take decades of flying a convoluted series of gravity assists before you get to where you need to go, and that's all within one system. (The two-body idea you proposed has the same problem. The mothership has to sit there and wait while the matter flies back and forth on multi-year long orbits. Also now you have to figure out how to 'catch' a hypervelocity projectile...)
- Rooster61 8y ago
  This idea was to try to get AROUND some of the limitations of a gravity assist. For instance, a gravity assist around a large body might require a solar powered spacecraft to be in the shadow of the object for quite some time, rendering the solar panels useless and requiring a radio blackout. Assuming that the method of firing off the projectile and catching it can move gimballed from the rest of the craft, you could allow the ship as a whole to resume the same attitude/trajectory, save for the acceleration of the returning projectiles. Another thought is that if the projectile were small and aerodynamic enough, you could dip closer into a body's gravity well than the spacecraft could due to atmospheric drag, grabbing more momentum than the spacecraft itself could. The lower periapsis might yeild more delta-v due to the more pronounced Oberth effect than the spacecraft could provide. That's all assuming you don't go TOO far into the atmosphere with the projectile.
  - jacobush 8y ago
    Or in the case of slingshot around a star, your projectile might be able to take more of a beating than the ship. Something like tungsten balls or something.

ajkjk 8y ago

So: shoot ourselves, catch the bullet, shoot again? I think the logistic issues of catching a bullet are probably the limiting factor here. Light at least _wants_ to be absorbed. Matter just wants to go through you.

deleted 8y ago

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lodi 8y ago

You're proposing to fire some material around a planet in such a way that it comes back to a mothership with more momentum than it started with. Now imagine that instead of going "there and back", you find a trajectory that sends it from planet A, to planet B, then back to the mothership. You're coming back even faster now! Why stop at two planets? Find a trajectory so you can do planet A, planet B, planet C, perhaps planet A again... and so on. Now just delete the mothership from this picture; the 'material' is the spacecraft itself. This is a gravity assist, and by stacking enough of them you can basically pick up as much extra delta-V as you want (at least until you reach Solar escape velocity). https://en.wikipedia.org/wiki/Interplanetary_Transport_Network https://en.wikipedia.org/wiki/Interplanetary_Transport_Netwo... The main drawback is that it can take decades of flying a convoluted series of gravity assists before you get to where you need to go, and that's all within one system. (The two-body idea you proposed has the same problem. The mothership has to sit there and wait while the matter flies back and forth on multi-year long orbits. Also now you have to figure out how to 'catch' a hypervelocity projectile...)

Rooster61 8y ago
This idea was to try to get AROUND some of the limitations of a gravity assist. For instance, a gravity assist around a large body might require a solar powered spacecraft to be in the shadow of the object for quite some time, rendering the solar panels useless and requiring a radio blackout. Assuming that the method of firing off the projectile and catching it can move gimballed from the rest of the craft, you could allow the ship as a whole to resume the same attitude/trajectory, save for the acceleration of the returning projectiles. Another thought is that if the projectile were small and aerodynamic enough, you could dip closer into a body's gravity well than the spacecraft could due to atmospheric drag, grabbing more momentum than the spacecraft itself could. The lower periapsis might yeild more delta-v due to the more pronounced Oberth effect than the spacecraft could provide. That's all assuming you don't go TOO far into the atmosphere with the projectile.
- jacobush 8y ago
  Or in the case of slingshot around a star, your projectile might be able to take more of a beating than the ship. Something like tungsten balls or something.