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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 th

by 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.

by lodi 8y ago

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.