I remember reading a short story in the 60/70's where there were two astronauts in spacesuits on an orbiting platform having some sort of dispute. One of them successfully threatens the other to by hurling him towards the planet whereby he believes that he doomed to keep falling. It turns out, however, that following orbital mechanics ( conservation of the center of gravity ) that the hapless astronaut will rejoin the platform halfway through the revolution. I thought this was a Clark or Asimov since it involved some real physics but I can't seem to locate the title.

  • I doubt this Clark, Asimov or Heinlein because it would be very difficult to make this actually work. Oxygen consumption during the trip being a key part. Even with lots of O2 is difficult to imagine the physics (sans thrust by body) that would return a body to a orbiting station, where it received an outward/planet side push. – James Jenkins Dec 29 '13 at 19:15
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    @JamesJenkins As a matter of fact, Clarke did write a short story with the exact same plot twist: Jupiter Five, though the wikipedia synopsis doesn't describe this part. In short, the good guys hurl the bad guy out from the Jovian moon Amalthea, which successfully threatens him and his team into submission; then it's revealed that the bad guy needs no saving, as he'll just come back at the next revolution. I also recall Clarke saying that the physics of it are sound. – SáT Dec 29 '13 at 20:48
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    @JamesJenkins If this was in low earth orbit, the rendezvous would be ~45 minutes or 90 if it took 1 revolution. I would assume there would be enough O2. The notion is that since both bodies were part of a single mass and then pushed apart by a common force, they have to intersect again at a period related to the orbital period. If the bodies were pushed apart in such a way (tangentially) that they had different tangential velocities, They would end up indefinitely apart in an upper and lower orbit. – Wayne Dec 29 '13 at 22:00
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    @SáT I bet that's the story the OP is looking for, maybe you should post it as an answer. – user14111 Dec 30 '13 at 0:42
  • The physics is sound to first order, but there are higher order perturbations, so you need some means to grab the victim on closest approach which will be reasonably close, but not exact. Nor, to first order, does it matter in which direction the victim is pushed, the orbits are still nearly intersecting on one full orbit (but not on a half orbit). – dmckee --- ex-moderator kitten Dec 30 '13 at 2:40

Sounds like Clarke's "Jupiter Five".

The Satellite in Question (we call it "Amalthea" now) has turned out to be be a giant spaceship built by an extinct alien race, and two rival expeditions learn this at the same time. One of them steals a valuable artifact from the other, who retaliate by throwing its leader into Jupiter - secure in the knowledge that in one orbit he'll be back where he started and can be picked up.

The story was anthologised in Reach For Tomorrow and no doubt elsewhere.

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