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when rockets are put in orbit, could they stay in orbit forever? if there was no one to man it, and it was not programmed to come back down, what would happen? would it stay up there, or would earth's gravity pull it back down?

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    $\begingroup$ Side note: Vanguard 1, the 4th artificial satellite ever launched (it was in 1958) is the oldest man-made object still in space. en.wikipedia.org/wiki/Vanguard_1 $\endgroup$ – Organic Marble Jan 18 '16 at 17:14
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    $\begingroup$ I hope the moon's pilot is still awake... :) $\endgroup$ – Steve Jan 18 '16 at 21:21
  • $\begingroup$ yes, that's what being in orbit means. $\endgroup$ – njzk2 Jan 18 '16 at 21:51
  • $\begingroup$ Well, eventually it would be destroyed by the Sun expanding ;) $\endgroup$ – Sarah Bailey Jan 18 '16 at 22:28
  • $\begingroup$ @SarahBailey That depends on the rocket's orbit, doesn't it? While perhaps not exactly rockets, I doubt the Voyager probes will be bothered much by the Sun expanding, for example... $\endgroup$ – a CVn Jan 19 '16 at 9:57
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There's the simplistic theory, and the more complicated practice.

In theory, yes, an object put in orbit would stay there forever. Earth's gravity pull keeps it in orbit, spinning it around the planet instead of flying off. It doesn't pull it back down, because the forces are already balanced.

However, in practice, there's other forces in play. Most importantly, on low Earth orbits, there's just a tiny bit of atmosphere leftovers slowing down the object. Depending on the altitude, it might take months, years, or decades, but eventually it will slow down enough to reenter. Also, there are minute forces from solar radiation and gravitational fields of other objects that might slow down the object (though that might take an awfully long time).

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