Gravicapture

[KvickFlygarn87]

Would it be possible to swing by a massive (as in, a lot of mass, not necessarily super large) satellite in order to get captured in a planet's gravity well?

[SargeRho]

Yes, it actually happened quite a few times in the solar system's past.

[Ralathon]

Yes, but only under some very specific circumstances.

First of all, the satellite needs to be moving extraordinarily slow when it passes the planet. As in, only barely faster than escape velocity.

Second, it needs to pass very close over the planets surface, the lower the better (provided you don't crash).

Thirdly, the planets needs to be easily deformable. So this won't work for very dense objects like neutron stars or black holes.

The planet needs to rotate slowly, so that the surface is moving slower than the satellite that passes over it.

Basically what happens is that the attraction of the satellite causes a tidal bulge on the surface of the planet. This bulge has some resistance and therefore moves slower than the satellite. Since any action has an equal and opposite reaction this resistance effectively slows down the satellite. But the effect is very small in most cases, that's why you need all the above things to maximize the effect.

We can see the reverse happening in the Earth-Moon system. The earth spins faster than the moon orbits. So in our case the tidal bulge is ahead of the moon, in effect slowing down the earth's rotation and accelerating the moon. This causes the moon to widen its orbit by about 4cm per year and slows down the earths rotation. Every year the day becomes 1.7 microseconds longer.

EDIT: Nevermind, reading comprehension = 0. Thought you where trying to capture a massive object in a single body's gravity well. What you're saying is possible too, and in fact much easier. You just need to get a gravity assist of the moon. You can even do this in KSP, the Jool system is great for gravity assists. You can easily capture yourself into the Joolian system without aerocapture and use grav assists to get you back out.

Edited March 13, 2014 by Ralathon

[KvickFlygarn87]

Alright, thanks!