[telescope115]

Gravity-assist is used to sling shot space probes around planets to speed them up on a long journey, say, to another more distant body. Gravity is ALSO used to slow down a spacecraft to allow it to be placed in orbit around that body, so its forward motion energy is being transferred so it can orbit that body.

I don’t know much about physics, but it seems that gravity can be used to “exchange” energy, as well as re-direct it.

[BobL]

I know, just having some fun here. In reality, when a spacecraft zips by a planet and speeds up (picks up energy), the planet, at the same time, slows down (loses energy)*...net result is zero new energy.

*of course the planet doesn’t slow down very much, maybe a trillionith of an MPH or something (probably much less, in fact), so not very noticeable!