View Full Version : gravity propulsion
2004-Jan-17, 02:57 PM
Hi again all, I was wondering how does the gravitational propulsion work? I have heard that they have to swing around several planets in order to reach their targets, which has benefits in itself but how does this gravitational 'slingshotting' work?
2004-Jan-17, 05:02 PM
Have you ever "cracked the whip" on skates (ice or roller)? Or watched a figureskating pair where the man whips the woman up to speeds that probably neither one could could get to on their own. I think it is a very comparable effect.
The follower goes around a corner on the outside of the leader, and as they turn the leader pulls on the follower. A large amount of momentum is transferred from the leader to the follower. The planet plays the role of the "whipper" and the satelite plays the role of the "whipee" <G>. When you do this on it on skates the pair have arms connected and the leader pulls with his (or her) muscles. With a planet and satelite there's no physical connection, and gravity does the pulling. With a pair of skaters, the leader is dramatically slowed by the process, but a planet has so much more momentun than the satelite, that no one could even measure the effect on the planet.
The geometry has to be right. And if you've ever done this on skates, you'll know that the exact direction you head off in is hard to control. It always amazes me that they can use this process so precisely with satelites, and do it three or four times in a row successfully.
BTW, for this to work, the satelite obviously has to be orbiting around a different object than the one giving the whip. A satelite orbiting the sun can get a whip off a planet, or a satelite orbiting the earth can get a whip off the moon, but a satelite orbiting the earth cannot get a whip off the earth.
I'm rambling again, but if you check this link out HGS-1 (http://www.spacetoday.org/Satellites/SatBytes/MoonCommsat.html)
You'll find a neat story about using two lunar gravity assist maneuvers to salvage a commercial communications satelite that got stuck in the wrong orbit when it's rocket failed. This was ingenious. It also was the first commercial mission to the moon.
2004-Jan-17, 08:38 PM
If I remeber correctly, you must be talking about Kepler's 2nd law or Newton, the Angular momentum : In the something about the net force thing, the total angular momentum remains constant.
2004-Feb-22, 09:30 AM
This is a different type of Gravitational Propulsion, but I would hate to see it over looked when you are on the topic. That is the Propulsion of machines, through the interaction of the machines parts with Gravity.
I have several designs of these type of machines (Stevenson Spheres) on my home research group, which can be downloaded for free ;
Anyone is free to review this material, photos files for a brief look or download zip files containing all in high res, good enough for examination by experts. Theory is also touched on as well as review on some subject matter by National Science Foundation.
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