Author Topic: Gravitational Assist  (Read 8741 times)

Offline Jim

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Re: Gravitational Assist
« Reply #20 on: 05/04/2007 10:00 pm »
Ankle-bone12 - 4/5/2007  5:30 PM

Jim - 3/5/2007  4:45 PM

Ankle-bone12 - 3/5/2007  5:09 PM

When a probe uses a gravity assist and takes a planets ( say Jupiter) gravity, does Jupiter eventually regain that lost "orbit" from when it slows down? if not, then we could theoretically send millions of Gravity Assist probes past jupiter and its rotation would slow drastically.

Sombody please correct me as i think i am wrong here.


it is a momentum exchange.  The amount gained by the spacecraft is lost by the planet.  But it is not the planet rotation that gravity assist affects, it is the orbit around the sun

Thanks so much for clarifying that. I can now sleep at night knowing that The planets will never stop spinning, ( though they may someday become a fixed star in are sky some day,.. if humans still around that is.

Actually, because of the lost of momentum, the orbital energy around the sun is decrease and the planets's orbit is smaller and the periond decreases

Offline Tom Ligon

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Re: Gravitational Assist
« Reply #21 on: 05/04/2007 10:20 pm »
I've not worked out the math myself, but Dr. Bussard once told me there is a second way to use a gravity well to pick up energy.  If you've got to burn some rocket fuel anyway, and your trajectory takes you in to a gravity well, try to arrange to do your burns at or near the bottom, when your velocity is highest.

A given burn produces a specific delta-v.  Do that delta-v at higher velocity and the kinetic energy gain is higher than if you do the burn moving slower out in flater space.  

Slingshot maneuvers take advantage of the relative velocity of the object you're using to do it ... you're doing a direction change into the orbital direction of the that object to pick up speed.  The Sun is pretty much stationary in reference to the rest of the solar system, so tends to be fairly useless for slingshots in the system.  But it sits in a heckuva deep gravity well, and doing a burn close in to it may make sense, if your trajectory is going to take you there.

Offline imfan

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Re: Gravitational Assist
« Reply #22 on: 05/04/2007 11:10 pm »
I cannot resist to promote Orbiter space simulator. It allows to plan also complex slingshot trajectories like Voyager, not even speaking of basic orbital maneuvers.