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Had an, oh, that's how moment - Slingshot manuever

  1. Jun 6, 2013 #1
    Had an, "oh, that's how" moment - Slingshot manuever

    So I've pondered on this off and on, could never see how it was possible, suddenly it just hit me.. tell me if I'm correct.

    In order to gain speed the object is using the orbital (or simply directional) trajectory of another. It allows itself to be pulled/tugged/towed towards, ideally on the same trajectory as the object, siphoning off it's momentum into itself for a boost. I'm assuming the ejection trajectory must be quite steeper than the insertion in order maintain this momentum, taking advantage of the exponential drop off of gravitational pull over distance.

    Makes sense to me, but did I get it right?


    I can also see how coming in the opposite direction could also work as well, by not doing the math though I'm not sure which would produce a better result.

    Sorry, also just realized this probably belongs in the Classical Physics thread. Don't know how to move/delete this original post.
    Last edited: Jun 6, 2013
  2. jcsd
  3. Jun 6, 2013 #2


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  4. Jun 6, 2013 #3


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    You cannot understand gravitational slingshots as two-body problem. Relative to the planet/moon where the slingshot happens, the initial and final speed are always the same*. The velocity relative to a third object (sun/planet) can increase in this process.

    *without propulsion. With propulsion this would use the Oberth effect.
  5. Jun 6, 2013 #4
    Thank you both. Why, oh why, do I think about problems involving the word 'relative'? Tweaks my brain a bit but, at least, it forces me to flex it.

    I'm gonna have to do the math now as my explanation seemed perfectly reasonable. Give me a bit, possibly a couple days, I'm no student and this might take me a bit to wrap my head around.

    Last edited: Jun 6, 2013
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