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  1. #1
    Senior Member Captain Blight's Avatar
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    Neil DeGrasse Tyson hasn't answered me

    ... On the Facebook, so naturally I thought I'd ask the foosters.

    Is orbital velocity the same no matter which dirction the orbit is moving? I say a polar orbit, a retrograde orbit, and an orbit with the rotation of a body are all the same given equal altitudes. My friend, who is WRONG, says that a retrograde orbit needs to be twice the speed of a co-rotational orbit.

    What says Foo? Asshat if you must, but if someone actually knows and can point me to the actual math, you'll have the satisfaction of knowing you've helped me win a 6er of delicious beer.
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  2. #2
    You Know!? For Kids! jsharr's Avatar
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    I think he is wrong. The formula V = square root of G*M/r seems straight forward. However, achieving retrograde orbit for an earth launched satellite takes much more energy to achieve that placing an earth launched satellite in prograde orbit. The end orbital velocity of both would be the same, assumed both satellites were placed into orbit equal distance from the center of the earth.
    Last edited by jsharr; 10-24-12 at 07:28 PM.
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    Quote Originally Posted by colorider View Post
    Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.

  3. #3
    Senior Member Captain Blight's Avatar
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    That's what I thought too, thanks for the math. I know planar changes are energy-expensive but if one were to (theoretically) launch in a co-rotational plane and over the course of several hundred orbits change direction over the pole, you could end up with a retrograde orbit. I suppose that it's like anything else, doing it slowly takes less energy than trying to do it fast.

  4. #4
    Senior Member Shimagnolo's Avatar
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    My favorite Tyson video clip: http://www.youtube.com/watch?v=8B6jSfRuptY
    A bit long, but the punchline (Cameron's response) is worth it.

  5. #5
    Senior Member
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    But the earth is not a perfect sphere is it? I wonder if this has something to do with it.

  6. #6
    Senior Member mikeybikes's Avatar
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    Moot discussion. The answer is always 42.
    My Bikes: 2009 Breezer Uptown EX | 1980 Miyata Six Ten | 1970 Hercules Three-Two-Speed
    Wife's Bikes: 2008 Globe City 7 | 1972ish Peugeot UO-18 (in progress)

  7. #7
    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by bjtesch View Post
    But the earth is not a perfect sphere is it? I wonder if this has something to do with it.
    jsharr posted the correct formula. Where the center of mass is located, is all that matters to the object orbiting it.

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