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Orbital mechanics: anomaly at epoch -> time of periapsis passage?

  1. Aug 25, 2011 #1
    Hi astrophysics people!

    I am a programmer trying to teach myself the (very) basics of orbital mechanics for a simulation project. Thanks to previous discussions on the subject here, and some articles on Wikipedia, I think I have figured out most of the pieces.

    There is still one thing left, though. Sometimes when I am collecting information about an orbit I have time of periapsis passage (call it Tp) and sometimes I have anomaly (call it m) at a given time (call it Tm).

    (The reason why is that sometimes I have orbital data for well-known celestial bodies, like planets, but other times I only know that at Tm, when it was at anomaly m, the satellite entered the orbit in question for the first time.)

    So the issue is that, as I understand it, the equations for predicting orbital position (v, r) and speed at a given future time depend on knowing Tp. That seems to mean that if I started with {m, Tm} that I need a way to figure out how long it takes to get from m to periapsis.

    So my questions:

    Is my understanding correct?

    If so, how do you get Tp from {m, Tm}?

    If not, what am I missing?

    Thanks to everyone on this forum -- you have already been incredibly helpful. And I apologize if this is really simple, I just have not been able to wrap my head around it.
    Last edited: Aug 25, 2011
  2. jcsd
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