Re: Geosynchronous satellites congregate?

From: Steve Walter (
Date: Sun Jun 11 2006 - 18:16:45 EDT

  • Next message: Tony Beresford: "Re: Geosynchronous satellites congregate?"

    I believe, but also don't remember the real Longitude values,
    that geosync satellites near the Atlantic
    have a tendency to drift Westward towards the U.S. West Coast;
    geosync satellites over the Pacific
    have a tendency to drift Eastward towards the U.S. West Coast;
    and there's probably another such area over Asia and/or Europe.
    ['Sorry -- I could have 1 or both of the drift directions wrong.]
    I learned long ago that geosync satellites really do NOT stay
    in 1 place in their orbit; they want to tend towards the gravitationally
    stable places in the orbit, and when there will "hover" near that point.
    Otherwise, their desired Longitude locations require periodic
    stationkeeping maneuvers (when they reach the edge of a pre-defined box
    as they drift in the direction of the stable points) ... the maneuvers will
    push the satellite just enough to reach the other edge of the box,
    and they will then slow down, and turn back towards the stable point.
    I agree that the predominant factors are
    different densities beneath Earth's surface,
    our planet being non-spherical, and
    the little ol' Moon (and Sun) pushing and shoving things
    [not necessarily in that order].
    _ _ _ _ _ _ _ _ _ _ _ _ _
    >Tom Wagner wrote:
    >>As an experiment I tried stepping ahead in time a day at a time. 
    >>What I saw was very peculiar. Within a year or two a lot of the 
    >>satellites that I saw generally south of my position of 92 degrees 
    >>W longitude began to congregate directly south of me. Is this a 
    >>phenomenon that would occur if the satellites did not compensate 
    >>via onboard propellant?
    >The concept of a geostationary orbit is an ideal solution of the two body
    >problem for spherical bodies of uniform density (which can be modeled
    >as points).  In the real world, err, solar system, the earth is not spherical
    >exactly (nor is it exactly an oblate sphere; it's very very slightly pear-
    >shaped).  Thus, there are a couple of longitudes (whose values, unfortunately,
    >I can't quickly lay why hands upon) toward which satellites at geosync
    >altitude are attracted.  They actually would tend to oscillate back and forth
    >past these points, I am told, rather than congregate.
    >Also, satellites' motions are perturbed by more than just Earth's gravity.
    >Every other body in the universe exerts some effect, though probably only
    >those of the Moon's and Sun's gravitational fields are very noticeable.
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