RE: A method of estimating pre-launch elements

Date: Wed Jun 26 2002 - 01:39:33 PDT

  • Next message: Sebastian Stabroth: "Re: RE: A method of estimating pre-launch elements"

    Thanks Ted for your very helpful posting!
    One remark concerning sun-synchronous orbits:
    >This must be by design, and my guess is that it has to do with the
    >perturbation caused by the sun's gravity, that strongly affects
    >sun-synchronous orbits. This perturbation varies somewhat depending upon
    >the orientation of the orbital plane with respect to the sun. In some
    >cases, it causes orbital inclination may vary by more than one degree
    >over a long period, causing the plane to wander away from its original
    In fact, there is nothing special about the sun's gravity in a sun-synchronous
    orbit. In such an orbit, you make use of an effect of the oblatness of the
    It causes the orbital plane (the line of nodes) to rotate in inertial space.
    Direction and speed depend on the orbital elements. If you choose a retrograde
    orbit with a certain inclination (typically abouy 98 degrees), the line
    of nodes rotates by about 1 degree per and compensates the anual motion of
    the sun (or earth, depending on your point of view). This is very helpful
    for many applications, especially all kinds of earth observation.
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