Re: RE: A method of estimating pre-launch elements

From: Sebastian Stabroth (
Date: Wed Jun 26 2002 - 02:02:45 PDT

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    > In fact, there is nothing special about the sun's gravity in a sun-synchronous
    > orbit.
    well, Mike and Ted were absolutely right in their statements!
    The inclination of an orbit only changes if there is a force normal to the
    orbital plane. In this case this force is the Sun's gravity. The Moon tries to
    change the inclination, too. But this force is at one time on the one side of
    the NOAA orbit and a "month" later on the other side. So this effect cancels
    out. Since the direction of a sun-synchronous orbit stays fixed to the Sun, it
    is the driving factor which changes the inclination.
    Now think of a sun-synchronous orbit with the plane exactly aligned into the
    Sun's direction. Then the Sun has no effect on the inclination. The same would
    be true if a NOAA orbit is exactly perpendicular to the Sun. In between the
    inclination can build up (NOAA 16) or down (NOAA 15) over time, depending on the
    initial nodes.
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