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

From: Ted Molczan (
Date: Tue Jun 25 2002 - 16:23:50 PDT

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    Sebastian Stabroth wrote:
    > the perturbation of the Sun's gravity is very small compared 
    > to other "anomalies" for this orbit type. The Moon's gravity 
    > would have about the same small disturbing effect or even more.
    The force is small, but it builds up over time, causing the inclination
    to change significantly, which in turn causes the orbital plane to drift
    far from its original location. I found several scientific papers on the
    web that mention this as a limitation on the usefulness of data from
    certain of the NOAA sensors.
    > My guess is that there are two different altitudes: one for 
    > the "afternoon" and one for the "morning" orbit. I don't know 
    > the reason for this. 
    I have found the reason on page 20 of this document:
    "Two nominal altitudes have been chosen: 833 km (450 n.mi.) and 870 km
    (470 n.m.). The choice between nominal altitudes will be made to keep
    the orbital periods of two operational satellites in similar orbits
    sufficiently different (1 minute) so that they do not both view the same
    point on the Earth at the same time each day."
    Ted Molczan
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