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

From: Sebastian Stabroth (
Date: Tue Jun 25 2002 - 15:03:43 EDT


> 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.

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.

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. But depending on
the altitude (mean motion) the inclination is simply chosen in such a way that
one gets a sun-synchronous orbit.

> The NOAA satellites are not manoeuvrable, probably because they are not
> required to maintain quite as precise planes as the Earth resources
> satellites. My guess is that their initial plane, mean motion and
> inclination are selected to achieve a mean plane-location during the
> planned mission that is close to some desired mean value.

The NOAA satellites have thrusters to compensate for altitude loss and perhaps
other small perturbing forces.


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