Spinup of geosyncs in eclipse

rkresken@esoc.esa.de
Thu, 20 May 1999 13:49:51 +0100

Hi!
A friend of mine who used to work as Meteosat
spacecraft controller told me about the following
effect:
The Meteosat satellites rotate at about 100 RPM.
Around the equinoxes, they are eclipsed for max
about 70 min. During that time, the satellite
body cools down (I would guess more than 100 K) and
shrinks a bit. This reduces the moment of inertia about
the spin axis and causes a spinup of about 0.1%.
(Conservation of angular momentum)

Shouldn't it be possible to observe this effect on our
beloved geosync flashers? It would certainly be difficult
to observe this directly by measuring the period
directly after eclipse exit, but a phase shift should be
observable.

Rainer