On the other hand, there is another component that is not ignorable,
for some purposes, the one due to the earth moon system. The
catch here is that the moon doesn't actualy orbit the earth, but,
to a two body approximation, the centre of gravity of the earth
moon system, which I estimate to be within the earth but fairly
near the surface.
I think this will be around 1,000 to 1,500 down on the equatorial
value for the earth's rotation for chirp rate, although only 30
to 50 down for peak to peak excursion. As such it would be on the
edge of detectability for a drift scan system at the 50 (or was it
20) mHz bandwidth suggested as a practical limit.