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I wrote:

> ...  if GPS is available for part of the voyage, it can be
> used to maintain the orbits.  These optical observations are pretty
> good and will start to contribute useful orbital corrections after
> only a few days (provided GPS position is available).  If and when GPS
> is lost, the orbits will be in better shape than they would have been
> otherwise.

Variation on this idea:  use lunar observations for the same purpose.
Of course lunars are much worse than GPS, but they have the merit of
being good long-term, so whatever accuracy is available from lunars
can be transferred to LEO objects, effectively making the lunars more
available.  The same would go for any object with a reliable long-term
orbit available, but the Moon would seem to be the biggest and
brightest in this category.

It would be quite a few weeks, though, before LEO orbits would degrade
to the accuracy obtainable from a lunar position.

Cheers,
Peter

   

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