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The phase dependence constraint triggers the scheduling of
observations at specified times of particular astronomical interest.
However, instead of specifying time absolutely (as is the case for
coordinated observations) time is specified in terms of phase by
giving the epoch (in modified Julian days) and the recurrence period
of the event (in days). A suitable observing window satisfying the
specified phase constraint as well as all other general viewing
constraints will then be selected. If the requested number of
observations is more than one, the requested observations will be scheduled
spaced by the specified period, dividing the requested
observing time approximately equally among the individual observations.
In order to avoid loss of accuracy the epoch should be given as nearest
epoch prior to 1 August 1991 in modified Julian date
where ( 
) and the phase must be given
with an accuracy sufficient to allow extrapolations over six months; note
that barycentric corrections are not important for scheduling such
observations.