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Mon Apr 17 12:19:38 2006
From: William Workman
Subject: HST Inertial Hold safemode recovery plans


The cause of the Inertial Hold safemode has been determined to be
related to a command scheduling logic problem between the FGS ITS
(Internal Test Source) test activity and the standard PCS termination
activity which must occur at the start of earth and moon occultation
events. The problem prevented the scheduling of the PCS termination
commanding which in turn allowed the FGS high voltage to remain turned
on during the occultation event that followed the FGS ITS activities.
The associated onboard Earth-Moon Bright Object Protection check
failure condition properly initiated the immediate spacecraft
transition to Inertial Hold. The current failure is strictly related to
the FGS ITS test scheduling and has no implications for recovery of the
science activities. As Tom's message indicates, all SI's are available
for immediate recovery for science operations. According to operations
procedure, a 12 hour Health and Safety SMS has been generated and was
uploaded to the spacecraft to begin execution at 107/15:00:00 (11:00am
local). Correspondingly, the science timeline will be begin at
108/03:00:00 (11:00pm tonight). The science schedule is being reworked
in an attempt to salvage time critical observations that have been
impacted by the safing event. We are hopeful that we will be able to
recover most of these activities on the current schedule. Rescheduling
of the FGS ITS test is deferred pending further investigation.
Additional updates on this and the status of the science recovery
schedule will be sent as information becomes available.

--Bill