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From chapman@stsci.edu Wed Sep 7 15:43:58 2011
Date: Wed, 7 Sep 2011 15:43:50 -0400
From: George Chapman
To: opm@stsci.edu
Subject: Gyro 4 & Science

As you will have seen by now, Gyro 4 suffered a motor current spike at
250:15:22:21 GMT resulting in attitude errors. б Until the gyro rate bias can be
corrected and attitude errors reduced HST science is expected to be compromised
due to failing guide star acquisitions. б Recovery is not expected before
250:00:15 GMT.
No critical science is scheduled between 250:15:22 and 251:12. б We only examined
out to 251:12. б A 6 hour STIS MAMA is currently in progress (250:19:24 -
251:01:16). б 

-George

Begin forwarded message:

From: "Smith, Daniel C."
Date: September 7, 2011 3:01:21 PM EDT
To: List - Ops Flash Report
Subject: Sci: Flash - Gyro 4 Motor Current Increase

Gyro 4 motor current flagged OOL high at 250/15:22:21. Initial PCS
assessment is G4 MC increased from ~120 mA to ~190 mA with a peak
transient of 254 mA. The event occurred during a maneuver, and rate
transients were observed during the event, resulting in a number of
control law parameter out of limits and KM firings.б  This event has been
documented with the generation of HSTAR б 13002.б 
б 
SAC processing of an OBAD executed following the maneuver (at 15:36)
indicated approximately 5000 as of attitude error.б  Initial commanding to
increase the correction limit for onboard determined attitude corrections
has been increased from 1 degree to 10 degrees with the execution of Ops
Request 19123.б  Recovery to the science timeline is extended due to long
periods of LOS.б  A plan is in place to correct rate bias error resulting
from the change in motor current, with recovery to the science timeline
expected no earlier than about 251/00:15 GMT.б  A second flash report will
be issued when recovery has been completed.

б 
Dan Smithб б б 
б 
MOSES II Systems Engineering Manager
Hubble Space Telescope Programб б 
Office 240.684.1166б б б 
Cell 240.472.3445
б 
б