ACE Weekly Report:  04-11-01

All ACE spacecraft subsystems are performing nominally.  An attitude
maneuver was performed on 04-10-01.  The next attitude maneuver is
scheduled for 04-16-01.

Maneuver Start Time=17:44:35	Maneuver End Time=17:51:39
Pre-Maneuver  HGA = -3.9 deg.  Sun Angle =  8.95 deg.
Post-Maneuver  HGA  = 4.4 deg. Sun Angle =  6.525 deg.
Current S/C range:     1417728.465 km

OCR ULEIS-037 was executed on 4-09-01 to return the ULEIS shutter to
the 100% position.  The shutter had been closed to the 6% position on
04-03-01 to avoid saturation during the recent solar flare.

March Data Recovery Statistics:  99.992%

Anomalies:
G01-0028:  ACE experienced an approximate two minute telemetry
dropout due to 'Antenna stopping unexpectedly' on 04-06-01.
Telemetry returned and no further problems were experienced.  All
affected SSR slices were redumped (DR# L05169).

S01-0003:  ULEIS Shutter Anomaly - The ULEIS shutter failed to close
to the 6% position when OCR ULEIS-036 was executed on 4-10-01.  The
Instrument PI was notified and monitored the re-execution of OCR
ULEIS-036.  A shutter motor error occurred and the shutter failed to
close to the directed 6% position.  OCR ULEIS-038 was submitted and
executed to clear the motor error and to attempt to close the shutter
for a third time.  The motor error occurred again.  The Instrument
team decided to leave the shutter open at the 100% position and
analyze their data regarding the anomaly overnight.
After checking their software code, the instrument team determined
that there was an "error in a software table which tells the s/w
where the center of 100%".  A temporary workaround to this problem
will allow ULEIS shutter to move to the "6% position by using lower
level commands that will bypass the motor test which is where the
error was occurring".  OCR ULEIS-039 was executed on 4-11-01 to close
the shutter to the 6% position using the lower level command.  The
instrument team is investigating the option of uplinking a memory
load to correct the value in the s/w  table.  This activity is TBD.

S01-0004:  ULEIS Shutter Motor Error - During execution of OCR
ULEIS-039 on 4-11-01, the shutter motor error flag was set
unexpectedly.  However the shutter did close to the commanded 6%
position.  The instrument team investigated and determined "that the
software command that moves the shutter by specifying the number of
motor steps to take DOES execute the motor motion test routine.  Just
as we experienced yesterday (4-10-01), executing this routine
sometimes causes the motor error flag to be set. The difference with
the motor stepping command, /ULEIS_MOVE_MOTOR, that was sent today
(4-11-01), is that it ignores the occurrence of this error and moves
the shutter anyway. The higher level commands sent [on 4-10-01] (e.g.
/ULEIS_MOV_TO_POS) do not continue to move the shutter if the motor
motion test fails. Hence, everything is fine with the shutter, other
than the bug which was described yesterday which we need to fix."