ACE Weekly 02/13/2008 - 02/19/2008
All ACE spacecraft subsystems are performing nominally.
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Orbit/Attitude:
DSS-27 is unavailable for the attitude maneuver on Tuesday 02/19/2008 (see
AR#G08-0024). The maneuver is being rescheduled for Wednesday 02/20/2008.
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OCRs:
None
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Activities:
None
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Anomalies:
DOY 045 02/14/2008 S-ACE-0278 G08-0018 Unknown TPOCC Error
TPOCC generated an error and returned a value of "[STM224] 0" when reading
the variable EXTERNAL_HOST_FWD#ENIF_1. The reason for the error is unknown
and has not occurred since.
IMPACT: Minimal. ACE MOC tried to bind SLE FCLTU for 10 minutes after End
Of Track.
DOY 047 02/16/2008 S-ACE-0279 G08-0019 AC1WS3 Workstation Failure
ACE MOC workstation on the prime string failed. ROBOTT did not successfully
fail over to string 2 for Saturday's pass (02/16/2008). FOT arrived at the
ACE MOC around Beginning Of Track and completed manual failover. Hardware
maintenance replaced the workstation on Monday 02/18/2008. System
configuration still needs to be performed.
IMPACT: Manual intervention required. Saturday pass activities delayed 45
minutes. The Sunday pass was extended 90 minutes. All SSR data has been
captured.
DOY 047 02/16/2008 S-ACE-0280 G08-0020 ROBOTT/C&C Unable to Connect
During the manual failover to string 2, C&C could not connect to TPOCC.
This is the same problem as AR#G08-0010 01/26/2008. This is an intermittent
problem and the cause remains unknown.
IMPACT: Manual failover to String 3 on Saturday 02/16/2008.
DOY 047 02/16/2008 S-ACE-0281 G08-0021 ROBOTT Not Configured for CMD
During the manual failover to String 3, the auto_env file was updated but
rtgeniecc.deffacts was not. On both Saturday and Sunday, TPOCC needed to be
manually connected to SLE. On Sunday (after fixing TPOCC),
rtgeniecc.deffacts was finally updated.
IMPACT: Sunday 02/17/2008 activities delayed 1 hour.
DOY 048 02/17/2008 S-ACE-0282 G08-0022 Postpass Activities Not Performed
For unknown reasons, ROBOTT thought the Sunday pass was deleted. This was
determined at 15 minutes before End Of Track. All pass activities were
completed, but postpass activities were not.
IMPACT: Minimal. Software cleanup and data archiving performed on Monday
02/18/2008.
DOY 049 02/18/2008 S-ACE-0283 G08-0023 String1 /trend Drive Fan Replaced
The cooling fan on the /trend hard drive had failed. The fan was replace by
SysAdmins.
IMPACT: If the cooling fan had not been replaced, the hard drive would have
failed due to overheating.
DOY 050 02/19/2008 S-ACE-0284 G08-0024 DSS-27 Red
DSS-27 is unavailable for the scheduled attitude maneuver due to a cut fiber
optic cable that has impacted all communications to Goldstone.
IMPACT: The attitude maneuver will be rescheduled for Wednesday 02/20/2008.
The High-Gain Antenna (HGA) aspect angle will reach 8.22 degrees.
Wednesday's expected high-rate downlink SNR is expected to be 6dB, which is
above the mission requirement of 3dB.
DOY 049 02/18/2008 S-ACE-0285 G08-0025 FORMATS Transmit Process Down
The ACE MOC FORMATS Transmit process was not running.
IMPACT: Clock Calibration Reports and Attitude Orbit Reports from the
weekend were not transmitted until Tuesday.
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Background Information on Attitude Constraints:
An HGA constraint of 8 degrees is used to give enough buffer to the
precipitous droppoff in HGA performance between 10-11 degrees.
If the HGA angle does go beyond 10 degrees and DSN could not acquire the
high-rate data from the HGA, then the downlink would be commanded to a lower
bit rate. If that failed, the spacecraft would be commanded to use the
broad beam antennas.
The other attitude constraint is the sun angle (4-20 degrees). If the sun
angle reaches 21.8 degrees, the ULEIS instrument shutter will be closed. If
the Sun angle goes below 4 degrees, an attitude maneuver can still be
performed, but there will be a larger error in the target attitude. The
reason is that at small sun angles, nutation has a larger impact on when the
sun pulse occurs and maneuver timing is based on the sun pulse. If the sun
angle was below 4 degrees, a more conservative attitude target would be
used.
With the current attitude:
HGA > 10 deg Friday 02/22/2008 at 1700z
Sun < 4 deg Would not happen
Sun > 20 deg In 3 weeks
The rate at which the spacecraft reaches the attitude constraints depends on
the attitude and the spacecraft's position in the L1 halo orbit.
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Background Information on Hardware Failures:
The following table shows various ACE MOC hardware failures from 2004 -
2008. Some of recent hardware failures have been due to repeated problems
with a specific workstation (ac1ws3). This workstation has now been
replaced.
2004 2005 2006 2007 2008 (as of 02/19)
WS Monitor 1 3 2 2 2
WS Power Supply 2 4
WS Hard Drive 5 1 2
WS/XT Motherboard 1 2 2 1
Tape Drive 1 2
PC drives+motherboard 1 1 1
Printer 1 1 1
Keyboard/Mouse 2 1
Voice/VDS 1 1
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10 9 9 10 6