ACE Weekly 07/19/02 - 07/25/02

All ACE spacecraft subsystems are performing nominally. No attitude 
maneuvers were executed this week. The next attitude maneuver is scheduled 
for 07/30/02.

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Ongoing Activity:
The engineering test to determine the new HGA constraint is continuing. The 
current constraint is 6.0 deg., with current tests reaching 6.5 degrees.

The FOT has been monitoring the Signal Strength, the MFR AGC levels, and 
the Signal-to-Noise Ratios(SNR). The drop in RF levels from an HGA angle of 
0 deg to 6 deg has been approximately 3dB. There has been no loss of 
telemetry due to the increased HGA angles.  Once all analysis has been 
completed, the new HGA constraint will be determined.

The following HGA angles and range values are from FDF.
Man Date Pre Man   Post Man    Earth-ACE Range
03/28/02 -4.58 deg  +4.38         1408287 km
04/04/02 -4.35      +4.50         1414808
04/11/01 -5.09      +3.79         1428491
04/18/02 -5.16      +3.85         1440512
04/26/02 -5.77      +5.56         1455949
05/06/02 -5.72      +5.43         1493008
05/17/02 -5.81      +5.31         1527979
05/28/02 -4.34      +4.88         1550263
06/06/02 -2.38      +5.96         1576064
06/20/02 -6.57      -3.66         1590405
06/26/02 -6.43      +5.94         1592458
07/12/02 -6.5       +6.5          1598879

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Stationkeeping Maneuver Information from FDF

We have a stationkeeping maneuver (SK-26) scheduled for Tuesday, July 30, 
to be followed by an attitude reorientation.  The delta-V direction will
be Sunward, requiring the aft-end canted axials 3A and 4A.  Based on the 
latest OD, halo re-targeting results show a delta-V of 0.908 m/sec is 
needed.  Preliminary finite burn modeling predicts a burn duration of 162.7 
sec (2.7 min) and a fuel usage of 0.634 lbm (0.288 kg).  Also, we expect to 
see a spin rate drop of around 0.037 rpm from this burn (no spin correction 
maneuver will be necessary).

The required spin range is 4.90 to 5.10 rpm.  Since we're at right about 
5.0 at the moment, we'll end up at about 4.96 rpm, well within the 
tolerances by 0.06 rpm.

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Anomalies:

DOY 02203 (07/22/2002) - ACE Anomaly #S02-0018  Prop Tank A2 Temp. at YL
At 13:45:43 the A2 propellant tank temperature, mnemonic TANK_A2_T, flagged 
as a YELLOW LOW database limit violation at a value of 9.65 degrees C. It 
returned within database limits at 13:45:48 with a value of 10.9 degrees 
C.  Duration = 5 seconds  IMPACT:  None

DOY 02204 (07/23/2002) - ACE Anomaly #G02-0087  DSN - Delayed Command Carrier
At approximately 12:40UT, the station called "go for command", but VCO 
levels were fluctuating around -30 kHz.  MOC requested that the station 
perform a resweep doubling the sweep range (i.e. 120 kHz). The station 
performed the resweep and the VCO level settled into its expected value of 
between 0 and 1.92 kHz at approxiamtely 12:46UT. No further problems were 
encountered.  IMPACT:  Minimal. Commanding was delayed by ~5 
minutes.  DR#G101423

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Glen A. Miller
Honeywell Technical Services Inc.

ACE Flight Operations Team
Goddard Space Flight Center
Bldg. 14, Rm. W10A
Mail Stop 428.2
Greenbelt, MD 20771

Office: 301-286-7071
Fax:    301-286-1729
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