ACE Weekly 11/08/2011 - 11/15/2011
This week's report covers 8 days. Problems with the downlink during
this week's Solar Exclusion Zone transit (SEZ) resulted in data loss.
All ACE spacecraft subsystems are performing as expected.
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Orbit/Attitude:
Type Attitude Attitude
Date 11/11/2011 11/14/2011
DOY 315 2011 318 2011
Thrusters 2R 4R+ 4R- 2R 4R+ 4R-
Duration 22:07 min 3:40 min
Start 20:35:56z 22:02:35z
Stop 20:58:03z 22:06:15z
HGAStart -7.93deg +5.84deg
HGAStop +8.50deg +3.43deg
SunStart 8.74deg 6.37deg
SunStop 7.62deg 4.07deg
SpinStart 5.0300rpm 5.0364rpm
SpinStop 5.0364rpm 5.0372rpm
Nutation 0.07deg 0.11deg
Firing 112 pulses 19 pulses
FuelUsed 0.34201lbs 0.0680lbs
FuelRemain 125.7080lbs 125.6400lbs
FinalSCMass 1359.968lbs 1359.900lbs
A second maneuver was performed on Monday 11/14/2011 to align the
spacecraft's antenna more closely with Earth. The HGA angle was moved
from 5.84 to 3.43deg and the SNR increased by 3dB. This improved the
chances of obtaining high-rate data on Tuesday 11/15/2011. The
spacecraft will drift down to a sun angle of 3 degrees over the next few
days (See MOCR 371).
The next attitude maneuver is scheduled for Monday 11/21/2011.
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OCRs:
DOY 318 (11/14/2011) MOCR 371 - 4 degree sun constraint
Approval was given to allow the spacecraft's sun angle to drift below
the 4 degree sun constraint. When ACE is along the Sun-Earth line
(small Sun-Earth-Vehicle angle), it is not possible to have the
spacecraft antenna pointing directly back at earth AND have the sun
angle be greater than 4 degrees. (see ascii figure below)
Large SEV angle Small SEV angle
Sun Sun
\ | \ |
ACE | \|
\ | ACE
\ | |\
\| | \
Earth Earth
The known reason for maintaining the 4 degree sun constraint is that
small sun angles cause spacecraft nutation to have a larger affect on
the sun pulse timing by a factor of 1/tan(sun angle). Nutation
affecting the sun pulse timing has the following impacts: (1) Maneuvers
starting with a small sun angle have greater error in reaching the
target. (2) Maneuvers ending with a small sun angle degrade the science
data for a longer period. However, there are no known reasons for not
allowing the spacecraft to drift through the 4 degree sun constraint
when there is no nutation.
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Activities:
SOLAR EXCLUSION ZONE
The following table provides the Sun-Earth-Vehicle (SEV) angles and the
Signal to Noise Ratio (SNR) of the downlink signal. The solar activity
was higher during this transit than in previous transits including the
August 2011 transit.
Date DOY DSS Time SEV angle hi-rate SNR hi-rate lock?
--------- --- --- ---------- --------- ----------- -------------
Sat 11/12 316 D27 1455-1825z 0.82-0.76 -5 to +2dB after 1700z
Sun 11/13 317 D34 0015-0115z 0.69-0.67 +1 to +2dB yes
Sun 11/13 317 D27 1950-0000z 0.46-0.44 -11 to -3dB no
Mon 11/14 318 D65 0820-0910z 0.42-0.42 -11dB no
Mon 11/14 318 D27 2040-2320z 0.48-0.50 -9 to -6dB no
Tue 11/15 319 D24 1955-2230z 0.77-0.80 +5 to +7dB yes
The DOY 316 problems were unexpected and resulted in ~2.5 hours of data
loss. DSN antenna availability has been reduced due to the GRAIL
mission. Unfortunately, TDRSS 10 declared a spacecraft emergency and
took the ACE pass on Tuesday 11/15. Fortunately, DSN Maintenance
released DSS-24 and 25 out of 43 hours of data was recovered. Some of
the data loss is covered by realtime ADC and Science data. The
following table provides the data gaps for the week.
Weekly Data Capture:
88.30% CRIS, EPAM, MAG, SWEPAM-Ion & SIS
89.78% SWEPAM-Electron, SWICS, SWIMS & ULEIS
DOY Gaps seconds Notes
--- ----------------- ------- -----------
315 20:31:31-20:31:32 2 ADC covers
315 20:33:23-20:33:24 2 ADC covers
315 20:53:01-20:53:02 2 ADC covers
316 14:27:42-16:30:37 7376 no data
316 16:30:38-17:00:29 1792 ADC covers
316 17:00:30-17:12:11 702 intermittent data
316 17:12:12-17:15:10 179 ADC covers
317 17:16:15-19:58:36 9742 no data
317 19:58:37-20:21:02 1346 ADC covers
317 22:26:07-00:00:07 5641 ADC covers
318 00:00:08-12:12:49 43962 no data
Total data loss
17 hrs 9 min 42 sec no data & intermittent data
2 hrs 29 min 24 sec ADC covers
--------------------
19 hrs 39 min 6 sec
The ADC data format includes data from 4.5 of the 9 instruments CRIS,
EPAM, MAG, SWEPAM-Ion & SIS. Not included are
SWEPAM-Electron, SWICS, SWIMS, SEPICA & ULEIS.
Additional antenna time is being scheduled for the Feb 2012 Solar
Exclusion Zone transit.
NOAA Space Weather Prediction Center (SWPC) started having gaps in
coverage beginning on DOY 316 0700z. SWPC had very minimal data
coverage from DOY 317 0700z to DOY 319 0700z. During these 48 hours,
DSN provided 8 hours of coverage and WCDA (12m, Wallops) provided 5.5
hours of coverage. NICT (11m, Japan) and DLR (4.5m, Germany) were not
able to provide coverage during this period (317-0700z to 319-0700z).
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Anomalies:
DOY 316 11/12/2011 S-ACE-0633 G11-0059 DSS-27 CMG problems
"Lost Connection to User" problem (1509z) with the ground station's CMG
(Command Modulation Generator) prevented commanding ACE to the medium
data-rate. The problem was resolved at 1630z (DR#11209). The same
problems also occurred on DOY 318, but was resolved within 5 minutes
(DR#G112119).
IMPACT: 35 minute delay in commanding to medium rate. 35 minute data
loss to NOAA SWPC and Science teams.