ACE Weekly 01/16/2013 - 01/22/2013
All ACE spacecraft subsystems are performing as expected.
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Orbit/Attitude:
Type Attitude
Date 01/22/2013
DOY 022 2013
Thrusters 2R 4R+ 4R-
Duration 5:20 min
Start 20:12:17z
Stop 20:17:37z
HGAStart -8.83deg
HGAStop +8.96deg
SunStart 11.32deg
SunStop 11.60deg
SpinStart 5.0724rpm
SpinStop 5.0735rpm
Nutation 0.06deg
Firing 27 pulses
FuelUsed 0.0907lbm
FuelRemain 116.7304lbm
FinalSCMass 1350.991lbm
The next attitude maneuver is scheduled for Tuesday 01/29/2013.
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OCRs:
DOY 022 (01/22/2013) 1958-2150z SIS-054 16 cmds
Telescope B threshold voltages adjusted and 4 detector strips were
re-enabled (M1B HV: 1,14,18,33). 3 detector strips were also
temporarily enabled (M1B GND: 46,48; M1B HV:2) and then disabled during
the pass. Currently 43 detector strips out of 512 are
disabled/unusable.
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Activities:
Data Capture: 100% DOY 013-020 2013
The WAVES instrument on the WIND spacecraft had a latch-up on 1/17/2013
(not an emergency, but the instrument recovery is urgent). With limited
DSN antenna time, Wind has been scheduling downlink only passes. With
the instrument latch-up, ACE released DSS-27 to provide an uplink to
Wind. As it turns out, DSN was able to establish an uplink with DSS-24
(originally scheduled downlink only for Wind) with some time and effort.
ACE did not return to using DSS-27 since we had extra time on 1/18/2013
with WS1. The noteworthy points in this: 1) ACE has flexibility for
scheduling antennas and 2) our single team operates both ACE and WIND,
so we juggle resources between the two missions.
The 2nd operational WS1 pass was taken on Friday 01/18/2013. The
following table provides WS1 EbN0 values and DSS-27 SNR values along
with the spacecraft antenna angle. The WS1 EbN0 are about 5dB less than
the DSS-27 SNR values.
date s/c antenna DSS-27 SNR WS1 EbN0
10/01/2012 1.7 deg 15.4 dB 10.0 dB
10/05/2012 3.0 deg 14.8 dB 9.0 dB
10/08/2012 9.1 deg 8.0 dB 2.9 dB
11/20/2012 8.6 deg 7.9 dB 2.8 dB
11/27/2012 8.4 deg 8.9 dB 3.4 dB
11/30/2012 8.0 deg 3.8 dB
01/18/2013 8.6 deg 7.2 dB 2.6 dB
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Anomalies:
DOY 022 01/22/2013 S-ACE-0658 G13-0002 DSN Input Data Time Out Alarm
The DCC (Downlink Channel Controller) stopped sending telemetry when a
"formatter frame input data time out" alarm occurred. DSS-24 put a
second DCC online and telemetry was restored after 11 minutes
(2024-2035z).
IMPACT: Eleven minute telemetry outage. Occurred during SIS commanding
and the instrument's cmd echo was lost during the outage. Based on the
instrument's data rates, it was assumed that the SIS command was
successfully processed. This will be confirmed when the recorded data
is retrieved on 1/23/2013.
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Average Sun Angles With Weekly Attitude Maneuvers
Dates Avg Sun Avg SEV Sun-SEV (indicates extra s/c tilt)
----------- ------- ------- ----------------------------------
10/18-10/23 11.0deg 5.1deg 5.9deg
10/23-10/28 9.3deg 3.3deg 6.0deg
10/28-11/06 7.3deg 2.0deg 5.3deg
11/06-11/13 8.4deg 3.8deg 4.6deg
11/13-11/20 10.3deg 6.3deg 4.0deg
11/20-11/27 12.7deg 8.6deg 4.1deg
11/27-12/04 14.9deg 10.1deg 4.8deg
12/04-12/11 16.0deg 10.9deg 5.1deg
12/11-12/18 16.8deg 11.3deg 5.5deg
12/18-12/27 16.5deg 10.7deg 5.8deg
12/27-01/03 16.0deg 9.1deg 6.9deg
01/03-01/08 15.2deg 7.2deg 8.0deg
01/08-01/15 13.8deg 6.0deg 7.8deg
01/15-01/22 12.3deg 4.0deg 8.3deg
This week marks 3 months (one half of the L1 orbit) that with weekly
attitude maneuvers. The average sun angle has been 12.9 degrees. The
sun angle values will cover the same range for the next 3 months (the
other half of the L1 orbit has the same impact on the sun angle). Note
that the L1 orbit opens up over the next few years so there will be a
slight increase in sun angle from one 3 month period to the next.
Nevertheless, this 3 month mark (10/18/2012 - 01/22/2013) could be used
to evaluate the cost/benefit of weekly maneuvers.
The following is background information that will be included in each
weekly report.
The project has accepted the SWEPAM team proposal to keep the spacecraft
at larger sun angles with weekly attitude maneuvers. The SWEPAM-Ion
instrument has a series of channel electron multipliers (CEMs) and
larger sun angles allows more responsive CEMs to measure the solar wind.
The maximum sun angle follows the Sun-Earth-Vehicle angle (SEV). The
SEV angle is determined by the size/shape of the orbit around L1. When
the spacecraft antenna is pointed directly towards earth, the
spacecraft's sun angle will be equal to the Sun-Earth-Vehicle angle.
With weekly maneuvers, the average sun angle can be kept 4-6deg more
than the SEV angle. This results in the spacecraft antenna aspect angle
being kept between 5 and 9 degrees and never pointing directly back at
earth. For reference, the SWEPAM team prefers sun angles above 13
degrees. With the current size of the L1 orbit, the sun angle will be
above 13 degrees for ~45% of the time.