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.