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.

========================================================================
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.

=======================================================================
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.

========================================================================
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).

========================================================================
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.