ACE Weekly 03/11/2015 - 03/17/2015

ACE spacecraft subsystems are performing as expected.
 
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Orbit/Attitude:

	Type            SK-74            Attitude
	Date          03/13/2015        03/17/2015
	DOY            072 2015          076 2015
	Thrusters       3A 4A           2R 4R+ 4R-
	Duration      27.45 seconds    11:03 minutes
	Start          13:37:03z        16:03:11z
	Stop           13:37:31z        16:14:14z
	ra,decStart   355.05,-15.97    355.27,-15.53
	ra,decStop    355.13,-15.53      4.42,-11.98
	ra,decExpect                     5.29,-11.26
	Deviation     0.45deg          1.12deg (-10%)
	HGAStart       +6.78 deg       -7.74 deg
	HGAStop        +6.43 deg       +8.46 deg
	SunStart       13.19 deg       14.28 deg
	SunStop        12.75 deg       13.06 deg
	SpinStart     5.0061 rpm      5.0007 rpm
	SpinStop      5.0006 rpm      5.0038 rpm
	Nutation        0.41 deg        0.15 deg
	Firing         continuous      56 pulses
	FuelUsed        0.0911 lbm      0.1728 lbm
	FuelRemain     99.9125 lbm     99.7396 lbm
	FinalSCMass   1334.172 lbm    1334.000 lbm


FDF preliminary estimate is that SK-74 was -11.8% cold.

The next attitude maneuver is scheduled for Monday 3/23/2015.

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OCRs:

DOY 076 (03/17/2015)  1626-1628z  ACE-349  Close B Latch Valves
After the review on 3/16/2015, everyone is in agreement that the B fuel
tanks are empty and that current maneuver underperformance is due to
nitrogen pressurant from the B tanks mixing with the fuel from the A
tanks.  Maneuver performance is expected to improve over the next 3-6
months as the nitrogen in front of the latch valves is expelled.

The reason for the B fuel tanks being empty is that the original
nitrogen pressurant was unevenly distributed between the A and B fuel
tanks.  The nitrogen expanded as an ideal gas as fuel was used and
removed.  The larger quantity of nitrogen in the B tanks displaced more
fuel causing the B tanks to empty first.

The ratio of nitrogen between the A and B tanks (37.5/62.5) was
calculated based on fitting the spacecraft's moment of inertia as it
changed throughout the mission.  The moment of inertia data was derived
by analyzing the using nutation rate relative to the spin rate.

If the nitrogen had been evenly distributed, the nitrogen volume in the
tanks at launch would have been 25% and the fuel volume would have been
75%.  With the derived ratio (37.5/62.5) the volumes are estimated in
the table below.  

                        A Tanks              B Tanks
                   Nitrogen Hydrazine   Nitrogen Hydrazine
Original volumes:    18.8%    81.2%       31.2%    68.8%   196.7kg fuel
2014 volumes:        60.2%    39.8%       99.9%     0.1%    61.4kg fuel

The "2014 volume" is for having 31.2% of the original fuel remaining &
having the nitrogen expanded by 3.2 times.
 
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Activities:

Data Capture:  99.999%  DOY 067-074 2015
  DOY 072 04:40:19-04:40:20  2 second gap while catching up on data

Antenna time is limited.  With the 1 hour problem with DSS-54 on Tuesday
(see anomaly below), playback of data will be behind for the next week.
Any future DSN problems will likely result in data loss.

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Anomalies:

DOY 076  03/17/2015  S-ACE-0695  G15-0004  DSS-54 Software Problem
DSS-54 was unable to configure for the ACE pass due to a security scan.
DR#M108626
IMPACT:  Activities delayed 1 hour.  Playback of data is behind due to
limited antenna time.  No impact to NOAA SWPC since the spacecraft was
in RTSW during this time.