ACE Weekly 07/14/2010 - 07/20/2010

All ACE spacecraft subsystems are performing nominally.

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Orbit/Attitude:

	Type        Attitude
	Date        07/15/2010
	DOY         196 2010
	Thrusters   2R 4R+ 4R-
	Duration    15:44 min
	Start       16:29:58z
	Stop        16:45:42z
	HGAStart    -7.60deg
	HGAStop     +8.37deg
	SunStart     7.20deg
	SunStop     18.88deg
	SpinStart   5.0604rpm
	SpinStop    5.0651rpm
	Nutation     0.13deg
	Firing      80 pulses
	FuelUsed      0.2502lbs
	FuelRemain  134.9868lbs
	FinalSCMass 1369.247lbs


The next attitude maneuver is scheduled for Friday 07/30/2010.

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OCRs:

DOY 200 (07/19/2010)   GND-202  Old ACE MOC String 2 Dismantled
String 2 in the old ACE MOC (Bldg 14 Rm W10F) has been turned off and
dismantled.  There are 3 activities that have not yet transitioned to
the Multi-Mission Operations Center (MMOC).  1) Maneuver Planning (APU)
2)Attitude Determination (ADS) and 3)DSN CDR Download.  Maneuver
Planning and Attitude Determination are waiting for the final MTASS
release.  DSN CDR Download is waiting for the correct network
configuration.

DOY 201 (07/20/2010)  MMOC-191  UPS-6 Replacement
The MMOC is powered by 2 Uninterruptible Power Supplies (UPS).  UPS-6 is
being replaced on Wednesday 07/21/2010.  Computers in the MMOC that use
UPS-6 will either be powered down or switched to UPS-14 on Tuesday
07/20/2010.  UPS-14 will be replaced at some point in the future.

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Activities:

Data Capture:  100%  DOY 192-199 2010


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Anomalies:

DOY 196  07/15/2010  S-ACE-0517  G10-0035 Incorrect Thruster Calibration
The attitude maneuver plan generated using the GMAN (General Maneuver)
software did not have the correct thruster calibration.  The thruster
calibration used was 0.675 and instead of 0.715.  The target attitude
was (134.70,22.99) and the resulting attitude was (135.42,22.57).
IMPACT:  The resulting attitude from the 07/15/2010 maneuver had a sun
angle of 18.88° (original target=18.64°) and a High Gain Antenna angle
of 8.37° (original target 7.52°).  The postmaneuver downlink SNR was
15.4dB which was more than sufficient to maintain the downlink.  The
longer maneuver on 07/15/2010 will result in a shorter maneuver on
07/30/2010.


Background Information

As ACE orbits the sun at the L1 point, the attitude maneuvers are used
to keep the spacecraft pointing towards the sun and the High Gain
Antenna (HGA) pointing towards the earth.  The sun angle constraint is
4°-20° and the HGA constraint is <8°.  

In 2002, ACE increased the HGA angle constraint and started performing
longer attitude maneuvers.  The FDF analysts noted an improved thruster
performance and started adjusting the thruster calibration in the GMAN
software.  The FDF analysts fit the thruster calibration as a function
of the number of thruster pulses to a line, which is roughly
	thruster calibration = 0.585 + (# pulses)/585
(the duplication of 585 is merely a coincidence ... and this is a rough
fit)

The previous attitude maneuver on 07/01/2010 had been a shorter maneuver
with 54 pulses and a thruster calibration of 0.675.  The attitude
maneuver on 07/15/2010 was longer and should have had a higher thruster
calibration.  With a thruster calibration of 0.675, the GMAN software
calculated a maneuver with 80 pulses.  With a thruster calibration of
0.715, GMAN would have calculated a maneuver with 75 pulses.  The 5
additional thruster pulses resulted in exceeding the target attitude
with a post-maneuver HGA of 8.37 degrees.

The HGA constraint of 8 degrees is used to give enough buffer to the
precipitous drop-off in HGA performance between 10-11 degrees.  On
07/15/2010, the premaneuver Signal to Noise Ratio (SNR) was 15.7db (HGA
angle=7.6°) and the postmaneuver SNR was 15.4db (HGA angle=8.37°).  This
is an enviable SNR and the downlink was not impacted by the postmaneuver
attitude.

The upper sun angle constraint (20°) is for the ULEIS instrument.  If
the sun angle reaches 21.8 degrees, the ULEIS instrument shutter will be
closed.