ACE Weekly 05/01/2013 - 05/07/2013

All ACE spacecraft subsystems are performing as expected.

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Orbit/Attitude:

	Type        Attitude
	Date        05/07/2013
	DOY         127 2013
	Thrusters   2R 4R+ 4R-
	Duration    17:37 min
	Start       14:13:40z
	Stop        14:31:17z
	HGAStart    -7.85 deg
	HGAStop     +8.57 deg
	SunStart     7.63 deg
	SunStop     13.15 deg
	SpinStart   5.0929 rpm
	SpinStop    5.0977 rpm
	Nutation     0.14 deg
	Firing      90 pulses
	FuelUsed      0.2653 lbm
	FuelRemain  114.3452 lbm
	FinalSCMass 1348.605 lbm

The next attitude maneuver and a spin down maneuver are scheduled for
Tuesday 05/14/2013.


This week's attitude maneuver (0.27 lbm) is larger than usual (0.10-0.16
lbm).  To maintain larger sun angles, the spacecraft is kept pointing
away from the ecliptic plane, and the large maneuver is because the
spacecraft crossed the ecliptic plane on Monday (5/6/2013; DOY 126).
This will happen every 3 months (last occurrence 2/12/2013).  Note, the
size of the "ecliptic crossing attitude maneuvers" will decrease as the
L1 orbit continues to open up.


Spin Rate Background Information

The spacecraft spin constraint is 4.9-5.1 rpm.  Attitude maneuvers
increase the spin rate and station keeping maneuvers decrease (to a
lesser extent) the spin rate.  Every 2-3 years, a spin down maneuver is
performed (4/21/2006, 9/2/2008, 6/27/2011).  Next week's spin down
maneuver will target 4.95 rpm.

The S3DPU is the documented driver for the 4.9-5.1 rpm spin constraint.
The S3DPU (SWICS/SWIMS/SEPICA Data Processing Unit) captures the most
data when the spin rate is 5.0 rpm.  The S3DPU inserts dummy frames if
the spin rate is less than 5.0 rpm and drops data if the spin rate is
greater than 5.0 rpm.  There may be more spin rate issues with other
instruments that we are not aware of.

The star scanner can work at a wider range of spin rates.  But if the
star scanner is started (or rebooted, which has never happened) and the
spin rate is not within 4.9-5.1 rpm, then a "SetYRate" command is needed
to acquire stars.

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OCRs:

None

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Activities:

Data Capture:  100%  DOY 118-125 2013

On Tuesday 5/7/2013 (DOY 127), DSN performed scheduled maintenance on
their Data Capture and Delivery (DCD) system.  Telemetry to the MOC was
delayed for 5 minutes (1501-1506z) and backfilled when the maintenance
was completed.  No problems were found.

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Anomalies:

None