ACE Weekly 04/24/2013 - 04/30/2013

All ACE spacecraft subsystems are performing as expected.

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Orbit/Attitude:

	Type        Attitude
	Date        04/30/2013
	DOY         120 2013
	Thrusters   2R 4R+ 4R-
	Duration     9:35 min
	Start       14:29:53z
	Stop        14:39:18z
	HGAStart    -7.77 deg
	HGAStop     +8.78 deg
	SunStart     8.47 deg
	SunStop     11.78 deg
	SpinStart   5.0910 rpm
	SpinStop    5.0930 rpm
	Nutation     0.18 deg
	Firing      48 pulses
	FuelUsed      0.1522 lbm
	FuelRemain  114.6104 lbm
	FinalSCMass 1348.870 lbm

The next attitude maneuver is scheduled for Tuesday 05/07/2013.

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OCRs:

None

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Activities:

Data Capture:  100%  DOY 111-118 2013


Dog-Leg Maneuvers (background information)

As ACE orbits the L1 point every 6 months, the relative position of the
sun (and the sun-pulse) changes.  The attitude maneuvers turn the
spacecraft to the left throughout the solar orbit.  To turn to the left,
the time between the sun-pulse and the thruster fire is adjusted each
week.  But there is a region of the L1 orbit (bottom left corner as seen
from Earth) where the sun-pulse and thruster firing would occur at the
same time.  When this occurs, the attitude maneuver is split into 2
segments (e.g. segment 1=turn left & up; segment 2=turn left & down).

We have avoided dog-leg maneuvers since 2008, because the L1 orbit had
elongated diagonally (upper left to bottom right as seen from Earth) and
the spacecraft didn't spend much time in the "dog-leg corner" of the
orbit.  Another factor was that the time between maneuvers was maximized
which allowed more time for the spacecraft to drift through the dog-leg
corner.

But as the L1 orbit opens up and we have weekly maneuvers, we will again
face dog-leg maneuvers.  Dog-leg maneuvers are more of an inconvenience
and are not a significant impact to fuel usage.  We have managed to skip
a dog-leg this month, but we expect to execute one or more dog-leg
maneuvers every 6-months starting Nov 2013.

ACE uses the 2R 4R+ 4R- thrusters for attitude maneuvers.  There are 3
opposing thrusters (1R 3R+ 3R-) that could be fired opposite the
sun-pulse.  However, using 1R causes significant nutation.  After the
first 2 weeks of the mission (Sep 1997), it was determined not to use 1R
for attitude maneuvers. The 1R thruster has only been used for orbit
shaping & z-axis maneuvers (1997, 1999-2001) and has not been used
since.

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Anomalies:

None