ACE Weekly 09/25/2013 - 10/01/2013

All ACE spacecraft subsystems are performing as expected.

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Orbit/Attitude:

	Type         Attitude
	Date         10/01/2013
	DOY          274 2013
	Thrusters    2R 4R+ 4R-
	Duration     9:57 min
	Start        14:24:17z
	Stop         14:34:14z
	HGAStart     -8.07 deg
	HGAStop      +8.93 deg
	SunStart     15.67 deg
	SunStop      12.24 deg
	SpinStart    4.9536 rpm
	SpinStop     4.9558 rpm
	Nutation      0.17 deg
	Firing       50 pulses
	FuelUsed       0.1594 lbm
	FuelRemain   111.5796 lbm
	FinalSCMass  1345.840 lbm

The next attitude maneuver is scheduled for Tuesday 10/08/2013.

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OCRs:

None

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Activities:

Data Capture:  100%  DOY 265-272 2013

ACE Science Center (ASC) server (otter) for distributing real-time ACE
data failed on Friday 9/27/2013.  ASC has a new server, but the GSFC
network group that updates the gateway has been furloughed.  NOAA Space
Weather real-time data is unaffected.

The MMOC has been working to route DSN Monitor Data directly to the MMOC
in order to reduce network costs.  A test data flow was performed Monday
9/30/2013 (DOY 273) but was blocked by the MMOC firewall.  The MMOC
firewall was updated and a successful data flow occurred on Wednesday
10/2/2013 (DOY 275).  DSN will complete their configuration changes
after the LADEE Lunar Orbit Insertion.  Background: DSN Monitor Data
provides ground antenna data, including downlink signal strength, that
is necessary for analyzing the spacecraft antenna constraints.

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Anomalies:

DOY 262 09/19/2013  S-ACE-0666  S13-0001  Tank Temperature & Spin Rate
At ~16:20z, the spacecraft spin rate increased slightly, from 4.9590rpm
to 4.9594rpm (~0.01%).  At 16:23z, the Fuel Tank B1 temperature
increased 2°C from 18.4°C to 20.3°C over 6 minutes (ACE has 4 fuel
tanks).  Over the next 90 minutes, the spin rate continued to slowly
increase to 4.9595rpm.  This may have been precipitated by the internal
fuel line heaters turning on (16:18:52z) which happens up to ~4 times a
day depending on the sun distance and spacecraft temperature.

Analysis
We believe that something shifted on the spacecraft and that Tank B1 is
in contact with a warmer section of the spacecraft.  To increase the
spin rate by 0.01%, the moment of inertia would have decreased by 0.01%
(e.g. from 450kg*m^2 to 449.955kg*m^2).  As an example, this change
could be caused by a 50kg mass (total spacecraft mass ~610kg) at the end
of the spacecraft (0.8m) moving inward by 0.5 millimeters.  Of course, a
different mass at a different location shifting by a different distance
can also cause that change in moment of inertia.

Impact
There may have been other small changes in the spacecraft structure over
the life of the mission.  This change was discovered and investigated.
An anomaly report was generated to document the investigation.  No other
impacts have been found.