ACE Weekly 11/19/2014 - 11/25/2014

ACE spacecraft subsystems are performing as expected.

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Orbit/Attitude:

	Type          Attitude
	Date         11/25/2014
	DOY           329 2014
	Thrusters     2R 4R+ 4R-
	Duration       7:56 min
	Start         16:34:07z
	Stop          16:42:03z
	ra,decStart  247.22,-9.66
	ra,decStop   254.61,-9.65
	ra,decExpect 254.93,-9.78
	Deviation      0.35 deg (-4% short)
	HGAStart      -9.16 deg
	HGAStop       +9.04 deg
	SunStart      12.67 deg
	SunStop       17.24 deg
	SpinStart    5.0038 rpm
	SpinStop     5.0043 rpm
	Nutation       0.17 deg
	Firing        40 pulses
	FuelUsed       0.1274 lbm
	FuelRemain   102.4844 lbm
	FinalSCMass  1336.745 lbm

The next attitude maneuver and Station Keeping #72 are scheduled for
Tuesday 12/02/2014.

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OCRs:

None

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Activities:

Data Capture:  99.994%  DOY 320-327 2014
DOY 322 16:20:41-16:20:44   4 second gap covered by ADC 
DOY 327 08:54:52-08:55:21  30 second gap during SSR failover

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Anomalies:


Update for S13-0001 - B1/B2 Fuel Tank Temperature Anomaly

Others (APL, AETD, SSMO) have proposed that the Fuel Tank Temperature
Anomaly is the result of the "B" fuel tanks being empty.  Given that the
B2 fuel tank temperature is now fluctuating (~2C) along with B1 (~4C),
the empty tank theory begins to seem more plausible than the detached
thermostat theory.  Some of the issues with which to fit the theory are
provided below.


* The B1 fuel tank temperature did not increase continuously.  There
were 3 distinct increases in the B1 temperature:

    09/19/2013  18.4C to 19.5C  spin increases 0.01%
    11/05/2013        to 20.9C  during maneuver
    12/22/2013        to 21.2C  fuel tank heaters start turning off


* For the spacecraft to spin up by 0.01% (9/19/2013), the moment of
inertia has to decrease by 0.01% (e.g. from 450kg*m^2 to 449.955kg*m^2).
Fuel emptying from one tank (B1) to a fuller tank (e.g. B2) would
decrease the moment of inertia by causing the fuel level in the fuller
tank to be closer to the center of rotation.  With ~50kg of fuel in
Sept. 2013, each tank has ~12.5kg.  The following scenarios (depending
on the tank volume at a particular fuel level) could decrease the moment
of inertia by 0.045kg*m^2:

    1 kg at 0.8m moves inward by  2.9cm (to 0.771m)
    5 kg at 0.8m moves inward by  0.6cm (to 0.794m)
   10 kg at 0.8m moves inward by  0.3cm (to 0.797m)

Could differences in pressure and temperatures be enough to cause fuel
to empty from one tank into a fuller tank?


* There is ~0.075kg of fuel in each of four the internal lines (0.3kg
total).  ACE's average fuel usage is 0.3kg/month.  There were 8 to 5
months from the increase in the B1 fuel tank temperature (Sep-Dec 2013)
to maneuver underperformance (May 2014) believed to be due to bubbles in
the line. 


* Could pressurant gas (nitrogen) flow from B1 fuel tank while the B2
tank still contained fuel?


Analysis of the fuel system continues.  This is just reporting the
current state of thinking.  The A fuel tank temperatures remain normal.


Correction on the Tank B2 temperature increase and -X External Fuel Line
temperature decrease during maneuvers on 11/5/2014 and 11/12/2014.
Investigation has found that the -X External Fuel Line has a history of
decreasing during maneuvers (this fuel line feeds the 2R thruster).
Therefore, the increase in the B2 temperature during the two maneuvers
is almost certainly not related to the -X External Fuel Line
temperature.