ACE Weekly 03/11/2015 - 03/17/2015
ACE spacecraft subsystems are performing as expected.
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Orbit/Attitude:
Type SK-74 Attitude
Date 03/13/2015 03/17/2015
DOY 072 2015 076 2015
Thrusters 3A 4A 2R 4R+ 4R-
Duration 27.45 seconds 11:03 minutes
Start 13:37:03z 16:03:11z
Stop 13:37:31z 16:14:14z
ra,decStart 355.05,-15.97 355.27,-15.53
ra,decStop 355.13,-15.53 4.42,-11.98
ra,decExpect 5.29,-11.26
Deviation 0.45deg 1.12deg (-10%)
HGAStart +6.78 deg -7.74 deg
HGAStop +6.43 deg +8.46 deg
SunStart 13.19 deg 14.28 deg
SunStop 12.75 deg 13.06 deg
SpinStart 5.0061 rpm 5.0007 rpm
SpinStop 5.0006 rpm 5.0038 rpm
Nutation 0.41 deg 0.15 deg
Firing continuous 56 pulses
FuelUsed 0.0911 lbm 0.1728 lbm
FuelRemain 99.9125 lbm 99.7396 lbm
FinalSCMass 1334.172 lbm 1334.000 lbm
FDF preliminary estimate is that SK-74 was -11.8% cold.
The next attitude maneuver is scheduled for Monday 3/23/2015.
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OCRs:
DOY 076 (03/17/2015) 1626-1628z ACE-349 Close B Latch Valves
After the review on 3/16/2015, everyone is in agreement that the B fuel
tanks are empty and that current maneuver underperformance is due to
nitrogen pressurant from the B tanks mixing with the fuel from the A
tanks. Maneuver performance is expected to improve over the next 3-6
months as the nitrogen in front of the latch valves is expelled.
The reason for the B fuel tanks being empty is that the original
nitrogen pressurant was unevenly distributed between the A and B fuel
tanks. The nitrogen expanded as an ideal gas as fuel was used and
removed. The larger quantity of nitrogen in the B tanks displaced more
fuel causing the B tanks to empty first.
The ratio of nitrogen between the A and B tanks (37.5/62.5) was
calculated based on fitting the spacecraft's moment of inertia as it
changed throughout the mission. The moment of inertia data was derived
by analyzing the using nutation rate relative to the spin rate.
If the nitrogen had been evenly distributed, the nitrogen volume in the
tanks at launch would have been 25% and the fuel volume would have been
75%. With the derived ratio (37.5/62.5) the volumes are estimated in
the table below.
A Tanks B Tanks
Nitrogen Hydrazine Nitrogen Hydrazine
Original volumes: 18.8% 81.2% 31.2% 68.8% 196.7kg fuel
2014 volumes: 60.2% 39.8% 99.9% 0.1% 61.4kg fuel
The "2014 volume" is for having 31.2% of the original fuel remaining &
having the nitrogen expanded by 3.2 times.
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Activities:
Data Capture: 99.999% DOY 067-074 2015
DOY 072 04:40:19-04:40:20 2 second gap while catching up on data
Antenna time is limited. With the 1 hour problem with DSS-54 on Tuesday
(see anomaly below), playback of data will be behind for the next week.
Any future DSN problems will likely result in data loss.
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Anomalies:
DOY 076 03/17/2015 S-ACE-0695 G15-0004 DSS-54 Software Problem
DSS-54 was unable to configure for the ACE pass due to a security scan.
DR#M108626
IMPACT: Activities delayed 1 hour. Playback of data is behind due to
limited antenna time. No impact to NOAA SWPC since the spacecraft was
in RTSW during this time.