ACE Weekly 05/27/2015 - 06/02/2015

All ACE spacecraft subsystems are performing as expected.

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Orbit/Attitude:

Type           Attitude
Date          06/02/2015
DOY            153 2015
Thrusters      2R 4R+ 4R-
Duration        2:47 minutes
Start          13:23:41z
Stop           13:26:28z
ra,decStart    75.74,36.75
ra,decStop     77.04,38.86
ra,decExpect   77.27,39.11
Deviation       0.30 deg (-11.5%)
HGAStart       +8.65 deg
HGAStop       +10.84 deg
SunStart       15.52 deg
SunStop        17.84 deg
SpinStart     5.0125 rpm
SpinStop      5.0131 rpm
Nutation        0.13 deg
Firing         14 pulses
FuelUsed        0.0495 lbm
FuelRemain     97.9728 lbm
FinalSCMass   1332.233 lbm

Notes:

- The maneuver was short in magnitude (14 pulses; the shortest
  maneuver to-date). While the observed deviation is in line with
  previous attitude maneuvers, it resulted in a larger cold
  percentage due to the small maneuver burn size.

- Current attitude maneuver planning more efficiently samples
  through the target selection choices and allows the FOT to
  choose the target that satisfies the HGA constraint while
  maximizing the average sun angle (i.e., yielding the attitude
  with the shortest maneuver duration, as was the case this week).

- The PROP subsystem performance was nominal during the maneuver
  (i.e, no indication of anomalous behavior was observed).

- The FOT will evaluate historical data for maneuver burn duration
  vs. burn deviation, to more confidently characterize and determine
  when a measured deviation is consistent (or not) with nominal
  maneuver performance.

The next attitude maneuver is scheduled for Tuesday, 6/09/2015.

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OCRs:

None

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Activities:

Data Capture:  99.586%  DOY 144-151 2015

Data gaps were observed during the SSR playback of DOY 147 (96.686% data
captured).  See additional information below.

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Anomalies:

DOY 147 05/27/15 S-ACE-0704 Data Gaps during SSR Playback (DR # TBD)

During the DSS-24 contact on DOY-147 (BOT=0000 UT, EOT=0230 UT),
multiple instances of data gaps were identified during the SSR
playback of ACE data.

Consecutive data gaps in playback data with a duration as long as
4.4 min and as low as 2 seconds were observed during the contact
(overall data gaps start: 147/16:01:56 (UT) and data gaps end
time: 147/21:54:16 (UT)).

Inspection of the ITOS event log indicates that (real-time) multiple
occurrences of frame sequence errors (and skipped frames) were recorded
during the 148:00:02:40.9 (UT) through 148:02:16:05.494 (UT) real time
contact time frame.

The ACE FOT has also confirmed that the data gaps are only present in
the playback data (vc4) and not real time frames (vc1). Furthermore, the
data gaps identified in the IDR data is consistent with the data gaps
observed via inspection of the SLE files.

IMPACT:
The net data captured for DOY 147 corresponds to 96.686% (that is, a
data loss of 3.314%).

The FOT is currently investigating and will determine if the data can
be recovered at the M-MOC.