ACE Weekly 01/22/2014 - 01/28/2014
All ACE spacecraft subsystems are performing as expected.
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Orbit/Attitude:
Type Attitude
Date 01/28/2014
DOY 028 2014
Thrusters 2R 4R+ 4R-
Duration 7:55 min
Start 21:38:09z
Stop 21:46:04z
HGAStart -8.90 deg
HGAStop -2.81 deg
SunStart 12.02 deg
SunStop 8.50 deg
SpinStart 4.9736 rpm
SpinStop 4.9751 rpm
Nutation 0.21 deg
Firing 40 pulses
FuelUsed 0.1298 lbm
FuelRemain 109.2112 lbm
FinalSCMass 1343.471 lbm
The next attitude maneuver is scheduled for Tuesday 02/04/2014.
ACE will cross the ecliptic plane next week (~2/8/2014). Previously
(e.g. 11/12/2013), the corresponding attitude maneuver would turn the
spacecraft from pointing far above the ecliptic plane to far below the
ecliptic plane. But now that the L1 orbit has opened up, maximizing the
sun angle results in a more stepped change in the spacecraft attitude
relative to the ecliptic plane. This also results in occasional periods
where the antenna will be more directly pointing towards the earth.
Note, as the L1 orbit opens, the spacecraft can be kept at slightly
higher sun angles (~0.2� more per year).
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OCRs:
DOY 027 (01/27/2014) 2120-2123z SIS-063 2 cmds
From the instrument team: These commands will test a new way of dealing
with noisy Matrix strips. As the number of noisy Matrix detector strips
increases as a result of higher on-board temperatures, we have reached
the limits of flight software arrays designed to store the threshold
information of the noisy strips. Thus we need to devise new ways of
dealing with the noisy strips in the future. This test will enable us
to try one approach that has been reserved only for the special case of
"dead" strips, and may free up valuable array space in the flight
software. The commands added Matrix detector strip M1A GND #33 to the
BADSTRP array and incremented the count of NBADSTP to 3. The instrument
team is analyzing the data over several days to determine how the test
went.
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Activities:
Data Capture: 100% DOY 019-026 2014
The Near Earth Network did not perform any range tests with WS1 or
Santiago this past week.
On 01/24/2014 (DOY 024) a DSN Project Interface Test (PIT) for software
upgrades to DSN's Downlink Telemetry and Tracking (DTT v11.3) was
completed. No problems were found. This is the second PIT, the
previous occurred on 12/12/2013.
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Anomalies:
Update for S13-0001 Tank Temperature & Spin Rate Anomaly
With the decreasing spacecraft temperatures (perihelion was on
1/4/2014), the fuel tank heaters are remaining on for periods of time
instead of turning off every 2 hours. In the next 1-2 weeks, we expect
the propulsion system heaters to return to their normal state (see
below). Previously, we speculated that Tank B1 was making contact with
a hot part of the spacecraft. Another explanation for the thermal
fluctuations is that Tank B1 is more thermally isolated than before.
Note that the heating system is performing as expected, this anomaly is
for the changes in the B1 tank temperature.
Background
09/19/2013 1620z B1 fuel tank temperature increases from 18.4C to 19.5C
Spin rate increases 0.01% (4.9590 to 4.9594rpm)
11/05/2013 2050z B1 fuel tank increases to 20.9C during maneuver
12/22/2013 2053z B1 fuel tank warmer as perihelion approaches. Fuel
tank heaters start turning off every 2 hours for
30 minutes. B1 fuel tank fluctuates between 17C and
21C. Other tanks stable and fluctuate less than 1C.
01/09/2014 1625z Spacecraft cools after reaching perihelion (1/4/2014).
Fuel tank heaters stay on for ~8 hours. Tank heater
continuous on time increases as the spacecraft moves
away from perihelion
The following is the typical state for the propulsion system heaters
Current Description State before 12/22/2013
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0.11A Top Deck Axial Thruster heaters never on
0.11A Top Deck Radial Thruster heaters never on
0.11A Btm Deck Axial Thruster heaters on ~30minutes every 2-3 hrs
0.22A Btm Deck Radial Thruster heaters on ~30minutes every 2-3 hrs
0.23A Internal Lines heaters occasionally on 30 minutes
0.08A External Lines heaters occasionally off 30 minutes
0.38A Tank heaters always on