ACE Weekly 01/22/2014 - 01/28/2014 All ACE spacecraft subsystems are performing as expected. ======================================================================== 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). ======================================================================== 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. ======================================================================== 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. ======================================================================== 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 ------- -------------------------------- ---------------------------- 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