ACE Weekly 01/16/2013 - 01/22/2013 All ACE spacecraft subsystems are performing as expected. ======================================================================== Orbit/Attitude: Type Attitude Date 01/22/2013 DOY 022 2013 Thrusters 2R 4R+ 4R- Duration 5:20 min Start 20:12:17z Stop 20:17:37z HGAStart -8.83deg HGAStop +8.96deg SunStart 11.32deg SunStop 11.60deg SpinStart 5.0724rpm SpinStop 5.0735rpm Nutation 0.06deg Firing 27 pulses FuelUsed 0.0907lbm FuelRemain 116.7304lbm FinalSCMass 1350.991lbm The next attitude maneuver is scheduled for Tuesday 01/29/2013. ======================================================================== OCRs: DOY 022 (01/22/2013) 1958-2150z SIS-054 16 cmds Telescope B threshold voltages adjusted and 4 detector strips were re-enabled (M1B HV: 1,14,18,33). 3 detector strips were also temporarily enabled (M1B GND: 46,48; M1B HV:2) and then disabled during the pass. Currently 43 detector strips out of 512 are disabled/unusable. ======================================================================== Activities: Data Capture: 100% DOY 013-020 2013 The WAVES instrument on the WIND spacecraft had a latch-up on 1/17/2013 (not an emergency, but the instrument recovery is urgent). With limited DSN antenna time, Wind has been scheduling downlink only passes. With the instrument latch-up, ACE released DSS-27 to provide an uplink to Wind. As it turns out, DSN was able to establish an uplink with DSS-24 (originally scheduled downlink only for Wind) with some time and effort. ACE did not return to using DSS-27 since we had extra time on 1/18/2013 with WS1. The noteworthy points in this: 1) ACE has flexibility for scheduling antennas and 2) our single team operates both ACE and WIND, so we juggle resources between the two missions. The 2nd operational WS1 pass was taken on Friday 01/18/2013. The following table provides WS1 EbN0 values and DSS-27 SNR values along with the spacecraft antenna angle. The WS1 EbN0 are about 5dB less than the DSS-27 SNR values. date s/c antenna DSS-27 SNR WS1 EbN0 10/01/2012 1.7 deg 15.4 dB 10.0 dB 10/05/2012 3.0 deg 14.8 dB 9.0 dB 10/08/2012 9.1 deg 8.0 dB 2.9 dB 11/20/2012 8.6 deg 7.9 dB 2.8 dB 11/27/2012 8.4 deg 8.9 dB 3.4 dB 11/30/2012 8.0 deg 3.8 dB 01/18/2013 8.6 deg 7.2 dB 2.6 dB ======================================================================== Anomalies: DOY 022 01/22/2013 S-ACE-0658 G13-0002 DSN Input Data Time Out Alarm The DCC (Downlink Channel Controller) stopped sending telemetry when a "formatter frame input data time out" alarm occurred. DSS-24 put a second DCC online and telemetry was restored after 11 minutes (2024-2035z). IMPACT: Eleven minute telemetry outage. Occurred during SIS commanding and the instrument's cmd echo was lost during the outage. Based on the instrument's data rates, it was assumed that the SIS command was successfully processed. This will be confirmed when the recorded data is retrieved on 1/23/2013. ======================================================================== Average Sun Angles With Weekly Attitude Maneuvers Dates Avg Sun Avg SEV Sun-SEV (indicates extra s/c tilt) ----------- ------- ------- ---------------------------------- 10/18-10/23 11.0deg 5.1deg 5.9deg 10/23-10/28 9.3deg 3.3deg 6.0deg 10/28-11/06 7.3deg 2.0deg 5.3deg 11/06-11/13 8.4deg 3.8deg 4.6deg 11/13-11/20 10.3deg 6.3deg 4.0deg 11/20-11/27 12.7deg 8.6deg 4.1deg 11/27-12/04 14.9deg 10.1deg 4.8deg 12/04-12/11 16.0deg 10.9deg 5.1deg 12/11-12/18 16.8deg 11.3deg 5.5deg 12/18-12/27 16.5deg 10.7deg 5.8deg 12/27-01/03 16.0deg 9.1deg 6.9deg 01/03-01/08 15.2deg 7.2deg 8.0deg 01/08-01/15 13.8deg 6.0deg 7.8deg 01/15-01/22 12.3deg 4.0deg 8.3deg This week marks 3 months (one half of the L1 orbit) that with weekly attitude maneuvers. The average sun angle has been 12.9 degrees. The sun angle values will cover the same range for the next 3 months (the other half of the L1 orbit has the same impact on the sun angle). Note that the L1 orbit opens up over the next few years so there will be a slight increase in sun angle from one 3 month period to the next. Nevertheless, this 3 month mark (10/18/2012 - 01/22/2013) could be used to evaluate the cost/benefit of weekly maneuvers. The following is background information that will be included in each weekly report. The project has accepted the SWEPAM team proposal to keep the spacecraft at larger sun angles with weekly attitude maneuvers. The SWEPAM-Ion instrument has a series of channel electron multipliers (CEMs) and larger sun angles allows more responsive CEMs to measure the solar wind. The maximum sun angle follows the Sun-Earth-Vehicle angle (SEV). The SEV angle is determined by the size/shape of the orbit around L1. When the spacecraft antenna is pointed directly towards earth, the spacecraft's sun angle will be equal to the Sun-Earth-Vehicle angle. With weekly maneuvers, the average sun angle can be kept 4-6deg more than the SEV angle. This results in the spacecraft antenna aspect angle being kept between 5 and 9 degrees and never pointing directly back at earth. For reference, the SWEPAM team prefers sun angles above 13 degrees. With the current size of the L1 orbit, the sun angle will be above 13 degrees for ~45% of the time.