STEREO Weekly Meeting Minutes for 2016-09-27 (Week 39) ANNOUNCEMENTS ------------- * None INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating nominally on the main lobe of the high gain antenna. * Work continues to recover the Behind spacecraft. See below for details. DISCUSSION AND OPERATIONS CONSTRAINTS ------------------------------------- Week 38 (Sep 19-25) * On day 263 (Sep 19), during the DSS-65 support for Ahead, turbo decoder lock was lost briefly at 1723z. This anomaly resulted in the loss of one frame of SSR data. * On day 264 (Sep 20), during the DSS-43 support for Ahead, telemetry lock was lost intermittently between 265-0051z and 0057z due to heavy rain at the Canberra complex. This anomaly resulted in the loss of 14,219 frames of SSR data. See DR #C112338 for more information. * On day 266 (Sep 22), during the DSS-55 support for Ahead, turbo decoder lock was lost briefly at 1044z. This anomaly resulted in the loss of four frames of SSR data. * On day 268 (Sep 24), during the DSS-63 RTS Engineering Demo support for Ahead, the command uplink was lost and telemetry performance was degraded from 1313z to 1414z due to several film height low alarms and subsequent antenna resets by the LCO. See DR# M109566 for more information. * On day 269 (Sep 25), during the DSS-26 support for Ahead, turbo decoder lock was lost intermittently between 1732z and 2305z. This anomaly resulted in the loss of eight frames of SSR data. * The average daily science data return for Ahead was 4.0 Gbits during this week. * Behind Observatory Status: Low main bus voltage, 2 (#6 & 9) out of 11 battery cells are currently not functioning, attitude uncontrolled, rotating at a ~45 second period about its principal axis of inertia. Current orientation support may support some solar array input; RF communications on the +Z LGA only supports uplink of short commands to an LGA. While propellant is suspected to be frozen, from the last telemetry received on day 262, both propulsion tank latch valves are open, and pressure transducer #2 is not functioning. Power switching boards are on; nearly all switched loads off including the IEM (avionics) and PDU 1553 bus with the TWTA in standby and propulsion primary and secondary heaters on and -Y panel (R4) heaters on. EA mode is enabled. The battery charge rate is C/10. As the uncontrolled communications link is degrading, necessary macro sequences have been tested to allow the peak power tracker in C&DH standby mode to protect the battery. Detailed status of the recovery activities to restore operations from the Behind loss of communication anomaly, which occurred on October 1, 2014, are listed below. Active recovery operations began with the carrier detection on August 21, 2016. * On day 263 (Sep 19), during the two hour support for Behind with DSS-14, after sending commands to protect the battery by setting the voltage controller to 2 and powering on additional loads (propulsion tank primary and secondary heaters), the carrier signal was unexpectedly lost after 5 minutes. It is suspected that the battery bus had collapsed however this cannot be confirmed without telemetry. While on the -Z LGA, the carrier signal was continuously fluctuating from -167 dBm to -174 dBm with a period of ~45 seconds. Subcarrier lock was intermittent. No telemetry frames were received. * On day 264 (Sep 20), during the two hour support for Behind with DSS-43, commands were sent for increasing the battery charge rate to C/4 and closing latch valves. The carrier signal was very low, intermittent, and carrier lock could not be maintained. After switching to the +Z LGA, no downlink signal was received. Commands were sent to the place the TWTA in standby and power on the propulsion tank primary heaters. No telemetry frames were received. * On day 267 (Sep 23), during the two hour support for Behind with DSS-43, a test macro containing only TWTA HV on and no-operation commands was loaded to RAM to simulate loading the larger of the two new autoexec macros, 0 (154 bytes) and 1 (190 bytes). While the actual macros 0 and 1 were loaded to the uplink buffer, they were not copied to EEPROM, since execution of the test macro failed to produce a carrier signal. The TWTA HV on command was then manually sent from the ground, but also failed to produce a carrier signal. At this point the decision was made to begin battery recovery - IEM switched power and 1553 off; TWTA to standby, primary and secondary tank and -y panel (R4) heaters on - all commands sent manually, multiple times. The battery charge rate, while temporarily set to C/4, was returned to C/10 prior to powering off the 1553. Subsequently the radio science team detected an extremely weak (~10 dB-Hz SNR) at 2200z for 15 seconds. * On day 268 (Sep 24), during the 3.25 hour support for Behind with DSS-26 (34 meter dish; 80 KW transmitter), multiple commands to power on the TWTA were sent shortly after BOT. Although using a 34-meter dish, carrier detection was expected, if the spacecraft was transmitting. At the expected time, no downlink carrier was detected, nor throughout the power subsystem leadŐs recommended maximum ~ 4 minute TWTA on/off period. Mission Ops directed DSN to begin configuring for automated battery recovery operations (i.e. repeated multiple sweeps in a 3 kHz range). At 1557z, automated battery recovery operations commenced, with Mission Ops repeatedly commanding the following configuration through EOT -IEM switched power and 1553 off; TWTA to standby, primary and secondary tank and -y panel (R4) heaters on. Week 39 (Sep 26-Oct 2) * No carrier was detected during the Behind support today (Sep 27) * The 36th SECCHI stepped calibration roll was completing during the telecon today (Sep 27). This was the fifth calibration roll without using the gyros. * Ahead has 11 passes during the week, and 70 meter time is short about four hours between Thursday and Friday. There are two passes at 720 kbps, five at 240 kbps, and four at 160 kbps. The in situ instruments are expected to ride out the shortage without any problems, but SECCHI will need to reduce their image cadence. * Behind has three tracks scheduled for protecting the battery. Tracks on Tuesday, Sep 27 and Friday, Sep 23, are using the 80 kW transmitter on station 26, while the track on Sunday, Oct 2 is using station 63. Week 40 (Oct 3-9) * Ahead has 12 passes during the week, and overall coverage is nominal. There are five passes at 720 kbps, three at 240 kbps, and four at 160 kbps. * Behind has five tracks scheduled during the week. Tracks on Tuesday, Oct 4, and Thursday, Oct 6, are for protecting the battery. The previously scheduled single station recovery attempts for Behind are Friday-Sunday, Oct 7-9. The battery recovery passes will be carried out with the 80 kW transmitter on station 26. Week 41 (Oct 10-16) * The 92nd momentum dump on Ahead is scheduled for Monday, Oct 10, with ignition at 23:45 UT. This is the 11th dump without using the gyros. * Ahead has 11 passes during the week, and overall coverage is nominal. There are seven passes at 720 kbps, and four at 160 kbps. * There are no passes currently scheduled for Behind during the week. Week 42 (Oct 17-23) * Ahead has 12 passes during the week, and overall coverage is nominal. There are three passes at 720 kbps, six at 240 kbps, and three at 160 kbps. * There are no passes currently scheduled for Behind during the week. Week 43 (Oct 24-30) * Oct 25 (Tuesday) the 10th STEREO Launch Date Anniversary. There will be a reception at the Air & Space Museum. * Ahead has 13 passes during the week, and overall coverage is nominal. There are four passes at 720 kbps, four at 240 kbps, and five at 160 kbps. * There are no passes currently scheduled for Behind during the week. Week 44 (Oct 31-Nov 6) * Daily savings time in the United States ends on Sunday, Nov 6. * Ahead has 12 passes during the week, and overall coverage is nominal. There is one track at 720 kbps, six at 240 kbps, and five at 160 kbps. * Behind starts the week at an SPE angle of 13.6 degrees. There are currently no passes for Behind scheduled during the week. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 39: M Sep 26 (270) T Sep 27 (271) Ahead: SECCHI stepped calibration roll, 11:55 UT W Sep 28 (272) T Sep 29 (273) F Sep 30 (274) S Oct 01 (275) S Oct 02 (276) ------------------------------------------------------------------------------- Scheduled activities for Week 40: M Oct 03 (277) T Oct 04 (278) W Oct 05 (279) T Oct 06 (280) F Oct 07 (281) Behind: Battery recovery pass with station 26 S Oct 08 (282) Behind: Battery recovery pass with station 26 S Oct 09 (283) Behind: Carrier recovery pass with station 14 ------------------------------------------------------------------------------- Scheduled activities for Week 41: M Oct 10 (284) Ahead: Momentum dump, 23:45 UT T Oct 11 (285) W Oct 12 (286) T Oct 13 (287) F Oct 14 (288) S Oct 15 (289) S Oct 16 (290) ------------------------------------------------------------------------------- Scheduled activities for Week 42: M Oct 17 (291) T Oct 18 (292) W Oct 19 (293) T Oct 20 (294) F Oct 21 (295) S Oct 22 (296) S Oct 23 (297) ------------------------------------------------------------------------------- Scheduled activities for Week 43: M Oct 24 (298) T Oct 25 (299) W Oct 26 (300) T Oct 27 (301) F Oct 28 (302) S Oct 29 (303) S Oct 30 (304) ------------------------------------------------------------------------------- Scheduled activities for Week 44: M Oct 31 (305) T Nov 01 (306) W Nov 02 (307) T Nov 03 (308) F Nov 04 (309) S Nov 05 (310) S Nov 06 (311) Daily savings time ends in U.S. ------------------------------------------------------------------------------- Upcoming events: Behind events are contingent on recovering the spacecraft. 2016: * Dec Behind: Resume LGA downlink capability on 70 m DSN 2017: 2018: * Mar 5 Ahead: Mercury transit 2019: * Mar Ahead: Switch downlink rate to 240 kbps for 34 meter * Apr Behind: Switch downlink rate to 240 kbps for 34 meter 2020: * May Behind: Switch downlink rate to 360 kbps for 34 meter * Jun Ahead: Switch downlink rate to 360 kbps for 34 meter * Jun Behind: Switch downlink rate to 480 kbps for 34 meter * Sep Ahead: Switch downlink rate to 480 kbps for 34 meter 2021: * Jul Behind: Switch downlink rate to 720 kbps for 34 meter * Aug Ahead: Switch downlink rate to 720 kbps for 34 meter