STEREO Weekly Meeting Minutes for 2016-09-20 (Week 38) ANNOUNCEMENTS ------------- * Daily two hour 70m supports have been requested to prevent further battery functional degradation and to allow for monitoring carrier performance and Doppler evolution through Oct 9th. Otherwise, current plans are for a monthly track coverage cadence for STB. * See the information below about the progress of the Behind recovery. 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 37 (Sep 12-Sep 18) * On day 258 (Sep 14),before the DSS-15 support began,the transmitter was declared red for the duration of the track. This anomaly resulted in the loss of 3.2 hours of commanding and two way tracking data. See DR #G117468 for more information. * On day 259 (Sep 15), during the DSS-43 support,the ranging pre-calibration failed due to a receiver issue. This anomaly resulted in 3.5 hours of degraded ranging data. See DR #C112332 for more information. * On day 261 (Sep 17), the Ahead observatory was used to phase calibrate the 10th uplink array, using DSS-24, 25, and 26 for 1.9 hours, to support the array use for STEREO Behind battery recovery. Due to a transmitter motor generator issue at DSS-24, the transmitter could only be calibrated to 10 kW reducing the array gain by approximately 1.6 dB. An approximate 10.4 dB gain in uplink AGC was observed in the spacecraft transponder data. No SSR playback was conducted as the phasing of the transmitters would have caused periodic dropped frames. * On day 262 (Sep 18), the Ahead observatory was used again to phase calibrate the 11th uplink array, using DSS-24 and 26 for 1.9 hours, to support the array use for STEREO Behind transmitter carrier recovery. Due to a transmitter motor generator issue at DSS-24, the transmitter could only be calibrated to 10 kW reducing the array gain by approximately 1.6 dB. An approximate 10.4 dB gain in uplink AGC was observed in the spacecraft transponder data. No SSR playback was conducted as the phasing of the transmitters would have caused periodic dropped frames. * The average daily science data return for Ahead was 5.1 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 supports some solar array input; RF communications only supports uplink of short commands to an LGA. Very limited telemetry can be received at 11.7 bps from the –Z LGA. While propellant is suspected to be frozen, both propulsion tank latch valves are open, and pressure transducer #2 is not functioning. Power switching boards are on; nearly all switched loads off with TWTA in standby and IEM (avionics) on. EA mode is enabled. The battery charge rate is C/10. As the uncontrolled communications link is degrading, necessary macro sequences are being developed 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 261 (Sep 17), the 10th uplink array for STEREO Behind recovery was conducted using DSS-24, 25, and 26. The uplink array was phase calibrated to provide approximate 10.4 dB gain, as compared to a single 34m station, using the Ahead observatory first for 1.9 hours then the arrayed stations were switched to point to the Behind observatory. The configuration consisted of three 34m stations at the Goldstone complex using the 80 kW, one 20 kW, and one 10 kW transmitters repeating a 3 kHz frequency acquisition sequence with the MOC sending 20 critical commands after each sweep. 360 commands were sent for configuring the spacecraft for a low power mode by powering off excess loads, powering on all power switching boards, and ensuring the reaction wheels are powered off in a known configuration. * On day 262 (Sep 18), the 11th uplink array for STEREO Behind recovery was conducted using DSS-24, 25, and 26. The uplink array was phase calibrated to provide approximate 10.4 dB gain, as compared to a single 34m station, using the Ahead observatory first for 1.9 hours then the arrayed stations were switched to point to the Behind observatory. The configuration consisted of three 34m stations at the Goldstone complex using the 80 kW, one 20 kW, and one 10 kW transmitters repeating a 3 kHz frequency acquisition sequence with the MOC sending 20 critical commands after each sweep. With the DSN 70m station DSS-43 monitoring the downlink and the Allen Telescope Array, during 2 brief TWTA sampling periods, the carrier signal was received on time with a continuously fluctuating signal of -170 dBm to -178 dBm with a period of ~45 seconds. Subcarrier lock was intermittent. While the uplink can support short critical commands, the downlink cannot support telemetry. The radio science receiver team reported a modulated downlink. As the SNR was not stable long enough for post-pass telemetry extraction, the LGA was swapped to the –Z LGA to improve SNR. This improved the carrier level by ~3 dB, with levels of -167 dBm to -174 dBm. Two telemetry frames were received. While the battery pressure was good, the battery temperature is high from overcharging and needs to be reduced. Macro 300 is not currently loaded in memory. * Important Note: We have been testing successfully with uplink array for most of the year with STA, but this is the first time to use it with STB and on Sunday we did receive telemetry and verified that the uplink array does work on the low gain antenna with improved gain. * Request support through Oct. 9 to send commands up at least every three days to help protect the battery and monitor the Doppler evolution. Expect more tracks in the schedule for STB. Week 38 (Sep 19-25) * On Tuesday and Friday this week, two STEREO AHEAD 70m tracks (station 43), below, have been shortened to a duration of 1.75 & 1.9 hours respectively to prevent further battery functional degradation and to allow for monitoring carrier performance and Doppler evolution (and get commanding) on STEREO BEHIND. It’s unclear if there will be any effect on data return at this point. 70-m Station 63 is available for two straight weeks. * A 2.6 hour return-to-service track for station 63 with STEREO Ahead is scheduled for Saturday, Sep 24. There will be no SSR playback or instrument commanding during this track. Given that the Madrid maintenance has been delayed, this event may be rescheduled. * Ahead has 9 passes during the week, and overall coverage is nominal. There are four passes at 720 kbps, one at 360 kbps, one at 240 kbps, and three at 160 kbps. * Behind had a track on Monday Sep 19 for 2 hours with DSS-43. Unfortunately, transmitter suddenly went off (suspect a battery bus collapse). Commands were sent to reconfigure it into a safe state. * Tuesday Sep 20, we have two hours of support with station 43 with another track on Friday Sep 23 for two hours and Saturday there is support from station 26, limited to sending commands only. Week 39 (Sep 26-Oct 2) * The 36th SECCHI stepped calibration roll is scheduled for Tuesday, Sep 27, starting at 11:55 UT. This is the fifth calibration roll without using the gyros. System momentum is expected to be about 1 N-m-s. * 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 track coverage is still being negotiated. Proposals for continued track time in the next few weeks is still on-going. 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. * Single station recovery attempts for Behind are scheduled for 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. * 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 for Behind scheduled during the week. Still planning on the monthly recovery track cadence. 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 for Behind scheduled during the week. Still planning on the monthly recovery track cadence. 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 for Behind scheduled during the week. Still planning on the monthly recovery track cadence. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 38: M Sep 19 (263) T Sep 20 (264) Behind: Station 43 support for 2 hours W Sep 21 (265) T Sep 22 (266) F Sep 23 (267) Behind: Station 43 support for 2 hours S Sep 24 (268) Ahead: Return-to-service track with DSS-63 (TBC) S Sep 25 (269) ------------------------------------------------------------------------------- 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 (298) 10th STEREO Launch Date Anniversary W Oct 26 (300) T Oct 27 (301) F Oct 28 (302) S Oct 29 (303) S Oct 30 (304) ------------------------------------------------------------------------------- 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