STEREO Weekly Meeting Minutes for 2016-08-23 (Week 34) ANNOUNCEMENTS ------------- * Contact was reestablished with the STEREO Behind spacecraft on Sunday, Aug 21, after 22 months without contact. See below for details. INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating nominally on the main lobe of the high gain antenna. * The Behind spacecraft has been successfully commanded to turn on its transmitter to downlink a carrier wave. Analysis of the carrier wave signal shows that the spacecraft is rotating at the rate of about once every two minutes. Daily communications with the spacecraft are being scheduled to keep the power system online, and to prevent the 3-day command loss timer from activating. Plans for recovering the spacecraft are being developed. DISCUSSION AND OPERATIONS CONSTRAINTS ------------------------------------- Week 33 (Aug 15-21) * On day 228 (Aug 15), during the DSS-65 support for Ahead, turbo decoder lock was lost briefly at 0908z and again at 1441z. This anomaly resulted in the loss of 2 frames of SSR data. * On day 231 (Aug 18), during the DSS-65 support for Ahead, turbo decoder lock was lost briefly at 1031z. This anomaly resulted in the loss of 1 frame of SSR data. * On day 231 (Aug 18), during the DSS-26 support for Ahead, turbo decoder lock was lost intermittently between 2017z and 2023z. This anomaly resulted in the loss of 50 frames of real-time telemetry and SSR data. * On day 233 (Aug 20), during the DSS-45 support for Ahead, telemetry lock was lost intermittently between 0128z and 0151z due to heavy rain at the Canberra complex. This anomaly resulted in the loss of 5461 frames of real-time telemetry and SSR data, which is equivalent to about 5 minutes for each instrument. See DR# C112283 for more information. * On day 234 (Aug 21), during the DSS-26 support for Ahead, turbo decoder lock was lost intermittently between 1718z and 2212z. This anomaly resulted in the loss of 42 frames of real-time telemetry and SSR data. * The average daily science data return for Ahead was 6.8 Gbits during this week. * On day 232 (Aug 19), during the DSS-26 34m support for Behind, using the 80 kW transmitter to minimize 70m contentions, at 1430z the transmitter could not be calibrated. The configuration was corrected and command began at 1447z. Later, the transmitter tripped off-line at 1502z. The transmitter re-calibrated and was placed back on-line at 1516z. This anomaly resulted in the failure to radiate approximately 36 battery recovery commands covering 4 frequency segments. 157 commands were sent for battery state of charge recovery. See DR# G117421 and G117422 for more information. * On day 233 (Aug 20), during the DSS-26 34m support for Behind, using the 80 kW transmitter to minimize 70m contentions, 350 commands were sent for battery state of charge recovery. * On day 234 (Aug 21), during the DSS-14 70m support for Behind for carrier recovery, the downlink carrier was detected at approximately 22:33:23z after contact was lost on October 1, 2014 during testing for a two month long superior solar conjunction. Radio science receivers confirmed a signal was present from 22:27:40z to end of track. Carrier signal level fluctuated between -166 to -179 dBm with an approximate 2 minute rotation. DSS-14 was able to lock up to the 25 kHz subcarrier, confirming the LGA is in use, however, no symbol lock was achieved as expected since commands were sent to power off the avionics for battery charge recovery. The downlink was received for 2.4 hours through end of track. The GSFC mission director declared spacecraft emergency at 235-0030z. No telemetry was received as expected since the avionics were purposely powered off to maintain battery state of charge. While quite early, recovery is expected to proceed slowly to preserve a positive power balance, assess observatory health, re-establish attitude control, and warm all subsystems and instruments. * The frequency segmented acquisition mode which was implemented by the DSN for STEREO Behind was critical for recovering communications with the spacecraft. * At the time of the telecon, Station 14 is observing STEREO Behind. It is still quite early in recovery operations, which will proceed slowly and carefully. Behind is essentially one step above off. The power system is online. The transponder is working, with the spacecraft accepting commands and downlinking the carrier signal. The rotation rate of once every two minutes is not slow enough to be countered using the reaction wheels alone. The MOC is working on refining the draft plan for recovery. The first step is to bring the avionics online to start getting telemetry, but without fault protection coming on, which would cause problems. A plan is being developed, and is expected to be tested and approved for implementation at the end of the week, possibly as early as Friday. After that the plan is to start warming the propulsion, to recover the G&C. There is a very long recovery process with many hurdles to jump through. Daily meetings are being held by the operations team. * Three hours per day of track time has been requested from the DSN for Behind recovery. Recovery of the avionics will require more time. The track for tomorrow (Aug 24), at 13:25 UT, has just been scheduled. Week 34 (Aug 22-28) * The station 34 engineering test of pointing to the Ahead spacecraft, originally scheduled for Monday, Aug 22, in support of the upcoming OSIRIS-REx mission, was cancelled because of the reshuffling of DSN schedules for Behind recovery. * An additional engineering test for the OSIRIS-REx mission is scheduled for Saturday, Aug 27, this time with station 35. * Behind will be at perihelion on Aug 25. * Ahead has 14 passes during the week, and overall coverage is nominal. There are three passes at 720 kbps, two at 360 kbps, and nine at 240 kbps. * Behind starts the week at an SPE angle of 14.3 degrees. The track schedule for Behind recovery is still being worked. Current operations are oriented towards maintaining the state of charge. The transmitter has been turned on for a few hours each day. Commands were sent to disable the EA mode bypass (i.e. reenable EA mode). Commands to reenforce the turning off of heaters, etc. to keep the battery from draining. In particular, the wheels or IMU should not come on. Week 35 (Aug 29-Sep 4) * Ahead has 12 passes during the week, and overall coverage is nominal. There is one pass at 720 kbps, two at 360 kpbs, eight at 240 kbps, and one at 160 kbps. * Behind starts the week at an SPE angle of 14.1 degrees. The track schedule for Behind recovery is still TBD. Week 36 (Sep 5-11) * Monday, Sep 5, is Labor Day, which is a holiday at APL. * The 91st momentum dump on Ahead is scheduled for Thursday, Sep 8, with ignition at 19:30 UT. This momentum dump is scheduled about 8-9 days early because of DSN coverage limitations, particularly in regards to the launch of OSIRIS-REx whose first launch window starts later that day, with additional daily opportunities up until Sep 15. * Launch contingency plans for the first three days of the OSIRIS-REx launch opportunity period have been received, and have minimal impact on the STEREO schedule. * Ahead has 11 passes during the week, and overall coverage is nominal. There are three passes at 720 kbps, four at 360 kbps, three at 240 kbps, and one at 160 kbps. * Behind starts the week at an SPE angle of 14.0 degrees. The track schedule for Behind recovery is still TBD. Week 37 (Sep 12-18) * Ahead has 8 passes during the week, and overall coverage is nominal. There are four passes at 720 kbps, one at 360 kbps, and three at 240 kbps. * Behind starts the week at an SPE angle of 13.8 degrees. * The uplink array attempts for Behind are still listed in the schedule. These will most likely be converted to tracks for Behind recovery, with the Ahead portions taken out. Week 38 (Sep 19-25) * 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. * 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 starts the week at an SPE angle of 13.7 degrees. The track schedule for Behind recovery is still TBD. 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 starts the week at an SPE angle of 13.6 degrees. The track schedule for Behind recovery is still TBD. 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. * There are currently three passes scheduled for recovering the Behind carrier. Now that the carrier has been recovered, these are expected to be converted to recovery operations. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 34: M Aug 22 (235) T Aug 23 (236) W Aug 24 (237) T Aug 25 (238) Behind: Perihelion F Aug 26 (239) S Aug 27 (240) Ahead: Station 35 pointing test for OSIRIS-REx S Aug 28 (241) ------------------------------------------------------------------------------- Scheduled activities for Week 35: M Aug 29 (242) T Aug 30 (243) W Aug 31 (244) T Sep 01 (245) F Sep 02 (246) S Sep 03 (247) S Sep 04 (248) ------------------------------------------------------------------------------- Scheduled activities for Week 36: M Sep 05 (249) Labor Day T Sep 06 (250) W Sep 07 (251) T Sep 08 (252) Ahead: Momentum dump, 19:30 UT F Sep 09 (253) S Sep 10 (254) S Sep 11 (255) ------------------------------------------------------------------------------- Scheduled activities for Week 37: M Sep 12 (256) T Sep 13 (257) W Sep 14 (258) T Sep 15 (259) F Sep 16 (260) S Sep 17 (261) S Sep 18 (262) Notes * The phased antenna passes currently scheduled for Behind on Sep 17-18 are expected to be converted to normal recovery tracks. ------------------------------------------------------------------------------- Scheduled activities for Week 38: M Sep 19 (263) T Sep 20 (264) W Sep 21 (265) T Sep 22 (266) F Sep 23 (267) S Sep 24 (268) Ahead: Return-to-service track with DSS-63 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) S Oct 08 (282) S Oct 09 (283) ------------------------------------------------------------------------------- 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