STEREO Weekly Meeting Minutes for 2015-05-12 (Week 20) ANNOUNCEMENTS ------------- * The next weekly telecon is delayed until Jun 30, unless contact is resumed with the Behind spacecraft before then. The MOC status report will still be generated and posted on line: http://stereo-ssc.nascom.nasa.gov/data/moc_sds/ahead/data_products/moc_status_report/2015/ INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating in "safe mode" for superior solar conjunction. Normal operations should resume in July 2015. * There are currently no communications with the Behind spacecraft. See below for details. DISCUSSION AND OPERATIONS CONSTRAINTS ------------------------------------- Since Ahead is currently in solar conjunction mode, no weekly telecons have been held since March 31. However, the weekly MOC status reports have continued to be generated, and can be found online at http://stereo-ssc.nascom.nasa.gov/data/moc_sds/ahead/data_products/moc_status_report/2015/ Week 19 (May 4-10) * On day 129 (May 9), the Green Bank Telescope, which has been using the Ahead observatory downlink signal for solar scintillation research, was unable to find the HGA downlink signal due to the very high level of solar interference at the 0.4 degree SPE angle. This was not unexpected. Their previous attempt, on day 123 (May 3) at an SPE ange of 0.7 degrees, was successful. They plan to resume their observations every three days beginning on day 150, May 30th. * The Ahead observatory entered superior solar conjunction at the 2.0 degree SPE angle on day 083, March 24th. It is in its safe mode configuration; rotating slowly at 5 degrees per minute with only the SWAVES instrument on and recording at one packet per minute. The rotation rate has been confirmed by Greenbank. The HGA is being held at 8.1 degrees, with respect to the spacecraft-Sun line, to prevent overheating of the HGA feed assembly. The next DSN support is on day 180, June 29th, to monitor the exiting of solar conjunction. Once the uplink communication link is stable at the 2.0 degree SPE angle on July 8th, the observatory will be recovered, instruments will be powered on, and limited science data collection will resume using the 2nd HGA side lobe. Dates for instrument power on and real-time commanding opportunities will be coordinated in June. Once the HGA returns to the main lobe use in mid-November, nominal daily science collection and data return will resume. * Quite a bit of DSN time has been allocated for recovering the Ahead spacecraft starting on July 8, about 8 hours per day, and mostly during daylight hours for the first 3 weeks. * On day 124 (May 4), Behind recovery operations resumed as the observatory has cleared solar interference for LGA communications. Based on the Failure Review Board recommendations, the recovery operations consist of recovering the battery state of charge for the first two days. On the third day, the transmitter will be commanded on to receive the carrier. Recovery operations are significantly different than what was conducted in January. This includes a faster frequency segmented acquisition sequence, sweeping a lower frequency range, battery state of charge recovery and powering on the transmitter using only short critical commands. The frequency segmented acquisition sequence is a significant departure for deep space communications which typically require a slow sweep of the entire best lock frequency range. The DSN staff cleverly developed a 10 second automated uplink sweep of consisting of 18 one kHz frequency segments followed by repeatedly sending short commands. Note that the use of the JPL radio science receiver capability for the carrier recovery tracks has been delayed until funding negotiations have been completed. * Greenbank is scheduled to assist in the Behind recovery efforts, and will cover 6 out of 7 of the carrier recovery tracks when the MOC will attempt to power on the transmitter. * On day 124 (May 4), during the DSS-43 70m support for Behind, 97 commands were sent for battery state of charge recovery. The timing and coordination of the commanding between the DSN and MOC continued to be refined. * On day 125 (May 5), during the DSS-14 70m support for Behind, the transmitter tripped off-line at 2236z for 10 minutes. 210 commands were sent for battery state of charge recovery. See DR #G116201 for more information. * On day 127 (May 7), before BOT, the DSS-43 70m station was declared red for the 3 hour duration of the Behind support due to a failed antenna servo drive. As a result, commands for powering on the transmitter did not occur. See DR #C111137 for more information. The next opportunity for attempting to power on the transmitter is tomorrow afternoon (May 13). * The current attempts to recover Behind depend on sending short critical commands, as opposed to longer flight software commands which require more of the spacecraft subsystems to be powered up and running. * Retrograde motion of Behind will bring it back close to the Sun at the end of June, and recovery operations will be suspended until late November, early December. Track requirements will need to be adjusted to account for this. * Testing of the DSN uplink array capability will resume with the Ahead spacecraft in the October-November timeframe. Once this mode is ready, it will be applied to the Behind recovery efforts. * Detailed status of the activities that occurred on the Behind loss of communication anomaly, which occurred on day 2014-274 (Oct 1), are listed below. * The Behind observatory entered superior solar conjunction at the 2.0 degree SPE angle on day 022. Recovery efforts resumed post solar conjunction on day 124, May 4th through day 179, June 28th, as the spacecraft will be clear of solar interference for recovering on the LGA. The Failure Review Board recommendations are being implemented consisting of battery state of charge recovery and powering on the downlink carrier. Due to Behind’s orbit going retrograde and re-entering the region of solar interference, recovery operations will be suspended from July through November. The DSN uplink arraying capability will be tested again with the Ahead observatory in October and November, and when it is ready, it will be used to increase the ground transmit power to assist with Behind recovery commanding. * Significant findings to date: 1. Analysis of the three DSN extracted telemetry frames from the carrier signal just before the planned observatory reset/anomaly occurred on day 2014-274, October 1st, showed nominal performance of the spacecraft, i.e., no anomalies, IMU off, and the star tracker providing an attitude solution. 2. Post reset, from the very limited telemetry, three packets, extracted from the carrier signal by the DSN, the X-axis gyro on IMU-A had failed. Unfortunately, this telemetry contained only G&C anomaly data and no spacecraft summary data, i.e., the state of the RF, G&C, fault protection and other subsystems is not known at the time of the anomaly. With a failed IMU and the star tracker being off-line for an undetermined duration, the sun sensors will keep the observatory pointed at the Sun, though the G&C will not have any roll knowledge, and cannot roll the observatory as part of the safing configuration to re-establish communications on the LGAs. From analysis of this telemetry and initial G&C simulations, it is highly suspected that the observatory is rotating about the principal axis of inertia due to an autonomous momentum dump initiated by biased gyro data flagged good by the IMU, but this has not yet been confirmed. 3. At least two anomalies occurred post reset, the star tracker not promoting to AAD mode and the X-axis gyro failure. Unfortunately, due to the number of possible combinations, the STEREO fault protection system is not designed for simultaneous failures. * The cause and effect analysis of the loss of communications from the LGAs is continuing. G&C simulations using the biased gyro data flagged good by the IMU are continuing to better understand the potential impact to the observatory state. Recovery from a negative power state is also being investigated. While the recovery and analysis efforts continue on Behind, as the Ahead observatory will enter superior solar conjunction in March, the primary focus of the engineering team is on developing operational configuration changes to add robustness to the G&C rate sensor usage to ensure the Ahead observatory’s continued safety. * Once communications are restored and the anomaly resolved, the Behind observatory will be returned to nominal science data collection as soon as it is safely possible. Week 20 (May 11-17) and subsequent weeks * Each week has DSN passes of 3 hours each over 3 consecutive days. * The first two days are devoted to recovery the battery state of change, and the third day is used to attempt to turn on the tranmitter. * Greenbank will be listening for a signal during each transmitter acquisition attempt through the end of June, except June 10. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 20: M May 11 (131) T May 12 (132) W May 13 (133) T May 14 (134) F May 15 (135) S May 16 (136) S May 17 (137) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 21: M May 18 (138) T May 19 (139) W May 20 (140) T May 21 (141) F May 22 (142) S May 23 (143) S May 24 (144) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 22: M May 25 (145) T May 26 (146) W May 27 (147) T May 28 (148) F May 29 (149) S May 30 (150) Ahead: Greenbank Faraday rotation observations resume S May 31 (151) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 23: M Jun 01 (152) T Jun 02 (153) W Jun 03 (154) T Jun 04 (155) F Jun 05 (156) S Jun 06 (157) S Jun 07 (158) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 24: M Jun 08 (159) T Jun 09 (160) W Jun 10 (161) T Jun 11 (162) F Jun 12 (163) S Jun 13 (164) S Jun 14 (165) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 25: M Jun 15 (166) T Jun 16 (167) W Jun 17 (168) T Jun 18 (169) F Jun 19 (170) S Jun 20 (171) S Jun 21 (172) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 26: M Jun 22 (173) T Jun 23 (174) W Jun 24 (175) T Jun 25 (176) F Jun 26 (177) S Jun 27 (178) S Jun 28 (179) Behind: Suspend Behind recovery efforts Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 27: M Jun 29 (180) T Jun 30 (181) W Jul 01 (182) T Jul 02 (183) F Jul 03 (184) S Jul 04 (185) S Jul 05 (186) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Upcoming events: Behind events are contingent on recovering the spacecraft. 2015: * Mar 24 - Jul 07 Ahead: Spacecraft behind Sun * Jul 8 Behind: HGA on 2nd side lobe * Jul 7-28 Ahead: S/C SSR Playback at 3 kbps * Jul 14 Ahead: Instrument power on * Aug 17 Ahead: HGA on 1st side lobe * Nov 10 Ahead: HGA on main lobe, offpoint 1 degree Ahead: SSR playback and reconfiguration, S/C checkout * Nov 12 Ahead: Instrument recommissioning * Nov 16 Behind: Resume Behind recovery efforts * Nov 20 Behind: HGA on 1st side lobe * Dec 30 Ahead: HGA on main lobe 2016: * Jan 2 Behind: HGA on main lobe Behind: SSR playback and reconfiguration, S/C checkout * Jan 5 Behind: Instrument recommissioning * Jan 27 Both: HGA calibration * Mar 16 Both: Post Solar Conjunction Assessment Review * Jul 5 Juno arrival at Jupiter 2017: * Jul 11 Ahead: Switch downlink rate to 160 kbps * Jul 22 Behind: Switch downlink rate to 160 kbps 2018: * Mar 5 Ahead: Mercury transit 2019: * Mar Ahead: Switch downlink rate to 240 kbps * Apr Behind: Switch downlink rate to 240 kbps 2020: * May Behind: Switch downlink rate to 360 kbps * Jun Ahead: Switch downlink rate to 360 kbps * Jun Behind: Switch downlink rate to 480 kbps * Sep Ahead: Switch downlink rate to 480 kbps 2021: * Jul Behind: Switch downlink rate to 720 kbps * Aug Ahead: Switch downlink rate to 720 kbps