STEREO Weekly Meeting Minutes for 2015-03-31 (Week 14) ANNOUNCEMENTS ------------- * STEREO weekly operations meetings will be suspended until May 12 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 ------------------------------------- Week 13 (Mar 23-29) * On day 080, at approximately 1300z, the Ahead and Behind observatories were in conjunction, i.e., their separation angle was zero. * The Ahead observatory is operating on the second side lobe of the HGA to prevent overheating of the HGA feed assembly which is currently at 113 degrees C with the HGA angle at 8.1 degrees, with respect to the spacecraft-Sun line. * On day 082, during the DSS-63 support for Ahead, turbo decoder lock was lost intermittently throughout the track due to the effects of solar scintillation. This anomaly resulted in the loss of four no-op commands not being received and 346 frames (14%) of spacecraft SSR playback and real-time data. * On day 083, during the DSS-63 support for Ahead, turbo decoder lock was lost intermittently throughout the track due to the effects of solar scintillation. Ranging was disabled at 1504z due to insufficient ranging margin. Three no-op commands were not received. At 1543z, the command to reset the Ahead observatory into its solar conjunction configuration was sent. This was the last command to be sent until exiting solar conjunction in July. While the RF communications were poor during the DSS-63 support with over 50% of the expected telemetry frames not received, most likely due to a CME that occurred 6 hours earlier, post reset, 93 good telemetry frames or 38% of the expected frames were received intermittently for 46 minutes with the observatory rotating at 5 degrees per minute on the second HGA side lobe. * On day 083, during the DSS-14 support for Ahead, with the observatory rotating at 5 degrees per minute on the second HGA side lobe, telemetry was received intermittently except for a 5 to 6 minute gap during each 72 minute rotation. 181 good telemetry frames or 25% of the expected frames were received. * On day 084, during the DSS-14 support for Ahead, with the observatory rotating at 5 degrees per minute on the –Z LGA, telemetry lock was never received due to the low signal strength as the LGA is on the edge of the hemispherical pattern. Carrier lock was maintained with the carrier power between -168 and –173 dBm. * On day 083, at 1600z the Ahead observatory initiated a commanded system reset to enter its configuration for solar conjunction. The DSN received a strong downlink signal at 1621z and telemetry was received at 1622z. The star tracker was “lazy” for 38 seconds longer than expected to re-acquire a solution causing IMU2 to power on for two hours. The SWAVES instrument remains on as planned. The IMPACT and PLASTIC space weather SSR partitions are at 53 and 51 percent full respectively, and SWAVES, which is continuing to record at one packet per minute, is at 34 percent full. The HGA feed temperature was at 114 degrees C. * On day 085, during the DSS-63 support for Ahead, with the observatory rotating at 5 degrees per minute on the –Z LGA, telemetry lock was never received due to the low signal strength as the LGA is on the edge of the hemispherical pattern. Carrier lock was maintained, except for a 7 minute loss starting at 1441z, with the carrier power between - 169 and –173 dBm. * On day 086, during the DSS-63 support for Ahead, with the observatory rotating at 5 degrees per minute on the +Z LGA, telemetry lock was never received due to the low signal strength as the LGA is on the edge of the hemispherical pattern. Carrier lock was intermittent with the carrier power between -169 and –173 dBm. Carrier lock was lost a t 1636z for 6 minutes due to the first hard command loss timer (HCLT) initiated system reset. At 1642z, telemetry lock was received from the HGA second side lobe. Telemetry lock was intermittent at 1656z for the remainder of the support. Post reset, 180 telemetry frames or 70% of the expected frames were received. * On day 086, during the DSS-14 support for Ahead, with the observatory rotating at 5 degrees per minute on the second HGA side lobe, telemetry was received intermittently. 887 good telemetry frames or 64% of the expected frames were received. * On day 086, at 1620z, the Ahead observatory initiated the first planned HCLT system reset during solar conjunction. The DSN received a strong downlink signal at 1641z and telemetry was received at 1642z. The star tracker was again “lazy” in re-acquiring a solution causing IMU2 to power on for two hours. The SWAVES instrument remains on as planned. The IMPACT and PLASTIC space weather SSR partitions remain at 53 and 51 percent full respectively, and SWAVES, which is continuing to re cord at one packet per minute, is at 34.3 percent full. The HGA feed temperature was at 113 degrees C. * On day 087, during the DSS-14 support for Ahead, with the observatory rotating at 5 degrees per minute on the second HGA side lobe, telemetry was received intermittently. 114 good frames or 22% of the expected frames were received. Two hours into the support, the spacecraft switched to the –Z LGA as planned. Carrier lock was maintained for the remaining 8.3 hours of the support, except for a 12 minute loss starting at 1822z, with the carrier power between -168 and –174 dBm. * On day 088, during the DSS-63 support for Ahead, with the observatory rotating at 5 degrees per minute on the –Z LGA, while carrier lock was intermittent for 7.7 hours, 2 telemetry frames were received. After the spacecraft switched to the +Z LGA as planned, carrier lock was intermittently lost for the remaining 45 minutes of the support with the carrier power between -172 and –174 dBm. * On day 088, during the DSS-14 support for Ahead, with the observatory rotating at 5 degrees per minute on the +Z LGA, telemetry lock was never received due to the low signal strength as the LGA is on the edge of the hemispherical pattern. Carrier lock was intermittent for duration of the support with the carrier power between -169 and –174 dBm. * Q: It seems routine for there to be a delay in the star tracker re-acquiring a solution after a HCLT system reset with the result that the IMU powers on for two hours. If this happens with each HCLT reset how does this impact the IMU lifetime? A: If IMU2 is activated for two hours every three days before we reestablish contact with the spacecraft _and_ we assume the limb current is the limiting factor (it might not be) the increased usage would reduce the IMU lifetime by a month or two. * Detailed status of the activities that occurred on the Behind loss of communication anomaly, which occurred on day 2014-274, are listed below. * The Behind observatory entered superior solar conjunction at the two degree SPE angle on day 022. Recovery efforts will resume post solar conjunction on day 124, May 4th; with implementing the Failure Review Board recommendations and increasing the ground transmit power through arraying uplink stations. * 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 ano malies, 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 protect ion 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 reestablish 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 sta r 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 bett er 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 develop ing 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 re solved, the Behind observatory will be returned to nominal science data collection as soon as it is safely possible. Week 14 (Mar 30-Apr 5) * The Ahead SPE angle starts off at 1.8 degrees, decreasing to 1.7 degrees on Thursday, Apr 2, and 1.6 degrees on Sunday, Apr 5. * DSN will continue to monitor the Ahead spacecraft during the week. The hard command loss timer is expected to fire on Monday, Mar 30, at 16:40 UT, Thursday, Apr 2, at 17:00 UT, and Sunday, Apr 5, at 17:20 UT. At this point the SPE angle will be at 1.6 degrees, and the HGA will be off-pointed by 0.3 degrees off the second side lobe. The radio science receiver will be recording after the resets on Mar 30, Apr 2, and Apr 5. * The HGA will be off-pointed from the second side lobe due to the soft stop on the HGA angle, and will remain that way until July 5. * DSN suspends coverage for the Ahead spacecraft after Sunday, Apr 5, until the spacecraft comes out of superior solar conjunction. * Behind coverage has been partially reallocated to Ahead, with the rest released. * Ahead has 7 passes during the week, and overall coverage is nominal. Week 15 (Apr 6-12) * No tracks for Ahead due to superior solar conjunction, until day 179 (Jun 28). * The Ahead SPE angle will be 1.6 degrees. The 5th and 6th hard command loss timer firings will happen during the week. * The previously scheduled tracks for Behind have been released. * The MOC will be shut down for 10 hours on Apr 11 to upgrade the UPS. Week 16 (Apr 13-19) * The SPE angles will be 1.4 degrees for Ahead, and 3.0 degrees for Behind. * The 7th hard command loss timer firing will be on Tuesday, Apr 14 at 18:19 UT, and the 8th on Friday, Apr 17 at 18:39 UT. * No tracks for either spacecraft due to superior solar conjunction. Week 17 (Apr 20-26) * The SPE angle will be 1.0 degrees on Ahead, and 3.3 degrees on Behind. * The 9th hard command loss timer firing will be on Apr 20 at 18:59 UT, the 10th on Apr 23 at 19:19 UT, and the 11th on Apr 26 at 19:39 UT. * The previously scheduled tracks for Behind have been released. * No tracks for Ahead due to superior solar conjunction. Week 18 (Apr 27-May 3) * The SPE angle will be 0.8 degrees on Ahead, and 3.5 degrees on Behind. * The hard command loss timer will fire at 19:59 on Apr 29, and 20:19 on May 2. * No tracks for either spacecraft due to superior solar conjunction. Week 19 (May 4 - 10) * Attempts to recover Behind will resume on May 4. * The SPE angle will be 0.6 degrees on Ahead, and 3.6 degrees on Behind. * No tracks for Ahead due to superior solar conjunction. * There will be three tracks for Behind, on Monday, Tuesday, and Wednesday (3 hours each). COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 14: M Mar 30 (089) Ahead: Hard command loss timer fires at 16:40 UT T Mar 31 (090) W Apr 01 (091) T Apr 02 (092) Ahead: Hard command loss timer fires at 17:00 UT F Apr 03 (093) S Apr 04 (094) S Apr 05 (095) Ahead: Hard command loss timer fires at 17:20 UT Notes: * Ahead in safe mode for superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 15: M Apr 06 (096) T Apr 07 (097) W Apr 08 (098) Ahead: Hard command loss timer fires at 17:40 UT T Apr 09 (099) F Apr 10 (100) S Apr 11 (101) Ahead: Hard command loss timer fires at 18:00 UT S Apr 12 (102) Notes: * No tracks for either spacecraft due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 16: M Apr 13 (103) T Apr 14 (104) Ahead: Hard command loss timer fires at 18:19 UT W Apr 15 (105) T Apr 16 (106) F Apr 17 (107) Ahead: Hard command loss timer fires at 18:39 UT S Apr 18 (108) S Apr 19 (109) Notes: * No tracks for either spacecraft due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 17: M Apr 20 (110) Ahead: Hard command loss timer fires at 18:59 UT T Apr 21 (111) W Apr 22 (112) T Apr 23 (113) Ahead: Hard command loss timer fires at 19:19 UT F Apr 24 (114) S Apr 25 (115) S Apr 26 (116) Ahead: Hard command loss timer fires at 19:39 UT Notes: * No tracks for either spacecraft due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 18: M Apr 27 (117) T Apr 28 (118) W Apr 29 (119) Ahead: Hard command loss timer fires at 19:59 UT T Apr 30 (120) F May 01 (121) S May 02 (122) Ahead: Hard command loss timer fires at 20:19 UT S May 03 (123) Notes: * No tracks for either spacecraft due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 19: M May 04 (124) T May 05 (125) Ahead: Hard command loss timer fires at 20:39 UT W May 06 (126) T May 07 (127) F May 08 (128) Ahead: Hard command loss timer fires at 20:59 UT S May 09 (129) S May 10 (130) 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 * Apr 25 Behind: HGA on 1st side lobe * May 4 - Jun 28 Behind: Resume Behind recovery efforts * 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