STEREO Weekly Meeting Minutes for 2014-10-21 (Week 43) ANNOUNCEMENTS ------------- * None. INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating on the first side lobe of the HGA to prevent overheating of the feed assembly. * There are currently no communications with the Behind spacecraft. See below for details. DISCUSSION AND OPERATIONS CONSTRAINTS ------------------------------------- Week 42 (Oct 13-19) * On day 290 (Oct 17), no real-time science telemetry was downlinked from Ahead as the scheduled 70 meter support with DSS-63 was changed to a 34 meter support with DSS-55 in support of the STEREO Behind communication recovery. * On day 290 (Oct 17), during the DSS-55 support for Ahead, initial telemetry acquisition was delayed by eight minutes until 0718z due to a DSN receiver problem that caused the telemetry output block count to stop updating. Another receiver was added to resolve the anomaly. See DR #M108396 more information. * On day 291 (Oct 18), no real-time science telemetry was downlinked from Ahead during the second support that day as the scheduled 70 meter with DSS-43 was changed to a 34 meter support with DSS-35 in support of the STEREO Behind communication recovery. * On day 292 (Oct 19), no real-time science telemetry was downlinked from Ahead as the scheduled 70 meter support with DSS-14 was changed to a 34 meter support with DSS-26 in support of the STEREO Behind communication recovery. * During days 279 through 285 (Oct 6-12), SWAVES science APIDs 0x503 and 0x504 were not downlinked from Ahead in real-time telemetry as the corrected RTDFD table had not yet been loaded to the Ahead observatory. The corrected RTDFD table, RTDFD #12, was loaded to the Behind observatory first to test after the planned momentum dump on day 271. This worked as expected with the SWAVES science APIDs flowing after the momentum dump. However, due to the Behind solar conjunction spacecraft testing and subsequent loss of communication anomaly, the corrected RTDFD was never loaded to the Ahead observatory. On day 293 (Oct 20), at 1300z, the SWAVES spooler queue was unblocked by using RTDFD #17, which has a wider SWAVES science range, 0x502 through 0x56F, for one hour before the start of the pass at 1440z. During the subsequent DSS-14 support, DHS release 1.1.9 was loaded successfully to C&DH RAM and EEPROM. This release contained only the corrected RTDFD #12. * The average daily science data return for Ahead, while operating on the first side lobe on the HGA, was 39 Mbits during this week. * The current HGA feed horn temperature on Ahead is 111 C, at an antenna angle of 8.5 degrees. When the angle reaches 8.1 degrees, it will hit the soft stop on the antenna. * Detailed status of the activities that occurred this week on the Behind loss of communication anomaly, which occurred on day 274 (Oct 1), are listed below. The project has requested three hour 70 meter supports every 12 hours through day 292 to re-establish communications while avoiding the level 3 Comet Siding Springs observations by the Mars missions on days 292 and 293 (Oct 19-20). * On day 286 (Oct 13), during the DSS-43 support for Behind, contingency commanding was resumed, after being discontinued for three days to allow the hard command loss timer to reset the observatory. Contingency commanding focused on ensuring that the TWTA is transmitting and the star tracker is in its operational AAD mode. No signal was received by the DSN radio science receivers. * On day 287 (Oct 14), during the DSS-63 and 43 supports for Behind, contingency commanding continued with ensuring that the TWTA is transmitting and the star tracker is in its operational AAD mode. No signal was received by the DSN radio science receivers. * On day 288 (Oct 15), during the DSS-63 support for Behind, contingency commanding continued with ensuring that the TWTA is transmitting and the star tracker is in its operational AAD mode. No signal was received by the DSN radio science receivers. The Green Bank radio telescope listened for the Behind downlink signal for 2.8 hours. The telescope was first calibrated using the STEREO Ahead signal, which was as expected, however, no signal from Behind was detected. With a diameter of 100 meters, this telescope has twice the effective area as the DSN 70 meter stations. Unfortunately, the observing window has set till the Spring for the 305 meter Arecibo Observatory’s view of STEREO Behind. During the DSS-43 support later this day, contingency commanding continued with ensuring that IMU-A is disabled as it has failed and only commanding at the emergency uplink rate, 7.8 bps. No signal was received by the DSN radio science receivers. * On day 289 (Oct 16), during the DSS-63 support for Behind, contingency commanding continued with ensuring that IMU-A is disabled as it has failed. No signal was received by the DSN radio science receivers. The Green Bank radio telescope again listened for the Behind downlink signal for 2.5 hours. During the DSS-14 support later this day, contingency commanding continued with ensuring that IMU-A is disabled as it has failed. No signal was received by the DSN radio science receivers. * On days 290, 291, and 292 (Oct 17-19), during the two 70 meter Behind contacts each day, contingency commanding continued with ensuring that IMU-A is disabled as it has failed. No signal was received by the DSN radio science receivers. * 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 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, the X-axis gyro on IMU-A had failed. (The fact that IMU-A was on means that the star tracker had failed to promote to AAD mode.) 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, it is highly suspected that the observatory is rotating due to an autonomous momentum dump initiated by bad gyro data flagged good, but this has not yet been confirmed. G&C simulations using the bad gyro data flagged good are being conducted on the hardware-in-the loop simulator to better understand the potential impact to the observatory state. If the spacecraft performed an autonomous momentum dump, the thrusters would have fired for at most 7 minutes, and then shut off. 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 of the anomaly and why no signal has been received from the LGAs is continuing to be actively investigated. * The project has requested three hour 70 meter DSN supports every 21 hours through day 313 (Nov 9) to re-establish communications. This ensures that communications on an LGA will be attempted daily. Once communications are restored and the anomaly resolved, the operational plan for exiting the solar conjunction testing will continue to return the BEHIND observatory back to nominal science data collection as soon as safely possible. * 70 meter contacts for Behind are already in place for weeks 46 and 47, in anticipation of starting solar conjunction operations. * There was some discussion about power cycling the transmitter. It's not currently anticipated that this would be helpful. The earlier commanding to power on the transmitter went through the entire power on procedure. * The knowledge of the location of the Behind spacecraft is definitely within the view of the DSN antennas, and will be for some time. Week 43 (Oct 20-26) * The updated R/T DFD table for SWAVES-prime data was uploaded yesterday (Oct 20) to Ahead. The SWAVES team reports that they're receiving their telemetry. * This morning (Oct 21), the priority of spacecraft housekeeping data was bumped up on Ahead. Since a number of 70 meter passes were switched to 34 meter stations to assist in the Behind recovery, the playback of spacecraft housekeeping was falling behind. * A new fault protection release to protect Ahead from the possibility of a similar problem that affected Behind will be uploaded in the next few days, depending on the DSN schedule. This release will disable the gyros sooner if the same situation occurs. * Saturday, Oct 25, is the eighth anniversary of the launch of STEREO. * Ahead has 7 passes during the week, all at 10 kbps on the first side lobe, in SWAVES-prime mode. However, it is anticipated that some of the supports could be shifted to 34 meter stations to assist in the Behind recovery efforts. * The 70 meter station 63 in Madrid was taken offline this week for planned maintenance, putting further pressure on 70 meter scheduling. * A 70 meter pass for Behind is scheduled for this evening (Oct 21). Supports for the remainder of the week are still being negotiated, with the hope of supports every 21 hours. Week 44 (Oct 27-Nov 2) * Daily savings time in the U.S. ends on Sunday, Nov 2. * Assuming that the spacecraft is recovered by then, the 68th momentum dump on Behind will be carried out on Tuesday, Oct 28, with ignition at 22:00 UT. The commands will be loaded on the previous pass. * Ahead has 6 passes during the week on the first side lobe, in IMPACT-prime mode. Four of the passes are at 10 kbps, and two are using 34 meter stations at 633 bps, on Wednesday and Friday. * Behind has 9 passes scheduled during the week, all using 70 meter stations. The Behind schedule was reworked for recovery operations. Week 45 (Nov 3-9) * The 73rd momentum dump on Ahead will be carried out on Nov 5, starting at 21:00 UT. * Ahead will be shifted to the second side lobe at the end of the track on Sunday, Nov 9. * Ahead has 8 passes during the week, all at 10 kbps on the first side lobe, in SWAVES-prime mode. * The pass schedule for Behind is still being negotiated. Week 46 (Nov 10-16) * Second side-lobe operations at 3 kbps begin on Ahead on Monday, Nov 10. * Ahead has 7 passes during the week, all at 3 kbps on the second side lobe. * Behind has 7 passes during the week, all on 70 meter stations, roughly one day apart. Week 47 (Nov 17-23) * Behind will reach the HGA soft stop on Nov 19. * Ahead has 7 passes during the week, all at 3 kbps on the second side lobe. * Behind has 7 passes during the week, all on 70 meter stations. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 43: M Oct 20 (293) T Oct 21 (294) W Oct 22 (295) T Oct 23 (296) F Oct 24 (297) S Oct 25 (298) 8th anniversary of STEREO launch S Oct 26 (299) Notes: * Emergency DSN contacts for Behind requested through Nov 9. * Ahead operating on first side lobe, in SWAVES-prime mode. ------------------------------------------------------------------------------- Scheduled activities for Week 44: M Oct 27 (300) T Oct 28 (301) Behind: Momentum dump, 22 UT (TBC) W Oct 29 (302) T Oct 30 (303) F Oct 31 (304) S Nov 01 (305) S Nov 02 (306) End of daily savings time in U.S. Notes: * Emergency DSN contacts for Behind requested through Nov 9. * Ahead operating on first side lobe, in IMPACT-prime mode. ------------------------------------------------------------------------------- Scheduled activities for Week 45: M Nov 03 (307) T Nov 04 (308) W Nov 05 (309) Ahead: Momentum dump, 21:00 UT T Nov 06 (310) F Nov 07 (311) S Nov 08 (312) S Nov 09 (313) Notes: * Emergency DSN contacts for Behind requested through Nov 9. * Ahead operating on first side lobe, in SWAVES-prime mode. * HGA on Ahead will be switched to second side lobe at the end of the track on Sunday, Nov 9. ------------------------------------------------------------------------------- Scheduled activities for Week 46: M Nov 10 (314) Ahead: Commence HGA operations on 2nd side lobe T Nov 11 (315) W Nov 12 (316) T Nov 13 (317) F Nov 14 (318) S Nov 15 (319) S Nov 16 (320) Notes: * Ahead operating on second side lobe. ------------------------------------------------------------------------------- Scheduled activities for Week 47: M Nov 17 (321) T Nov 18 (322) W Nov 19 (323) Behind: HGA antenna reaches soft stop T Nov 20 (324) F Nov 21 (325) S Nov 22 (326) S Nov 23 (327) Notes: * Ahead operating on second side lobe. ------------------------------------------------------------------------------- Upcoming events: 2014: * Nov 19 Behind: HGA hits soft stop * Nov 28 Behind: SSR reconfiguration * Dec 1 Behind: HGA on 1st side lobe * Dec 8 Behind: Test with 34 meter at 633 bps, both side lobes 2015: * Jan 6 Behind: HGA on 2nd side lobe * Jan 12 Behind: Test with 34 meter at 633 bps * Jan 20 Behind: Instrument power down * Jan 22 - Mar 23 Behind: Spacecraft behind Sun * Mar DAWN - Ceres arrival * Mar 22 Ahead: Instrument power down * Mar 23 - Apr 06 Behind: S/C SSR Playback at 3 kbps * Mar 24 - Jul 07 Ahead: Spacecraft behind Sun * Mar 30 Behind: Instrument power on * Apr 25 Behind: HGA on 1st side lobe * Jul DAWN - End of nominal mission * 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 * Sep 24 Ahead: HGA on 1st side lobe * Nov 20 Behind: HGA on 1st side lobe * Dec 29 Ahead: HGA on main lobe, offpoint 1 degree Ahead: SSR playback and reconfiguration, S/C checkout * Dec 31 Ahead: Instrument recommissioning 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 * Feb 19 Ahead: HGA on main lobe * 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