STEREO Weekly Meeting Minutes for 2015-03-25 (Week 13) ANNOUNCEMENTS ------------- * The Ahead spacecraft was reset into solar conjunction mode yesterday, Mar 24. See below for details. 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 12 (Mar 16-22) * On day 075 (Mar 16), during the DSS-43 support for Ahead, turbo decoder lock was lost intermittently throughout the track due to the effects of solar scintillation. While the uplink was locked, no commands were received. These anomalies resulted in 10 no-op and 3 SECCHI commands not being received, which were resent on the subsequent track, and the loss of 1052 frames (29%) of spacecraft SSR playback and real-time data. * On day 075 (Mar 16), 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 5 no-op, 2 SECCHI, and 2 C&DH commands not being received and 761 frames (38%) of spacecraft SSR playback and real-time data. * On day 075 (Mar 16), during the DSS-14 support for Ahead, the spacecraft transponder did not lock uplink until 1843z. The station performed a re-sweep at 1855z. Because of the late uplink acquisition, all initial no-op commands and PLASTIC commands failed to be received; however, 7 of 11 SECCHI commands were successfully received. POC queue “Sent” commands were moved back to the staging queues and uplinked again. For the 2nd transmission attempt, 26 of 30 PLASTIC commands and 5 of 11 SECCHI commands were successfully uplinked. The turbo decoder lock was lost intermittently throughout the track corrupting the Stored Command Buffer dump data due to the effects of solar scintillation. These anomalies resulted in the loss of 54 commands not being received and 595 frames (25%) of spacecraft SSR playback and real-time data. * On day 076 (Mar 17), during the DSS-14 support for Ahead, turbo decoder lock was lost intermittently throughout the track due to the effects of solar scintillation. Three attempts were made to downlink the Stored Command Buffer image for PLASTIC timetag command verification; however, all three sets of dump data were corrupted by missing packets lost in downlink. This anomaly resulted in the loss of 295 frames (8%) of spacecraft SSR playback and real-time data. * On day 077 (Mar 17), during the DSS-63 support for Ahead, due to the effects of solar scintillation, only 4 of 15 initial NO_OP commands were received by the spacecraft. Two attempts to load instrument power-off timetags failed with only 2 of 10 commands successfully received. The write pointer for SSR partition #7 was successfully reset to 1 to free space for solar conjunction recording; however, commands to reset the write pointers for partitions #6 and #11 were not received by the spacecraft (i.e., 1 of 3 commands successfully received). Out of 9 SECCHI commands radiated, none were received by the spacecraft. These anomalies resulted in the loss of 30 commands not being received and 593 frames (25%) of spacecraft SSR playback and real-time data. Note – During days 076 and 077 (Mar 17-18), the strongest geomagnetic storm of this solar cycle occurred with a Kp index of 8. * On day 078 (Mar 19), during the DSS-63 support for Ahead, due to the effects of solar scintillation, 11 of 15 initial no-op commands were received by the spacecraft. Instrument power-off timetags were loaded and verified successfully. Write pointers for partitions #6 and #11 were successfully reset to 1 to free space for solar conjunction recording. Out of 6 SECCHI commands radiated, only 2 were received by the spacecraft. These anomalies resulted in the loss of 8 commands not being received and 333 frames (14%) of spacecraft SSR playback and real-time data. * On day 078 (Mar 19), during the DSS-14 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 one no-op command not being received and 333 frames (18%) of spacecraft SSR playback and real-time data. * On day 079 (Mar 20), during the DSS-63 support for Ahead, due to the effects of solar scintillation an earlier CME emanating from a region perpendicular to the observatory-Earth line, 4 of 15 initial no-op commands were received by the spacecraft. PLASTIC, IMPACT, and SECCHI powered down were verified with SWAVES remaining on for solar conjunction. As SECCHI is powered down, loaded G&C wheel gains parameter (3 of 10 repeated load commands succeeded, 2 of 4 repeated dump commands succeeded). Dumped the Data Summary Table (2 of 2 dump commands succeeded). These anomalies resulted in the loss of 20 commands not being received and 2296 frames (58%) of spacecraft SSR playback and real-time data. * On day 079 (Mar 20), during the DSS-14 support for Ahead, turbo decoder lock was lost intermittently throughout the track due to the effects of solar scintillation. At 2032z, the 500 bps uplink rate was tested as commanding at a higher uplink rates have a better probability of success. 31 out of 40 commands were received at the 500 bps uplink rate. This anomaly resulted in the loss of 9 no-op command not being received and 657 frames (20%) of spacecraft SSR playback and real-time data. * On day 080 (Mar 21), 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 6 no-op commands, and 132 frames (4%) of spacecraft SSR playback and real-time data. * On day 080 (Mar 21), during the DSS-14 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 3 no-op commands, and 8 frames (0.2%) of spacecraft SSR playback and real-time data. * On day 081 (Mar 22), 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 4 no-op commands, and 45 frames (2%) of spacecraft SSR playback and real-time data. * On day 081 (Mar 22), during the DSS-14 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 4 no-op commands, and 350 frames (9%) of spacecraft SSR playback and real-time data. * 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 076 (Mar 17), the 77th momentum dump was executed successfully at 2300z, which imparted a delta V of 0.106 m/sec. The momentum target was set to 13 Nms vice 15 Nms so as to have a relatively low (~7 Nms) system momentum level while rotating during solar conjunction. * On day 079 (Mar 20), the PLASTIC and IMPACT instruments were powered down at 1600z and SECCHI at 1605z on STEREO Ahead in preparation for superior solar conjunction entry on day 083 (Mar 24). The SWAVES instrument remains on as planned. * The average daily science data return for Ahead, while operating on the second side lobe on the HGA, was 12 Mbits during this week. * 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 two degree SPE angle on day 022 (Jan 22). 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 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 13 (Mar 23-29) * Both spacecraft were at an SPE angle of 2 degrees at the start of the week, with Ahead going into solar conjunction, and Behind coming out of it. * At 1600z yesterday, March 24th, the STEREO 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. While the RF communications were poor during the DSS-63 support with over 50% of the expected telemetry frames not received due to solar scintillation effects, post reset, telemetry was received intermittently for 46 minutes with the observatory rotating at 5 degrees per minute on the second HGA side lobe, quite surprising. * Daily DSN 70m supports will be used through April 5th to monitor the AHEAD observatory RF performance and overall health and safety. * The passes for the remainder of the week will be monitoring the signal from the spacecraft. Most of these supports will be on one of the low gain antennae, and there will be little signal margin even with the 70 meter stations. Each day, the spacecraft will switch between one of the three antennae. The hard command loss timer will reset the spacecraft 35 times during the conjunction period. * The first hard command loss timer reset should occur on Friday, Mar 27, at 16:20 UT. The SPE angle will be 1.9 degrees. The HGA antenna will also be bumping up against the soft stop angle, so the signal will be expected to fade after that. The soft stop will continue to be in affect until day 186 (Jul 5). A DSN track will cover the reset, and the radio science receiver will record it. * After the reset, DSN will remain in 1-way mode for all the tracks. * Behind coverage has been reallocated to Ahead. * Ahead has 10 passes during the week, and overall coverage is nominal. 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. * Attempts to recover Behind will resume on May 4. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 13: M Mar 23 (082) T Mar 24 (083) Ahead: Reset into solar conjunction mode, 16:00 UT W Mar 25 (084) T Mar 26 (085) F Mar 27 (086) Ahead: Hard command loss timer fires at 16:20 UT S Mar 28 (087) S Mar 29 (088) Notes: * Ahead operating on second side lobe. No commanding after the reset on Mar 24. The signal will continue to be monitored during the week, but the signal margin may be too low to lock on. * Attempts to reestablish communications with Behind start on Mar 23. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- 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