STEREO Weekly Meeting Minutes for 2015-03-17 (Week 12) ANNOUNCEMENTS ------------- * Next week's meeting has been rescheduled for Wednesday, March 25, starting at 12:00 EDT (16:00 UTC). * Efforts to recover the Behind spacecraft have been postponed to May 4 to allow the SPE angle to get above 3.5 degrees, to avoid the effects of solar scintillation currently being seen by the Ahead spacecraft. These efforts will be suspended again on June 28 due to the SPE angle dropping back down, and then resumed sometime in late November, early December. INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating on the second 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 11 (Mar 9-15) * On day 068 (Mar 9), during the DSS-63 support for Ahead, turbo decoder lock was lost intermittently between 1514z through 1620z due to the effects of solar scintillation. This anomaly resulted in the loss 3 frames of spacecraft SSR playback and real-time data. *On day 069 (Mar 10), during the DSS-54 support for Ahead, a DCD swap occurred unexpectedly between 1303z and 1304z due to a fault tolerance check. This anomaly did not result in any data loss. See DR #M108612 for more information. * On day 069 (Mar 10), during the DSS-14 support for Ahead, turbo decoder lock was lost intermittently between 2146z through 2157z due to the effects of solar scintillation. This anomaly resulted in the loss 2 frames of spacecraft SSR playback and real-time data. * On day 071 (Mar 12), during the DSS-43 support for Ahead, turbo decoder lock was lost intermittently between 0524z through 0724z due to the effects of solar scintillation. This anomaly resulted in the loss of one SECCHI command not being received, which was resent on the subsequent track, and 14 frames of spacecraft SSR playback and real-time data. * On day 071 (Mar 12), during the DSS-65 support for Ahead, turbo decoder lock was lost intermittently between 1219z through 1336z due to the effects of solar scintillation. This anomaly resulted in the loss 3 frames of real-time data. * On day 071 (Mar 12), during the uplink array test with DSS-24 and 25 supports for Ahead, turbo decoder lock was lost intermittently between 1551z through 1615z due to the effects of solar scintillation. This anomaly resulted in the loss 13 frames of real-time data. * On day 072 (Mar 13), during the DSS-43 support for Ahead, turbo decoder lock was lost intermittently between 0541z through 0701z due to the effects of solar scintillation. This anomaly resulted in the loss of 73 frames of spacecraft SSR playback and real-time data. * On day 072 (Mar 13), during the DSS-63 support for Ahead, turbo decoder lock was lost intermittently between 1414z through 1635z due to the effects of solar scintillation. This anomaly resulted in the loss of one no-op command not being received and 66 frames of spacecraft SSR playback and real-time data. * On day 073 (Mar 14), during the DSS-65 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 157 frames of real-time data. * On day 073 (Mar 14), during the DSS-43 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 2 no-op commands, and 683 frames of spacecraft SSR playback and real-time data. * On day 074 (Mar 15), during the DSS-25 support for Ahead, in addition to losing turbo decoder lock intermittently throughout the track, the downlink telemetry lock was lost between 1550z and 1613z, and again between 1619z and 1647z due to the effects of solar scintillation. These anomalies resulted in the loss of 51 minutes of continuous, and 395 intermittent frames of real-time data, and 2 no-op commands were dropped. See DR #G116063 for more information. * 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 112 degrees C with the HGA angle at 8.3 degrees, with respect to the spacecraft-Sun line. * On day 071 (Mar 12), an uplink array test with DSS-24 and 25 was successfully conducted by the DSN which increased the Ahead uplink received power by 6 dB. * On day 068 and 072 (Mar 9, 13), PLASTIC loaded timetag commands to the C&DH stored command buffer in preparation for powering down the instrument on day 079 (Mar 20) for solar conjunction entry. * The average daily science data return for Ahead, while operating on the second side lobe on the HGA, was 16 Mbits during this week. * Starting Saturday, Mar 14, the SECCHI telemetry had degraded to the point where the images could not be processed for the SSC web pages. * 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. A preliminary report from the board is now available. One of the recommendations is to use a faster frequency segmented acquisition sequence to accommodate a rotating spacecraft. The process of arraying uplink stations is still being tested and refined. * 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 12 (Mar 16-22) * Preparations for solar conjunction on Ahead will start during the week. The SPE angle will be 2.2 degrees at the beginning of the week, approaching 2 degrees toward the end of the week. * Telemetry problems continued through the three tracks yesterday (Mar 16), and some PLASTIC commands were lost. * The 77th momentum dump on Ahead is scheduled for today, Mar 17, with ignition at 23:00 UT. Time-tagged commands were loaded last Friday. The system momentum target will be 13 N-m-s, selected to minimize the chance of an autonomous momentum dump during the solar conjunction period. DSN will be taking recordings with their radio science receivers during the momentum dump. * Adjusted G&C parameters will be uploaded to take into account the turning off of the Guide Telescope. * The instrument teams (except SWAVES) are requested to start configuring their instruments between Mar 16-19 for power down. IMPACT, PLASTIC, and SECCHI will be powered off via time-tagged command on Friday, Mar 20, at 16:00 UT. The SPE angle will be 2.1 degrees. At such a small angle, the X-band may be affected. Given the problem with dropped commands, the instrument teams should make sure to have sufficient time to prepare for shut down. PLASTIC already has a plan in place. No preparations are necessary for IMPACT, since the SWEA high voltage is already shut down. SECCHI plans to shut their instrument doors on Thursday via their internal schedule via commands loaded ahead of time. Those commands are already on board. The COR1 door will be closed at 09:45 UT on Thursday, and the COR2 door will be closed at 09:50 UT. The EUVI door will stay open. * Scheduled track coverage for Behind has been reallocated to Ahead. The SPE angle for Behind will be 1.6 degrees. * Ahead has 13 passes during the week, and overall coverage is nominal. * The spacecraft housekeeping continues to play back from the SSR recorder, though the telemetry suffers from the same gaps as the instrument teams are seeing. Week 13 (Mar 23-29) * Both spacecraft will be 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. * Monday, Mar 23, will be the last nominal 3 kbps pass before solar conjunction. This pass will be used to reset the SSR pointers. * On Tuesday, Mar 24, at 16:00 UT, the spacecraft will be commanded to reset into solar conjunction mode, and no more commands will be sent to the spacecraft. This will set the spacecraft to rotating at 5 degrees per minute until Jul 7. The radio science receiver will be recording during the reset. * 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. Other * The MOC met with the SOHO team last week to discuss lessons learned from the 1998 recovery of the SOHO spacecraft. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 12: M Mar 16 (075) T Mar 17 (076) Ahead: Momentum dump, 23:00 UT W Mar 18 (077) T Mar 19 (078) F Mar 20 (079) Ahead: Instrument power down (except SWAVES), 16:00 UT S Mar 21 (080) S Mar 22 (081) Notes: * Ahead operating on second side lobe. * No passes for Behind due to superior solar conjunction. ------------------------------------------------------------------------------- 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