STEREO Weekly Meeting Minutes for 2015-03-10 (Week 11) ANNOUNCEMENTS ------------- * None. 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 10 (Mar 2-8) * On day 062 (Mar 3), during the DSS-43 support for Ahead, turbo decoder lock was lost intermittently between 0320z through 0504z due to the effects of solar scintillation from an M8.2 class solar flare from active region 12290. This anomaly resulted in the loss of 3 SECCHI commands not being received, which were resent on day 063, and 41 frames of spacecraft SSR playback and real-time data. * On day 063 (Mar 4), during the DSS-43 support for Ahead, turbo decoder lock was lost intermittently between 0551z through 0729z due to the effects of solar scintillation. This anomaly resulted in the loss of 3 SECCHI commands not being received and 109 frames of spacecraft SSR playback and real-time data. * On day 064 (Mar 5), during the DSS-63 support for Ahead, turbo decoder lock was lost intermittently between 1402z through 1626z due to the effects of solar scintillation. This anomaly resulted in the loss 123 frames of spacecraft SSR playback and real-time data. * On day 065 (Mar 6), during the DSS-14 support for Ahead, turbo decoder lock was lost intermittently between 2051z and 066-0014z due to the effects of solar scintillation. This anomaly resulted in the loss of 17 frames of spacecraft SSR playback and real-time data. See DR #G116027 for more information. * On day 066 (Mar 7), during the DSS-65 support for Ahead, turbo decoder lock was lost intermittently between 0742z and 1038z due to the effects of solar scintillation. This anomaly resulted in the loss of 79 frames of real-time data. * On day 066 (Mar 7), during the DSS-14 support for Ahead, the downlink was lost between 2152z and 2305z due to an antenna power anomaly which resulted in the antenna being stowed. Once back on point, turbo decoder lock was lost intermittently between 2305z and 0028z due to the effects of solar scintillation. These anomalies resulted in the loss of 73 minutes of continuous, and 9 intermittent frames of spacecraft SSR playback and real-time data. See DR #G116029 for more information. * On day 067 (Mar 8), during the DSS-63 support for Ahead, turbo decoder lock was lost intermittently between 0757z and 1003z due to the effects of solar scintillation. This anomaly resulted in the loss of 9 frames of spacecraft SSR playback and real-time data. * On day 067 (Mar 8), during the DSS-35 support for Ahead, turbo decoder lock was lost intermittently between 2101z through 2305z due to the effects of solar scintillation. This anomaly resulted in the loss of 3 SECCHI reset recovery commands not being received, which were resent on day 068, and 41 frames of spacecraft SSR playback and real-time data. * The solar scintillation effects described above tend to cover almost the entire duration of most of the tracks. * 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 111 degrees C with the HGA angle at 8.5 degrees, with respect to the spacecraft-Sun line. * On day 064 (Mar 5), the last timetag command load, covering days 068 through 083 (Mar 9-24), before the Ahead observatory enters solar conjunction was loaded and verified. * On day 064 (Mar 5), PLASTIC conducted a stored command buffer timing test and after verifying the contents on day 065, the commands were flushed. * On day 067 (Mar 8), the SECCHI instrument reset due to a critical task not responding at 00:00:20z. The SECCHI team reconfigured the instrument to operational mode at 068-1445z. This was the 37th reset of SECCHI on the Ahead observatory. * The average daily science data return for Ahead, while operating on the second side lobe on the HGA, was 17 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 082 with increasing the ground transmit power through arraying uplink stations and implementing the Failure Review Board recommendations. * 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 11 (Mar 9-15) * Frames continue to be dropped due to solar scintillation during the two supports during the week so far. * PLASTIC will perform tests on their entrance system starting at 4:40 UT on Thursday, Mar 12. * On Thursday, Mar 12, during overlapping tracks for 34 meter stations 24 and 25, there will be an uplink array test with Ahead. There will be telemetry downlink, but no commanding during this time. This test is in preparation for Behind recovery efforts. Arraying the stations together is expected to increase the uplink signal strength by 3 dB. * Later on Thursday, the last ephemeris before solar conjunction, which goes through 2016, will be uploaded to RAM on Ahead. It's already in EEPROM. * The first launch opportunity for the MMS satellite is on Friday, Mar 13, for 30 minutes starting 02:44. Launch windows continue daily through Mar 18. Since STEREO is using the 70 meter stations, there is no impact on scheduling. * Ahead has 12 passes during the week, six at 3 kbps and six at 633 kbps (five without overlap). Overall 70 meter coverage is short 3.6 hours between Monday-Wednesday. * No passes are scheduled for Behind due to superior solar conjunction. * The SECCHI team asks whether some passes are better than others, considering the problem with dropped commands. The MOC answered that those with higher elevation are probably better. The station 65 passes on Thursday at 12:10, and on Saturday at 08:40 have relatively high elevations. The Track Plan data product lists the elevations. 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. * The 77th momentum dump on Ahead is scheduled for Tuesday, Mar 17, with ignition at 23:00 UT. Commands will be loaded the previous day. 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 6 critical supports leading into solar conjunction. The first of these supports will be during the momentum dump. * 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 via their internal schedule via commands loaded ahead of time. After some discussion, it was decided to shut the SECCHI doors on Thursday to allow time for contingency commanding if necessary. * 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. 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 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. * Ahead has 7 passes during the week, and overall coverage is nominal. * Communications recovery operations are scheduled to begin on the Behind spacecraft on Mar 23. Six passes are scheduled during the week. However, given the problems with solar scintillation, the MOC is recommending waiting until the SPE angle reaches 3 degrees. 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, Tuesday, 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 and Apr 2. * 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. * Ahead has 7 passes during the week, and overall coverage is nominal. * Behind has 6 passes during the week to attempt recovery. However, the MOC is recommending releasing these passes due to the low SPE angle. 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. * Behind begins 3 hour tracks for 3 days in a row each week to attempt recovery. The tracks will be Monday-Wednesday, Apr 6-8. The SPE angle will be 2.7 degrees, and these tracks may be released. * The MOC will be shut down for 10 hours on Apr 11 to upgrade the UPS. * No tracks for Ahead due to superior solar conjunction. * The SPE angle for Behind slowly increases to 3 degrees, but then decreases back down to close to 2 degrees due to orbital eccentricity. It starts increasing again in the fall. Week 16 (Apr 13-19) * The 8th hard command loss timer firing will be on Friday, Apr 17 at 18:39 UT. * No tracks for Ahead due to superior solar conjunction. * Behind has 3 tracks to attempt recovery, from Monday-Wednesday. The SPE angle will be 3 degrees. Week 17 (Apr 20-26) * The SPE angle on Ahead will be 1.1 degrees. 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. * No tracks for Ahead due to superior solar conjunction. * Behind has 3 tracks to attempt recovery from Monday-Wednesday. The SPE angle will be 3.3 degrees. Other * The MOC will be meeting with the SOHO team later this week to discuss lessons learned from the 1998 recovery of the SOHO spacecraft. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 11: M Mar 09 (068) T Mar 10 (069) W Mar 11 (070) T Mar 12 (071) Ahead: Uplink array test with stations 24 and 25. F Mar 13 (072) S Mar 14 (073) S Mar 15 (074) Notes: * Ahead operating on second side lobe. * No passes for Behind due to superior solar conjunction. ------------------------------------------------------------------------------- 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) T Apr 09 (099) F Apr 10 (100) S Apr 11 (101) S Apr 12 (102) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 16: M Apr 13 (103) T Apr 14 (104) W Apr 15 (105) T Apr 16 (106) F Apr 17 (107) S Apr 18 (108) S Apr 19 (109) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 17: M Apr 20 (110) T Apr 21 (111) W Apr 22 (112) T Apr 23 (113) F Apr 24 (114) S Apr 25 (115) S Apr 26 (116) Notes: * No tracks for Ahead due to superior solar conjunction. ------------------------------------------------------------------------------- Upcoming events: Behind events are contingent on recovering the spacecraft. 2015: * Jan 22 - Mar 23 Behind: Spacecraft behind Sun * Mar 24 - Jul 07 Ahead: Spacecraft behind Sun * 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 * 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 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