STEREO Weekly Meeting Minutes for 2015-02-24 (Week 09) 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 08 (Feb 16-22) * On day 047 (Feb 16), during the DSS-43 support for Ahead, turbo decoder lock was lost briefly at 2255z. This anomaly resulted in the loss of one frame of real-time data. * On day 049 (Feb 18), during the DSS-14 support for Ahead, four PLASTIC commands failed to be loaded to the C&DH stored command buffer at 2244z. Later in the support, turbo decoder lock was lost intermittently beginning at 2313z through 2350z. These anomalies resulted in the loss of four PLASTIC timetag commands and four frames of real-time data. * On day 051 (Feb 20), during the DSS-63 support for Ahead, turbo decoder lock was lost briefly at 1607z. This anomaly resulted in the loss of one frame of real-time data. * On day 052 (Feb 21), during the DSS-14 support for Ahead, turbo decoder lock was lost briefly at 2215z. This anomaly resulted in the loss of one frame of real-time data. * On day 053 (Feb 22), during the DSS-43 support for Ahead, turbo decoder lock was lost intermittently beginning at 2036z through 2226z. This anomaly resulted in the loss of 9 frames of real-time data. * The apparent angle between the spacecraft and the Sun is currently 2.7 degrees. As this gets smaller, there will be more communications dropouts. * SECCHI raised a question about their housekeeping telemetry. They noticed that they were seeing significantly fewer housekeeping packets in the realtime data than in the level-0 data. The reason for this is not clear. * 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 110 degrees C with the HGA angle at 8.9 degrees, with respect to the spacecraft-Sun line. * On day 051 (Feb 20), PLASTIC tested the entrance system at 1440z to determine the cause of an increasing power supply current indication. The team is still looking at the data. When the entrance system voltage is held static, they're seeing results consistent with the preflight measurements. However, when the voltage is sweeped, there is a larger than expected current drain. They're looking into the possibility of a different sweep table. * The average daily science data return for Ahead, while operating on the second side lobe on the HGA, was 16 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 (Mar 23) 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 09 (Feb 23-Mar 1) * Heavy rain during the station 43 pass for Ahead last niht (Feb 23) resulted in lost frames and commands. * Ahead has 7 passes during the week, all at 3 kbps. Overall coverage is short 3.7 hours between Monday-Thursday. * No passes are scheduled for Behind due to superior solar conjunction. Week 10 (Mar 2-8) * On Wednesday, Mar 4, at 15:00 UT, the restricted IONet at APL will be taken down while the prime router is replaced. There are no tracks during this period. * Daylight saving time begins on the US east coast at 07:00 UT on March 8. * Ahead has 8 passes during the week, seven at 3 kbps, one at 633 kbps. Overall coverage is nominal. * No passes are scheduled for Behind due to superior solar conjunction. Week 11 (Mar 9-15) * 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. * 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 4 hours between Monday-Wednesday. * No passes are scheduled for Behind due to superior solar conjunction. 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. 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 during the next three weeks to quantify scintillation. This will also be useful for Solar Probe Plus. * 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. * Scheduled track coverage for Behind has been reallocated to Ahead. * 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 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. * After the reset, DSN will remain in 1-way mode for all the tracks. Two DSN recievers will be used for every support. * Ahead has 7 passes during the week, and overall coverage is nominal. * Communications recovery will begin on the Behind spacecraft on Mar 23. Six passes are scheduled. If communications can be reestablished, battery recovery is the first priority. Week 14 (Mar 30-Apr 5) * The 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. * 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. Little signal is expected from the HGA. * 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. Other * The team planning to use the Green Bank Telescope to study Faraday rotation had some questions about the polarization of the STEREO signals. The MOC said that one should expect to see some leakage of left-hand circularly polarization into the normal right-hand signal on the second side lobe. They're still looking into some of the other questions. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 09: M Feb 23 (054) T Feb 24 (055) W Feb 25 (056) T Feb 26 (057) F Feb 27 (058) S Feb 28 (059) S Mar 01 (060) Notes: * Ahead operating on second side lobe. * No passes for Behind due to superior solar conjunction. ------------------------------------------------------------------------------- Scheduled activities for Week 10: M Mar 02 (061) T Mar 03 (062) W Mar 04 (063) T Mar 05 (064) F Mar 06 (065) S Mar 07 (066) S Mar 08 (067) Start of daylight savings time in U.S. Notes: * Ahead operating on second side lobe. * No passes for Behind due to superior solar conjunction. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- Upcoming events: Behind events are contingent on recovering the spacecraft. 2015: * Jan 22 - Mar 23 Behind: Spacecraft behind Sun * Feb 12 Solar Conjunction Readiness Review * Mar DAWN - Ceres arrival * 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 * 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