STEREO Weekly Meeting Minutes for 2015-02-17 (Week 08) 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 07 (Feb 9-15) * On day 043 (Feb 12), the STEREO Solar Conjunction Readiness Review was held at JHU/APL. Some RFAs are being put together, but there were no major issues. * On day 043 (Feb 12), during the DSS-43 support for Ahead, initial telemetry lock was six minutes late due to an operator error at the station. This anomaly resulted in the loss of 6 minutes of real-time data and 4 minutes of spacecraft SSR data. See DR #C110950 for more information. * On day 044 (Feb 13), during the DSS-63 support for Ahead, turbo decoder lock was lost briefly at 1619z. This anomaly resulted in the loss of 5 frames of 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 109 degrees C with the HGA angle at 9.1 degrees, with respect to the spacecraft-Sun line. * On day 041 (Feb 10), the 76th momentum dump on Ahead was executed successfully at 1530z, which imparted a delta V of 0.109 m/sec. * On day 043 (Feb 12), the last update of ephemerides for solar conjunction, which span 2015-043 through 2016-032, were loaded to G&C EEPROM on Ahead. * On day 043 (Feb 12), PLASTIC tested the entrance system at 2125z to determine the cause of an increasing power supply current indication. The test showed nominal values. The next step in the debugging process is to download the onboard table to look for bit slips. * The average daily science data return for Ahead, while operating on the second side lobe on the HGA, was 14 Mbits during this week. * Detailed status of the activities that occurred on the Behind loss of communication anomaly, which occurred on day 2014-274, 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 08 (Feb 16-22) * Ahead has 7 passes during the week, six at 3 kbps and one at 633 bps. Overall 70 meter coverage is short 4.5 hours between Tuesday to Sunday. * No passes are scheduled for Behind due to superior solar conjunction. Week 09 (Feb 23-Mar 1) * 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. * 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. * 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 part of the solar conjunction period 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. * 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. * Ahead has 7 passes during the week, and overall coverage is nominal. * The optimal pass schedule for Behind recovery has not yet been determined. The currect schedule calls for six 70 meter passes with a total of 30 hours duration, but this is being revised. Week 14 (Mar 30-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. * 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. * The original schedule for Behind called for 8 hours per day. This is still being negotiated. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 08: M Feb 16 (047) T Feb 17 (048) W Feb 18 (049) T Feb 19 (050) F Feb 20 (051) S Feb 21 (052) S Feb 22 (053) Notes: * Ahead operating on second side lobe. * No passes for Behind due to superior solar conjunction. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- 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