STEREO Weekly Meeting Minutes for 2016-10-18 (Week 42) ANNOUNCEMENTS ------------- * There will be a public event on space weather at the Smithsonian Air and Space Museum on Tuesday, October 25, in conjunction with the 10th anniversary of the launch of STEREO. There will also be a live webcast for those who cannot attend in person. See the link below for details. https://airandspace.si.edu/events/sun-360-our-solar-system%E2%80%99s-space-weather-watchdog INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating nominally on the main lobe of the high gain antenna. * Attempts to recover Behind have transitioned back to a monthly schedule. See below for details. DISCUSSION AND OPERATIONS CONSTRAINTS ------------------------------------- Week 41 (Oct 10-16) * On day 284 (Oct 10), during the DSS-25 support for Ahead, turbo decoder lock was lost briefly at 1638z. This anomaly resulted in the loss of one frame of SSR data. * On day 285 (Oct 11), during the DSS-55 support for Ahead, turbo decoder lock was lost briefly at 0908z and again at 0911z. This anomaly resulted in the loss of two frames of SSR data. * On day 286 (Oct 12), during the DSS-65 support for Ahead, turbo decoder lock was lost briefly at 1239z. This anomaly resulted in the loss of one frame of SSR data. * On day 290 (Oct 16), during the DSS-43 support for Ahead, turbo decoder lock was lost briefly at 2205z. This anomaly resulted in the loss of 99 frames of SSR data and 2 frames of real-time data. * On day 284 (Oct 10), the 92nd momentum dump was executed successfully on Ahead at 2345z, which imparted an estimated delta V of 0.096 m/sec. This was the 11th momentum dump that did not use the IMU. After thruster operations completed, there was a 0.45 degree of roll angle error which was dampened out over the next 7.2 minutes. Fine pointing stabilized 2.3 minutes after completion of the momentum dump. * On day 290 (Oct 16), the SECCHI instrument on Ahead reset at 19:05:57z. The SECCHI team reconfigured the instrument to operational mode by 291-0000z. This was the 42nd reset of SECCHI on the Ahead observatory. * The average daily science data return for Ahead was 5.5 Gbits during this week. * Behind loss of communication anomaly occurred on October 1, 2014. Active recovery operations began with carrier detection by the DSN on August 21st, through September 23, 2016. At a spacecraft range of 2 AU, the observatory was found to be rotating slowly about its principal axis of inertia for which the uncontrolled attitude allowed some solar array input and continuous uplink and downlink communications on the LGA at emergency data rates. Over the next 22 continuous days, significant obstacles to recovery were overcome with a coordinated effort of the engineering team, NASA GSFC, DSN, FDF, SSMO scheduling, and Mission Operations teams. This consisted of: - Reliably commanding a rotating spacecraft with uncontrolled attitude at a distance of 2 AU - How to power on the spacecraft that was never designed to be off without collapsing the battery voltage - Acquiring telemetry at 35 bps from a spacecraft that is rotating with an uncontrolled attitude - Warming a frozen propulsion subsystem with a degraded battery (2 out of 11 cells not functioning) and limited solar array input with an uncontrolled attitude - Configuring, loading, and verifying EA, C&DH, and G&C parameters and macros with very limited telemetry - Conducting an autonomous momentum dump in the blind and transitioning to C&DH standby mode and successfully receiving telemetry indicating star tracker lock and decreasing system momentum. However, system momentum level remained above the threshold for re-establishing attitude control with the reaction wheels. Due to the uncontrolled attitude, communication degraded and the last detection of the carrier was on September 23rd . * Behind Observatory Status - From the last telemetry received on September 18th, main bus voltage is low, 2 (#6 & 9) out of 11 battery cells are currently not functioning, attitude uncontrolled, rotating at a ~45 second period about its principal axis of inertia. While propellant is suspected to be frozen, both propulsion tank latch valves are open and pressure transducer #2 is not functioning. EA mode is enabled. The battery charge rate is C/10. Necessary macro sequences have been tested to allow the peak power tracker in C&DH standby mode to protect the battery. These macro sequences will be loaded to EEPROM when the communications supports longer commands. * Monthly recovery efforts will consist of attempting to power on the TWTA for 30 minutes. If no carrier signal is detected, battery recovery operations will commence which consist of repeatedly sweeping a 3 kHz uplink range and sending commands for IEM switched power and PDU 1553 interface bus off. * With the experience gained with the recovery attempts in August and September, the MOC is now much better prepared for the next opportunity to recover Behind. Enough telemetry has been gathered to be able to access the current state of the spacecraft, which wasn't possible when Behind was first lost. * Two momentum dumps occurred during the attempt to recover Behind. The first dump used the B thrusters as planned, but with a partially crippled set of gyros, which was all that was available. This successfully brought the spacecraft rotation down from about 3 degrees per second to the about 1 degree per second or less needed to allow the star tracker to acquire stars, which it was able to do. However, the momentum wheels were taking up too much of the momentum, and a second momentum dump occurred on the A thrusters. It was thought that this momentum dump would also employ the B thrusters as backup, but it was found out that these were not armed. Two packets were received during the dump through the HGA. This second momentum dump was not as successful. There is speculation that this second dump may have increased the spacecraft momentum. The A thrusters may not have been completely thawed. Older telemetry showed that they were close to thawed, and were expected to be thawed by the time of the momentum dump. It's also possible that there is something wrong with the A thrusters, and they have sprung a leak. Depending on where the leak is, it is still possible to operate the spacecraft. Only a handful of telemetry data, just 211 packets, was collected during the 22 consecutive days of the spacecraft recovery attempt; this paucity of data contributed to the difficulty of recovering the spacecraft. Week 42 (Oct 17-23) * Turbo decoder lock was lost briefly yesterday (Oct 17) during the station 63 support for Ahead, resulting in the loss of 84 frames of data. * Ahead has 12 passes during the week, and overall coverage is nominal. There are three passes at 720 kbps, six at 240 kbps, and three at 160 kbps. * Behind starts the week at an SPE angle of 13.5 degrees. There are no passes scheduled for Behind during the week, as recovery attempts for Behind are back to a monthly schedule. Week 43 (Oct 24-30) * Oct 25 (Tuesday) the 10th STEREO Launch Date Anniversary. See the notice above about the event at the Smithsonian Air and Space Museum. * Ahead has 13 passes during the week, and overall coverage is nominal. There are four passes at 720 kbps, four at 240 kbps, and five at 160 kbps. * Behind starts the week at an SPE angle of 13.6 degrees. There are no passes scheduled for Behind during the week, as recovery attempts for Behind are back to a monthly schedule. Week 44 (Oct 31-Nov 6) * Daily savings time in the United States ends on Sunday, Nov 6. * Ahead has 13 passes during the week, and overall coverage is nominal. An additional 70 meter track using station 43 for 2.4 hours was added on Monday, Oct 31. There are now two tracks at 720 kbps, six at 240 kbps, and five at 160 kbps. * Behind starts the week at an SPE angle of 13.6 degrees. There are no passes scheduled for Behind during the week, as recovery attempts for Behind are back to a monthly schedule. Week 45 (Nov 7-13) * The DSN schedule still lists uplink array passes for Behind on Friday, Nov 11, and Sunday, Nov 13. These will be converted to a battery recovery pass with the 80 kW transmitter on station 26 on Friday, and a carrier recovery pass with station 14 on Sunday. The remaining passes will either be used for Ahead or released for other missions. * Ahead has 9 tracks during the week, and overall coverage is nominal. There are four tracks at 720 kbps, three at 240 kbps, and two at 160 kbps. * Behind starts the week at an SPE angle of 13.8 degrees. There are no passes for Behind beyond the recovery passes discussed above. Week 46 (Nov 14-20) * The 93rd momentum dump for Ahead is scheduled for Wednesday, Nov 16, with ignition at 14:30 UT. This will be the 12 dump without the gyros. * Ahead has 11 passes during the week, and overall coverage is nominal. There are three passes at 720 kbps, one at 240 kbps, and seven at 160 kbps. * Behind starts the week at an SPE angle of 13.9 degrees. There are no passes scheduled for Behind during the week, as recovery attempts for Behind are back to a monthly schedule. Week 47 (Nov 21-27) * Thursday, Nov 24, is Thanksgiving. Both Thursday and Friday are holidays at APL. * Ahead has 13 passes during the week. Three ESA New Norcia passes were added on Monday and Tuesday to make up for the previous shortage, and overall coverage is now nominal. There are four tracks scheduled at 720 kbps, three at 240 kbps, and six at 160 kbps. * Behind starts the week at an SPE angle of 14.1 degrees. There are currently no passes scheduled for Behind during the week. Week 48 (Nov 28-Dec 4) * Ahead has 8 passes during the week, and overall coverage is short 10 hours of 70 meter time between Monday and Thursday. The mission has now entered the annual winter period of high contention for DSN time, when many missions are in the same part of the sky. The MOC is looking into the possibility of ESA time to make up for the shortage. There are three passes at 720 kbps, four at 240 kbps, and one at 160 kbps. * Behind starts the week at an SPE angle of 14.4 degrees. There are no tracks for Behind scheduled during the week. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 42: M Oct 17 (291) T Oct 18 (292) W Oct 19 (293) T Oct 20 (294) F Oct 21 (295) S Oct 22 (296) S Oct 23 (297) ------------------------------------------------------------------------------- Scheduled activities for Week 43: M Oct 24 (298) T Oct 25 (299) W Oct 26 (300) T Oct 27 (301) F Oct 28 (302) S Oct 29 (303) S Oct 30 (304) ------------------------------------------------------------------------------- Scheduled activities for Week 44: M Oct 31 (305) T Nov 01 (306) W Nov 02 (307) T Nov 03 (308) F Nov 04 (309) S Nov 05 (310) S Nov 06 (311) Daily savings time ends in U.S. ------------------------------------------------------------------------------- Scheduled activities for Week 45: M Nov 07 (312) T Nov 08 (313) W Nov 09 (314) T Nov 10 (315) F Nov 11 (316) Behind: Battery recovery pass with station 26 S Nov 12 (317) S Nov 13 (318) Behind: Carrier recovery pass with station 14 ------------------------------------------------------------------------------- Scheduled activities for Week 46: M Nov 14 (319) T Nov 15 (320) W Nov 16 (321) Ahead: Momentum dump, 14:30 UT T Nov 17 (322) F Nov 18 (323) S Nov 19 (324) S Nov 20 (325) ------------------------------------------------------------------------------- Scheduled activities for Week 47: M Nov 21 (326) T Nov 22 (327) W Nov 23 (328) T Nov 24 (329) Thanksgiving F Nov 25 (330) S Nov 26 (331) S Nov 27 (332) ------------------------------------------------------------------------------- Scheduled activities for Week 48: M Nov 28 (333) T Nov 29 (334) W Nov 30 (335) T Dec 01 (336) F Dec 02 (337) S Dec 03 (338) S Dec 04 (339) ------------------------------------------------------------------------------- Upcoming events: Behind events are contingent on recovering the spacecraft. 2016: * Dec Behind: Resume LGA downlink capability on 70 m DSN 2017: 2018: * Mar 5 Ahead: Mercury transit 2019: * Mar Ahead: Switch downlink rate to 240 kbps for 34 meter * Apr Behind: Switch downlink rate to 240 kbps for 34 meter 2020: * May Behind: Switch downlink rate to 360 kbps for 34 meter * Jun Ahead: Switch downlink rate to 360 kbps for 34 meter * Jun Behind: Switch downlink rate to 480 kbps for 34 meter * Sep Ahead: Switch downlink rate to 480 kbps for 34 meter 2021: * Jul Behind: Switch downlink rate to 720 kbps for 34 meter * Aug Ahead: Switch downlink rate to 720 kbps for 34 meter