STEREO Weekly Meeting Minutes for 2014-10-14 (Week 42) ANNOUNCEMENTS ------------- * None. INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating on the first 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 41 (Oct 6-12) * On day 281 (Oct 8), no real-time science telemetry was downlinked from Ahead as the scheduled 70 meter support with DSS-43 was changed to a 34 meter support with DSS-45 in support of the STEREO Behind communication recovery. * The average daily science data return for Ahead, while operating on the first side lobe on the HGA, was 72 Mbits during this week. * Since the hard command loss timer initiated system reset on at the end of the solar conjunction testing on Behind on day 274 (Oct 1), no carrier signal has been received on any of the DSN supports. On day 278 (Oct 5), during the DSS-63 support, three days after the expected command loss timer should have expired again to reset the observatory to a known configuration, a series of negative acquisition contingency commands were transmitted repeatedly in the blind at different uplink rates to re-establish communications with the observatory. After failing to establish communications following this activity, a spacecraft emergency was declared at 278-2000z to acquire the necessary DSN 70 meter station support to re-establish communications. The project requested three hour 70 meter supports every 12 hours starting at 1100z on day 281, through day 292 (Oct 8-19), to re-establish communications. The engineering began failure mode and effects discussions after all negative acquisition contingency procedure options were unsuccessful. The DSN RF data from the DSS-14 support on day 274, when the anomaly occurred, was reviewed with the engineering team and the DSN radio science receiver staff and it was concluded that the Behind observatory did reset on day 274 as expected and transmitted for a few minutes before the carrier signal faded. Using the recorded radio science receiver data, the DSN was able to extract a telemetry frame from the carrier signal just after the reset on day 274. From this very limited telemetry, three packets, it was concluded that at the time of the anomaly both C&DH and G&C processors were operating, however, there is an indication that an IMU failure may have occurred. After 1700z on day 283 (Oct 10), contingency commanding was discontinued for three days to allow the hard command loss timer to reset the observatory. This will provide the best known state for subsystem focused contingency commanding. * Attempts to command the Behind spacecraft in the blind resumed yesterday. * Some additional packets recovered from just before the reset on Oct 1 show that everything appeared to be nominal at that time. * The IMU on Behind was off at the time of the reset. It is believed that the star tracker was slow to promote to full operational mode after the reset, as has been seen in previous resets. After 30 seconds, the spacecraft will automatically turn on the IMU. From the limited telemetry that was recovered, it appears that the IMU immediately started reporting a failure in the X-axis, along with bogus data. When the IMU reports a failure, the spacecraft is supposed to disable it after 55 seconds. Otherwise, the spacecraft may perform an autonomous momentum dump after 2 minutes, based on the bogus data. It's not currently believed that a momentum dump occurred. With the star tracker unpromoted, and the IMU disabled, the spacecraft will be depending on the sun aspect sensors only. These should keep the spacecraft pointed at the Sun, and thus keep the solar panels power positive, but roll will be uncontrolled. * An agressive program of sending commands to the spacecraft at various telemetry rates, in the hopes that some of them will get through, has been started. Some of these commands are intended to aid the star tracker, some are for disabling the IMU, and some are for turning on the transmitter high voltage, in case it got turned off for some unknown reason. There are also discussions about possibly power cycling the transmitter, but the engineers are reluctant to take that step at this stage, since it might cause the transmitter to fail. * There have been discussions with some radio telescope observatories to try to listen for the Behind spacecraft. Arecibo reports that Behind is currently at too low a declination for them to observe it. However, Greenbank will try to listen for the spacecraft today and tomorrow (Oct 14, 15). Some issues today with the coolant system may mean that the attempt tomorrow is the more likely to succeed. The Greenbank dish is 100 meter diameter, and thus has twice the effective area of the DSN 70 meter dishes. * A question was asked about whether STEREO Behind's orbit could have changed. The answer was that it was extremely unlikely for enough delta-V to be imparted to the spacecraft to significantly change its location in the sky, even if it did fire its thrusters, which is felt to be unlikely. * Surprise was expressed at the apparent failure of the IMU on Behind. According to information received from the vendor in 2012, it was thought that 1200 hours of operation were left. However, it was also expressed that power cycling could have brought on the failure. Week 42 (Oct 13-19) * A question was raised about the switching between IMPACT- and SWAVES-prime telemetry modes. SWAVES reported that they haven't received any of their prime-mode telem since Sep 28, even though they should have been in prime-mode during week 41. The last momentum dump on Ahead was Sep 30. It's possible that the DFD problem associated with momentum dumps still persists. * Ahead has nine passes during the week; eight are regular DSN passes at 10 kbps. There will also be an additional ESA pass with New Norcia on Thursday, Oct 17, for spacecraft health and safety. There will be no science coming down on this track and, because it is only 1.3 hours long, probably not enough time to send commands. All commanding is on the first side lobe, in IMPACT prime mode. * Emergency 70 meter DSN contacts for Behind have been requested through Oct 19. Prior to that, if communictions have not yet been restored, the situation will be re-evaluated to decide how best to proceed. Week 43 (Oct 20-26) * Saturday, Oct 25, is the eighth anniversary of the launch of STEREO. * Ahead has 7 passes during the week, all at 10 kbps on the first side lobe, in SWAVES-prime mode. Week 44 (Oct 27-Nov 2) * Daily savings time in the U.S. ends on Sunday, Nov 2. * Assuming that the spacecraft is recovered by then, the 68th momentum dump on Behind will be carried out on Tuesday, Oct 28, with ignition at 22:00 UT. The commands will be loaded on the previous pass. * Ahead has 7 passes during the week, all at 10 kbps on the first side lobe, in IMPACT-prime mode. Week 45 (Nov 3-9) * Ahead will be shifted to the second side lobe at the end of the track on Sunday, Nov 9. * Ahead has 7 passes during the week, all at 10 kbps on the first side lobe, in SWAVES-prime mode. Week 46 (Nov 10-16) * Second side-lobe operations at 3 kbps begin on Ahead on Monday, Nov 10. * Ahead has 7 passes during the week, all at 3 kbps on the second side lobe. Week 47 (Nov 17-23) * Ahead has 7 passes during the week, at at 3 kbps on the second side lobe. Other * The long-term ephemeris update for Behind was delivered on Friday (Oct 10). * Emergency DSN contacts for Behind have been requested every 21 hours through Nov 9. Any plans past this date haven't been formulated yet. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 42: M Oct 13 (286) T Oct 14 (287) W Oct 15 (288) T Oct 16 (289) F Oct 17 (290) S Oct 18 (291) S Oct 19 (292) Notes: * Emergency DSN contacts for Behind requested through Oct 19. * Ahead operating on first side lobe, in IMPACT-prime mode. ------------------------------------------------------------------------------- Scheduled activities for Week 43: M Oct 20 (293) T Oct 21 (294) W Oct 22 (295) T Oct 23 (296) F Oct 24 (297) S Oct 25 (298) 8th anniversary of STEREO launch S Oct 26 (299) Notes: * Emergency DSN contacts for Behind requested through Nov 9. * Ahead operating on first side lobe, in SWAVES-prime mode. ------------------------------------------------------------------------------- Scheduled activities for Week 44: M Oct 27 (300) T Oct 28 (301) Behind: Momentum dump, 22 UT (TBC) W Oct 29 (302) T Oct 30 (303) F Oct 31 (304) S Nov 01 (305) S Nov 02 (306) End of daily savings time in U.S. Notes: * Emergency DSN contacts for Behind requested through Nov 9. * Ahead operating on first side lobe, in IMPACT-prime mode. ------------------------------------------------------------------------------- Scheduled activities for Week 45: M Nov 03 (307) T Nov 04 (308) W Nov 05 (309) T Nov 06 (310) F Nov 07 (311) S Nov 08 (312) S Nov 09 (313) Notes: * Emergency DSN contacts for Behind requested through Nov 9. * Ahead operating on first side lobe, in SWAVES-prime mode. * HGA on Ahead will be switched to second side lobe at the end of the track on Sunday, Nov 9. ------------------------------------------------------------------------------- Scheduled activities for Week 46: M Nov 10 (314) Ahead: Commence HGA operations on 2nd side lobe T Nov 11 (315) W Nov 12 (316) T Nov 13 (317) F Nov 14 (318) S Nov 15 (319) S Nov 16 (320) Notes: * Ahead operating on second side lobe. ------------------------------------------------------------------------------- Scheduled activities for Week 47: M Nov 17 (321) T Nov 18 (322) W Nov 19 (323) T Nov 20 (324) F Nov 21 (325) S Nov 22 (326) S Nov 23 (327) Notes: * Ahead operating on second side lobe. ------------------------------------------------------------------------------- Upcoming events: 2014: * Nov 19 Behind: HGA hits soft stop * Nov 28 Behind: SSR reconfiguration * Dec 1 Behind: HGA on 1st side lobe * Dec 8 Behind: Test with 34 meter at 633 bps, both side lobes 2015: * Jan 6 Behind: HGA on 2nd side lobe * Jan 12 Behind: Test with 34 meter at 633 bps * Jan 20 Behind: Instrument power down * Jan 22 - Mar 23 Behind: Spacecraft behind Sun * Mar DAWN - Ceres arrival * Mar 22 Ahead: Instrument power down * 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 * Sep 24 Ahead: HGA on 1st side lobe * Nov 20 Behind: HGA on 1st side lobe * Dec 29 Ahead: HGA on main lobe, offpoint 1 degree Ahead: SSR playback and reconfiguration, S/C checkout * Dec 31 Ahead: Instrument recommissioning 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 * Feb 19 Ahead: HGA on main lobe * 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