STEREO Weekly Meeting Minutes for 2014-10-07 (Week 41) ANNOUNCEMENTS ------------- * The solar conjunction readiness review originally scheduled for Thursday, October 23, has been postponed for no earlier than November, considering the current status of the Behind spacecraft. 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 40 (Sep 29-Oct 5) * On day 273 (Sep 30), the 72nd momentum dump on Ahead was executed successfully at 2200z, which imparted a delta V of 0.092 m/sec. * The average daily science data return for Ahead, while operating on the first side lobe on the HGA, was 85 Mbits during this week. * On day 272 (Sep 29), during day 3 of the Behind solar conjunction spacecraft testing monitoring of operations on the second HGA side lobe during a simulated solar conjunction entry was conducted. At AOS of the DSS-43 support, the downlink signal was acquired on the second side lobe at the 633 bps downlink rate. As the spacecraft was rotating to minimize the buildup of system momentum, approximately eight minutes of telemetry were received on the HGA second side lobe during each rotation of the spacecraft, quite impressive DSN and RF performance. The fault protection system promoted the star tracker to AAD mode 12 minutes after the planned system reset on day 271 and also powered off IMU-A two hours later. The SWAVES instrument remained on, as it will be for the actual solar conjunction, continuing to record space weather data at one packet/minute. As a planned result of the system reset, the SSR was re-partitioned to the solar conjunction configuration, which is identical to the current SSR configuration on the Ahead observatory. At 0530z the observatory resumed 3-axis stabilized attitude, via an on board timetag. No ground commands were sent to allow the three day hard command loss timer to expire on day 274. * On day 273 (Sep 30), during day 4 of the Behind solar conjunction spacecraft testing, monitoring continued. At AOS of the 70 meter DSS-63 support, the downlink signal was acquired on the second side lobe at the 633 bps downlink rate with good signal level. The first planned switch to the –Z LGA was monitored using a DSN 34 meter station, DSS-25, while the carrier power level verified the antenna switch, as expected, the signal level was too low for telemetry lock on the LGA. Before the switch, as a test of opportunity, this 34 meter station was used to test the downlink signal level at 633 bps on the second HGA side lobe, for which sufficient downlink margin, 2.5 to 4 dB, was received. The SWAVES instrument remained on, as it will be for the actual solar conjunction, continuing to record space weather data at one packet/minute. No ground commands were sent to allow the three day hard command loss timer to expire on day 274. * On day 274 (Oct 1), on day 5 of the Behind solar conjunction spacecraft testing, during the DSS-14 support, while monitoring the final two hours before the three day hard command loss timer expired, the performance of the +Z LGA was calibrated with the spacecraft rotating. Even though the received carrier power level was as expected, telemetry lock never occurred during the two hour test as the +Z LGA pattern is not favorable at this point in the orbit. At 1750z, the observatory was reset as expected from the expiration of the command loss timer. During the remaining 50 minutes of the support, carrier lock was not received. The DSN radio science receiver controller reported a weak signal that faded. • Since the hard command loss timer initiated system reset on day 274, the DSN has been unable to achieve carrier lock with Behind on any of the subsequent nine supports. On day 278, during the DSS-63 support, three days after the expected command loss timer should have expired again to reset the observatory, a series of commands were transmitted repeatedly in the blind at different uplink rates to re-establish communications with the spacecraft. After failing to establish communications following this activity, a spacecraft emergency was declared at 2000z to acquire the necessary DSN 70 meter station support to re-establish communications. * For the Behind spacecraft emergency, a 70 meter support of 3 hours duration has been requested once every 12 hours to attempt to command on the LGA. * The engineering team has met every day, and the original spacecraft designers have been consulted. * A question was asked whether the Behind orbit will carry it to a location where the signal strength from the LGA will be stronger. This is difficult to answer, because the true attitude of the spacecraft is not known. However, assuming nominal Sun pointing, the signal strength will not improve until significantly past solar conjunction. We're currently on the edges of the LGA patterns. At optimal attitude, the signal strength would increase by 10 dB or more. * A question was asked whether the solar aspect sensors on the spacecraft will keep the solar panels pointed at the Sun, to keep the spacecraft power positive. There are five solar aspect sensors on the spacecraft, between them covering 4 pi steradians. The G&C system will default to these sensors if both the star tracker and IMU are down. There is a possibility of "bad data marked good" from either the star tracker or IMU, but these tend to be self-correcting. This happened with IMU-B where bad data indicated that the spacecraft was rolling at a high speed, and the spacecraft prepared to do an autonomous momentum dump. However, an autonomy rule detected the problem with the IMU, and cancelled the momentum dump. There was also a momentary problem with the star tracker getting a false solution, but it quickly resolved itself. Week 41 (Oct 6-12) * Ahead has seven passes during the week, all at 10 kbps on the first side lobe, in SWAVES prime mode. However, due to the request for additional 70 meter time on Behind for the communication anomaly, this may affect the Ahead schedule. Some passes may be converted to 34 meter stations, in which case only spacecraft data will come down. * There is a proposal to increase the side-lobe science return by bringing down space weather beacon data with the 34 meter stations at either 0.6 kbps, or 1 kpbs. If this is accepted by NASA, then there will need to be some coordination with the science teams for the implementation. * The pass schedule for Behind isn't known yet. Week 42 (Oct 13-19) * 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. * For this and the following weeks, the discussion of the Behind pass schedule assumes that the spacecraft has been recovered. * Behind has 13 passes during the week, and overall coverage is nominal. There are three passes at 160 kbps, and ten passes at 120 kbps. Three of the passes are with the ESA New Norcia station. * Increased use of ESA stations is expected as the STEREO spacecraft move into contention with other missions. Week 44 (Oct 27-Nov 2) * Daily savings time in the U.S. ends on Sunday, Nov 2. * 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. * Behind has 12 passes during the week, and overall coverage is nominal. Two passes are at 720 kbps, two at 160 kbps, and eight at 120 kbps. Four of the passes are with the ESA Malargue and New Norcia stations. Week 45 (Nov 3-9) * The long duration ephemeris for Behind will be loaded onto RAM on Tuesday, Nov 4. * 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. * Behind has 13 passes during the week, and overall coverage is short 13 hours between Monday-Thursday, Nov 3-6, and on Sunday, Nov 9. There is one pass at 720 kbps, two passes at 160 kbps, and ten passes at 120 kbps. Five of the passes are with ESA stations. Week 46 (Nov 10-16) * Second side-lobe operations at 3 kbps begin on Ahead on Monday, Nov 10. * The long duration ephemeris for Behind will be loaded into EEPROM on Nov 11. * Ahead has 7 passes during the week, all at 3 kbps on the second side lobe. * Behind has 7 passes during the week, and overall coverage is nominal. All passes are at 720 kbps. Other * Flight dynamics asked whether the Oct 28 momentum dump is expected to be typical. The answer was yes. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 41: M Oct 06 (279) T Oct 07 (280) W Oct 08 (281) T Oct 09 (282) F Oct 10 (283) S Oct 11 (284) S Oct 12 (285) Notes: * Communications have not yet been re-established with the Behind spacecraft. * Ahead operating on first side lobe, in SWAVES-prime mode. ------------------------------------------------------------------------------- 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: * 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 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: * 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: * 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. ------------------------------------------------------------------------------- Upcoming events: 2014: * Nov 17 Ahead: Test with 34 meter at 633 bps * 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