STEREO Weekly Meeting Minutes for 2016-08-30 (Week 35) ANNOUNCEMENTS ------------- * Contact was once again reestablished with the STEREO Behind spacecraft today (Aug 30). See below for details. INSTRUMENT and SPACECRAFT STATUS -------------------------------- * Ahead is operating nominally on the main lobe of the high gain antenna. * The Behind spacecraft has been successfully commanded to turn on its transmitter to downlink a carrier wave. Analysis of the carrier wave signal shows that the spacecraft is rotating at the rate of about once every 2-3 minutes. Operations to recover the spacecraft are ongoing. DISCUSSION AND OPERATIONS CONSTRAINTS ------------------------------------- Week 34 (Aug 22-28) * On day 238 (Aug 25), the DSS-14 support for Ahead was deleted to support the Behind observatory recovery. This did not impact science data return. * On day 238 (Aug 25), during the DSS-35 support for Ahead, telemetry lock was lost at 239-0427z and remained off for the last 8 minutes of the support. This anomaly resulted in the loss of 3 to 11 minutes of SSR data and 8 minutes of real-time telemetry and tracking data. A DR has been requested. * On day 240 (Aug 27), during the DSS-25 support for Ahead, turbo decoder lock was lost briefly at 2031z, 2049z and 2055z. These anomalies resulted in the loss of 3 frames of SSR data. * On day 241 (Aug 28), during the DSS-55 support for Ahead, turbo decoder lock was lost intermittently between 1119z and 1138z. This anomaly resulted in the loss of 257 frames of real-time telemetry and SSR data. See DR# N110377 for more information. * On day 241 (Aug 28), during the DSS-26 support for Ahead, turbo decoder lock was lost briefly at 2019z. This anomaly resulted in the loss of 1 frame of SSR data. * On day 241 (Aug 28), during the DSS-34 support for Ahead, turbo decoder lock was lost briefly at 242-0004z. This anomaly resulted in the loss of 1 frame of SSR data. * The average daily science data return for Ahead was 6.4 Gbits during this week. * The DSN once again detected the carrier signal from Behind today (Aug 30) after contact was lost near the end of the pass on Friday. * Behind Observatory Status - Unknown state of power, uncontrolled attitude, complex rotation (~14 minute rotation with the previous ~2 minute rotation) about the principal axis of inertia. Current orientation may support communication near the edge of the + Z LGA with some solar array input. Propulsion tanks are frozen. A spacecraft emergency remains in effect. Detailed status of the recovery activities to restore operations from the Behind loss of communication anomaly, which occurred on October 1, 2014, are listed below. * On day 235 (Aug 22), a 3.2 hour DSS-43 support starting at 0205z was added to continue Behind recovery operations. The uplink best lock frequency was found to be in the range of 7188.881000 to 7188.884000 MHz, which corresponds to a transponder baseplate temperature of -23 to -17.5 deg C. The carrier signal fluctuated over a 109 second period from -158 dBm to -167 dBm. The TWTA high voltage was powered off by the first command sent at 0425z after being on for approximately 6 hours. * On day 235 (Aug 22), a 4.4 hour DSS-14 support starting at 1900z was added to continue Behind recovery operations. The first command powered on the TWTA at 1941z. The EA mode bypass discrete was reinforced as well as ensuring that all heaters, IMUs, HGARA, star tracker, and reaction wheels were off. The carrier signal fluctuated over a 109 second period from -161 dBm to -169 dBm. The TWTA high voltage was powered off by the first command sent at 2300z after being on for approximately 3.3 hours. The DSN verified no data modulation using carrier and subcarrier FFT. * On day 236 (Aug 23), a 3 hour DSS-14 support starting at 1545z was added to continue Behind recovery operations. The first command powered on the TWTA at 1629z. The carrier signal fluctuated over a 109 second period from -162 dBm to -172 dBm. The TWTA high voltage was powered off by the first command sent at 1840z after being on for approximately 2.2 hours. * On day 237 (Aug 24), a 3 hour DSS-63 support starting at 1325z was added to continue Behind recovery operations. The first command powered on the TWTA at 1335z. The carrier signal fluctuated over a 109 second period from -160 dBm to -170 dBm. The TWTA high voltage was powered off by the first command sent at 1523z after being on for approximately 1.8 hours. The spin axis is estimated to be 12 to 14 degrees from the Earth-Sun line to the spacecraft. Due to the 22 degree/year mean drift rate, the current geometry which provides solar input and continuous RF communications will not occur again till 2022. A separate analysis using the Doppler shift data was conducted by the RF lead and the FDF which was in close agreement with the G&C observations. It was concluded that the solar arrays are generating ~250W at this time. * On day 238 (Aug 25), a 3.7 hour DSS-14 support starting at 1530z was transferred from STEREO Ahead to continue Behind recovery operations. The first command powered on the TWTA at 1538z. Selected power switching boards were powered off to prevent unwanted loading in preparations for powering on the IEM (avionics). This was successfully tested by sending the command to power off the board that contains the TWTA. After the TWTA powered off, the secondary propulsion tank heaters were powered on. The carrier signal fluctuated over a 109 second period from -162 dBm to -172 dBm. The TWTA high voltage was powered off by the first command sent at 1523z after being on for approximately 2 hours. * On day 239 (Aug 26), a 4 hour DSS-14 support starting at 1305z was added to continue Behind recovery operations. The secondary propulsion tank heaters were powered and the first command powered on the TWTA at 1322z. After the TWTA powered off, the primary and secondary propulsion tank heaters were powered on. The carrier signal fluctuated over a 109 second period from -161 dBm to -171 dBm. The TWTA high voltage was powered off by the first command sent at 1504z after being on for approximately 1.5 hours. * On day 239 (Aug 26), a 4 hour DSS-43 support starting at 2050z was added to continue Behind recovery operations. After powering off both propulsion heaters, the IEM (avionics) were powered on. The downlink signal began dropping out periodically. From analysis of the Doppler residual data from the FDF, the rotation is more complex, there is an ~14 minute rotation with the previous ~2 minute rotation. This appears to have shifted the spin axis from 10.5 deg to 22 deg. Three packets of critical telemetry were received. From this very limited data, as expected, the observatory is quite cold, with the battery at 30% state of charge and generating power to support ~150W. From the propulsion tank pressures, the tanks appear to be frozen, however, no propulsion temperature data was received. The Sun angle averaged ~ 60 degrees. As the main bus voltage was 24v and falling, the transmitter was powered off early. While early in recovery, 2 of 11 battery cells appear not to be functioning. Verified that the increased battery charge rate command to C/4 was received. From engineering team discussions, it was decided to power off the IEM and power on the secondary battery heater to allow the battery to recharge. The secondary propulsion tank heaters were also powered on to continue thawing of the hydrazine. * On day 240 (Aug 27), a 4 hour DSS-43 support starting at 2050z was added to continue Behind recovery operations. No downlink signal was received after repeatedly commanding the transmitter on. Battery recovery commands were sent for the last hour of the support. The FDF delivered an updated ephemeris for Behind, with a predicted error between 200 and 2200 km, which the DSN began using. In preparation for recovering attitude control, an autonomous momentum dump was simulated on the hardware simulator using only the Y & Z gyros (X gyro has failed in both IMU units). This was successful, however the subsequent commanded rotation, about the Sun-line to establish communication on an LGA, was slower than expected. * On day 241 (Aug 28), a 4 hour DSS-14 support starting at 1315z was added to continue Behind recovery operations. The DSN created a new acquisition sequence for only sweeping a 3 kHz range about the best lock frequency and sending commands for 3 minutes, then repeating the sweep and commanding. 297 commands were sent for battery state of charge recovery. No downlink signal was received, however, none was expected. * On day 241 (Aug 28), a 4 hour DSS-43 support starting at 2050z was added to continue Behind recovery operations. 297 commands were sent for battery state of charge recovery. No downlink signal was received, however, none was expected. Week 35 (Aug 29-Sep 4) * The carrier wave from Behind was detected again today (Aug 30). The signal levels show that the spacecraft is still undergoing complex rotation, which might be starting to diminish. The rotation period may now be ~3 minutes. It's suspected that the momentum wheels came on when the IEM was activated, which caused the complex rotation. From the telemetry that was received, the batteries were at 30% state of change, and dropping. Main bus voltage was lower than expected. Carrier was lost six minutes early, which suggests that the bus collapsed. * Commands have been sent to turn the mechanical latching relays off for the reaction wheels. * Estimates are that it will take between 44 hours and 3.5 days to warm up enough hydrazine to perform an attitude maneuver to illuminate the solar arrays. * Now that the best lock frequency is known, a shorter acquisition sequence has been developed. This sequence was successful today. * DSN has recovered five additional telemetry frames from Friday, which are being processed now. * Two of the eleven pressure vessels in the battery are not working. It is not known whether this is due to being cold or a different problem. * Ahead has 12 passes during the week, and overall coverage is nominal. There is one pass at 720 kbps, two at 360 kpbs, eight at 240 kbps, and one at 160 kbps. * Behind starts the week at an SPE angle of 14.1 degrees. Eight hour tracks each day have been scheduled for the rest of the week. If the telemetry link is not stable, then the track durations will be cut in half. A stable uplink is needed to power up the IEM for command verification. The transmitter will only be powered up for a limited amount of time. Maintainence at Madrid has been held off to assist with the Behind recovery. Week 36 (Sep 5-11) * Monday, Sep 5, is Labor Day, which is a holiday at APL. * The 91st momentum dump on Ahead is scheduled for Thursday, Sep 8, with ignition at 19:30 UT. This momentum dump is scheduled about 8-9 days early because of DSN coverage limitations, particularly in regards to the launch of OSIRIS-REx whose first launch window starts later that day, with additional daily opportunities up until Sep 15. * Launch contingency plans for the first week of the OSIRIS-REx launch opportunity period have been received, and have some impact on the STEREO schedule. * Ahead has 11 passes during the week, and overall coverage is nominal. There are three passes at 720 kbps, four at 360 kbps, three at 240 kbps, and one at 160 kbps. * Behind starts the week at an SPE angle of 14.0 degrees. Eight hour tracks each day have been scheduled with Madrid, but that will end on Sunday, Sep 11. Week 37 (Sep 12-18) * Ahead has 8 passes during the week, and overall coverage is nominal. There are four passes at 720 kbps, one at 360 kbps, and three at 240 kbps. * Behind starts the week at an SPE angle of 13.8 degrees. * The uplink array attempts for Behind are still listed in the schedule. These will most likely be converted to tracks for Behind recovery, with the Ahead portions taken out. Week 38 (Sep 19-25) * A 2.6 hour return-to-service track for station 63 with STEREO Ahead is scheduled for Saturday, Sep 24. There will be no SSR playback or instrument commanding during this track. Given that the Madrid maintenance has been delayed, this event may be rescheduled. * Ahead has 9 passes during the week, and overall coverage is nominal. There are four passes at 720 kbps, one at 360 kbps, one at 240 kbps, and three at 160 kbps. * Behind starts the week at an SPE angle of 13.7 degrees. The track schedule for Behind recovery is still TBD. Week 39 (Sep 26-Oct 2) * The 36th SECCHI stepped calibration roll is scheduled for Tuesday, Sep 27, starting at 11:55 UT. This is the fifth calibration roll without using the gyros. System momentum is expected to be about 1 N-m-s. * Ahead has 11 passes during the week, and 70 meter time is short about four hours between Thursday and Friday. There are two passes at 720 kbps, five at 240 kbps, and four at 160 kbps. The in situ instruments are expected to ride out the shortage without any problems, but SECCHI will need to reduce their image cadence. * Behind starts the week at an SPE angle of 13.6 degrees. The track schedule for Behind recovery is still TBD. Week 40 (Oct 3-9) * Ahead has 12 passes during the week, and overall coverage is nominal. There are five passes at 720 kbps, three at 240 kbps, and four at 160 kbps. * There are currently three passes scheduled for recovering the Behind carrier. Now that the carrier has been recovered, these are expected to be converted to recovery operations. Week 41 (Oct 10-16) * The 92nd momentum dump on Ahead is scheduled for Monday, Oct 10, with ignition at 23:45 UT. * Ahead has 11 passes during the week, and overall coverage is nominal. There are seven passes at 720 kbps, and four at 160 kbps. * The track schedule for Behind is still TBD. COORDINATED OBSERVATIONS ------------------------------------------------------------------------------- Scheduled activities for Week 35: M Aug 29 (242) T Aug 30 (243) W Aug 31 (244) T Sep 01 (245) F Sep 02 (246) S Sep 03 (247) S Sep 04 (248) ------------------------------------------------------------------------------- Scheduled activities for Week 36: M Sep 05 (249) Labor Day T Sep 06 (250) W Sep 07 (251) T Sep 08 (252) Ahead: Momentum dump, 19:30 UT F Sep 09 (253) S Sep 10 (254) S Sep 11 (255) ------------------------------------------------------------------------------- Scheduled activities for Week 37: M Sep 12 (256) T Sep 13 (257) W Sep 14 (258) T Sep 15 (259) F Sep 16 (260) S Sep 17 (261) S Sep 18 (262) Notes * The phased antenna passes currently scheduled for Behind on Sep 17-18 are expected to be converted to normal recovery tracks. ------------------------------------------------------------------------------- Scheduled activities for Week 38: M Sep 19 (263) T Sep 20 (264) W Sep 21 (265) T Sep 22 (266) F Sep 23 (267) S Sep 24 (268) Ahead: Return-to-service track with DSS-63 S Sep 25 (269) ------------------------------------------------------------------------------- Scheduled activities for Week 39: M Sep 26 (270) T Sep 27 (271) Ahead: SECCHI stepped calibration roll, 11:55 UT W Sep 28 (272) T Sep 29 (273) F Sep 30 (274) S Oct 01 (275) S Oct 02 (276) ------------------------------------------------------------------------------- Scheduled activities for Week 40: M Oct 03 (277) T Oct 04 (278) W Oct 05 (279) T Oct 06 (280) F Oct 07 (281) S Oct 08 (282) S Oct 09 (283) ------------------------------------------------------------------------------- Scheduled activities for Week 41: M Oct 10 (284) Ahead: Momentum dump, 23:45 UT T Oct 11 (285) W Oct 12 (286) T Oct 13 (287) F Oct 14 (288) S Oct 15 (289) S Oct 16 (290) ------------------------------------------------------------------------------- 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