last update
12:35 UTC
SFI: 75 | Ap index:  2  | Kp index:  2  ( n\a @--:--,  n\a @--:--)| X-ray flux:  A8.6 
SW: Density= 2.3 p/cm3 | Speed= 347.6 km/s | Temp=43(x1000)K
IMF: Bx=-1.9nT | By=5.4nT | Bz= -0.9 nT | Bt= 5.8 nT | Lat= -8.9 ° | Lon=109.2°
Sunspots: 23 | Area: 280 10-6/Hemi | New regions: 0
[i]X-ray flares: C=0 M=0 X=0 | Optical flares: M1=0 M2=0 M3=0 | Sub-flares=0
Today, while the spacecraft was configured for switching to the +Z LGA and powering on the TWTA before the track this morning, no signal was received today after repeatedly attempting to power on the TWTA. As the spacecraft rotation will settle out about its principal axis of inertia which should continue to provide limited solar array input and communications, battery state of charge recovery has commenced today. As it appears that the momentum dump in EA mode was not as effective as we had hoped for during the STEREO BEHIND recovery into C&DH standby mode late Wednesday, it is suspected that battery voltage collapsed on Thursday due to sustained high wheel speeds.

BEHIND observatory status: low main bus voltage, 2 (#6 & 9) out of 11 battery cells are currently not functioning, attitude uncontrolled. Current orientation supports some solar array input, with possible communications on an LGA.

Late on Wednesday, September 7, a momentum dump maneuver was carried out on STEREO Behind. This reduced the spacecraft spin rate from once every two minutes to once every 38 minutes, approximately. At this lower rate, the star tracker managed to lock onto a guide star. Telemetry continues to be received. Mission operations personnel are working on improving the spacecraft attitude and fully controlling the spin.

Over the Labor Day weekend, the mission operations team continued to work on recovering the Behind spacecraft. The primary emphasis has been on warming up the propulsion tanks and fuel lines, and on uploading macros in preparation for an upcoming maneuver to despin the spacecraft and get the solar panels fully pointed at the Sun again. The power system is stable, and the battery continues to charge up. Yesterday (September 5) an unexpected feature in the flight software autonomy rules brought the reaction wheels online for 1.3 hours, perturbing the spacecraft attitude. The wheels have been turned off, and indications are that the perturbations are damping down again.

Five telemetry frames were received on Wednesday, August 31. With a good signal level, -159 to -164 dBm and a ~3 minute period, there was continuous communications with the TWTA on for 30 minutes. Subsequent analysis showed that the telemetry from the PDU was stale, so there was no sun vector. From the one sample, the battery appears to be charging with the TWTA on, with battery pressures 634 psi and 19 psi, and main bus voltage at 24.9v. As the uplink was good, the mission operations team began loading uplink time consuming commands to EEPROM, i.e., autoexec macro 1 and bad gyro data parameter to EA and G&C. The S/C emergency was reinstated (had ended at midnight) and a 6.2 hour DSS-14 support was added starting at 1815z. As the signal had sufficient margin, the downlink rate was increased to 35 bps, which provides one (1 packet/frame) every 102 seconds. Eight good telemetry frames were received, including 3 memory dump packets and one temperature packet. Unnecessary systems that were found to be on were turned off to decrease the load on the battery. The 3 loads to EEPROM were verified from dumps received.


Today, during 4 brief TWTA sampling periods this morning, communications are still continuous with the carrier signal fluctuating between -158 dBm and -164 dBm. The battery charge rate increased to C/4 for approximately 4 hours during the track this morning increasing the battery pressure by ~50 psi. An autonomous momentum dump parameter was loaded, dumped, and verified to EA RAM and EEPROM and G&C EEPROM. Detailed power subsystem telemetry was received and cell #6 and #9 (2 out of 11 cells) are indicating 0 volts. Propulsion tanks are slowly warming and have increased by ~2 deg C. IMU2 was powered on briefly and initial indications show that it is healthy and was used to confirm the estimated system momentum level (high). 54 telemetry packets were received. From the Doppler data analysis by the FDF, the nutation is slowing and returning to the previous spin axis orientation.

Progress continues on developing the plan and procedure to re-establish attitude control with very limited battery capacity by conducting an autonomous momentum dump in EA mode, powering on reaction wheels, and promoting the observatory to Standby mode.

On Tuesday, Aug 30, the DSN once again detected the downlink carrier signal at 1321z from STEREO Behind. The signal was intermittent with a peak level of -159 dBm. FDF analysis of the Doppler residuals shows the signal fluctuating at ~140 seconds and a spin-axis to Earth angle of ~36 degrees. Note that the TWTA was only on for 30 minutes to conserve battery state of charge. A more stable uplink is required to load parameters necessary for conducting an autonomous momentum dump to re-establish attitude control. From Friday's IEM power on, four additional telemetry packets were processed (one was a duplicate) and will be distributed. The reaction wheel latching relays were commanded off along with all unnecessary power loads.

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