Sol24.net logo

last update
02:10 UTC
SFI: 67 | Ap index:  5  | Kp index:  2  ( n\a @--:--,  n\a @--:--)| X-ray flux:  A6.2 
SW: Density= 2.8 p/cm3 | Speed= 352.6 km/s | Temp=101(x1000)K
IMF: Bx=-1.2nT | By=1.9nT | Bz= -0.7 nT | Bt= 2.4 nT | Lat= -16.9 ° | Lon=121.6°
Sunspots: 0 | Area: 0 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
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.

The DSN has been able to extract 5 additional telemetry frames from Friday's IEM power on. These frames are being processed and the telemetry from the 5 critical packets will be distributed. An updated recovery plan was developed and discussed during the daily telecon. On Tuesday, carrier recovery will be commanded, attempting to power on the TWTA. If the downlink signal is detected, the TWTA on time will be limited to ~21 minutes, which is 1.5 times the period of the beat frequency of rotation and nutation. The reaction wheel latching relays will be commanded off. If no signal is detected, the battery recovery commands will be sent for the remainder of the support and the next day's support will be shortened to 4 hours. This operational cadence will continue until BEHIND is restored to active attitude control or the DSS-63 time ends on Sep 11th.

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.

-

UPDATE:

The DSN detected the carrier signal again from STEREO Behind on the morning of Tuesday, August 30. More details to follow.

On Saturday, August 27, during the evening recovery track, no downlink signal was received after repeated commanding the transmitter on. Battery recovery commands were sent for the last hour of the support.

On Friday evening, as battery voltage was decreasing from the three telemetry packets received, the transmitter was powered off early. However, the downlink signal was lost 6 minutes earlier than expected. It is speculated that with the complex roll, which resulted from powering on the IEM, the battery voltage may have collapsed at some point.

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.

-

UPDATE:

Today, the DSN created a new acquisition sequence for only sweeping a 3 kHz range about the best lock frequency. This was used successfully during the morning Goldstone support to repeatedly sweep and send battery recovery commands. It was agreed to continue battery recovery tonight and on a 4 hour support on Monday. The carrier recovery is scheduled for Tuesday during a 4 hour support with radio science receivers recording.

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.

The primary propulsion tank heaters (~30W) were enabled at 1530z on Friday, Aug 26. During the second track, after the IEM was powered, the downlink signal would drop 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 temperature data were 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.

BEHIND observatory status: Avionics off, uncontrolled attitude, complex rotation about the principal axis of inertia. Current orientation supports nearly continuous communication near the edge of the + Z LGA with some solar array input. Propulsion tanks are frozen. Secondary battery and propulsion tank heaters are on in between DSN tracks.

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 two minutes. Daily communications with the spacecraft are being scheduled to keep the power system online, and to prevent the 3-day command loss timer from activating. Plans for recovering the spacecraft are being developed.

-

On day Aug 21, during the DSS-14 70m support for Behind for carrier recovery, the downlink carrier was detected at approximately 22:33:23z after contact was lost on October 1, 2014 during testing for a two month long superior solar conjunction. Radio science receivers confirmed a signal was present from 22:27:40z to end of track. Carrier signal level fluctuated between -166 to -179 dBm with an approximate 2 minute rotation. DSS-14 was able to lock up to the 25 kHz subcarrier, confirming the LGA is in use, however, no symbol lock was achieved as expected since commands were sent to power off the avionics for battery charge recovery. The downlink was received for 2.4 hours through end of track. The GSFC mission director declared spacecraft emergency at 235-0030z. No telemetry was received as expected since the avionics were purposely powered off to maintain battery state of charge. While quite early, recovery is expected to proceed slowly to preserve a positive power balance, assess observatory health, re-establish attitude control, and warm all subsystems and instruments.

The frequency segmented acquisition mode which was implemented by the DSN for STEREO Behind was critical for recovering communications with the spacecraft.

At the time of the telecon, Station 14 is observing STEREO Behind. It is still quite early in recovery operations, which will proceed slowly and carefully. Behind is essentially one step above off. The power system is online. The transponder is working, with the spacecraft accepting commands and downlinking the carrier signal. The rotation rate of once every two minutes is not slow enough to be countered using the reaction wheels alone. The MOC is working on refining the draft plan for recovery. The first step is to bring the avionics online to start getting telemetry, but without fault protection coming on, which would cause problems. A plan is being developed, and is expected to be tested and approved for implementation at the end of the week, possibly as early as Friday. After that the plan is to start warming the propulsion, to recover the G&C. There is a very long recovery process with many hurdles to jump through. Daily meetings are being held by the operations team.

Three hours per day of track time has been requested from the DSN for Behind recovery. Recovery of the avionics will require more time.

-

UPDATE [25.08.2016]

The spin axis is estimated to be 12 to 14 degrees from the Earth-Sun line to 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 and loading during recovery must stay below this to prevent battery collapse. The draft plan for powering on the avionics (IEM) and G&C recovery was reviewed. Command procedures and testing on the hardware simulator are in progress.

-

UPDATE [26.08.2016]

Based on recent thermal analysis, the propulsion tanks will take from 65 to 308 hours, depending upon current temperature and how many heaters circuits can be used, to warm the hydrazine in the tanks to 2 deg C. As power is available now, the secondary propulsion tank heaters (~30W) have been enabled. Also, selected power switching boards were powered off to prevent unwanted loading in preparations for powering on the avionics. To allow for sufficient time for procedure testing and review, the powering on of the avionics has been moved to the second track on Friday.

BEHIND observatory status: Avionics off, uncontrolled attitude, rotating about the principal axis of inertia. Current orientation supports continuous communication near the edge of the + Z LGA with some solar array input. No telemetry has been received and therefore detailed status is still unknown. Secondary propulsion tank heaters are on in between DSN tracks.

Go to page  1 2 [3] 4 ... 10 11 12
Render: 0.1107s, 0.0044 for queries.

Powered by a penguin
Protected by a devil