ROSAT S/C Status 1999-01-15 ... 1999-02-12 (End of Mission)

Compiled by Jakob Englhauser
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Fri 1999-01-15 (DoY  15)

    Spacecraft is in 'deep' safemode:
      AMCS is in safemode; receiver is on;
      FIs are in safemode and off focus.


    ROSAT has not been tracked by GSOC since the spacecraft
    was switched off on 1998-Dec-18.

    In preparation of the observations in February 1999,
    GSOC will now start to collect spacecraft track information.
    on 1999-Jan-18 (Monday) a 'blind on' command will be sent
    in order to switch on the transmitter on ROSAT.


Mon 1999-01-18 (DoY 18) Spacecraft is in 'deep' safemode. During the Weilheim cycle in the evening: All attempts to switch on the transmitter failed. There were some discrepancies in the orbit prediction (to be solved tomorrow). Tue 1999-01-19 (DoY 19) Spacecraft is in 'deep' safemode. During the Weilheim cycle in the evening: This time there was response from the ROSAT transmitter as soon as the 'transmitter on' command was sent. ROSAT will be tracked during the next days in order to further improve the orbit prediction.
Mon 1999-02-01 (DoY 32) Check out S/C. Initialize tape recorders. Perform FI reset / time correlation. Correct Weilheim time correlation file in order to be prepared for future tape dumps. Tue 1999-02-02 (DoY 33) Operate S/C for a complete day. Check battery status during day AND night. Collect track data. 12:21:45 WHM1 First tape dump (90 min) after a 6 weeks break. Tapes were at 0.9 deg C (critical: -5 deg C), since they were not operated for several weeks. Problems with the S/C bus / DHS: 'Transmission on' switches on carrier, but not the downlink of the data stream. Downlink currently has to be enabled manually. That's why only 90 min of tape dump data is available. Problems with groundstation software (had to be updated for spacecraft clock reset and the year 1999). Wed 1999-02-03 (DoY 34) 12:15:30 WHM1 Initialize DHS. Tape dump of a complete ROSAT day: failed. 13:51:30 WHM2 Downlink for only 4 minutes? 15:31:45 WHM3 Telemetry on / off / on / off (each event for several minutes) - still problems with downlink? First telemetry data arrived at MPE (see NRTA directory). Fri 1999-02-05 (DoY 36) No more valid dumps are available up to this point. 10:17:45 WHM1 Short contact; nothing can be done. 11:54:00 WHM2 tape dump failed (scrambled data) The problems are probably related to a clock inconsistency between the onboard data processing system (DPS) clock and the taperecorder clock. A DPS coldstart had to be performed to bring the DPS into a clean status. Before that, it had been performed only once immediately after launch, and then never again. The coldstart was achieved by switching forth and back between the two DHS CPUs, after having set the coldstart flag. The spacecraft clock was NOT reset during the coldstart (achieved by a patch). 13:33:30 WHM3 no longer FI HK data As a consequence of the DPS coldstart, the FI was completely switched off (accidentally) - no further HK data. No contacts during the weekend.
Mon 1999-02-08 (DoY 39) 09:48:30 WHM1 - Blind acquisition was necessary - Tape dump successful on the second try - FI HK is present again - contact was to short for AMCS recovery 11:26:45 WHM2 AMCS: - Recovery step 1 started (no longer AMCS safemode) - Actual quaternion was not commanded (?) 12:24:00 RW 4 is considered to be 'bad' by AMCS 12:24:42 RW 4 was automatically switched off by the AMCS (probably due to discrepancy between measured and modeled rate) 13:06:30 WHM3 AMCS: back in safemode WFC: start of (ab initio) recovery (?) 14:46:15 WHM4 AMCS: - recovery step 1 completed - 2 large magnetometer updates (by roughly 10 deg) - updates on 10 s timescales towards the end of the contact Dump of taperecorder 1 contents (taperecorder 2 will be used during the next night) 16:25:45 WHM5 AMCS: - again in safemode - ram_test.ins commanded (checks status of various AMCS parameters): parameters are set as expected (good) - next recovery not before tomorrow / WHM1 Dump of taperecorder 1 contents Taperecorders / DPS / telemtry seem to be ok now. Problems remaining: STCW - eg PROM checksum errors AMCS - attitude control is not yet possible (check output of ram_test.ins via the next tape dump!) WFC, HRI, PSPC: not yet checked Tue 1999-02-09 (DoY 40) PSPC operating system will be newly uplinked today (roughly 5000 commands; 2 contacts required). No AMCS recovery until the reasons for the safemodes of yesterday are understood (3 times sun on the back of ROSAT!). The first tape dump of today should contain certain AMCS parameters (output of ram_test.ins). 09:39:00 WHM1 - Tape dump ok - Uplink of the first part of the PSPC operating system Reaction wheel 4 was automatically switched off on 990208, sod 44682 (yesterday); however, the health status of this RW was still "ok". This could have led to the erroneous behaviour observed yesterday, even after the second safemode (more than 1500 s were needed to stabilize the sun pointing!). WFC HK check shows that the excessive STCW PROM checksum errors were gone as soon as the 'ab initio' recovery was completed yesterday (990208, sod 53332). 11:16:49 WHM2 - Uplink of complete AMCS software (in order to make sure that everything is ok with the software onboard) 12:56:43 WHM3 - Uplink of the second part of the PSPC operating system 14:36:27 WHM4 AMCS: - set health status of RW 4 to 'bad' - start recovery - initially within +- 60 arcmin on target - lateron large updates (by a few degrees), sometimes within a few seconds (unexplained; sun sensors?) - sometimes systematically jumping forth and back within a few seconds - suspicion: AMCS safemode in WHM5 - slew (before WHM5) to new target was uplinked 16:15:54 WHM5 AMCS: in safemode (as expected ...) - tape dump Wed 1999-02-10 (DoY 41) AMCS is in safemode. The HRI final door test is scheduled for today. 09:28:52 WHM1 PSPC B: - initialized - moved into focus - filter in closed position HRI: preparations for final door test - initialized - HV at step 6 11:07:46 WHM2 HRI: final door test part A - HRI off focus (PSPC B is in focus) - commands according to test procedure / part A - HV at step 14 (E) - UV Cal: 100 valid / 50 invalid events - HRI off at the end of the contact 12:47:43 WHM3 HRI: final door test part B - commands according to test procedure / part B - completed without problems Thu 1999-02-11 (DoY 42) AMCS is in safemode. 10:59:15 WHM2 AMCS: - no reaction wheel 4 - switch from safemode to degraded pointing mode - 30 s x+s gyro - 4 minutes only s gyro - rest again s+x gyro - switch back to safemode at the end of the contact RW rates were perhaps improved in s gyro configuration. Actual quaternion was commanded (originally not intended). 12:39:30 WHM3 AMCS: - no reaction wheel 4; no x gyro - switch from safemode to degraded pointing mode - observe offsets to nominal RA and Dec (not much improved) - do NOT command actual quaternion - not switched back to safemode (though it is expected one will occur before the next contact ...) 14:19:00 WHM4 AMCS: - not in safemode (!) - actual quaternion commanded PSPC: - fill in gas (986 mB at the end of the contact) - temperature of carroussel motor at > 71 deg C (due to 'brake open', already since several days) 15:58:30 WHM5 AMCS: - again in safemode PSPC: - pressure at 580 mB - commanded 'close brake' (worked) Fri 1999-02-12 (DoY 43) The continuing problems with the attitude control led to the common decision of all involved parties that ROSAT will be switched off today. 09:11:00 WHM1 AMCS: - in safemode PSPC: - pressure at 1450 mB (close to nominal) - pressure at tanks A / C unchanged at 1820 mB - leakage valve was opened - a small amount of gas will remain in the tanks WFC: - saved; HV is off Taperecorders - remain active 09:18:53 Transmitter onboard ROSAT was switched off ======================================================================== E n d o f t h e R O S A T M i s s i o n ========================================================================
The future of ROSAT: As soon as the voltage of any battery cell drops below 1.1 V a power DNEL will be triggered; all subsystems not important for the surveillance of ROSAT will then be switched off. Reentrance into the atmosphere is not to be expected within the next 10 years.