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GERB-2 Operations Report

GERB-2 Operations Report. GIST 23 Frankfurt 27-29 April 2005. J. Hanafin. Overview. Summary of operations since GIST 22 GERB-2 status Long term trends Mirror performance Detector loss 28/2/05 GERB overview paper status. Operations since GIST 22. Shortwave calibration scans:

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GERB-2 Operations Report

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  1. GERB-2 Operations Report GIST 23Frankfurt 27-29 April 2005 J. Hanafin

  2. Overview • Summary of operations since GIST 22 • GERB-2 status • Long term trends • Mirror performance • Detector loss 28/2/05 • GERB overview paper status

  3. Operations since GIST 22 • Shortwave calibration scans: • Series 1 (pre and post-eclipse season) continues • 8/9 Feb 2005 • 27 April 2005 • Series 2 (equinoxes) missed March 2005 due to mirror problems

  4. GERB-2 status • No data for most of eclipse season • 28/2/05 – 24/4/05 • Now back in NORMAL mode

  5. Instrument trends • Power configuration stable • On-board temperatures • continue to increase at 2-3ºC per year • daily/annual ranges have not changed significantly • Detector temperature • mean temp has increased by 0.1ºC (now at 22ºC) since Jan 2004 • daily range has not changed significantly

  6. Mean BB temperatures Inter-thermistor differences have been stable throughout operations to date at <0.2ºC

  7. Mirror performance • Comprehensive summary by B. Stewart to follow • Mirror parameters show increase in noise from early Feb 2005, after very quiet Dec/Jan 2004. • 15/2/05 torque level increased to 5 • image geolocation noisier • increase in number of small mispointing errors • 2/3/05 torque level decreased to 4

  8. Std dev mirror velocity 2004 2005 TL 5

  9. Mirror pointing error 2004 2005 TL 5

  10. Increase in time required for mirror to reach SAFE position once commanded

  11. Detector loss 28/2/05 Level 0 SW and TOT image 1/3/05

  12. Incident summary • Mirror had been showing increased number of mispointing events since early Feb • AutoSAFEs triggered by mirror mispointing events had occurred on Feb. 10th, 11th, 16th and 19th. • On Feb 28th, the mirror became stuck while in the Earth view during a mirror mispointing event • The detectors were exposed to direct solar radiation before the AutoSAFE mechanism safed the mirror.

  13. Incident summary, cont. • The mirror was protected by the QFM going to blocked position – the mirror did not go to safe position for ~20 s/craft rotations following the initial mispointing. • Known problem with AutoSAFE mechanism – finite amount of time between the trigger and the instrument reaching SAFE mode. • Possible patch to speed up QFM blocking response is under discussion.

  14. Extent of detector damage • Detector elements 233 and 234 were short-circuited • Detector elements 229, 230, 231, 232 and 235, 236, 237, 238 are still responding to earth radiances but show a gain change of 20-50% (depending on proximity to 233/234) • These detectors are on the edge of the GERB science FOV at ~60°S

  15. Eclipse operations spring 2005 • The probability of a mirror mispointing occurring in the Earth view, and damaging more detectors, is 1 in 8 • During this eclipse season, from Feb 15th to April 24th, there were 18 such events • As the risk of damaging more detectors had increased, it was decided to leave GERB in SAFE mode for the remainder of the eclipse season 2005.

  16. Future eclipse operations • Options: • Operate as normal throughout the entire eclipse season. • Put GERB into a safe mode for the entire eclipse season. • Operate normally during some of the eclipse season, safing GERB at certain times to protect the detectors in certain geographic regions. • The choice is definite permanent loss of data in time, versus possible permanent loss of data in space. • Eclipse operations will also be an issue for GERB-1. • GERB 3/4 have a different mirror control system mechanism, which will help this problem.

  17. Future eclipse operations Eclipse season lasts for 136 days/year Protecting 10S to 60N would result in loss of ~70 days/year

  18. Future eclipse operations • Feedback for future operations policy in eclipse season encouraged • Particular issues: • Preference for loss of data in time v. loss of data in space • Latitude ranges of most importance • Support for ground campaigns - AMMA • Overlap with next GERB for inter-calibration • Discussion / email

  19. GERB overview paper • Revisions accepted by BAMS • In press, to appear in June 2005 issue • In negotiation re: GERB front cover for that issue

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