GERB-2 Operations Report

J. Hanafin

GIST 23Frankfurt

27-29 April 2005

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:– 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

GERB-2 status

• No data for most of eclipse season – 28/2/05 – 24/4/05

• Now back in NORMAL mode

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

Mean BB temperatures

Year Mean BBT (Jan)

Mean BBT (equinox)

Mean BBT (Dec)

Annual Range

2003 21 16/17 22 8

2004 22.5 18.5/18.5 23.5 6

2005 24 20 4

Inter-thermistor differences have been stable throughout operations to date at <0.2ºC

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

Std dev mirror velocity

2004

2005

TL 5

TL 5

Mirror pointing error

2004

2005

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

Date Time Mode Min

GVMPERR (V)

Max GVMPERR (V)

# packets with GVMPERR >0.1V

10/2/05 00:40 Normal/SAFE -1 1.3 5 11/02/05 00:42 Normal/SAFE -2.4 1.7 95 16/02/05 11:23 Normal/SAFE -2.4 0.9 40 19/02/05 13:07 Normal/SAFE -0.5 1.7 8 28/02/05 16:12 Normal/SAFE -2.4 1.9 20 14/3/05 20:06 Sunblock -0.7 1.7 25 15/3/05 20:52 Sunblock -1.0 0.1 8 21/3/05 00:28 Sunblock -2.0 1.5 8 21/3/05 06:17 Sunblock -1.4 1.1 60 27/3/05 18:36 Sunblock -1.0 1.5 4

30/3/05 21:31 Sunblock -2.0 1.8 10

1/4/05 17:39 Sunblock -1.7 0.1 9

6/4/05 11:18 Sunblock -1.8 1.6 360

6/4/05 13:24 Sunblock -1.7 1.5 96

12/4/05 10:55 Sunblock -1.0 0.4 14 [10 smooth] + 2

13/4/05 08:30 Sunblock -1.4 1.6 7

13/4/05 10:33 Sunblock -1.3 1.6 20

13/4/05 12:33 Sunblock -1.7 1.2 7

Detector loss 28/2/05

Level 0 SW and TOT image 1/3/05

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.

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.

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

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.

Future eclipse operationsOptions:

• 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.

Future eclipse operations

Latitude range

Detector range

Geographic area Dates when detectors are at risk (vernal equinox dates only shown)

Total days lost (both equinoxes)

35-60ºS 192-256 Southern Atlantic 22nd Feb – 8th March 27 10-35ºS 138-224 Southern Africa, South

America 1st – 19th March 35

10ºS - 10ºN 89-170 ITCZ 12th – 28th March 32 10-30ºN 45-121 Sahara, North Africa,

Middle East 21st March – 6th April 31

30-60ºN 1-77 Europe, Mediterranean 30th March – 16th April 32

Eclipse season lasts for 136 days/yearProtecting 10S to 60N would result in loss of ~70 days/year

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

GERB overview paper

• Revisions accepted by BAMS

• In press, to appear in June 2005 issue

• In negotiation re: GERB front cover for that issue