GERB 4 Instrument Status GIST 25 23rd October 2006 Presenter: N Morris

GERB-4 Status IEU built completed in March 2005 Successfully passed vibration tests TVAC test will be done together with IOU, so is currently on hold until IOU is finished IOU fully assembled with FM1 Focal Plane Assembly in March 2005 Following IOU vibration test a problem was found on the Quartz Filter Mechanism Unit returned to Galileo Avionica for repair.

QFM Anomaly Extensive investigation into QFM conducted Out of tolerance parts plus suspected movement of the Stator under vibration caused Rotor and Stator to come into contact Selection of in-tolerance parts plus a redesign of the Stator Clamp is expected to fix the problem Vibration levels for the IOU will be notched at critical frequencies to avoid overtesting the QFM at IOU level QFM vibration tests (to qualification levels in one axis) are being performed this week Provided there are no other problems, the QFM should be back at RAL by the beginning of December 2006.

FPA Status Currently FM1 FPA is fitted in the IOU There was some concern that the pixels exhibited a very long time constant, due to the high thickness of the gold black coating Decision was taken to replace the detector with FM3, which had lower time constants and slightly less noisy response, but one pixel response was suspect (#193) Because of problem with QFM the swap out of FPAs could take place before the instrument level tests were completed (original plan was to retrofit the FM3 detector) Leicester University have been busy calibrating FM3 and should be ready for delivery to RAL this week. Calibration of FM2 will follow. This will be the flight spare. John Remedios will present some results on the detector spectral response tomorrow.

GERB-4 Schedule FM3 FPA will be fitted in the next two weeks Most of IOU can be re-assembled because the QFM is the last subsystem to be fitted QFM delivered back to RAL in December IOU assembly and functional tests completed in Jan 2007 IOU + IEU environmental test campaign will take ~ 3 weeks GERB-4 Delivery Review Board February 2007 Will then go into storage until start of calibration in June 2007 After calibration the instrument will return to RAL and stored until launch (2013).

GERB-3 Status GERB-3 IEU is currently on MSG-4 to assist with check-out at spacecraft level Will be returned to RAL when spacecraft testing completed (Jan 2007?) Minor updates are needed to IEU to bring to the same build standard as the GERB-4 IEU. Proposal into EUMETSAT for the re-calibration of the GERB 1/2/3 flight spare detector. If significant differences found between GERB-4 detector and GERB spare then EUMETSAT may consider re-calibrating the GERB-3 detector. The GERB-3 QFM is showing some similar anomalies to those found recently on GERB- 4, so we may have to make some minor repairs. GERB-3 instrument re-calibration will take place after GERB-4 (and after the detector re- calibration if needed).

Mirror Pitting Update Concern raised over pitting seen on GERB-3 Flight Spare Telescope mirrors This was just prior to the launch of GERB-1 on MSG-2 Qualitative assessment made at Kourou of GERB-1 DSM mirror confirmed that there was not a significant problem (hopefully the data from GERB-1 now confirms this). Still a concern remains about whether pitting (or corrosion) of the mirror surfaces on GERB-3 and GERB-4 will continue up to launch To help answer this question a detailed survey of some of the GERB coating witness samples was carried out using microscopy techniques. Each sample was photographed over an area of approximately 32mm2 with a resolution of 0.32 microns The photographs were individually assessed using image processing software to look for defects up to 5 microns in diameter Ratio of max to min diameter was set at >0.2 to exclude scratches Area of defects calculated for each sample as well as histograms of defect size.

Defects under bright field illumination

Mirror Survey Results H5A defectsDefect area =  m 2 Area % defects 0.08 H8I defects Defect area =  m 2 Area % defects 0.04 H9I defects Defect area =  m 2 Area % defects 0.02 H9J defects Defect area =  m 2 Area % defects 0.1

Mirror Pitting Will re-measure samples every 12 months and look for signs of defects increasing in number or size. Evidence to date suggests the defects to not grow, but reach a finite size and then stop. GERB 3 and 4 instruments will be stored under vacuum, so this should help reduce growth rate if it is still happening.