18th gist 14 th -16 th may 2003 e sawyer ral

18th GIST 14th-16th May 2003E Sawyer RAL

• Status of GERB1,2,3 and 4

• Descan mirror bearing life tests

• Battery issues

• Operations during eclipse

18th GIST 14th-16th May 2003E Sawyer RAL

Status• GERB1-

– Currently Integrated onto MSG 2– AIV programme complete– Pre storage/flight readiness review started– GERB returned for modifications and possible

recalibration

18th GIST 14th–16th May 2003E Sawyer RAL

Status• GERB2

– In orbit– Switched off for eclipse season– Back on 28th April– 9/5/03 One anomalous switch off triggered by a scan

mirror position error out of limits.– MRB held, decision to switch back on with no

modification.

18th GIST 14th-16th May 2003E Sawyer RAL

Status• GERB3

– Delivery to Alcatel 21/5/03– Will be returned for battery modifications and

calibration check

18th GIST 14th-16th May 2003E Sawyer RAL

Status• GERB4

– ATP received from Eumetsat for 70% funding to match the approval by Eumetsat council.

– Some activities started, parts procurement, detector blacking.

– Some electronics manufacture will start at RAL.

– Most subsystems will kick of Jan 04.

18th GIST 14th-16th May 2003E Sawyer RAL

Bearing life test - Status

18 g

18th GIST 14th-16th May 2003E Sawyer RAL

Bearing life test - Status– The test is complete!!– Centrifuge test started with two lead one grease

lubricated bearing pairs.

– 230 million revs completed. 230 was the goal for a 7 year mission, plus 20% margin.

– One dry test bearing switched off at 138 million to give bench mark.

– Good performance from all bearings for the whole test

18th GIST 14th-16th May 2003E Sawyer RAL

Bearing life test – Status continued– Post test torque measurements

LTM No Lubrication Revs completed

Initial torque (gcm)

Final Torque (gcm)

1 Dry 138M 39 74

2 Grease 75M 44 105

3 Dry 230M 38 71

18th GIST 14th-16th May 2003E Sawyer RAL

Bearing life test – Status continued• The bearing preload was measured and found to

be very close to the initial setting less than 10% variation.

• Strip down and visual inspection carried out• LTM1 – some wear debris, mostly in the debris

traps, moderate wear of ball pockets.• LTM2 – very little wear (only 75 million revs)• LTM3 – less wear than LTM1

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

18th GIST 14th-16th May 2003E Sawyer RAL

Other bearing issues

• Back up DSM mechanism, using grease lubricated bearings, has been constructed at Officini Galileo and is available for GERB 3 if required.

• Contamination studies show that the grease can evaporate under the in orbit conditions.

• If any grease gets on the mirror it will be fixed by the solar UV and significantly effect optical performance.

• This can be reviewed in the light of in orbit data.

18th GIST 14th-16th May 2003E Sawyer RAL

Battery

• GERB carries a battery to enable safe power down in the event of sudden loss of power and thus avoid sun damage to the detectors.

• During final tests of GERB on MSG 1 at Kourou, the battery was found to be discharged.

• GERB on MSG 1 was launched with a flat battery

• The discharge mechanism is not fully understood.

• Proposals have been discussed with ESA that enable safe switch down without battery power, these are being assessed by Alcatel.

18th GIST 14th-16th May 2003E Sawyer RAL

Battery continued

• Minor modifications will be required to GERB 1 and 3

• GERB on MSG1 has no battery assisted power down capability

• Eumetsat intend to modify MSG software to minimise risk to GERB in the event of a spacecraft emergency.

18th GIST 14th-16th May 2003E Sawyer RAL

Eclipse

• First Sun avoidance period started 12 February

• No battery safe switch down

• GERB switched to SAFE mode

• No MSG modified software

• There was one unplanned switch off of GERB during this period

• Strategy for next eclipse period (end August to end Oct)

• Current plan is that during eclipse periods, GERB will be in sunblock mode for approximately 5 hours.