Download - 18th GIST 14 th -16 th May 2003 E Sawyer RAL
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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
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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
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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.
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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
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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.
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18th GIST 14th-16th May 2003E Sawyer RAL
Bearing life test - Status
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18 g
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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
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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
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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
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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18th GIST 14th-16th May 2003E Sawyer RAL
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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.
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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.
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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.
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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.