SOFIA Telescope Manufacturing - Lessons Learned

Transcription

1 SOFIA Telescope Manufacturing - Lessons Learned Hans J. Kaercher, Senior Telescope Engineer MT Mechatronics GmbH, Mainz, Germany hans.kaercher@mt-mechatronics.de 1

2 Experience with Telescopes at Exposed Sites Radio Telescopes 50m LMT Mexico 30m IRAM Spain 9m O Higgins Antarctica 15m IRAM France APEX, ALMA 2

3 Experience with Telescopes at Exposed Sites Optical Telescopes 2.7m Airborne Telescope SOFIA 1m Solar Balloon Telescope Sunrise 1.5m Solar Telescope GREGOR 3

4 SOFIA Main Telescope Components Imagers Counter Weights Secondary Mirror Metering Structure Science Instrument Suspension Assembly Tertiary Mirror Primary Mirror 4

5 SOFIA Main System Requirements Access to the Science Instrument during flight Research flight hours per year 960 hours Time per flight at 12.5 km altitude > 6 hours Unvignetted elevation range degrees Effective telescope aperture 2.5 m Telescope optical image quality 1.5 arcsec Telescope pointing stability rms 0.2 (0.8) arcsec 5

6 SOFIA Telescope Optics will be in Cold Environment (- 50 C, 0.2 bar) 6

7 SOFIA Telescope Science Instrument Flange Accessible during Operations from the Cabin Side 7

8 Steady State Type Environmental Influences on the Telescope 0,8 bar + 20 C - 50 C 0,2 bar Cabin Thermal Barrier Pressure Barrier Cavity 8

9 SOFIA Structural System Carbon Fiber Composites Metering Structure Nasmyth Tube Bearing Sphere Mirror Cell 9

10 SOFIA Primary Mirror System 10

11 Suspension Assembly 11

12 Secondary Mirror Assembly Attitude Control with fiber-optical gyros 12

13 M2 Mirror SiC/C 35cm Ø 13

14 M2 Focus-Center Mechanism Hexapod Qualified for 50 C Operational Environment 14

15 15

16 Environmental Influences on the Telescope Cabin Shear Layer at Cavity Opening Science Instrument Standing Waves Excited by the Shear Layer Wind in Cavity Induced by the Shear Layer Aircraft Vibrations 16

17 End-to-end Simulation Model image motion estimator for M 2 estimated image motion feed forward filter M 2 position commands mirror 2 56 f orces 1 aerodynamic disturbance angular displacement of M2 raytrace 1 image m u,v,w acceleration 2 aircraft acceleration gyro v elocity and displacement image motion estimator for position controller torque commands torque drive torque (as forces to rotor segments) accelerometers position controller Vibration Isolation Assembly (VIA) unbalance all VIA f orces torque to telescope telescope rotational displacement and v elocity cradle rotational displacement and v elocity torque to cradle all VIA displacements and v elocities bearing Telescope Assembly (TA) Structure 17

18 End-to-end Simulation Results Servo Domain Aero-acoustic Domain Low structural damping (0,5 1 %) RMD for 32,2 Hz mode (5 %) High structural damping (1 2 %) 22,4 Hz dumbbell Influence of SMM via FBC 32,2 Hz mode ~ 75 Hz rocking mode Image Quality 18

19 Summary of SOFIA Experience System Level Thermal System Design Pointing System Design Material Selection etc. Structures in Carbonfiber Composites Dedicated Metals for Mechanisms Same for Motors, Drives etc. Subsystem Level Optics, Structure Suspension Assembly Secondary Mirror Mechanism Servo Control System QA, RAMS Quality Control absolute essential Reliability, Maintainability same Methods qualified in Aircraft and Space Business are adequate Management has to accept 19

20 Recommendations for Arena Sunrise Carbonfiber Technology < 2m Primary Mirror Cell Outer Ring Spokes Inner Ring - Material Choice - Low Temperature qualified Mechanical Component Tube Elements Cleat Glued - Low Temperature qualified Motors, Encoders CFRP Tube elements with integrally manufactured stringers - Thermal Concept for Optics, Controllers - QA, RAMS Spiders / Headring A B A-A A B B-B 20

21 Thermal Concept for Sunrise Cold Sky < 100 K?? 0-70 el IR Radiation to Cold Sky Balloon- Gondola- Telescope Temperature 200 K Surrounding Air Temperature 200 K / 290 K? Insolation 6000 K Heat Rejection Cooler IR Radiation to Warm Earth Primary Mirror Cooling IR Radiation and Reflection from Warm Earth Antarctic Ice 250 K 21

22 Recommendations for Arena > 2m Combination of O Higgins Pedestal with SOFIA Mirror Compare with exposed design (e.g. Gregor) 22

23 Conclusions from Engineers Point of View Challenging! Interesting! Nice, Funny! Let s do it! 23