CXCI. Optical design of a compact telescope for the next generation Earth Observation system CXCI. Vincent COSTES. Octobre 2012

Transcription

1 CXCI Optical design of a compact telescope for the next generation Earth Observation system Vincent COSTES Octobre 2012 CXCI

2 CXCI SUMMARY INTRODUCTION CXCI TECHNOLOGICAL PROGRAM COMPACTNESS REQUIREMENT F/20 DESIGN F/20 DESIGN & PERFORMANCES DESIGN SENSITIVITY ACTIVE OPTICS PRINCIPLE ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR CONCLUSION & FUTURE ACTIVITIES 2

3 INTRODUCTION CXCI TECHNOLOGICAL PROGRAM Pléiades-HR CXCI Next Generation Ground pixel size : 70 cm Altitude : 695 km Pupil dimension : 0.65 m Instantaneous image : 21 km Field of view : 1.7 Telescope aperture : F/20 TDI image sensor Visible Spectral band [450nm ; 800nm] Ground pixel size : 20 to 30 cm Instantaneous image : 15 km Altitude : around 700 km Pupil dimension : 1.5 m Field of view : 1.2 Telescope aperture : F/20 to F/5.4 Image sensor : TDI or two-dimensional array of pixels Satellite compatible with VEGA launcher 3

4 COMPACTNESS REQUIREMENT Pleiades telescope 1300 mm Design based on Pleiades configuration volume uncompatible with VEGA launcher stringent need for compactness 650 mm VEGA Pleiades homothetic design with 2.3 factor: 1500 mm 5500 mm 3000 mm 4700 mm 4

5 CXCI SUMMARY INTRODUCTION CXCI TECHNOLOGICAL PROGRAM COMPACTNESS REQUIREMENT F/20 DESIGN F/20 DESIGN & PERFORMANCES DESIGN SENSITIVITY ACTIVE OPTICS PRINCIPLE ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR CONCLUSION & FUTURE ACTIVITIES 5

6 F/20 DESIGN & PERFORMANCES M2 M1 Flat folding mirrors M3 Exit pupil CNES & SOPHIA CONSEIL optical study Focal plane Extremely compact telescope a 30 m focal length in 2.2 m axial dimension similar to Pleiades Primary mirror aperture: M O 0.6 D U L 0.5 A T I O 0.4 N DIFFRACTION MTF 30-May-12 DIFFRACTION LIMIT Y X (-0.50,0.500) DEG Y X (0.500,0.500) DEG Y X (-0.40,0.500) DEG Y X (0.400,0.500) DEG Y X (-0.30,0.500) DEG WAVELENGTH WEIGHT NM NM NM NM 55 DEFOCUSING Severe optical sensitivity : position sensitivity for 20 nm Rms ZM2 = 1 m, X,YM2 = 10 m, Rx, Ry M2 = 20 rad KORSCH concept three mirrors, intermediate image, real exit pupil Diffraction limited X Y SPATIAL FREQUENCY (CYCLES/MM) 6

7 F/20 DESIGN & PERFORMANCES Tolerance analysis : calculation of the coefficient applied to Pleiades optomechanical stability in order to guarantee a 0.25 optical MTF for our spatial frequency 38 cycles/mm CXCI mechanical stability = x Pleiades mechanical stability with an optical MTF of = 0,17 We need a stability 6 times better than Pleiades A big step is necessary for CXCI optomechanical structure This step can t be afforded by structure technology We need active optics

8 F/20 DESIGN SENSITIVITY F/1 M1 F/1,5 M1 F/2 M1 M1 aperture 1,0 1,5 2,0 M2 aperture 1,2 1,8 2,5 M3 aperture 4,6 5,7 6,8 Distance between M1 M2 1,14 1,8 2,5 M1 axial magnification M2 axial magnification M3 axial magnification minimum 38 cycles/mm 0,33 0,36 0,32 for min MTF > 38 cycles/mm 0,10 0,28 0,45 X Distortion (%) 0,74 0,93 1,25 Y Distortion (%) 0,26 0,31 0,41 intermediate image dimension (mm) ± 97 ± 132 ± 170 Distance between Focal Plane and exit pupil (mm)

9 F/20 DESIGN SENSITIVITY M3 Focal Plane distance 1700 mm 2300 mm 2700 mm 3300 mm M1 aperture 1,64 1,66 1,65 1,62 M2 aperture 1,29 1,13 1,13 1,17 M3 aperture 0,72 0,87 0,94 1,01 M2 axial magnification M3 axial magnification 1,53 1,70 1,95 2,57 Distortion 7% 3% 2,2% 0,9% This sensitivity has been calculated with M1M2 = 2.0 m 9

10 ACTIVE OPTICS PRINCIPLE Stringent mirror position requirements active optics Big primary mirror active optics Primary mirror Mirror shape errors Secondary mirror Mirror position errors Position correction Focal plane 10 Shape correction

11 CXCI SUMMARY INTRODUCTION CXCI TECHNOLOGICAL PROGRAM COMPACTNESS REQUIREMENT F/20 DESIGN F/20 DESIGN & PERFORMANCES DESIGN SENSITIVITY ACTIVE OPTICS PRINCIPLE ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR CONCLUSION & FUTURE ACTIVITIES 11

12 ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR 2,4m F/8 KORSCH DESIGN M1 aperture 1,5 1,2 M2 aperture 1,85 1,43 M3 aperture 4 3,9 M1 axial magnification M2 axial magnification M3 axial magnification MM min 90cy/mm 0,27 0,26 for min MTF > ,27 90 cycles/mm X Distortion (%) 1,4 1,45 Y Distortion (%) 1,05 1,23 M1 M2 distance (m) Interesting compact design with real exit pupil A very compact F/5.4 telescope has been designed but is not diffraction limited 12

13 ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR 3m F/8 TMA DESIGN GCA 1.0 TMA EFL12000 EPD1500 FOV1.25x0.2 DIFFRACTION MTF 05-Aug-11 DIFFRACTION LIMIT Y (0.625,-2.12) DEG X Y X (-0.62,-2.25) DEG Y (0.000,-2.25) DEG X Y X (0.625,-2.25) DEG WAVELENGTH WEIGHT NM NM NM NM 45 DEFOCUSING M1 aperture 3,4 M2 aperture 4,4 M3 aperture 23,4 M1 axial magnification 4,45 M2 axial magnification 5 M3 axial magnification 1,5 min 90cy/mm 0,39 for min MTF > 90 cycles/mm 0,15 X Distortion 0,07 Y Distortion 0,03 Diffraction limited (also for F/5.4 TMA design) Optomechanical tolerances ( ) similar to Korsch M O 0.6 D U L 0.5 A T I O 0.4 N As expected, TMA solution is very big not adapted for high resolution telescope no real exit pupil SPATIAL FREQUENCY (CYCLES/MM) Y X 13

14 ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR 2m Exit pupil F/8 CATADIOPTRIC DESIGN M1 aperture 1,6 M2 aperture 2,4 M1 axial magnification 23 M2 axial magnification 26 min 90 cycles/mm 0,31 0,19 Distortion 7 1,5m MM Extremely compact Good image quality with 4 lenses (also for F/5.4) Difficult to implement baffles Dioptric elements no mirror on real exit pupil primary or secondary active mirror 14

15 CXCI SUMMARY INTRODUCTION CXCI TECHNOLOGICAL PROGRAM COMPACTNESS REQUIREMENT F/20 DESIGN F/20 DESIGN & PERFORMANCES DESIGN SENSITIVITY ACTIVE OPTICS PRINCIPLE ALTERNATIVE SOLUTIONS WITH 2D ARRAY SENSOR CONCLUSION & FUTURE ACTIVITIES 15

16 CONCLUSION & FUTURE ACTIVITIES CXCI Design : a 30 m focal length in 2.2 m! KORSCH design is our reference design : very compact design, real exit pupil, intermediate image Compactness requirement leads to low primary mirror aperture leads to optical design with stringent optical sensitivity mechanical requirements are very hard to guarantee : 5 to 10 times the state of the art Active optics is necessary 16

17 CONCLUSION & FUTURE ACTIVITIES CNES CXCI activities CNES system studies with satellite and instrument designs CNES technological analysis: deformable mirrors metrology : Shack Hartmann, phase diversity, others New mirror technology : design studies done preliminary mirror breadboards prototype mirror development Telescope activities: Telescope studies about active optics are going on till the end of 2012 Development and tests of a fully representative Telescope using active optics:

18 CXCI Thank You CXCI 18