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Periscope Configuration

X. Z. Periscope Configuration. Detector. Periscope Module. 2, 10, or 30 cm. 30 cm. Mirror Parameters. Reflecting surface. TBD. Active area is 30cm long x 2, 10 or 30cm wide. Surface figure requirement: l /400 rms (at 633nm) -- Mounted Mirror mass must be minimized Geometry TBD. X.

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Periscope Configuration

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  1. X Z Periscope Configuration Detector Periscope Module

  2. 2, 10, or 30 cm 30 cm Mirror Parameters Reflecting surface TBD • Active area is 30cm long x 2, 10 or 30cm wide. • Surface figure requirement: l/400 rms (at 633nm) --Mounted • Mirror mass must be minimized • Geometry TBD

  3. X Z=LOS Yaw Roll Y Pitch Mirror Module Coordinate System Mirror Control: X – linear Roll about LOS Pitch LOS Fixed Mirrors Module Control: Yaw Pitch Roll about LOS To Detector

  4. Mirror Geometry and Figure Mirror geometry must: • Meet the surface figure requirement • 1g release • Operating temperature range • Thermal gradient • Mount distortions • Have minimum mass • Accommodate mount and mechanisms • Survive launch and environment extremes

  5. First Order Wavefront Error Budget Error Budget for /400 RMS Mirror Mount All values given in RMS wavefront error  = 6328Å Thermal gradient .0011 Jitter .0006 Mount interface surface finish .0003 Mirror blank surface figure .0013 Stability .0013 Assembly (neglected) Surface distortion due to gravity .0004 Motion due to gravity (neglected) Manufacturing .0013 Test .0013 Alignment .0013 Reflective coating .0009 Bolt preload .0002 Adhesive strain .0002 Bulk temp (5°C) .0005 1g sag .0004 Total RMS error .0025

  6. X Y Z Initial Geometries considered: • Rectangular, held from back • Various lightweighting patterns/pockets cut from back • Single Arch • Various thicknesses • Double arch over length on backside • Lightweighting pockets in back of main rib

  7. First Order FEM results of different geometries for 1m long mirror

  8. Attempted Wavefront Analysis

  9. Wavefront analysis • Wavefront analysis not adequate: Zernike polynomials do not fit to long rectangular optical surface • Consider using LeGendre polynomials? • Good for cylindrical optic fits (used Chandra mirror analysis) • Orthogonal polynomials? Ref. Integrated Optomechanical Analysis Doyle, Genberg, Michels, p.61

  10. Optical Tolerances • Goal: Good fringe clarity at the focal plane • Maintain phase information as it passes through each channel of the interferometer simultaneously • Analytical Analysis: • Limit OPD < l/10 • Raytrace Analysis: • Limit relative Strehl ratio > 80%

  11. Mirror Separation within a periscope h2 h1

  12. Analytical vs. RaytraceMirror Position Tolerances where l = 20Å, g =2°, m = 83cm, and L = 400km

  13. MAXIM Pathfinder Parameters • Baseline = 2 m • Focal Length = 200 km • Mirror length = 30 cm • Graze angle = 2° • l = 10Å

  14. MAXIM Pathfinder Position Tolerancesl=1nm, F=200km, D=2m, m=30cm, g=2deg, dh=1mm

  15. Full MAXIM Parameters • Baseline = 1km • Focal Length = 20,000 km • Mirror length = 30 cm • Graze angle = 1° • l = 10Å

  16. X-direction Sensitivity F X D Z y Allowable Mirror Motion: ± 1.7nm Allowable Periscope Motion: ± 4mm

  17. Y-direction Sensitivity X Z=LOS Y Allowable Mirror Motion: ± 0.3mm Allowable Periscope Motion: ± 0.5mm

  18. X Z Z-direction Sensitivity F D y Allowable Mirror Motion: ± 94.7nm Allowable Periscope Motion: ± 0.32m

  19. Y Z Allowable Mirror Motion: ± 6.9arcmin X-rotation “yaw” Sensitivity msin(g) m Allowable Periscope Motion: ± 7.8 arcmin

  20. X Z Allowable Periscope Motion: ± 10 arcsec Y-rotation “pitch” Sensitivity F y D Allowable Mirror Motion: ± 2.3 marcsec

  21. Allowable Periscope Motion: ± 18.5 arcsec Z-rotation “roll” Sensitivity LOS X Z=LOS Roll Y Allowable Mirror Motion: ± 0.13 arcsec To Detector

  22. MAXIM Position Tolerancesl=1nm, F=20,000km, D=1km, m=30cm, g=1deg, dh=1mm

  23. ISAL Raytrace Position Tolerancesl=1nm, F=200km, D=4m, m=30cm, g=1deg, dh=1mm

  24. Move one mirror pair wrt other mirror pair -d +d Pathlength is self-correcting

  25. Move one mirror in Z-direction +d dcos2q 2q -d dsinq

  26. Trade Studies • Three grating sizes: • 2cm, 10cm, and 30cm wide x 30 cm long • Optimize graze angle vs. mass • Lower graze angle can loosen some tolerances • Lower graze angle will reduce throughput or increase mass

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