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Super Star Tracker

Explore the design baseline of a compact telescope with long focal length and precise optical components. Analyze error signals, beacon systems, and the impact of different materials on stability. Learn about interferometry and detector geometries for improved tracking accuracy. Consider the advantages and challenges of implementing diamond roof prisms, polarizing beamsplitters, and alternate detection schemes in advanced star-tracking systems.

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Super Star Tracker

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  1. Super Star Tracker Optical Design & Analysis Dennis Charles Evans 8 February 2002

  2. Design Baseline • 125 mm diameter aperture (small size) • Long focal length (4848mm = f/38 beam) • Modified Schmidt Cassegrain • Spherical primary • Rigid secondary & beam quadrature • No spider diffraction (not certain if advantage or disadvantage) • Optical block base for alignment reference and mounting • Optically contacted or fused optics for structural stability • Approximately 5 x 109 photons into aperture (25% obscuration) • Approximately equivalent to mv=0 magnitude star • Input flux of 109 photo electrons/sec per “quadrant” • 10mm cathode diameter PMTs • Self contained, flight quality pulse counting units available • Present count rate is 500 MHz

  3. Y-Fan Layout

  4. Solid Model Y-Fan, 10-degree Rotation

  5. Prescription SC-02.ZMX

  6. Dimensions

  7. GPB Telescope

  8. 50:50 Beam Splitter A Sharp Corner Roof Prism (2 places) Path 1 B Path 2 (OUT) C D (IN) Rotated 90 deg WRT AB Error Signal Generation

  9. Error Signal Generation Optical Path 1 Optical Path 2 C A B D Yaw = (A-B)/(A+B) Pitch = (C-D)/(C+D)

  10. Photo Real Rendering

  11. Photo Real Rendering

  12. Mass of Optical Components • F_Silica=2.2 g/cm*3 Vol(cm*3) Mass(grams) • VCor: 169.3868219 × F_Silica = 372.65100818 • VPri: 348.0089929 × F_Silica = 765.61978438 • VSec: 14.5525599 × F_Silica = 32.015631780000008 • VTer: 12.2558027 × F_Silica = 26.962765940000004 • VCyl: 3036.2764147000004 × F_Silica = 6679.8081123400008 • VBas: 2000 × F_Silica = 4400 • Total Mass 12277.05730262 grams

  13. Spot Diagram

  14. Huygens Point Spread Function5.34 arc-sec square; Strehl Ratio = 0.999

  15. Huygens Point Spread Function5.34 arc-sec square; Strehl Ratio = 0.999

  16. Huygens Point Spread Function5.34 arc-sec square; Strehl Ratio = 0.999

  17. Huygens Point Spread Function5.34 arc-sec square; Strehl Ratio = 0.999

  18. Huygens Point Spread Function5.34 arc-sec square; Strehl Ratio = 0.999

  19. Huygens Point Spread Function16.04 arc-sec square; Strehl Ratio = 0.999

  20. Huygens Point Spread Function16.04 arc-sec square; Strehl Ratio = 0.999

  21. Huygens Point Spread Function16.04 arc-sec square; Strehl Ratio = 0.999

  22. Huygens Point Spread Function16.04 arc-sec square; Strehl Ratio = 0.999

  23. Monochromatic Diffraction Profile

  24. Broad Band Diffraction Smoothing

  25. “A” Knife-edge Profile

  26. Tracking Error

  27. Error Analysis • Error: s2A±B= s2A+ s2B± 2ABs2AB • etc. • Integration Time • Increasing integration time from seconds to hours would result in nanoarcsecond error signals.

  28. Concerns • At micro arc-second resolution everything effects everything else. • Cryo environment for structural stability • Zerodur may be more stable than Fused Silica • There may be some cost and performance advantages of using diamond roof prisms. • Error signal analysis is not easily understood without detailed model • One second integration period used for present modeling • Time integration can improve error signal by many orders of magnitude • Smoother/Broader Point-Spread-Function might improve error signal range and accuracy • Broadband beacon (Incandescent) • “Spider Masks”

  29. History Slides Various considerations in developing the design

  30. Alternate Quadrature Detection Schemes • Interferometry offers 5 -10 x signal processing advantage • Need 100 to 10,000 x increase • Koesters Prisms – a la HST Fine Guidance • Scale makes exit pupil on order of 0.2 mm • Small size fabrication and sensitivity are problematic • Four Tracker “long” baseline Interferometry • Baseline deployment, alignment, and stability concerns • 4 to 10x mass increases (equivalent cost increases)

  31. Polarizing Beamsplitters

  32. Koesters Prism Interferometer Tracker

  33. GPB Design Reference C. W. F. Everitt, D. E. Davidson, and R. A. Van Patten (1986) “Cryogenic star-tracking telescope for Gravity Probe B”, SPIE Proceedings, Vol. 619, Cryogenic Optical Systems and Instruments II, Ramsey K. Melugin, Chairman/Editor.

  34. GP-B Telescope

  35. GP-B Tracking Error

  36. Quadrant Detector Geometry

  37. Microscope Magnifier

  38. Hamamatsu Pulse Counting Photomultiplier

  39. Hamamatsu Pulse Counting Photomultiplier

  40. Pulse Counting Photomultiplier

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