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MSFC’s Heritage in Segmented Mirror Control Technology

MSFC’s Heritage in Segmented Mirror Control Technology. John Rakoczy Advanced Optical Systems Development Group NASA Marshall Space Flight Center john.rakoczy@msfc.nasa.gov. MSFC’s Segmented Mirror Control Technology Heritage. SELENE (1991-94) PAMELA (1993-Present) SIBOA (1998-Present)

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MSFC’s Heritage in Segmented Mirror Control Technology

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  1. MSFC’s Heritage in Segmented Mirror Control Technology John Rakoczy Advanced Optical Systems Development Group NASA Marshall Space Flight Center john.rakoczy@msfc.nasa.gov

  2. MSFC’s Segmented Mirror Control Technology Heritage • SELENE (1991-94) • PAMELA (1993-Present) • SIBOA (1998-Present) • HET SAMS (1999-Present) • NGST (1996-Present)

  3. MSFC Program Relevance to GSMT:SpacE Laser ENErgy (SELENE) • Background • $5M advanced concept defintion and technology development • funded by NASA Headquarters 1991-94 • transmit electrical power from the ground to satellites and spacecraft via high energy laser illumination of photovoltaic array • Relevant Products • Post-Keck, 12 meter-class ground imaging telescope design • Broad exposure to state-of-the-art • 1000 meters of highest tow, pultruded graphite composite tubes • 12 meter primary mirror truss engineering drawings - checked. • Prototype tetrahedron including nodes & tube-end fittings • Experimentally verified finite element models

  4. SELENE Trade Studies Relevant to GSMT • Control algorithms for huge numbers of segments • Optimum segment size and keystone families • Optimum actuator stroke and resolution at segment vs. cluster level • Telescope performance for parabolic vs spherical primary • Adaptive optics reqmts vs, altitude, geography, and high zenith angle • Cost vs. performance of low(angle iron), moderate(stainless steel), and high (composite) tech primary mirror truss materials. • Sources and size of error off homology in truss assemblages vs. tip angle • Fixtures/instruments/procedures for precise assembly of large telescope trusses • Roles of edge sensing and image-based wavefront control techniques • Evaluation of several prototype mirror flexures • Damping qualities of composite components in a large telescope • Distributeds processor architectures for highly segmented active mirrors • Comparison of various wavefront control techniques and instruments • Self-sensing, high resolution, long stroke,low power, linear actuators • Industrialization of small segment production capacity • Advanced mirror materials and fabrication techniques

  5. PAMELA: Phased Array Mirror Extendible Large Aperture • 36-segment adaptive spherical primary mirror • Shack-Hartmann wavefront sensor • Inductive edge sensors • 5 kHz sample rate • Tip/tilt/piston control via voice coil actuators • Closed-loop bandwidth exceeding 100 Hz

  6. PAMELA Control Challenges • Utilized Shack-Hartmann sensor for local tip/tilt feedback and edge sensors for nearest neighbor edge-matching • More than 100 modes within control bandwidth • Segment dynamics coupled through primary mirror backplane

  7. SIBOA Testbed Systematic Image Based Optical Alignment (SIBOA) testbed to demonstrate quasi-deterministic image-based alignment and phasing techniques at low temporal bandwidths • Seven spherical segments • Aspheric secondary • Broadband, multiwavelength and monochromatic sources • PC/LabVIEW/MATLAB software interface • New Focus picomotor actuators for tip/tilt/piston control • Blue Line HET-grade edge sensors

  8. SIBOA Quasi-deterministic Phasing 3-segment Aperture Mask for quasi-deterministic phasing Next slide shows PSFs when one segment is pistoned out of phase from 0 to 2p in 1/8 wave increments

  9. Segment Alignment Maintenance System (SAMS) for theHobby-Eberly Telescope (HET) Correct thermoelastically induced misalignment of primary mirror segments using inductive edge sensors

  10. SAMS’s Inductive Edge Sensors Accuracy ~ 50 nm RMS Noise < 25 nm RMS • 480 edge sensors on HET’s 91 mirror segments • 1 Hz sample rate • Give PMC updates every 10 seconds • Control software in LabVIEW for Solaris on Sun UltraSparc 5 • Successful demonstration on 7-segment sub-array in April 2001

  11. On-sky Image 5-April 02:00 M20 EE50 = 1.15 arcseconds Reference Stack SAMS Stack EE50 = 1.57 arcseconds Sub-array SAMS On-sky Performance 74 hours after last stack

  12. NGST: Next Generation Space Telescope • Contributed to preliminary design and government “yardstick” concept • Hands-on experience in integrated modeling utilizing JPL’s IMOS (integrated modeling of optical systems) MATLAB toolbox • Studied application of edge sensor architecture for aligning NGST segments (rigid or flexible) • Managed lightweight mirror development and advanced cryogenic actuator development contracts

  13. NGST Simulink Example

  14. NGST Simulink Optics Block Diagram Example

  15. MSFC’s Unique Capabilities • Operation of 2 unique active/adaptive optics testbeds • PAMELA: adaptive, high temporal bandwidth, 36 segments, lots of dynamic coupling • SIBOA: active, low temporal bandwidth, 7 segments, relatively benign disturbance environment • Developed a MATLAB toolkit for analyzing segmented mirror control, including edge sensor configurations, radius of curvature control, and image point spread functions • Utilized LabVIEW and MATLAB for rapid software development of segmented mirror control systems • Over 40 nights of engineering-time experience on-site as PI on HET • Integrated thermal, structural, optics, controls modeling of telescope structures

  16. Recent Bibliography •    J. Rakoczy, D. Hall, R. Howard, J. Weir, E. Montgomery, G. Ames, T. Danielson, P. Zercher, “Demonstration of a segment alignment maintenance system on a seven-segment sub-array of the Hobby-Eberly Telescope,” No. 4494-10, SPIE: Adaptive Optics Systems and Technology II, July 30-August 1, 2001, San Diego, California.      • J. Rakoczy, E. Montgomery, J. Lindner, “Recent Enhancements of the Phase Array Mirror Extendible Large Aperture (PAMELA) Telescope Testbed at MSFC,” No. 4004-61, SPIE: Astronomical Telescopes and Instrumentation 2000, March 27-31, 2000, Munich, Germany. •        J. Booth, M. Adams, G. Ames, J. Fowler, E. Montgomery, J. Rakoczy, “Development of the Segment Alignment Maintenance System (SAMS) for the Hobby-Eberly Telescope,” No. 4003-20, SPIE: Astronomical Telescopes and Instrumentation 2000, March 27-31, 2000, Munich, Germany. •         J. Rakoczy, “An Edge Sensor Architecture Concept for Coarse Figure Initialization of the Next Generation Space Telescope,” NASA/MSFC Internal Memo ED11(12-98-124), June 9, 1998. •        G. Mosier, M. Femiano, K. Ha, P. Bely, R. Burg, D. Redding, A. Kissil, J. Rakoczy, “Fine Pointing Control for a Next Generation Space Telescope,” No. 3351-06, SPIE: Astronomical Telescopes and Instrumentation, March 20-28, 1998, Kona, Hawaii. •    G. Mosier, M. Femiano, K. Ha, P. Bely, R. Burg, D. Redding, A. Kissil, J. Rakoczy, L. Craig, “Integrated Modeling Environment for Systems-Level Performance Analysis of the Next Generation Space Telescope,” No. 3356-08, SPIE: Astronomical Telescopes and Instrumentation, March 20-28, 1998, Kona, Hawaii. •        D. Redding, S. Basinger, A. Lowman, A. Kissil, P. Bely, R. Bur, G. Mosier, M. Femiano, M. Wilson, D. Jacobson, J. Rakoczy, J. Hadaway, “Wavefront Sensing and Control for a Next Generation Space Telescope,” No. 3356-47, SPIE: Astronomical Telescopes and Instrumentation, March 20-28, 1998, Kona, Hawaii. •        G. Ames, R. Howard, J. Lindner, E. Montgomery, A. Patterson, J. Rakoczy, G. Zeiders, H. Waites, “Phase 1 Testing and Verification on a 0.5 Meter Diameter Telescope with a 36 Segment Adaptive Primary Mirror,” No. 2376-22, SPIE: Laser Power Beaming II, February 4-10, 1995, San Jose, California.

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