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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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slide1

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
MSFC’s Segmented Mirror Control Technology Heritage
  • SELENE (1991-94)
  • PAMELA (1993-Present)
  • SIBOA (1998-Present)
  • HET SAMS (1999-Present)
  • NGST (1996-Present)
msfc program relevance to gsmt space laser energy selene
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
slide4

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
pamela phased array mirror extendible large aperture
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
pamela control challenges
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
slide8

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
slide9

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

slide11

Segment Alignment Maintenance System (SAMS)

for theHobby-Eberly Telescope (HET)

Correct thermoelastically induced misalignment of primary mirror segments using inductive edge sensors

slide12

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
slide13

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

ngst next generation space telescope
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
msfc s unique capabilities
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
slide18

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.