MSFC

1
MSFCs Heritage in Segmented Mirror Control
Technology
John Rakoczy Advanced Optical Systems Development
Group NASA Marshall Space Flight
Center john.rakoczy_at_msfc.nasa.gov
2
MSFCs 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 GSMTSpacE 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
(No Transcript)
8
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

9
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
10
(No Transcript)
11
Segment Alignment Maintenance System (SAMS) for
theHobby-Eberly Telescope (HET)
Correct thermoelastically induced misalignment of
primary mirror segments using inductive edge
sensors
12
SAMSs Inductive Edge Sensors
Accuracy 50 nm RMS Noise lt 25 nm RMS

• 480 edge sensors on HETs 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

13
Sub-array SAMS On-sky Performance
74 hours after last stack
14
NGST Next Generation Space Telescope

• Contributed to preliminary design and government
  yardstick concept
• Hands-on experience in integrated modeling
  utilizing JPLs 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

15
NGST Simulink Example
16
NGST Simulink Optics Block Diagram Example
17
MSFCs 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

18
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.