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
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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)
• 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
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
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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
• Utilized Shack-Hartmann
sensor for local tip/tilt
feedback and edge sensors
for nearest neighbor edgematching
• More than 100 modes
within control bandwidth
• Segment dynamics coupled
through primary mirror
backplane
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
SIBOA Quasi-deterministic Phasing
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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
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Segment Alignment Maintenance System (SAMS)
for theHobby-Eberly Telescope (HET)
Correct thermoelastically
induced misalignment of
primary mirror segments
using inductive edge
sensors
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 7segment sub-array in April 2001
Sub-array SAMS On-sky Performance
On-sky Image 5-April 02:00
Reference Stack
M20
EE50 = 1.15 arcseconds
SAMS Stack
EE50 = 1.57 arcseconds
74 hours after last stack
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
NGST Simulink Example
Attitude
Sensors
ACS
Reaction
Wheels
Clock
Vibration
Isolation
Structure
Optics
NGST Simulink Optics Block Diagram Example
yout .mat
Op t ical St at e
1
output vector
from FEM
Mux
K
m2r
cent .mat
cent roid ing
met ers
Cent roid
mat rix
t o rad
Mux2
fsm.mat
K
FSM Angles
FSM
FSM
Cont roller
Coord inat e
1/ m2r
rad t o met ers
Sum3
GS Noise
Coup ling
gsnoise.mat
I mage Noise
MSFC’s Unique Capabilities
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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
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Developed a MATLAB toolkit for analyzing segmented mirror control,
including edge sensor configurations, radius of curvature control, and image
point spread functions
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Utilized LabVIEW and MATLAB for rapid software development of
segmented mirror control systems
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Over 40 nights of engineering-time experience on-site as PI on HET
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Integrated thermal, structural, optics, controls modeling of telescope structures
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.