Segment Alignment Maintenance System

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Segment Alignment Maintenance System for
the Hobby-Eberly Telescope
John Rakoczy NASA MSFC
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HET SAMS Objective

• HET is a spectroscopic survey telescope built by
  McDonald Observatory.
• HET has an effective 9-meter aperture seeking
  seeing-limited performance.
• SAMS is intended to be an edge sensor system on
  the HET to maintain the primary mirror figure in
  the presence of thermoelastic disturbances to the
  HET.

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SAMS Program

• MSFC is prime contractor under Space Act
  Agreement and Memorandum of Understanding with
  the University of Texas at Austin. MSFC manages
  system integration and verification.
• Blue Line Engineering of Colorado Springs,
  Colorado is subcontractor. Blue Line provides
  inductive edge sensors and processing
  electronics.

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Hobby-Eberly Telescope Primary Mirror
11.0 meters
Sub Array Test Cluster
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Sub Array Test Sensor Layout
30
25
24
19
15
88
10
x denotes active coil o denotes passive coil
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Basic Sensor Design
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(No Transcript)
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Edge Sensors mounted at intersection of 3
segments
Local Segment Electronics Node
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Stackable System Processor
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MSFCs Key Responsibilities

• Control System architecture definition and
  algorithm development
• System software development
• FEM analysis and experimental validation of
  mirror mass loading requirements
• System integration and testing

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Program Milestones Accomplished

• Completed Edge Sensor Proof-of-Concept Test
• Completed Preliminary Design Review
• Completed Sub Array Test on 7-segment subarray of
  HET
• Completed Critical Design Review

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Sub Array Test Quantitative Results Achieved

• RMS Tip/Tilt errors lt 0.08 arcseconds
• RMS Piston errors lt 2 microns
• Global Radius of Curvature (GRoC) maintained lt
  300 microns
• Edge Sensors provide better than 50 nm accuracy
  RMS
• Sensor head mass lt 50 grams
• Reliable continuous operation gt 10 days
• Seeing limited image on 14th magnitude star

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On-sky Image 5-April 0200
M20 EE50 1.15 arcseconds
Reference Stack
SAMS Stack EE50 1.57 arcseconds