In-Process Testing for Cryo-Figuring 1.5 meter Diameter Auto-Collimating Flats

Abstract

Three auto-collimating flats (ACFs) of 1.5 meter clear aperture are being manufactured for use in the JSC Cryo-Optical Metrology test of the James Webb Space Telescope. In-process interferometric testing of the ACFs is used to guide their surface-figure processing. The surface measurement is performed in a vacuum chamber at both room (+20 degrees C) and cryogenic (-240 degrees C) temperatures. With a 12-inch beam diameter FizCam interferometer, sub-aperture measurements are taken across the ACF diameter at multiple rotations. These measurements are stitched together to compute the surface figure. The figure change between room-temperature and cryogenic temperature is measured and used to enable cryo-figuring based on room-temperature measurements. The data analysis is calibrated to account for gravity sag on test-set optics and surface aberrations caused by vacuum pressure and temperature gradients on vacuum-chamber windows. The completed ACFs will have a surface error of less than 75 nm RMS.

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Document Details

Document Type
Technical Report
Publication Date
Jun 07, 2010
Accession Number
ADA536311

Entities

People

  • David J. Fischer

Tags

Communities of Interest

  • Energy and Power Technologies
  • Materials and Manufacturing Processes

DTIC Thesaurus Topics

  • Buildings And Structures
  • Chambers
  • Data Analysis
  • Department Of Defense
  • Diameters
  • Errors
  • Geometry
  • Interferometers
  • Measurement
  • Measuring Instruments
  • Residuals
  • Rotation
  • Temperature Gradients
  • Test Sets
  • Vacuum
  • Vacuum Chambers

Fields of Study

  • Physics

Readers

  • Astronomy/Astrophysics
  • Phased Array Antenna Design.
  • Thermal Physics or Thermal Science.

Technology Areas

  • Space