Surface measurement of a large inflatable reflector in cryogenic vacuum

Henry Quach, Hyukmo Kang, Siddhartha Sirsi, Aman Chandra, Heejoo Choi, Marcos Esparza, Karlene Karrfalt, Joel Berkson, Yuzuru Takashima, Art Palisoc, Jonathan W. Arenberg, Christopher Walker, Christian Drouet D’aubigny, Daewook Kim

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


The metrology of membrane structures, especially inflatable, curved, optical surfaces, remains challenging. Internal pressure, mechanical membrane properties, and circumferential bound-ary conditions imbue highly dynamic slopes to the final optic surface. Here, we present our method and experimental results for measuring a 1 m inflatable reflector’s shape response to dynamic pertur-bations in a thermal vacuum chamber. Our method uses phase-measuring deflectometry to track shape change in response to pressure change, thermal gradient, and controlled puncture. We use an initial measurement as a virtual null reference, allowing us to compare 500 mm of measurable aperture of the concave f/2, 1-meter diameter inflatable optic. We built a custom deflectometer that attaches to the TVAC window to make full use of its clear aperture, with kinematic references behind the test article for calibration. Our method produces 500 × 500 pixel resolution 3D surface maps with a repeatability of 150 nm RMS within a cryogenic vacuum environment (T = 140 K, P = 0.11 Pa).

Original languageEnglish (US)
Article number1
Issue number1
StatePublished - Jan 2022


  • Deflectometry
  • Inflatable optics
  • Terahertz astronomy
  • Thermal vacuum testing

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Instrumentation
  • Radiology Nuclear Medicine and imaging


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