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Proceedings Paper

Two unique aspects of gravity probe-B star-tracking space telescope: (1) focal-plane roof-edge diffraction and (2) fused-quartz bonding for 2.5-Kelvin applications
Author(s): Dz-Hung Gwo
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Paper Abstract

The Gravity Probe-B cryogenic star-tracking telescope provides the inertial pointing reference, as established by a distant 'fixed' guide star, with milli-arc-second resolution per year for the NASA/Stanford general-relativity gyroscope experiment. The design of the f/27 modified- Cassegrain telescope is briefly reviewed. Then discussed are two of its unique aspects: (1) focal-plane roof-edge diffraction and (2) fused-quartz bonding for 2.5 Kelvin applications. The star image in the telescope is split by roof prisms to generate quadrant pointing information within few arc-seconds about the guide-star direction. The corresponding roof-edge diffraction effects due to the roof- prisms were compared with theoretical calculations, which successfully interpreted the test result and indicate the need for enlarging post-focal-plane detection apertures, as compared with ray-trace situation. On the other hand, a novel fused-quartz bonding technique was developed and found superior in many aspects to index-matching epoxies, optical contacting, and Corning's proprietary frit bonding for both room-temperature and cryogenic applications. The bonding was simple, economical, yet extremely reliable and optically precise. It resulted in strengths near that of fused quartz, with less than 10 nano-meter interface thickness demonstrated.

Paper Details

Date Published: 28 August 1998
PDF: 12 pages
Proc. SPIE 3356, Space Telescopes and Instruments V, (28 August 1998); doi: 10.1117/12.324446
Show Author Affiliations
Dz-Hung Gwo, Stanford Univ. (United States)


Published in SPIE Proceedings Vol. 3356:
Space Telescopes and Instruments V
Pierre Y. Bely; James B. Breckinridge, Editor(s)

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