Design and Fabrication of a Single Crystal Silicon (SCSI) Telescope:A Success Story

Published in SPIE Proceedings Vol. 6666:
Optical Materials and Structures Technologies III

Douglas R. McCarter, Roger A. Paquin, Eloise McCarter

McCarter Technology Inc. dba McCarter Machine, Inc., P.O. Box 520, Deer Park, TX 77536

ABSTRACT

Silicon components such as mirrors and infrared lenses have been manufactured for many years, primarily from polycrystalline silicon (poly). There are inherent advantages that Single Crystal Silicon, (SCSi), has over poly, such as strength and dimensional stability, that make it more suitable for telescopes.  However, there are challenges in the design of an all-SCSi telescope.  SCSi is brittle and has low tensile strength compared to its compressive strength.  These properties therefore dictate designs that minimize tensile stresses and eliminate direct mechanical attachments.  McCarter has accepted these challenges and has designed and is fabricating a lightweight telescope that can replace one of beryllium at substantial savings of cost and schedule.

The challenge of direct attachment has been solved with the use of bonded threaded inserts of low expansion metal.  Bonding has been studied extensively as described in a companion paper, but the proprietary frit-bonding technique developed by Frank Anthony proved to be the most predictable, stable, and reliable.  This technique is also used to fabricate complex components from an assembly of simpler parts.

To minimize tensile stresses, the mechanical design had to be modified from the original without changing the optical prescription.  This has been successfully accomplished through a “design for manufacturing” approach teaming designers, the stress analyst and manufacturing personnel.  This approach has provided a design that is being produced at lower risk, lower cost and with higher predicted reliability with no loss in performance.

(Our paper can be downloaded here or email Doug McCarter at dmccarter@mccarteret.com.)