For ground-based large diameter lightweight Pyrex mirrors, internal ventilation is a necessity in order to minimize the thermal distortions. However, the demand on the ventilation system does not appear to be significant. Measurement on a sample blank showed significant effects on the blank's thermal time constant and temperature distribution. Compared with the unventilated case, a mild air flow (17 feet per minute) reduces the thermal time constant from 3 hours to 1 hour. A similar kind of flow (21 feet per minute) reduces the internal temperature difference from 2.4°C to 0.3°C, as well as reduces the temperature difference between the blank and the ambient air from 3.2°C to 0.5°C.

Date Published: 3 November 1983
PDF: 7 pages
Proc. SPIE 0444, Advanced Technology Optical Telescopes II, (3 November 1983); doi: 10.1117/12.937979

Published in SPIE Proceedings Vol. 0444:
Advanced Technology Optical Telescopes II
Lawrence D. Barr; Brian Mack, Editor(s)