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Transpiration Cooled Ultraviolet Sol-Gel Silica Optics
Final rept. 15 Aug 1990-15 Mar 1991
GELTECH INC ALACHUA FL
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All rocket guidance systems essentially require broad-band optical transmission windows. These windows must also be temperature insensitive to transmission, thermal shock resistant, thermally stable, reasonably strong, and impact resistant. At hypersonic velocity convective cooling is preferred to radiative cooling. Transpiration cooling is a novel and effective mode of convective cooling. Porous silica windows offer excellent rocket windows for transpiration cooling at a relatively inexpensive price. Sol-gel technology to demonstrate the concept of transpiration-cooled porous silica windows. These windows were fabricated with various pore sizes and characterized with respect to gas diffusion, transpiration, high temperature transmission, thermal stability and shock resistance, hardness, impact resistance, and strength. The manufacturability aspect was also addressed. The diffusion of various gases through porous silica windows was studied and their permeabilities measured. In the experimental range, Knudsen diffusion seemed to be the predominant mass transport mechanism. At a low transpiration velocity of 0.52 cms of helium, a 44 C temperature drop was observed showing the promise of this material for rocket window application. High temperature spectroscopy showed improved performance. The porous silica windows had thermal stability and thermal shock resistance and reasonable mechanical properties.
APPROVED FOR PUBLIC RELEASE