Nitrogen snow cleaning inside a large cryogenic telescope

Christopher G. Shaw

doi:10.1117/12.258341

11 November 1996 Nitrogen snow cleaning inside a large cryogenic telescope

Christopher G. Shaw

Proceedings Volume 2864, Optical System Contamination V, and Stray Light and System Optimization; (1996) https://doi.org/10.1117/12.258341
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

A 50-cm cryogenic mirror at one end of an aluminum telescope was successfully cleaned by nitrogen snow in a series of demonstration tests. The mirror was maintained below 70 Kelvin under vacuum during the cleaning, with a 15 Kelvin cold cap pumping the nitrogen gas to maintain a realistic space environment. The snow was produced by an assembly of 6 nozzles and valves attached to the exterior of the telescope. The nozzles protruded less than 1 cm into the telescope and were well outside the mirror diameter. Contamination of the mirror was produced by silica and alumina dusts propelled into the telescope by special velocity-moderating sources. Cleaning effectiveness was measured by scatter of 10.6-mu laser light at 2 degrees from three spots on the mirror surface. All scatter system components were exterior to the telescope, with only small holes for the passage of laser radiation. The clean mirror BRDF of 5 multiplied by 10^-4 sr^-1 was raised as high as 3 multiplied by 10^-2 sr^-1 by the contamination process and subsequently reduced to the original level by one or two seconds of nitrogen snow spraying. Nitrogen snow cleaning under vacuum proved much more effective than carbon-dioxide snow cleaning of the same mirror in air.

Citation Download Citation

Christopher G. Shaw "Nitrogen snow cleaning inside a large cryogenic telescope", Proc. SPIE 2864, Optical System Contamination V, and Stray Light and System Optimization, (11 November 1996); https://doi.org/10.1117/12.258341

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available