Accession Number : ADA180131

Title :   Prevention of Primary Mirror Contamination by Helium Purging.

Descriptive Note : Technical rept.,

Corporate Author : AEROSPACE CORP EL SEGUNDO CA CHEMISTRY AND PHYSICS LAB

Personal Author(s) : Herm,Ronald R ; Johnson,Bernard R ; Young,Stephen J

PDF Url : ADA180131

Report Date : 27 Feb 1987

Pagination or Media Count : 115

Abstract : Telescopes mounted on space platforms may be subject to performance degradation by the condensation of gaseous species on cryogenically cooled optical surfaces. Attenuations of the flux of impinging contaminants by a purging counterflow of helium (He) gas at the telescope entrance aperture have been calculated by a Monte Carlo procedure that follows individual trajectories selected at random. The calculations involve no significant approximations and should be quite accurate. In particular, multiple-collision trajectories are treated, employing the best available information on the atomic and molecular collision cross sections. Extensive calculations on protection of the Shuttle-mounted CIRRIS I and CIRRIS IA telescopes are presented which illustrate the extent of protection afforded. Keywords: Cryogenic optics; Helium purge; Mirror contamination; Molecular gas dynamics; Monte Carlo calculation; Spacecraft contamination.

Descriptors :   *OPTICAL MATERIALS, *TELESCOPES, *HELIUM, *PURGING, ATOMIC SPECTRA, COLLISIONS, COMPUTATIONS, CONDENSATION, CONTAMINATION, COOLING, CROSS SECTIONS, CRYOGENICS, DEGRADATION, DYNAMICS, FLOW, GAS DYNAMICS, GASES, MIRRORS, MOLECULAR PROPERTIES, MONTE CARLO METHOD, OPTICAL PROPERTIES, OPTICS, PARTICLE COLLISIONS, PLATFORMS, SPACE FLIGHT, SPACECRAFT, SURFACES, TRAJECTORIES

Subject Categories : Optical Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE