Prevention of Primary Mirror Contamination by Helium Purging.
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 27, 1987
- Accession Number
- ADA180131
Entities
People
- Bernard R. Johnson
- Ronald R. Herm
- Stephen J. Young
Organizations
- The Aerospace Corporation