Ground-to-orbit transfer of the AXAF-I flux scale: in-situ contamination monitoring of x-ray telescopes

Details Ground-to-orbit transfer of the AXAF-I flux scale: in-situ contamination monitoring of x-ray telescopes Ground-to-orbit transfer of the AXAF-I flux scale: in-situ contamination monitoring of x-ray telescopes

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994spie.2279..332e&link_type=abstract

Proc. SPIE Vol. 2279, p. 332-342, Advances in Multilayer and Grazing Incidence X-Ray/EUV/FUV Optics, Richard B. Hoover; Arthur B

Physics

Optics

5

Scientific paper

Grazing-incidence optics are quite sensitive to molecular and particulate contamination. For NASA's Advanced X-ray Astrophysics Facility-Imaging (AXAF-I), the sensitivities of the flux scale to contamination on the mirrors' surfaces are typically 0.4% per angstrom of a hydrocarbon film and 0.4% per 10-5 fractional areal coverage by particulates. In view of the goal of calibrating the flux-scale to a few-percent accuracy, it is clearly essential to adopt rigorous procedures to control and to monitor both molecular and particulate contamination. Traditional approaches to monitoring contamination for optical surfaces--using optical witness samples in conjunction with facility airborne monitors--are essential during ground operation. However, such techniques do not directly monitor changes in x-ray reflectance or even in contamination of the mirrors themselves; nor can they determine differences in contamination between ground calibration and orbital operations. In order to transfer the AXAF-I flux scale from ground to orbit, AXAF-I will incorporate x-ray- fluorescing radionuclide sources in the forward contamination cover. Comparison of the telescope's throughput, for these x rays, at ground calibration with that at the commencement of orbital operations will validate the flux-scale calibration. If ground-to-orbit changes were to occur, such a comparison would facilitate correction of the flux scale.

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