Wide field, large aperture, Schmidt camera for the detection of high energy cosmic rays from space
Authors: Mazzinghi P., Bratina V., Tiribilli B.
Autors Affiliation: Istituto Nazionale di Ottica Applicata, Largo E. Fermi 6, 50125 Firenze, Italy
Abstract: An optical system consisting of a reflecting mirror with a Schmidt corrector plate is presented as a possible design of a space-based observatory for high energy (up to 1020 eV) cosmic rays, by monitoring the fluorescence showers induced after interaction by cosmic rays with the Earth atmosphere. An instrument of that kind is currently into the evaluation phase as an external payload for the International Space Station. The basic requirements demand a system with large field of view, up to ± 30°, and large collecting aperture, = 2 m Ø, to achieve a sufficient sensitivity and event statistics. Among several possible optical systems for this purpose, the Schmidt camera is the simplest, matching most of the optical technical requirements, with some problem for the obscuration due to the focal plane at such extreme field of view. This paper presents ray-tracing simulations for different designs of large aperture (< 2m) Schmidt cameras with FOV from 40° to 50°, with F/# ˜ 0.7 and ground resolution from 1 to 2 km from a LEO. Better performances are achieved with an aspheric mirror, but performances using of a spherical mirror are acceptable with some compromise in resolution. The overall geometrical transmission ranges from 40% to 78%, according to the selected geometry and FOV. Possible technologies for the construction of the main mirror and all other components, including supporting mechanics will be also discussed.
KeyWords: Cameras; Cosmic rays; High energy physics; Observatories; Optical design; Optical systems; Radiation detectors; Space telescopes, Aspheric mirror; Schmidt camera; Spherical mirror, AstrophysicsDOI: 10.1117/12.458540