Conceptual design of a stray light facility for earth observation satellites
Authors: Stockman Y., Hellin M.L., Marcotte S., Mazy E., Versluys J., François M., Taccola M., Zuccaro Marchi A.
Autors Affiliation: Centre Spatial de Liège, Université de Liège, Avenue du Pré-Aily, Angleur, 4031, Belgium; OIP Sensor Systems, Westerring 21, Oudenaarde, B-9700, Belgium; ESTEC – European Space Agency, Keplerlaan 1, Noordwijk ZH, NL-2200 AG, Netherlands
Abstract: With the upcoming of TMA or FMA (Three or Four Mirrors Anastigmat) telescope design in Earth Observation system, stray light is a major contributor to the degradation of the image quality. Numerous sources of stray light can be identified and theoretically evaluated. Nevertheless in order to build a stray light model of the instrument, the Point Spread Function(s) of the instrument, i.e., the flux response of the instrument to the flux received at the instrument entrance from an infinite distant point source needs to be determined. This paper presents a conceptual design of a facility placed in a vacuum chamber to eliminate undesired air particles scatter light sources. The specification of the clean room class or vacuum will depend on the required rejection to be measured. Once the vacuum chamber is closed, the stray light level from the external environment can be considered as negligible. Inside the chamber a dedicated baffle design is required to eliminate undesired light generated by the set up itself e.g. retro reflected light away from the instrument under test. This implies blackened shrouds all around the specimen. The proposed illumination system is a 400 mm off axis parabolic mirror with a focal length of 2 m. The off axis design suppresses the problem of stray light that can be generated by the internal obstruction. A dedicated block source is evaluated in order to avoid any stray light coming from the structure around the source pinhole. Dedicated attention is required on the selection of the source to achieve the required large measurement dynamic.
KeyWords: Conceptual design; Light; Light sources; Mirrors; Observatories; Optical transfer function, Earth observation satellites; Earth observation systems; External environments; Illumination system; Off-axis parabolic mirrors; Reflected light; Telescope design; Vacuum chambers, Stray light