Suppression of sun interference in the star sensor baffling stray light by total internal reflection

Abstract

We have developed a star sensor as an experimental device onboard the SERVIS-1 satellite launched in October 2003. The in-orbit data have verified its fundamental performance. One of the advantages of our star sensor is that the baffle has a small length of 120 mm instead of 182 mm in the conventional two-stage baffle design. The key concepts for light shielding are total internal reflection phenomena inside a nearly half sphere (NHS) lens and scattering light control by gloss black paint. However, undesirable background noise by the sun outside of the field of view (FOV) was observed in the corner of the FOV in the orbital experiment. Ray trace simulations revealed that slight scattering light on the specular baffle wall entered the NHS lens and reached the corner of the image sensor through the multi-reflection path inside the lens. It was found that the stray light path can be shielded effectively if the diameter of the aperture under the NHS lens was reduced. We redesigned the baffle and evaluated the light shielding ability with our sun interference test facility on the ground, and confirmed that the stray light was reduced below the acceptable level. As a result, the light shielding technique which we have proposed was proved to be effective for a small-size baffle. The redesigned star sensor is planned to be installed as a main attitude sensor for the SERVIS-2 satellite scheduled to be launched in February 2008.

On the testing and validation of stray light attenuation for microsatellite star tracker baffles

“…All of their baffle attenuation measurements were at least an order of magnitude above this level. Kawano et al [12] also used an enclosed clean room environment for their stray light testing. To alleviate surface scattering within their experiment, they erected a light trap internally coated with a specular black surface to direct rays entering the field of view into a dark cavity.…”

Fast Stray Light Performance Evaluation Based on BSDF and Radiative Transfer Theory

“…The design of internal and external stray light suppression structures, such as baffles, is based on the structural characteristics of the optical system, and the placement of the structure increases the volume and mass of the space optical payload [11]. Therefore, an optical system with a good stray light elimination capability is the focus of achieving lightweight miniaturization and improving imaging quality.…”