Design for High Accuracy Critical-Angle Sun Transit Sensor.

摘要

A sun transit sensor is used to detect the sun's passing a meridianal coordinate plane of the satellite. Accuracy of operation of earlier sensors is limited by curvature of the fan beams associated with the critical angle prism. A new, two-element critical angle prism assembly was described having the following properties: (a) curvature of the fan beam can be cancelled, or balanced against higher order terms, (b) reflection occurs at the interface between the glasses, (c) achromatism is possible. A sensor utilizing two such prism assemblies operating in push-pull exhibits a planar fan beam having accuracy of + or - sun latitude range of + or - 30 deg (equatorial orbit requirement), or + or - 5 arc seconds for sun latitudes of 5 deg (ecliptic orbit requirement). Equations governing the design, the choice of radiation resistant glasses, fabrication and testing will be discussed.