Galileo spacecraft autonomous attitude determination using a V-slit star scanner

Absolute attitude determination and the rotor spin rate of the Galileo spacecraft are derived solely from a two-axis star scanner, (SS) that is sensitive (outside the Jovian magnetosphere) to at least 200 brightest stars. With the 200-star sensitivity, the SS always provides at least three stars for attitude determination anywhere in the spacecraft orbit. Because the SS must function in the intense Jupiter radiation environment, which consists primarily of high-energy electrons and photons, the Galileo SS is designed with radiation hardness as a prime objective. The Galileo SS is described together with an entirely autonomous attitude determination algorithm. The SS analytical model is also presented. The selection process for the model´s critical parameters which are used by the attitude determination algorithm is explained. Post launch operation of the attitude determination algorithm is discussed and actual flight data are presented.<>