Technique and accuracy estimation of SIRIO attitude determination

This paper describes the general technique used to determine the SIRIO attitude and certain systematic errors, the biases, which affect the onboard sensor measurements. This technique is implemented in the Attitude Determination Program (ADP) used at CNUCE for determining SIRIa attitude. Tne ADP produces very accurate attitude and bias Determinations. During the various mission phases, the accuracy obtained for the attitude has always been well within mission constraints. As the spacecraft spin axis has different criEURn~ations during different mission phases, bias determination is a most delicate task. The best situation far bias determination is the intermediate attitude (INTA) phase, vhen the attitude lies halfway between the orbit co-planar position and the orbit ,normal position. This situation is carefully examined here. The results of the bias determinations discussed here make it possible to evaluate the reliability of the determination method and the uncertainty of the results obtained in attitude determination, at the present point in the mission.