Abstract: A method of determining the attitude of a spacecraft is provided. The method may include sensing the projections of a plurality of stars on a sensor, converting the projections into sensor-star directions, and determining the angular values of the spacecraft relative to the stars. The method uses equations to introduce focal length errors into the equations which convert the projections into star-sensor directions, thereby reducing the uncertainty introduced by incomplete knowledge of the errors on the results of the attitude angles of the spacecraft.

Abstract: The invention provides a method of determining the attitude (?, ?, ?) of a spacecraft, the method comprising the steps consisting in: a) sensing the projections (xmi, ymi) of a plurality of stars on an optical star sensor mounted on the spacecraft; b) providing a reference focal length (fref) for said sensor, said focal length serving to convert the projections of the stars (xmi, ymi) as picked up on the sensor into sensor-star directions (wi) in a frame of reference associated with the sensor; and c) determining the angular values of the attitude of the spacecraft relative to the stars by solving a system of equations which has as its input data in particular the projections of the stars (xmi, ymi) on the sensor and the reference focal length of the sensor; the method being characterized by introducing, as unknowns in the system of equations, at least one parameter (D1, . . .