Satellite roll and yaw attitude control method

Claim 1

A method for controlling the roll and yaw attitude of an artificial satellite following an orbit in the solar system and provided with roll, yaw and pitch axes, where the satellite has a satellite body with North and South sides, North and South solar generator panels extending from said North and South sides and connected to said satellite body by respective independent drive motors adapted to be controlled separately so as to orient said North and South solar generator panels about said pitch axis with respective depointing angles γ n and γ s relative to respective nominal instantaneous orientations in which said panels face towards the sun, an attitude measuring system adapted to provide instantaneous roll and yaw attitude signals; and calculation means at least partly carried on board the satellite being provided for calculating from said attitude signals theoretical command torques to be generated in the plane of the roll and yaw axes for cancelling any instantaneous attitude error of the satellite in said plane of the roll and yaw axes; this method comprising the steps of: A. as a preliminary stage: selecting respective acceptable ranges for said respective depointing angles of said North and South solar generator panels; determining for any pair of respective depointing angles within said respective acceptable ranges a respective pair of resulting command torques C s -C p parallel to two predetermined torque axes in said plane of said roll and yaw axes induced by the solar radiation pressure acting on said solar generator panels; reporting in a C s -C p diagram points having as coordinates said respective pairs of resulting command torques and determining in said diagram a locus consisting of the whole of said points, any pair of coordinates in this diagram thus determining either a possible command torque if said coordinates define a point inside said locus, or a non-possible command torque if said coordinates define a point outside said locus; and, drafting a law of correlation between each point of said locus and a corresponding pair of depointing angles able to induce due to solar radiation pressure the possible command torque determined by said each point; B. then cyclically at a specific frequency that is constant or not as the satellite follows its orbit: selecting the geometrical axes x and z, fixed or not, in said plane of the roll and yaw axes and selecting for said geometrical axes respective maximum values of tolerable command torque error such that the maximum value for the z axis is substantially lower than the maximum value for the x axis; tracing these geometrical axes in said C s -C p diagram; calculating from instantaneous roll and yaw attitude signals supplied by said attitude measuring system, a respective instantaneous theoretical command torque in said plane of the roll and yaw axes adapted to cancel any instantaneous attitude error; identifying in said locus a point, having relative to said z geometrical axis a torque component substantially identical to the torque component of the point corresponding to said respective instantaneous theoretical command torque and having relative to the x axis a torque component as near as possible to the torque component of said point corresponding to said respective instantaneous theoretical command torque; identifying with said law of correlation from said point in said locus a respective pair of depointing angles; and, controlling said drive motors so as to orient said solar generator panels to said pair of depointing values.

Claim 2

A method for controlling the roll and yaw attitude of an artificial satellite following an orbit in the solar system and provided with roll, yaw and pitch axes, where the satellite has a satellite body with North and South sides, North and South solar generator panels extending from said North and South sides and connected to said satellite body by respective independent drive motors adapted to be controlled separately so as to orient said North and South solar generator panels about said pitch axis with respective depointing angles γ n and γ s relative to respective nominal instantaneous orientations in which said panels face towards the sun, an attitude measuring system adapted to provide instantaneous roll and yaw attitude signals; and calculation means at least partly carried on board the satellite being provided for calculating from said attitude signals theoretical command torques to be generated in the plane of the roll and yaw axes for cancelling any instantaneous attitude error of the satellite in said plane of the roll and yaw axes; this method comprising the steps of: A. as a preliminary stage: selecting respective acceptable ranges for said respective depointing angles of said North and South solar generator panels; determining for any pair of respective depointing angles within said respective acceptable ranges a respective pair of resulting command torques C s -C p parallel to two predetermined torque axes in said plane of said roll and yaw axes induced by the solar radiation pressure acting on said solar generator panels; reporting in a C s -C p diagram points having as coordinates said respective pairs of resulting command torques and determining in said diagram a locus consisting of the whole of said points, any pair of coordinates in this diagram thus determining either a possible command torque if said coordinates define a point inside said locus, or a non-possible command torque if said coordinates define a point outside said locus; and, drafting a law of correlation between each point of said locus and a corresponding pair of depointing angles able to induce due to solar radiation pressure the possible command torque determined by said each point; B. then cyclically at a specific frequency that is constant or not as the satellite follows its orbit: selecting the geometrical axes x and z, fixed or not, in said plane of the roll and yaw axes and selecting for said geometrical axes respective maximum values of tolerable command torque error such that the maximum value for the z axis is substantially lower than the maximum value for the x axis; tracing these geometrical axes in said C s -C p diagram; calculating from instantaneous roll and yaw attitude signals supplied by said attitude measuring system, a respective instantaneous theoretical command torque in said plane of the roll and yaw axes adapted to cancel any instantaneous attitude error; identifying in said locus a point, having relative to said z geometrical axis a torque component substantially identical to the torque component of the point corresponding to said respective instantaneous theoretical command torque and having relative to the x axis a torque component as near as possible to the torque component of said point corresponding to said respective instantaneous theoretical command torque; identifying with said law of correlation from said point in said locus a respective pair of depointing angles; and, controlling said drive motors so as to orient said solar generator panels to said pair of depointing values.