Attitude Control for Agile Satellite Applications

Abstract

The present invention relates, in general, to attitude control and, in particular, to control of the attitude of a space platform, conveniently of a satellite and/or a spacecraft. In detail, an aspect of the present invention concerns the use, in an attitude control system, of several Control Moment Gyroscopes with limited gimbal revolutions. Moreover, another aspect of the present invention concerns an improved logic for controlling a Control Moment Gyroscope assembly of an attitude control system.

1 . An attitude control unit ( 110 ), which is designed to be:
 installed on a platform to control the attitude of the latter; and   coupled to a Control Moment Gyroscope assembly ( 4 , 6 , 120 ), that is installed on board said platform and comprises four or more Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 );   said attitude control unit ( 110 ) being configured to:
 select, on the basis of a reference attitude trajectory of the platform, three Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) to be simultaneously operated while keeping the unselected Control Moment Gyroscope(s) ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) stationary; 
 compute, on the basis of the reference attitude trajectory and of a current attitude of the platform, an overall angular momentum to be provided by the Control Moment Gyroscope assembly ( 4 , 6 , 120 ); 
 compute, on the basis of the overall angular momentum to be provided by the Control Moment Gyroscope assembly ( 4 , 6 , 120 ) and of an angular momentum of the unselected Control Moment Gyroscope(s) ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ), a triplet-related angular momentum to be provided by the three selected Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ); and 
   simultaneously operate the three selected Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) so as to cause these latter to provide said triplet-related angular momentum computed, while keeping the unselected Control Moment Gyroscope(s) ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) stationary.   
     
     
         2 . The attitude control unit ( 110 ) of  claim 1 , configured to:
 compute, on the basis of the triplet-related angular momentum computed and of current angular positions and velocities of gimbals ( 32 ) of the three selected Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ), new angular positions and velocities to be assumed by the gimbals ( 32 ) of said three selected Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) such that these latter provide said triplet-related angular momentum computed; and   simultaneously operate the gimbals ( 32 ) of the three selected Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) so as to cause said gimbals ( 32 ) to assume the new angular positions and velocities computed, thereby causing said three selected Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) to provide the triplet-related angular momentum computed.   
     
     
         3 . An attitude control system ( 100 ), which is designed to be installed on a platform to control the attitude of the latter, and which comprises:
 a Control Moment Gyroscope assembly ( 4 , 6 , 120 ) comprising four or more Control Moment Gyroscopes ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ); and   the attitude control unit ( 110 ) as claimed in  claim 1 , which is coupled to said Control Moment Gyroscope assembly ( 4 , 6 , 120 ) to control operation thereof.   
     
     
         4 . The attitude control system ( 100 ) of  claim 3 , wherein each Control Moment Gyroscope ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) has a respective gimbal ( 32 ) that is mechanically constrained so as to be operable to perform a limited number of full revolutions on a respective gimbal axis. 
     
     
         5 . The attitude control system ( 100 ) of  claim 4 , wherein each Control Moment Gyroscope ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) is equipped with respective sensors and is coupled to a respective flexible cable ( 33 ) to receive therethrough power supply and to provide therethrough signals from the respective sensors; and wherein each Control Moment Gyroscope ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) is coupled to the respective flexible cable ( 33 ) so that rotation of the respective gimbal ( 32 ) causes said respective flexible cable ( 33 ) to be rolled and unrolled round said respective gimbal ( 32 ) thereby mechanically limiting the number of full revolutions performable clockwise and counterclockwise by the latter. 
     
     
         6 . The attitude control system ( 100 ) of  claim 5 , wherein each Control Moment Gyroscope ( 3 ,  41 ,  42 ,  43 ,  44 ,  61 ,  62 ,  63 ,  64 ) includes:
 a respective casing ( 31 ); and   a flywheel housed inside said respective casing ( 31 ) and operable by a respective flywheel motor to spin on a respective flywheel axis, said respective flywheel motor and said respective sensors being arranged inside said respective casing ( 31 ); and   wherein the respective gimbal ( 32 ) of each Control Moment Gyroscope ( 3 , 41 , 42 , 43 , 44 , 61 , 62 , 63 , 64 ) is coupled, externally to the respective casing ( 31 ), to said respective flexible cable ( 33 ) to receive therethrough power supply for the respective flywheel motor and to provide therethrough signals from the respective sensors.   
     
     
         7 . The attitude control system ( 100 ) according to  claim 3 , wherein the Control Moment Gyroscopes include first Control Moment Gyroscopes ( 41 , 42 ;  61 , 62 ) and second Control Moment Gyroscopes ( 43 , 44 ;  63 , 64 ); and wherein:
 the first Control Moment Gyroscopes ( 41 , 42 ;  61 , 62 ) have gimbal axes that are parallel or lie along one and the same straight line;   the first Control Moment Gyroscopes ( 41 , 42 ;  61 , 62 ) have angular momentum vectors rotatable in one and the same plane or in parallel planes;   the second Control Moment Gyroscopes ( 43 , 44 ;  63 , 64 ) have gimbal axes that
 are parallel or lie along one and the same straight line, and 
 are not parallel to the gimbal axes of the first Control Moment Gyroscopes ( 41 , 42 ;  61 , 62 ); 
   the second Control Moment Gyroscopes ( 43 , 44 ;  63 , 64 ) have angular momentum vectors rotatable in one and the same plane or in parallel planes; and   the plane(s) in which the angular momentum vectors of the first Control Moment Gyroscopes ( 41 , 42 ;  61 , 62 ) are rotatable intersects/intersect the plane(s) in which the angular momentum vectors of the second Control Moment Gyroscopes ( 43 , 44 ;  63 , 64 ) are rotatable.   
     
     
         8 . The attitude control system of  claim 7 , wherein:
 the gimbal axes of the first Control Moment Gyroscopes ( 41 , 42 ) are parallel;   the angular momentum vectors of the first Control Moment Gyroscopes ( 41 , 42 ) are rotatable in one and the same plane;   the gimbal axes of the second Control Moment Gyroscopes ( 43 , 44 ) are parallel and lie on the same plane of the gimbal axes of the first Control Moment Gyroscopes ( 41 , 42 );   the angular momentum vectors of the second Control Moment Gyroscopes ( 43 , 44 ) are rotatable in one and the same plane that intersects the plane in which the angular momentum vectors of the first Control Moment Gyroscopes ( 41 , 42 ) are rotatable; and   the plane in which the angular momentum vectors of the first Control Moment Gyroscopes ( 41 , 42 ) are rotatable is perpendicular to, or tilted with respect to, the plane in which the angular momentum vectors of the second Control Moment Gyroscopes ( 43 , 44 ) are rotatable.   
     
     
         9 . The attitude control system of  claim 7 , wherein:
 the gimbal axes of the first Control Moment Gyroscopes ( 61 , 62 ) lie along one and the same straight line;   the angular momentum vectors of the first Control Moment Gyroscopes ( 61 , 62 ) are rotatable in parallel planes;   the gimbal axes of the second Control Moment Gyroscopes ( 63 , 64 ) lie along one and the same straight line that is perpendicular to the straight line along which the gimbal axes of the first Control Moment Gyroscopes ( 61 , 62 ) lie; and   the angular momentum vectors of the second Control Moment Gyroscopes ( 63 , 64 ) are rotatable in parallel planes that are are perpendicular to the planes in which the angular momentum vectors of the first Control Moment Gyroscopes ( 61 , 62 ) are rotatable.   
     
     
         10 . A space platform equipped with the attitude control system ( 100 ) claimed in  claim 3 . 
     
     
         11 . The space platform of  claim 10 , wherein said space platform is a satellite or a spacecraft.