Research On Attitude Tracking Control Of Agile Satellite Using Control Moment Gyros

For high-resolution LEO earth observation satellite, the field of view of itshigh precision optical payload is usually small; its efficiency depends on thecapability of line-of-sight rapid reorientation. Rather than driving the payload axis,swing the entire satellite is more reliable and accurate. The core value of agilesatellite’s application in observation mission is to work in different observationmode, enlarging its observation range through rapid reorientation. In order to realizeversatile working modes, highly relevant problems of trajectory planning, attitudedetermination and attitude maneuver/tracking control must be solved. Agile satelliteshould adopt the single gimbal control moment gyro (SGCMG) cluster as theactuator in order to meet the mission requirements. This paper aims to research onthe problems of SGCMG cluster singularity and attitude tracking control whenperforming tracking on designed trajectory.Firstly, the dynamics models for rigid-body satellite attitude rotation andconstant speed control moment gyroscope are established, analysis of itstorque-outputting characteristics is made, and, under a series of simplificationconditions, the output torque equation of constant speed control moment gyrocluster is given. In the end, relative to the system’s public mass center, the wholesatellite’s attitude dynamics equation is established.Secondly, according to the output torque equation, the manipulation singularityproblem is presented and analysis of singularity types, discussion about the nullmotion and its existing condition are made. In the angular momentum space,geometric interpretation to the singularity problem is presented, and the influence offrame configuration on the singularity is discussed. Several forms of singular metricfunction are given and their numerical as well as gradient-changing relationshipswith singularity are presented.Then, the mechanisms of SGCMG cluster steering-laws are analyzed andcompared, and, by the mathematical means of singular value decomposition (SVD),analysis is carried out and the error upper limit is estimated for robust inverse typesteering-laws. The mechanism of constrained steering law is introduced andsingularity is analyzed for the roof-type configuration, putting forward a new designidea. By simulation, open loop torque output effects of several configurations andsteering-laws are compared.Finally, in order to realize multiple observation mode of agile satellite, theattitude control problem of tracking any designed3D trajectory is studied. Using the information of the designed3D trajectory and the satellite orbit, the relative motionrelations between the moving target and agile satellite are described. Calculatingattitude quaternion of the target relative to the satellite, so as to obtain deviationattitude and attitude angular velocity, meanwhile, considering the shielding problemof line-of-sight by central body, target visibility to the satellite is analyzed. UsingSGCMG cluster as the actuator, a cascade-saturation control law is designed, theattitude tracking control of the designed3D trajectory is realized, and numericalsimulation is carried out for verification.