Attitude Commands Avoiding Bright Objects and Maintaining Communication With Ground Station (AAS 98-376)

The objective of the paper is to develop attitude commands for slewing a vehicle such that the angle of its boresight with the centroid of a bright object is not less than a minimum angle and its antennae do not lose communication with the ground. These commands involve three angles: the required pitch/yaw slew angle, the bright object’ s exclusion angle normal to the slew angle, and a roll angle for maintaining communication. The location of the bright object’ s centroid is formulated in terms of an angle normal to the ideal slew plane. If the ideal,minimum-angleslew path enters the forbidden perimeteraround thebrightobject, two alternativeexclusion angles are determined so as to pass the object tangentially from either side. Between the two angles, that exclusion angle is selected, which steers the ground station trace, in the communication beam, toward beam axis and not away from it. Communication links of the antennae are maintained by rolling the vehicle before, during, or after slewing. The three-axis attitude and rate commands are illustrated for a stressing scenario in which two bright objects are close by and hence pose special circumstances for the algorithm to tackle.