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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 perimeter around the bright object, two alternative exclusion 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.

This paper presents a novel autonomous inertial relative navigation technique with a sight-line-stabilized integrated sensor system for midrange (20-1 km) spacecraft rendezvous. A continuous-discrete six-state extended Kalman filter is developed for this purpose. The integrated sensor suite onboard an active chaser satellite comprises an imaging sensor, a coboresighted laser range finder, the space-integrated Global Positioning System/inertial navigation system, and a star tracker. For high accuracy of the relative navigation, the Kalman filter state vector consists of the inertial position and velocity of the client satellite governed by a high-fidelity nonlinear orbital dynamics model. The error covariance matrix is formulated in terms of the estimation error in the relative position and velocity of the client satellite, consistent with the sensor measurements. Inertial attitude pointing and rate commands for tracking the client satellite are determined using the estimates of the client's inertial relative position and velocity. To estimate the inertial attitude of the chaser satellite outside the space-integrated Global Positioning System/inertial navigation system, a new three-axis steady-state analytical attitude estimator is developed that blends the gyro-and the star-tracker-measured attitudes. The simulation results of a midrange spacecraft rendezvous using glideslope guidance validate this new six-state autonomous inertial relative navigation technique. The simulation results show that the imaging sensor's sight line can be stabilized at the client satellite in midrange accurately enough to enable the laser range finder to measure the range occasionally, but these measurements are not necessary for the midrange rendezvous phase, because the extended Kalman filter can estimate the range with the angle measurements of the imaging sensor.

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