Communications via optical cross-link between two satellite stations require reciprocal spatial beam tracking. This tracking is achieved by a quadrant detector, which attempts to align the received beam Airy disc on the quadrant cross hairs. Errors due to offset images on the quadrant detector are used to continually realign the gyros so as to aim the pointing optics directly at the received beacon direction. The error voltages at one receiving satellite station depend also on both the pointing errors and the antenna gain pattern at the other transmitting station at the line of transmission. The steady state joint tracking errors of two direct-detection cooperative beam tracking systems are analyzed. In particular, the stable steady state angular pointing errors at both ends are found for constant relative angular motions. Curves of steady state tracking errors will be shown to relate the key system parameters and the type of angular motions. Two of the most important functions for determining steady state stability regions are transmitting aperture functions and the tracking loop S curves. Both first and second order tracking loops at each end of the system are considered.