The pointing, acquisition and tracking (PAT) subsystem is a very substantial part of a free-space optical communication system. The requirements, strategies and performances of the PAT functions are presented, together with their influence on the link quality.
M. Wittig, M. Wittig,
"The Importance Of Pointing-Acquisition And Tracking For Optical Communication Payloads", Proc. SPIE 1131, Optical Space Communication, (6 October 1989); doi: 10.1117/12.961529; https://doi.org/10.1117/12.961529