Modeling Pointing, Acquisition, and Tracking Delays in Free-Space Optical Satellite Networks

Free-space optical inter-satellite links (OISLs) enable high-capacity space communications but require precise Pointing, Acquisition, and Tracking (PAT) between links. Current scheduling approaches often overlook or oversimplify PAT delays, leading to inefficient contact planning and overestimated network capacities. We present a validated model for quantifying retargeting delays, defined as the delay-inducing portion of PAT before data transmission begins, encompassing coarse pointing, fine pointing, and the handover to tracking. The model is grounded in mission data from NASA TBIRD, LLCD, DSOC, and ESA's Lunar Optical Communication Terminal. We find that PAT delays exhibit multimodal distributions based on prior link geometry and scale nonlinearly with initial pointing uncertainty and optical beam width. Integrating these delay models into routing and scheduling algorithms will enable more accurate contact planning and higher utilization in optical networks. The proposed model provides a foundation for evaluating performance and designing algorithms for future large-scale optical satellite networks.