Free-space optical communications on board high-altitude platform stations (HAPS) promises commercial upside for supplying internet connectivity to regions underserved by space constellations. However, platform vibrations and stringent hardware constraints make pointing, acquisition, and tracking (PAT) of optical links difficult to implement. This work investigates the effectiveness of a cascaded control architecture for the combined actuation of a coarse pointing assembly and fine-steering mirror for PAT between HAPS and LEO spacecraft. The laser communications hardware and platform dynamics are simulated in detail, followed by a systematic control design using H∞ optimization. An Extended Kalman Filter combining recorded light measurements from the target and trajectory propagations provide the system with continuous pointing input. Results show that the cascade control architecture can
reject disturbances up to 300Hz in tracking and correct pointing errors up to 40mrad in acquisition. The EKF output accuracy significantly degrades after 15 seconds due to GNSS antenna instability caused by the bending of the HAPS air frame.