Laser satellite communications are increasingly being adopted throughout the space sector, with large-scale constellations relying on optical links to provide high-data-rate and secure communications. A key challenge in optical communications is the acquisition phase, during which two optical communication terminals (OCTs) must establish a bidirectional link despite the presence of pointing uncertainties. Reducing these uncertainties can significantly improve acquisition performance and reduce the associated search burden.

This thesis investigates an in-orbit calibration strategy for predicting OCT pointing errors using sensors and telemetry already available within the terminal. A review of existing calibration approaches identified a research gap in the use of OCT-internal measurements for the continuous estimation and prediction of pointing errors throughout the mission lifetime. To address this gap, a mission-lifetime calibration strategy was developed and evaluated using a dedicated simulation and development framework.

The dominant pointing-error contributors considered in this work are mechanical alignment errors, thermal distortions, satellite attitude determination and control system (ADCS) errors, and counter-satellite propagation errors. It is shown that a significant portion of the resulting pointing error can be predicted using operational parameters such as time, temperature, and gimbal orientation. An ordinary least squares regression framework was developed using time, temperature, azimuth, and elevation as inputs, and pointing errors in the terminal frame as outputs. The calibration model is continually updated using data collected during operational tracking phases, enabling the prediction of pointing errors under a wide range of mission conditions.

Simulation results demonstrate that the proposed approach can substantially reduce residual pointing errors and generalise across multiple mission scenarios and link geometries. Furthermore, calibration performance improves as calibration data are accumulated throughout the mission lifetime. The results also show that acquisition performance can be enhanced through informed acquisition scheduling, whereby links are established during periods of favourable operating conditions and reduced predicted pointing errors.

Overall, this work demonstrates that mission-lifetime in-orbit calibration can reduce pointing uncertainty, improve acquisition performance, and increase the operational robustness of optical communication terminals without requiring additional dedicated calibration hardware. ... Read more