Geometric Characterization of LEO–GEO Inter‐Satellite Links for Bidirectional Communications

Incorporating geosynchronous Earth orbit (GEO) and low Earth orbit (LEO) satellites can extend communication services far beyond the reach of terrestrial infrastructure. A key enabler of such architectures is the establishment of inter‐satellite links (ISLs) between LEOs and GEOs to support bidirectional communications. However, existing research has placed limited emphasis on the inherently dynamic and asymmetric nature of the LEO–GEO connectivity. This study presents a comprehensive numerical analysis of LEO–GEO ISL geometric characteristics, incorporating geometric visibility and pointing constraints, and evaluating link‐availability performance and timeline dynamics across a wide range of constellation configurations. The analysis evaluates ISL availability and temporal dynamics using a dual approach: (i) simulations of operational constellations (Iridium, Starlink, and OneWeb) and (ii) a large‐scale geometric performance assessment of a wide variety of synthetic orbital shells spanning diverse altitude–inclination combinations. Numerical results show that inclination is the primary driver of LEO–GEO ISL availability, whereas altitude plays a secondary role except beyond a critical height of about 950 km, where GEO field‐of‐view (FOV) constraints rapidly erode downlink opportunities. Two‐GEO configurations generally provide near‐continuous downlink for non‐FOV‐limited constellations (e.g., Iridium and Starlink), with a third GEO offering diminishing, mostly uplink‐centric gains. In contrast, FOV‐limited systems (OneWeb‐like or high‐inclination shells) require additional GEO diversity to achieve high downlink availability and to extend contact‐arc durations. Low‐inclination LEO constellations yield higher uplink availability, whereas higher inclinations reduce uplink opportunities. Overall, these results highlight the need for tightly integrated orbital and link‐layer design to fully exploit LEO–GEO ISLs in future space‐based communication systems.