Relay Satellites for High Throughput Transmission in Earth Observation Missions

Research proposals to utilize relay satellites for high-throughput transmission in earth observation (EO) missions have attracted significant interest in recent years. Relay satellites can increase communication time windows between EO satellites and ground stations (GS). In particular, Walker Delta (WD) satellite constellations in medium-earth orbit (MEO) can keep persistent inter-satellite links at specific altitudes and inclinations. As such, WD relay satellites in MEO can enhance the overall throughput for EO missions. The capacity analysis of relay satellites in MEO will be of interest in practice. In this work, we present capacity analysis across four scenarios: (1) a direct link between low-earth orbit satellite and GS, (2) using a geosynchronous orbit (GEO) relay satellite, (3) using WD 3/3/0 relay constellation in MEO, and (4) using WD 4/2/1 relay constellation in MEO. We analyze the systems throughput using MATLAB and Systems Tool Kit and generate the required design curves. The obtained numerical results show that the WD 4/2/1 relay constellation has superior throughput and access durations. As such, it can deliver the highest average number of daily images to the GS.