A New Approach for Enhanced Communication to LEO Satellites

Operations of satellites in Low-Earth Orbit (LEO) have been based on exploiting the maximum time of visibility of satellites over their ground stations. In this paper, it is shown that a key parameter for communication between a satellite and a ground station is not the time of visibility but the amount of telemetry data which can be transmitted from the satellite to the ground station in the downlink. Given the fact that advanced satellites may allow a variety of data rates for downlink, switching on and off the transponder at higher elevations (i.e. at lower slant ranges) than the minimum possible elevation allows for a higher data rate, and thus, despite of less contact time, for a higher total data volume to be transmitted during a given pass. The paper motivates this new approach for space-ground communication of satellites in LEO on the background of recent technology advances and develops the theoretical framework for enhanced communication. To this extent, an analytical relation is established of the total data volume which can be downlinked for a single pass as a function of the elevation at which the transponder shall be switched on and off. The analysis is limited to a circular LEO and zenith passes. Numerical simulations of the total data volume as a function of this minimum elevation angle are presented as well. Finally, associated opportunities and challenges for enhanced communications are identified and discussed. Conclusions are drawn for future optimized operations of LEO satellites based on given ground segments