Topology design and performance analysis for networked earth observing small satellites

In order to network small satellite constellations for Earth observation and communication, several limitations must be addressed, including distributed topology management, slow down-link data-rates, and single point-to-point communication. Since distributed satellite constellations exacerbate the severity of these limitations, thorough analysis of a constellation´s network performance is required to ensure that task objectives are achievable. In this paper, we designed network topologies using Satellite Toolkit (STK) for two low Earth orbit (LEO) Earth observing small satellite constellations: a sun-synchronous repeating ground track constellation and a flower (an elliptical repeating ground track) constellation. Both constellations include six sink satellites that provide a high speed down-link relay point to a ground station. We compared the constellations´ inter-satellite links and down-links with respect to network metrics including access window time, drop-ratio, and throughput. We evaluated these network metrics using the Network Simulator (ns-2). Though previous works have proposed sun-synchronous and flower small satellite constellations for Earth observation, these constellations have not been analyzed for these network metrics. Results show that the sun-synchronous constellation with a repeating ground track outperforms the flower constellation with respect to more access time, lower drop-ratio, and higher throughput. Additionally, our simulations determined the optimum media access control slot time and packet transmission intervals for long distance satellite links. Further, our method of designing satellite constellation topologies in STK and exporting them to ns-2 can be used for future studies on any desired constellation network performance evaluations.