User Datagram and Bundle Protocol for Distributed Small Satellite Topologies

Many planned Earth observation satellite missions use distributed satellite systems in constellation or cluster orbits instead of one, large satellite with many instruments. This network of satellites and ground stations allows data to be efficiently downlinked. However, to create a networking protocol for constellations of small Earth observing satellites, several limitations need to be addressed, including distributed topology management, slow downlink data-rates, and single point-to-point communication. Since distributed satellite constellations exacerbate the severity of these limitations, a thorough analysis of a constellation's network performance is required to ensure that task objectives are achievable. In this paper, we compared low Earth orbit (LEO) Earth observing satellite constellations using delay tolerant networking protocols and the user datagram protocol (UDP). The constellations' inter-satellite links and downlinks were evaluated using network metrics such as access window time, drop-rat io, and throughput. We simulated these network metrics using the Network Simulator 3 (ns-3). Prev ious works have proposed satellite constellations for Earth observation, however, constellations of s mall satellites have not been analyzed for network metrics. Results show that a sun-synchronous constellation with a repeating ground track outperforms a flower constellation with respect to increased access time, reduced drop-ratio, and higher throughput. The simulat ions also determined the optimum media access control slot time and packet transmission intervals for long distance satellite links. Additionally, we were able to compare the throughput performance of UDP to abundle protocol by adding nodes with delay tolerant networking protocol implementations.