Support of latency-sensitive space exploration applications in future space communication systems

Abstract

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017.Cataloged from PDF version of thesis.Includes bibliographical references (pages 283-300).Latency, understood as the total time it takes for data acquired by a remote platform (e.g. satellite, rover, astronaut) to be delivered to the final user in an actionable format, is a primary requirement for several near Earth and deep space exploration activities. Some applications such as real-time voice and videoconferencing can only be satisfied by providing continuous communications links to the remote platform and enforcing hard latency requirements on the system. In contrast, other space exploration applications set latency requirements because their data's scientific value is dependent on the timeliness with which it is delivered to the final user. These applications, henceforth termed latency-sensitive, are the main focus of this thesis, as they typically require large amounts of data to be returned to Earth in a timely manner. To understand how current space communication systems induce latency, the concept of network centrality is first introduced. It provides a systematic process for quantifying the relative importance of heterogeneous latency contributors, ranking them, and rapidly identifying bottlenecks when parts of the communication infrastructure are modified. Then, a custom-designed centrality measure is integrated within the system architecture synthesis process. It serves as a heuristic function that prioritizes parts of the system for further in-depth analysis and renders the problem of analyzing end-to-end latency requirements manageable. The thesis includes two primary case studies to demonstrate the usefulness of the proposed approach. The first one focuses on return of satellite-based observations for accurate weather forecasting, particularly how latency limits the amount of data available for assimilation at weather prediction centers. On the other hand, the second case study explores how human science operations on the surface of Mars dictate the end-to-end latency requirement that the infrastructure between Mars and Earth has to satisfy. In the first case study, return of satellite observations for weather prediction during the 2020-2030 decade is analyzed based on future weather satellite programs. Recommendations on how to implement their ground segment are also presented as a function of cost, risk and weather prediction spatial resolution. This case study also serves as proof of concept for the proposed centrality measure, as ranking of latency contributors and network implementations can be compared to current and proposed systems such as JPSS' Common Ground Infrastructure and NPOESS' SafetyNet. The second case study focuses on supporting human science exploration activities on the surface of Mars during the 2040's. It includes astronaut activity modeling, quantification of Mars Proximity and Mars-to-Earth link bandwidth requirements, Mars relay sizing and ground infrastructure costing as a function of latency requirements, as well as benchmarking of new technologies such as optical communications over deep space links. Results indicate that levying tight latency requirements on the network that support human exploration activities at Mars is unnecessary to conduct effective science and incurs in significant cost for the Mars Relay Network, especially when no optical technology is present in the system. When optical communications are indeed present, mass savings for the relay system are also possible, albeit trading latency vs. infrastructure costs is less effective and highly dependent on the performance of the deep space optical link.by Marc Sanchez Net.Ph. D