A Delay Tolerant Networking-Based Approach to a High Data Rate Architecture for Spacecraft
Historically, it has been the case that SWaP placed such severe constraints on radios that the links between spacecraft and the ground were relatively slow. This meant that the radio link was normally a significant bottleneck in returning scientific data. Over recent years, however, a combination of more efficient radio design, intelligent waveforms, and highly directed, high-frequency RF / optical systems have led to a rapid increase in the amount of data that can be pushed through radio and optical links. This has led to some cases where the radio links are capable of moving data much more quickly than the spacecraft and instruments are capable of actually generating it! In some instances, scientific data can therefore be lost not because the downlink is too slow to support the data rate, but instead because the spacecraft was not designed in a way that would let it fully utilize both the radio and the networking services available to it.The High Data Rate Architecture (HiDRA) project describes a packet-based approach to building modern, distributed spacecraft systems. It presents a means for spacecraft and other assets to participate in both present and future Delay Tolerant Networks (DTN), while simultaneously ensuring that the asset is able to fully utilize the new, high-speed links that have been seeing more widespread development and deployment in recent years. With this in mind, this paper begins with a discussion regarding HiDRA's evolution. Next, it discusses the capabilities and limitations of NASA's present DTN-enabled networks. Of particular note is the way in which principles of network design at the terrestrial level (e.g. use of programmable networks / software-defined networks, separation between data and control plane, infusion of COTS Ethernet switch chips, etc.) can all be translated into the space environment as well. After this, the paper discusses the design and implementation of a present prototype reference implementation of High-Rate DTN (HDTN), which is intended to demonstrate future high-rate networking concepts as part of a coherent demonstration on the International Space Station (ISS). The goal, of both the research and of this implementation, is to help develop a ready-made toolbox of ideas, approaches, and examples from which mission designers can draw when putting together new missions. Assuming all goes as planned, this should not only work to reduce the cost of individual mission design, but also improve the rate at which science data can be returned for mission participants to review.