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Low cost deep space hybrid optical/RF communications architecture

This paper reports on a study of hybrid optical/Radio Frequency (RF) architectures for deep space missions. Previous proposed optical deep space communication architectures were generally designed to achieve 90% or better availability 24/7. This study, instead, considered alternative metrics and architectures. It focuses on a strategy to use RF links and existing RF infrastructure for navigation and for communications requiring high availability, and optical communication links only for high volume downlink data. The optical link can then be designed to maximize data volume rather than availability. Utilizing Automatic Repeat Request (ARQ) with this strategy, a high level of completeness is possible even with low link availability - though with an increase in latency and spacecraft memory requirements. This strategy is suitable for deep space missions whose high volume links are dominated by science data that can tolerate long delays. The study found that with this optical downlink strategy, a single ground telescope can provide the principal expected benefit of optical communications (high data volume) at much lower cost than optical infrastructures designed to provide 90% availability 24/7. The study found also that data volume can, in some cases, be maximized by arraying all ground telescopes at a single site so that they have identical weather statistics. This low cost architecture, here named Single Optical Site (SOS), can eventually be augmented with multiple sites to provide high optical availability.