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For thousands of years, humankind has utilized star tracking to measure both time and geographical location. In the modern technological era, the problem of telling one's orientation and position from images of the stars has newfound importance when related to satellite communication systems. For example, developments in laser-based communication systems promise huge gains in data rates; however, they tend to require a much finer pointing accuracy in order to hit and track their target as compared to radio frequency due to having a more focused emission pattern. As such, satellites with laser-based communications systems require the ability to obtain their attitude with a much higher degree of accuracy than traditional radio-based communication. For example, in [1], the Mars-to-Earth optical communications system studied requires a pointing accuracy on the order of 2-5 microradians, with an estimated update clock of several hundred Hertz. For contrast, the high-gain antenna of the Mars Reconnaissance Orbiter (MRO) had a pointing accuracy requirement of 2.08 milliradians that could update at 10Hz-10kHz [2] (note that MRO did not use star trackers, but rather used the Electra radio; one can study its performance in [3]).

The goal of Delay Tolerant Networking (DTN) is to take a collection of heterogeneous, disparate connections between satellites, space assets, ground stations, and ground infrastructure and bring it together into a cohesive, functioning overlay network. Depending on the systems being considered, one can find links with a one-way light time exceeding minutes (and hours), periodic links which can sometimes be predicted by orbital mechanics, and restrictions based on the variety of capabilities built into these systems. These characteristics preclude traditional network models and routing techniques and have classically led to either rigid routing tables or purely probabilistic models. As the deeper underlying structures remain unknown, development of more DTN-optimized algorithms has lacked the necessary foundation. In a continuation of previous work, the goal of this paper is to identify and study these fundamental structures that exist in delay tolerant networks (DTN), with a focus on space networks. The current routing methodology has been to use contact graph routing (CGR) algorithms. CGR models a series of known contacts as a static graph. For CGR to work, this graph must be globally consistent and must have an accurate picture of the network. Because this is a globally controlled structure, there is little room for flexibility in the event of changes to the network which would naturally occur as the network grows. As a response to the desire for flexibility as the network changes, we introduced the mathematical structure known as sheaves to DTNs last year. The tag-line for sheaves is that they are a mathematically precise way of gluing local data together into unique global data. Thus, sheaves lend extra power to traditional models (and routing algorithms) by taking additional information and merging it, in as consistent a manner as possible, with the representation itself. The clearest example of how Earth-bound networks exhibit behavior that is “sheafy” is link state routers, which build a local-to-global picture of their network by gluing local information together into a global network, exactly as a sheaf would do. For routing within delay tolerant networks to truly exploit this structure, a deeper structure than a graph is required. In this paper, we develop sheaves that can work over directed graphs such as temporal flow networks, we construct a sheaf representation for Dijkstra's algorithm, and we outline a construction for routing sheaves capable of modeling multicast scenarios. Finally, there is a section of future work suggesting follow-on research.