Daniel Raible is an Electronics Engineer within the Optics and Photonics Branch at NASA’s John H. Glenn Research Center (GRC) at Lewis Field in Cleveland, OH. He serves as GRC’s optical communications subject matter expert, and the majority of Daniel’s work supports NASA’s Space Communications and Navigation (SCaN) program. His areas of research include developing and characterizing devices to support high bandwidth communications and navigation systems, as well as studying architectures for enabling new satellite capabilities and the migration towards higher performance and autonomy.
Classically there has existed an asymmetry between the computing and communicating sides of aerospace systems. Over the past few decades, this asymmetry has shifted to favoring communication link technologies, meaning that advancements in available central processing units (CPUs), storage devices, and internal data buses have stagnated. Indeed, the increased emphasis placed on refining subsystem performance such as with antenna bandwidth in phased arrays, amplifier power efficiency, software defined radio (SDR) flexibility and encoding for data compression and error correction has given rise to successful debuts of multi-gigabit-per-second data return from long space-link distances. These accomplishments are easily quantifiable through link budgets and illustrate what is possible, but also reveal the deficiencies in overall communications capabilities. In particular, the ever-accelerating presence of aerospace vehicles gives rise to newer and larger classes of challenges to address the needs of 21st century systems. Furthermore remote sensing and imaging capabilities have far outpaced our ability to transmit their products to the ground, exacerbating dependence on pre-processing and file downselection to contend with the communications bottleneck. Moreover, reliance upon the established logistics of manual reconfigurations, static event scheduling and execution on a per-vehicle basis are precluded, as these rigid and constrained methods for end-to-end data delivery do not scale and therefore must give way to dynamic, networked approaches with an overall systems view in mind.
Emerging mission requirements exhibit a trend toward multiple smaller-scale vehicles working together to perform dissimilar observations. Such operations necessitate sensor fusion across a constellation, and where data processing may be distributed throughout a fairly disconnected network whose topology changes over time in non-deterministic manners. Individual communications link performance is still very relevant to deploying an effective communications system, but now must be embedded within a greater architecture of capability to optimally utilize the bandwidth available from each link to generate an ultimate end-to-end quality of service. The deleterious effects of timing uncertainty across the arrangement presents a challenge to measurement synchronization and delivery, so a successful deployed system needs to be tolerant to the delays inherent in time-of-light between elements and digital processing latencies existing at each node.
In this presentation we share the flight test results from a high performance Gbps laser communications terminal evaluated with a suite of store and forward capabilities called High-rate Delay Tolerant Networking (HDTN). The communications payload is operated over Lake Erie across a range of configurations including several convergence layers, and is evaluated to determine recovery time after link disruptions, information loss, efficiency and speed. The effectiveness of utilizing a flying laboratory to increase the Technology Readiness Level (TRL) of an integrated system in relevant environments is discussed, as well as the value of conducting aeronautics experiments to retire risk for technology infusion into space missions. Upcoming flight campaigns will be presented, including opportunities to demonstrate reliability, secure command and control, data intensive hyperspectral imaging, quantum link characterization, 4k High Definition (HD) video streaming and internetworked space-ground-aero relay operations. These experiments will pave the way for future missions which will depend upon interoperability across disparate government and privately owned networks, involve contention with uncertain and dynamic timing, and require agility to autonomously configure optimal parameters across networks of ever-increasing size and complexity to ensure data delivery.
https://www1.grc.nasa.gov/space/scan/acs/tech-studies/dtn/
Discussion of challenges facing high performance aerospace communications systems, and presentation of flight test results involving laser communications, quality of service metrics and upcoming technology demonstrations.
