On the Physical Realizability of Hybrid RF and Optical Communications Platforms for Deep Space Applications

Abstract

There are hefty constraints levied on all space systems, and some of the most fundamental of them are purely physical. Much of the literature published on optical communications for space data systems focuses on the increased capabilities that optical communication systems have to offer, but ignores the practical infusion strategies of the technology into an operable network. Significant resources have been spent over the better half of the last century across multiple governments to establish robust radio frequency (RF) infrastructure around the world, and any new spacecraft will include provisions to utilize that investment. Therefore, every optical communication system flown will be a functional subset of a larger communication architecture dominated by RF. The key is to optimize the architecture and integrated components into a system that can be used to support hybridized RF and optical communications within the same asset, throughout diverse atmospheric (weather) and in-space conditions. The focus of this paper is on the physical realizability of a hybrid optical and RF communications system, and its ability to increase mission capability without imparting extra burden to the host spacecraft in the form of either increased physical mass or power requirements or additional operational requirements. The space applications may feature a hybrid RF/optical aperture this conjunction of a telescope and an antenna has been dubbed the teletenna. The teletenna is a single co-boresighted aperture that combines the radio and optical beams together into one physical package. The tradeoffs associated with the teletenna optimization are discussed, as well as the pointing requirements and strategies. Initial optical terminals on spacecraft have utilized Earth-based beacons Aerospace Technologist in Telecommunications, Optics and Photonics Branch (LCP), 21000 Brookpark Road/Mail Stop 54-1, AIAA and Technical Committee Member Aerospace Technologist in Telecommunications, High Frequency Branch (LCH), 21000 Brookpark Road/Mail Stop 54-1 Senior Aerospace Technologist in Telecommunications, Architectures, Networks and System Integration Branch, (LCA), 21000 Brookpark Road/Mail Stop 54-1 Aerospace Technologist in Data Systems, Information and Signal Processing Branch (LCI), 21000 Brookpark Road/Mail Stop 54-1 Research Aerospace Technologist in Data Systems, Networking and Architectures Branch (LCA), 21000 Brookpark Road/Mail Stop 54-1 Research Aerospace Technologist in Telecommunications, Information and Signal Processing Branch (LCI), 21000 Brookpark Road/Mail Stop 54-1 Aerospace Technologist in Mechanical Components, (LMT), 21000 Brookpark Road/Mail Stop 86-2 to establish beam tracking, but eventually beacon-less pointing will be developed. Investments in technologies to implement autonomous on-board navigation (and maneuvering) will permit a reduction in dependence on ground-based tracking, ranging, trajectory/orbit/attitude determination and maneuver planning support functions resulting in increased intelligence and autonomy of the complete payload. Innovative approaches include exploiting the optical communications terminal to perform navigational measurements such as star sighting, or a star tracker technology developed to process images at very high data rates. This paper discusses how such a beaconless strategy may be incorporated to work with the proposed hybrid communications system, and highlights the synergistic benefit to both communication and navigation functions for the purpose of decreased size, mass and power burden to users. A common constraint between both deep space and near Earth scenarios is mass. As elegant as a proposed optical communications solution may be, it must be shown that the final product is not so cumbersome as to outweigh the benefits, and that includes the necessary RF technology to complete the full communications payload. We establish a stringent goal of compressing the aforementioned highly capable hybrid RF/optical system into a package which installs within a comparable size, mass, and power envelope as the telecommunications subsystem of Mars Reconnaissance Orbiter (MRO). The goal of this paper is to demonstrate that with modern technology our goal is feasible and therefore has a place in today’s space data systems as well as building a bridge to tomorrow’s.