Creating a NASA Deep Space Optical Communications System

Abstract

We expect data rates from deep space missions to increase by approximately one order of magnitude per decade for the next 50 years. The first order of magnitude improvement will come from existing plans for radio frequency (RF) communications including enhancements to both spacecraft and Deep Space Network (DSN) facilities. The next two orders of magnitude are predicted to come from the introduction of deep space optical communications. Studies indicate that optical receive apertures of between 8 and 12 m are desired. The large cost of dedicated receive telescopes makes this method unrealistic—at least in the near-term. The cost of large optical ground terminals is driven primarily by the cost of the optics and by the cost of a stable structure for the telescope. We propose a novel hybrid design in which existing DSN 34 m beam waveguide (BWG) radio antennas can be modified to include an 8 m equivalent optical primary. By utilizing a low-cost segmented spherical mirror optical design, pioneered by the optical astronomical community, and by exploiting the already existing extremely stable large radio aperture structures in the DSN, we can minimize both of these cost drivers for implementing large optical communications ground terminals. Two collocated hybrid RF/optical antennas could be arrayed to synthesize the performance of an 11.3 m receive aperture to support more capable or more distant space missions or used separately to communicate with two optical spacecraft simultaneously. NASA is currently building six new 34 m BWG antennas in the DSN. The final two are planned to be built at the DSN Goldstone, California, and Canberra complexes. We are now investigating building these last two antennas as RF/optical hybrids. By delaying their operational dates by two years, we would be able to add the 8 m optical receive capability for these two antennas while fitting within existing budgetary constraints. This paper, which derives material from a paper the authors delivered at the SpaceOps 2018 conference [1], describes the hybrid antenna design, the technical challenges being addressed, and plan for using this concept, together with ongoing work on optical flight terminals, to infuse operation optical communications into deep space missions. All included figures are reproduced here with permission of the American Institute of Aeronautics and Astronautics (AIAA) the publishers of the transactions of SpaceOps.