Ground Optical Coherent Array Terminal

The US Space Development Agency (SDA) needs cost-effective high-data-rate communications and navigation knowledge for connecting ground, air, Unmanned Aerial Vehicle (UAV), High Altitude Platform and small spacecraft networks.  Relative Dynamics Inc. (RDI) proposes a Phase I effort to develop theoretical and experimental knowledge to support developing a multiple aperture Ground Optical Coherent ARray Terminal (GOCART) in the Phase II effort to support 10-100 Gbps space-to-ground links with a cost less than $1M per ground terminal and platform or station.  Key areas of interest listed in the BAA that apply to the ground terminal are: Demonstration of a path to 100 Gbps for space-to-space FSOC Development of low-cost, mobile or fixed optical ground terminals (OGTs) Demonstration of enhanced space-to-ground and space-to-air FSOC links Development of compact FSOC systems capable of supporting coherent (e.g., QPSK) and non-coherent (e.g., OOK) optical links. Demonstration of enhanced position, navigation, and timing technology Our design approach includes leveraging commercial telecommunication modular, standardized and high-reliability hardware, investigating designs, components and techniques that are amenable to mass-production and ease of assembly, and using low-maintenance components that are easily replaced or repaired.  The primary GOCART systems are the gimbals/telescopes, the controller and the modem.  The gimballed telescopes, the associated PAT system, and designing for atmospheric mitigation are crucial areas for concepts and technology for cost reduction. RDI will examine lower cost alternatives to adaptive optics for atmospheric turbulence mitigation. We propose the use of a small telescope array as a means for atmospheric turbulence mitigation for both downlinks and uplinks. In addition, the use of piston (delay/phase adjustment), mirror tip/tilt and piezo-electric transducer fiber positioning mechanisms will be studied and analyzed.  For astronomical imaging, an optical “sparse aperture” arrangement can use multiple small apertures to realize the high imaging resolution equivalent to a single large one. To better protect against fading, a system can measure the atmospheric state at the receiver, feed back the atmospheric state to the transmitter, and use that state information to couple into the spatial mode that propagates the most efficiently.   RDI will further investigate the use of a sparse aperture system with feedback for the ground-LEO optical communication links. Photonic lanterns  provide low-loss interfaces between single-mode and multimode systems, where the precise optical mapping between cores and individual modes is unimportant. . RDI will investigate the performance-cost trade space for the use of photonic lanterns in GOCART. RDI will investigate and leverage the use of  commercial telecommunications direct detection and coherent modems.  We will investigate both incoherent and digital coherent combining.