| Summary: | The development of free-space optical communication (FSOC) systems for space is key to enabling orders of magnitude more bandwidth and throughput for space communication systems. In addition, the recent developments in CubeSat technology can enable significant new small satellite capabilities. This technology has successfully been implemented and demonstrated for optical downlinks on the CubeSat platform, but work remains toward enabling lower-cost terminals as well as developing and demonstrating optical crosslink terminals. In this thesis, advancements are made in the development of CubeSat-scale optical communication terminals through two efforts: First is hardware demonstration and, second is modeling tools for and analysis of free-space optical communication terminals for interfacing with constellations. The first effort, hardware demonstration, involves contributions to the NASAsponsored CubeSat Laser Infrared Crosslink (CLICK) program in designing, building, and operating optical communication terminals in space on both the CLICK-A and CLICK-B/C terminals. The 1.2U CLICK-A downlink terminal, whose goal is to establish a 10 Mbps link to a low-cost portable 28 cm optical ground station called PorTeL (Portable Telescope for Lasercom), operated in space to demonstrate key technologies for risk reduction of the CLICK-B/C crosslink terminal. We present the f irst results of in-space operation of a microelectromechanical systems (MEMS) fine steering mirror (FSM), used for precision pointing of the space terminal. This mirror, used within a novel optical design, enabled the terminal to correct for an average blind spacecraft pointing error of 8.494 mrad and maintain a total RMS pointing error of 0.164 mrad, equal to-0.194 dB of pointing loss of the 1.3 mrad FWHM transit beam, after initial blind pointing error correction across three optical downlink experiments. Key contributions are also made for the flight build of the 1.5U CLICKB/C terminals, whose goal is to establish a 20 Mbps intersatellite optical crosslink at separations from 25 to 580 km. The developments primarily focus on the optical bench assembly, upon which all the free-space optics used for pointing control and full-duplex communications on the terminal are mounted. Optical ground support equipment for testing the performance of the terminal is developed and utilized to confirm the as-designed 1/𝑒² beam divergence of 0.120 mrad has been achieved in a prototype assembly of the optical bench. The second modeling effort involves the development of orbit and link modeling tools for designing CubeSat-scale optical communication terminals to communicate with FSOC-enabled proliferated low Earth orbit (pLEO) constellations. In addition to the physical aspects of the laser beam pointing, the architectures used for delivery of CubeSat-collected data to its final destination can significantly impact its utility. An interesting new architecture has been recently enabled with the advent of pLEO constellations where their networking infrastructure can be implemented as a relay and downlink communication architecture with the potential to dramatically increase link availability time for small satellites. While this infrastructure provides a potential new architecture for satellites in LEO to use for communication, the link dynamics between the satellites that comprise the constellation and external LEO satellites and are not intuitive or well studied. The modeling tools developed are used to analyze the link dynamics between satellites in these constellations and external (non-constellation) satellites in typical orbits used by Earth observation missions. This analysis determines the geometric link availability and calculates how long windows of link availability windows persist. The pLEO constellations analyzed include the first generation of SpaceX Starlink, Amazon Project Kuiper, OneWeb, and the Space Development Agency Proliferated Warfighter Space Architecture Tranche 1 Transport Layer. Results from the modeling show which constellation designs are better suited for this type of external link architecture with certain constellations enabling continuous link availability for external satellites in both sun-synchronous and mid-inclination orbits at range and lateral velocity limits suitable for CubeSat-scale terminals. A link modeling tool is developed to determine the driving design choices for this CubeSat-scale optical crosslink terminal. The results from these orbit and link modeling tools are used in the development of link budgets that support the feasibility of CubeSat-scale optical communication terminals to communicate with FSOC-enabled pLEO constellations. The technological advancements detailed in this thesis encompass the in-space demonstration of technology to reduce pointing loss, optical subassembly design validation for an optical crosslink demonstration, and the development of link modeling capabilities for a novel optical data relay architecture within the field of CubeSat communications. These developments contribute to the further deployment of CubeSat-scale optical communication terminals for both downlinks and crosslinks. This technology has the potential to significantly increase connectivity for CubeSatscale spacecraft and revolutionize spacecraft operations in low Earth orbit.
|
|---|