29 been demonstrated many times and in-space power beaming was demonstrated by the Naval Research Lab (NRL) in March 2023 (Hamisevicz, 2023). Beaming from space to Earth was first demonstrated in June 2023 (Caltech 2023), at a very small experimental scale. There is additional active U.S. federal research aimed at developing advanced power beaming capabilities. The Defense Advanced Research Projects Agency (DARPA, 2022) Persistent Optical Wireless Energy Relay (POWER) program is focused on power beaming for terrestrial applications, while the Air Force Research Laboratory (AFRL) is developing an in-space power beaming experiment. NASA’s efforts are currently focused on research rather than technology development, examples being the NASA Innovative Advanced Concepts (NIAC) Low TRL concept for power beaming on Venus (Brandon, et al., 2020) and Lunar Surface Technology Research (LusTR) Beamed Lunar Power on the Moon concept (Lubin, 2021). Other countries, such as Japan and South Korea, are working on power beaming. Japan (Kawahara, 2023) plans to test beaming energy from space to Earth in 2025, for example. International collaboration could speed up development of key SBSP technologies. 5.5 Ongoing Improvements to SBSP Economic Needs It is important to note the significant overlap between technical and economic opportunities as they relate to SBSP. These technologies, while not directly required for SBSP operation, would make SBSP more cost effective. 5.5.1 Electric Propulsion Orbital Transfer Using EP to transport SBSP payloads from LEO to GEO will significantly decrease the number of launches, in turn decreasing overall system cost as well as GHG emissions. EP for orbital transfers is a proven technology in use by GEO satellite operators seeking to reduce launch costs in exchange for a longer travel time (de Selding, 2013) (Werner, 2018). However, there is no history of moving so much mass from LEO to GEO and this may require EP capabilities that do not exist today. Currently, several companies have small space tugs with EP, such as Spaceflight’s Sherpa-LTE Orbital Transfer Vehicle (OTV), Starfish Space’s Otter, Momentus’ Vigoride, and Atomos Space’s Proton and Quark OTVs. Exolaunch’s Reliant eco-friendly space-tug vehicle has a “Pro” version that combines electric and green propulsion. Sherpa-LTE by 2022 had achieved its 300th on-orbit burn. These tugs are sized for satellites that have two orders of magnitude less mass than could be launched by a single Starship rocket. Hybrid electric and chemical OTVs were not explored in this study but could offer a faster solution that is not significantly worse for the environment than conventional chemical systems.
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