24 Using baseline assumptions, the SBSP systems assessed perform competitively on GHG emissions when compared to terrestrial forms of renewable electricity production. It is important to note, however, that the effects of burning rocket fuel in the upper atmosphere are not yet quantified by science (NOAA, 2022), but widely assumed to be much worse than burning these fuels on the ground. Given the large number of launches required, we would expect the measurable impacts of these systems to rise as we learn more. Manufacturing at scale for these massive systems and thousands of launches of rockets using methane-oxygen fuels produce the most GHG emissions. Options to reduce GHG emissions: 1. Reducing the number of launches by using EP for orbital transfer, deploying the system at a lower altitude, or using non-combustive launch technologies (e.g. spin launch or magnetic launch) would reduce launch related emissions. Fewer launches also would reduce the environmental footprint associated with launch vehicle manufacturing, even taking reusability into account. 2. Although the baseline assessment assumes autonomy is fully developed, it is important to note the significant reduction in emissions this provides during assembly and operations. 3. On-orbit manufacturing of photovoltaic arrays and other components would remove manufacturing emissions that would otherwise occur on Earth. 4. Any technologies that reduce the mass of an SBSP system would reduce both the launches and manufacturing required to build, assemble, and maintain the system. 5.0 Challenges and Opportunities Fielding either of the two SBSP reference designs analyzed in this report will require major capability advances in three key areas: 1) ISAM, 2) autonomous distributed systems, and 3) power beaming. 5.1 Challenges to Operational System Development Across all technology areas, the single most distinguishing factor is the sheer scale of operations, mass, and coordination required to deploy systems larger and more massive than anything built in space before, except perhaps the combined mass and area of very large satellite constellations. 5.1.1 Large-scale ISAM Capability Challenges ISAM capabilities required for developing and operating an SBSP system (ConOps Assemble and Maintain phases) are not currently available. There are few existing commercial capabilities for activities such as assembly, refueling, in-space manufacturing, and formation flying. The market for ISAM is unproven, with many proposed technologies as yet untested in space. The ISAM business case has development and operational risks that may limit private investment. Unless the Government steps in to support this nascent industry, services will be limited and expensive.
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