62 Approach to GHG Emissions Calculations Figure 17. SBSP GHG emissions calculations graphical summary GHG Emissions gCO2eq./kWh = (Σ total kg * gCO2eq./kg + total m2 * gCO2eq./m2 + total $ * gCO2e.q/$) / (system electricity generation * operational years * hours in a year) The Aerospace Corporation provided expert assessment of the bill of materials for modules, launch vehicles, servicers, and the ground segment. This gave us high-level estimates of how much steel, circuitry, or other material inputs were required for each hardware element, which in turn allowed us to estimate the total materials required. However, several factors, such as transportation, processing, assembly, and more were not being accounted for. We spoke with an expert at the National Renewable Energy Laboratory (NREL) who suggested we consider the Economic Input Output Life Cycle Assessment (EIO-LCA) (Cobas-Flores, 1998) method. This method is based on aggregate sector-level economic data, such as the North American Industry Classification System (NAICS). Input-output analysis, developed by Wassily Leontief (Leontif, 1951) is a technique for capturing economy-wide interdependencies. For example, automobile manufacturing needs steel, and steel needs iron ore and coal, which in turn need automobiles to transport them from mines to factories. This method allows for a far more accurate understanding of changes to economic outputs of individual sectors as they ripple across the economy. Data collected on environmental impacts by organizations like the Environmental Protection Agency (EPA) may also be organized by the same industry classification codes. By adding environmental impact data to quantified direct and indirect economic inputs of purchases, environmental implications for economic activities and their dependencies are derived. We use a mix of mass and spend-based assessments, preferring mass wherever possible. Carnegie Melon University and DoD
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