required power output. The other subsystems, except the storage, are less dependent on the size of the SPS. For Earth to LEO transportation either expendable heavy launch vehicles (HLV) with a payload in the order of 100 Mg or fully reusable systems with a pay load of around 10 Mg have been considered. The studies presented in this paper were based on the HLV option, because it turned out to be the less energy consuming option although with little impact on the total energy balance. The installation scenario used for these studies is that the components are integrated in LEO to an autonomous system which then spirals upwards to its final orbit propelled by electric propulsion systems driven by electricity from the solar power modules. Consequently, the only energy relevant activities of the installation procedure are associated with the transport of the required propellants, manned missions to LEO and possibly to the final orbit of the SPS. This installation scenario also was the selected baseline for the NASA reference system studies. The infrastructure on Earth consists of a receiver, either a microwave rectenna (receiving antenna) or a photovoltaic or thermal system converting the incoming laser energy to electricity, and an electrical power station which is able to feed the electricity into the electrical net. Terms and Definitions In order to determine the performance of a SPS it is helpful to consider certain values which are defined in this chapter. The accumulated consumed energy (ACE) describes the sum of all amounts of energy required to operate the power system i.e. it includes the energy needed for fabrication, transportation, installation, maintenance etc. The evaluation of ACE can be performed in three ways: 1) the energy cost analysis is based on the assumption that the ACE is reflected in the price of a product. This macro-analysis approximates the ACE with the price of a component in a certain country multiplied with the total primary energy consumption divided by the GNP of that country. The energy cost analysis presents the best guess if no data on the production process is available. 2) the energy input-output analysis considers average branch specific values by determining typical energy flows. This macro- analysis also results in a rough estimation of the ACE.
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