3) the analysis of the individual production processes requires a precise knowledge and data of the production steps but it is the most accurate procedure to determine the ACE. As far as possible the latter method was used for the studies presented in this paper. The only major exception was the evaluation of the expendable launcher system's structure. In this case the energy cost analysis was used. This can be considered as a conservative approach yielding higher than actual ACE values. The impact of this approximation on the obtained results is less than 10 %. Another important factor is the energetic amortization time (EAT). It is defined as ACE divided by the energy delivered by the power system per year. It describes after how many years the energetic break-even point will be reached, starting from that day when the system is operational, i.e. the time for production, transportation and final installation is not included. The transfer of a SPS from LEO to GEO with electric propulsion will take in the order of one year. During this time the solar power system is operating and the solar cells are degraded by high energy radiation. Therefore, when comparing the EAT with the lifetime of the SPS this year for climbing up to the final orbit should be kept in mind. In this paper the EAT is always counted from start of operation. Figure 2 illustrates these relations. Dividing the lifetime by EAT yields the energy recovery factor (ERF) of the power system.
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