1.2.16.3 Energy Requirements There are no consistent and confident data available of the amounts of energy for transportation, manufacturing, support and operation. The reason for this is the fact, that no common base for such investigations has been established yet. Some publications compare only the manufacturing energies of different approaches with each other, while others include transportation without a consideration of operating energies. The total energy payback time is reported in several publications. Because of lack of a common base, these figures vary in a range between 0.5 to approx. 3 years. The most frequently used figures are 1.2 to 1.5 years. 1.2.16.4 Land Requirements The main land requirements are for the rectennas with poten-~ tial buffer zones. One rectenna requires a minimum of 100 km2 and the buffer zones (for limited stay) are not yet defined. Another requirement is for launch and recovery sites. The estimates for this requirement range up to 850 km2. 1.2.17 Programme Planning and Development (References: 76/1,76/2,76/3,76/6,76/7,76/8,76/10,77/3, 77/6,77/9,77/10,77/11,77/14,77/18,77/19,77/21,77/23, 77/24,78/13,78/14,78/15,78/16,78/24,78/34,78/35,78/37, 78/40,78/43,78/45,78/46,78/48,78/55,79/2,79/3.) 1.2.17.1 General This category implies current near term SPS concept evaluation planning as well as long term development phasing including milestones definition. Specifically the logistics planning and technology advancement areas are pointed out. 1.2.17.2 Current DOE/NASA 3-Year Plan Since 1977 a SPS concept development and evaluation programme has been sponsored by DOE (former ERDA) and NASA to identify critical areas of environmental, socioeconomic and technical concerns and to gain a reference system definition for a final SPS programme recommendation in 1980. Figure 2.17.1 presents a rough time schedule of this 3 year plan und shows the proposed milestones.
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