As an example. Dr. K. K. Reinhartz of the European Space Agency, Noordwijk, Netherlands, called attention to Europe’s energy future. Europe will continue to import at least 50% of its energy, mainly in the form of oil, although substantial nuclear energy production is anticipated by the year 2000. Chief among environmental considerations cited by Mr. Pelegrin is the exponential increase of carbon dioxide in the atmosphere which will enhance the “glass-house effect.” Major availability of solar energy would help greatly to reduce this dangerous condition. How attractive is the SPS from an economic point of view? Evidently, the earliest possible date for the launching of an SPS would be by the year 2000. It is difficult, if not impossible, to establish a clear picture of the cost of energy generated by an SPS at that time and compare it reasonably with yet unknown energy costs from other sources. Nevertheless, cost figures presented by C. Covington of NASA Johnson Space Center, Houston TX, seem to indicate that the SPS might eventually be competitive with coal-fired plants. Similar projections were made by various other speakers during the discussions. One of the unknown quantities at this time is the cost of the conversion devices. I.V. Franklin of British Aerospace Dynamics Group, Filton-Bristol, U.K., estimated the cost per square meter of silicon photovoltaic cells to be about $35, while GaAlAs cells, which require concentrators, would cost about $71. On the other hand, the former would require periodic annealing at about 500°C in space. Mr. Franklin also considered the problem of the supply of cells. The number of silicon cells, each 7.44 x 6.55 cm in size, required by one SPS is about 10“’, while present capacity for production of all types of solar cells is only about 2.5 x 10G per year. Dr. J. Rath of AEG-Telefunken, Wedel, FRG, elaborated on the same question. It would require nearly doubling of the annual production of photovoltaic cells for each of the next fifteen years to reach the requirement for one SPS. Mr. Covington estimated the development cost of the first SPS of 5 GW capacity to be about $38 billion to $40 billion and the construction and launching about $32 billion to $43 billion. Further satellites would cost about $12 billion. An estimate quoted by Dr. Reinhartz set the cost at $102 billion with the cost of subsequent satellites to be about $11.5 billion each. Although these figures are such as to stagger the imagination, they must be compared with the possible cost of construction of new power stations. In Europe alone, that cost may reach $80 billion per year. Transportation of the satellite into orbit affects, of course, the ultimate cost of an SPS. The NASA scenario, which is merely a study and not an immutable plan, considers launching of manned units into low earth orbit (LEO) and from there into the geostationary orbit (GEO). On the other hand. Dr. D. E. Koelle of MBB Space Division, Ottobrunn. FRG, presented a study according to which unmanned ballistic vehicles placed into GEO would be more economical mainly because of the absence of life-support systems. The important question of energy payback was discussed in some detail. Dr. Glaser estimated that, considering the life of an SPS to be 30 years, the energy payback period would lie between two and six years, depending on the type of photovoltaic conversion system chosen. A detailed presentation of technical aspects of the SPS was given by C. Covington, who covered the NASA study at its present stage. He stressed the tentative nature of the conclusions which must be considered to be flexible. The NASA study looks at a 5 GW SPS placed in GEO. The structure would consist of graphite composites and would be assembled in space by equipment similar to that developed by Grumman Corporation. Attitude changes for optimal coverage would
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