Thus, the thermal conversion systems are clearly more complex than the photovoltaic systems in terms of construction, operation and maintenance. Nevertheless, the efficiency and terrestrial mastery of these techniques lead to the consideration of their potential space applications. Transportation Access to space today costs approximately $ 10,000/kg to Low Earth Orbit (LEO): this is obviously only acceptable for very small-scale technology demonstrations. New launch systems are needed to bring about significant reductions in launch costs and to multiply launch rates. No doubt there are promising possibilities for meeting these objectives. Among these are NASP, IIOTOL, Sanger and SSTO. New technologies are being explored: electromagnetic launch systems, laser-powered launchers, and so on. All this is constructive and necessary, but the practical outcomes will only be visible at the start of the coming millennium. Energy Transmission Microwave power beaming is already well-developed at wavelengths of 2.45 GHz (DC satellite to DC utility bus > 60 %) but it requires large transmitting and receiving antennae (rectennae). It is therefore also appropriate to carry out developments in the field of sub-millimeter wavelengths. The use of lasers with wavelengths approximately 1000 times shorter than submillimeter waves leads to a virtually negligible dispersion phenomenon and thus to a considerable reduction in the size of the antennae. Admittedly, the efficiency of laser transmission is lower than microwave transmission at present. Within perhaps ten or fifteen years, further advances to improve laser beaming can be expected. There are other challenges to be overcome such as wavelength selection for safety and for optimum transmission through the atmosphere. Perspectives on Extraterrestrial Materials The particular richness of the Moon’s surface in elements such as iron, silicon, oxygen, etc., and helium 3 and the gradual overcoming of the space transport problem to and from the Moon lead to proposals for major new scenarios : construction of solar power satellites from the Moon, construction of power stations on the Moon’s surface, tapping of lunar helium 3 for terrestrial energy production using fusion. The first approach would use lunar raw materials to construct a large solar power satellite in geosynchronous Earth orbit capable of beaming thousands of megawatts of power to Earth continuously day or night. The use of lunar material would reduce by up to a factor of 50 the number of launches required from the Earth to
RkJQdWJsaXNoZXIy MTU5NjU0Mg==