Space Transportation Past and contemporary studies of space transportation provide a broad spectrum of concepts to consider. The key to understanding the potential transportation cost for the reflector is understanding that the size and technology level for most economic transportation systems varies with traffic level. There are two reasons: (1) The amount of research and development which can be amortized is clearly a function of traffic level; and (2) Economies of production and operations improve with increasing traffic. Review of the costs of present-day GEO transportation systems indicates that roughly 5/6 of the cost to GEO is in launch to LEO, the remainder in transport from LEO to GEO. Cost reductions must occur in both segments of the transportation function. Also, increasing the fraction of LEO delivery' mass that ends up as useful payload in GEO has important leverage on cost. An increase of the net useful mass to GEO to 1/2 or more of that delivered to LEO reduces the cost to GEO by almost a factor of 3, other things being equal. This clearly indicates electric propulsion for LEO to GEO transfer. Use of high-power free-electron lasers based on Earth is a promising source of radiation for electric power in cislunar space. Preliminary systems analyses indicate greater economy than either solar or nuclear power, because laser beams can reach intensities of several suns and yield photovoltaic conversion efficiencies greater than 50% at the receiver. Solar characteristics of an electric propulsion system for orbit transfer were estimated based on delivery to LEO of 14 payloads of 50 t. each, along with the propellant needed to deliver it to GEO by electric transfer vehicle. If an equatoral launch site were used, the electric propulsion delta V would be reduced to about 4700 m/sec. The savings could be applied in some combination to shorter trip time and less power for the transfer vehicle. The optimum trip time is about 75 days. The overall transportation cost is estimated as $1700/kg for Earth to LEO and $50 million per trip for orbit transfer. The total launch mass is 1050 t. (including transfer propellant, and there are 14 transfer trips. The grand total transportation cost for one reflector is $1,785 billion for Earth launch and $700 million for transfer operations, resulting in a cost of $2,485 billion. This transport cost presumes very modest advances in launch vehicle technology, but significant advances in electric propulsion technology, primarily in size and power. Performance of the components of the electric propulsion system is in the range of performance demonstrated in the laboratory. Most of the technology advances are assumed to take place in electric propulsion technology. The relatively small size of the electric propulsion system compared to the launch system (20 t. vs. roughly 150 t.) indicates a lower cost.
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