pleted modules could be “self-powered” to geosynchronous orbit. The electrical output of less than 20% of the satellite module solar array would provide sufficient electrical power to panels of ion-driven electric propulsion rocket engines. The remaining 80% of the array on the satellite module would remain protected from the Van Allen Belt radiation. While this approach might be estimated to be cost competitive with the independent electric orbital transfer vehicle, it does require construction in low Earth orbit with its attendant problems. The possible environmental effects of the launch vehicle emissions are primarily related to the launch vehicle size and rate of use necessary to construct a Solar Power Satellite network. The construction of a 5000 MW satellite will require about 200 flights of the heavy-lift launch vehicle to low Earth orbit. The resulting combustion products of 272,000 Mg (300,000 tons) of methane and 54,000 Mg (60,000 tons) of hydrogen are primarily carbon dioxide and water vapor. For perspective, an equivalent amount would be produced by fossil-fired powerplants of equal electrical generating capacity to the satellite in about 7 months of operation. If the combustion products predicted for Solar Power Satellite launch activity are compared with those produced by automobiles, gas flaring in oil production, industrial boiler use, etc., it is apparent that a large Solar Power Satellite launch activity would not be a significant contributor to the total combustion products generated by our present economy. The launch vehicle, unlike ground sources, traverses the atmosphere and distributes its exhaust products over a range of altitudes. The methane-fueled first stage operates to about a 50-km (31 statute mile) altitude and the hydrogen-fueled second stage completes the insertion into orbit at an altitude of about 120 km (75 statute miles). Water vapor and hot hydrogen exhaust products are therefore injected into the lower ionosphere (D and E layers) but not into the “F” region at 200 to 300 km (124 to 186 statute miles) altitude. Specific environmental studies (18, 19) are now underway to further identify and quantify the effects of launch vehicle and orbital transfer vehicle emissions. All systems studies conducted to date have shown that the cost of the transportation of construction material to space from Earth will be a significant cost element of a commercial system. Because of cost considerations, this new system, illustrated in Fig. 14, must be designed and operated in a manner to greatly reduce transportation costs. The approach to achieving this goal involves total reusability and a high utilization rate of the space transportation system in a manner similar to commercial aircraft operations. Fortunately, the nation has already embarked on a program of space transportation system reusability. The reusable Shuttle Orbiter (Fig. 15) has been in development for the last 6 years. A major goal of this program is to reduce space transportation costs, and the approach to this reduction in recovery and reuse of the Orbiter component of the Shuttle system. The Shuttle system is scheduled for its first orbital test in 1980. It will be the primary U.S. space transportation system of the 1980's. The Shuttle Program will provide quantitative data on the economics of reusable space systems and thus contribute valuable information for Solar Power Satellite cost assessment. The Shuttle system with its crew of 7, its payload capability of 27 Mg (30 tons), and its large volume will also provide a vital capability for the development and demonstration of various Solar Power Satellite technologies, as well as providing pertinent economic information.
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