5.3.5 Ionospheric Interaction Technology Item — Ionospheric Interaction Criticality — Critical to program success Each SPS satellite transmits large amounts of microwave power through the ionosphere. Interactions may interfere with the beam structure, increasing spill-over losses and reducing transmission efficiency. In addition, the structure of the ionosphere may be altered leading to unknown environmental affects. Present Capability: Numerous existing microwave systems are transmitting power through the ionosphere. However, none are transmitting power at levels close to that of SPS. The highest powers in use are transmitted by large radar systems. Required Capability: Interaction between high power microwave beams and the ionosphere must be sufficiently understood to meet SPS requirements. Power of several gigawatts must be transmitted through a region of the ionosphere several kilometers across without adverse affects on the beam structure or the ionosphere. Development Plan: Analytical studies of ionosphere interactions are needed to predict conditions for satisfactory transmissions. Experimental data are required to verify the adequacy of the prediction. 5.3.6 Transportation Technology Item — Low-Cost Earth Launch Vehicle Criticality — Critical to program success Deployment of each SPS vehicle requires the transport of 27 x 10$ kg or more of satellite material to low-earth orbit. Necessary construction equipment and interorbit propulsion will increase the required materials to low orbit by a factor of two. These transportation requirements can be met only with a new earth launch transportation system that is able to move large quantities of materials at high rates and low cost. Present Capability: The present capability for earth launch has been limited to expendable boosters ranging from Thor to the Saturn V. Expendable boosters are unable to transport large quantities of materials on a continuing basis because of high costs. Beginning in the early 1980's, Shuttle will be able to transport quantities of materials more economically. However, its 30,000-kg payload limit and turn around times are not sufficient for meeting SPS mass flow requirements. Launch costs for all of this launch vehicle booster may be in excess of $440/kg transported to low-earth orbit. Engineering studies have examined various concepts for large boosters capable of transporting large payloads to low-earth orbit at low cost. Payloads of 250 to 300 metric tons can be placed in low-earth orbit at projected costs as low as $33/kg.
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