2.1.1.1 Microwave Power Transmission Subsystem (MPTS) The MPTS is the transmission subsystem used in the current NASA reference SPS concept. The system, to be constructed and deployed in geostationary earth orbit (GEO), will be powered by a solar cell array having a platform of approximately 55 sq. km. Table 2.2 provides MPTS details from which the following observations can be made: • The system radiates a large amount of power. • Power density at its highest level near the center of the antenna is a relatively low 2.2 W/cm2 (approximately 16 solar constants), from which workers near the antenna can be shielded for short periods of time. (Figure 2.1 is a plot of maximum power density versus distance from the antenna toward the ground receiver.) • There should be no trouble designing spacecraft that can travel in this beam with passengers aboard. Spacecraft or satellites not designed for,this radiation field could overheat when moving slowly through it- resulting in temporary disability or permanent damage to their electronic systems. Two possibilities exist for weapon use. First, the beam could be defocused and noise introduced to render selected communications ineffective (an electronic warfare weapon). Second, the beam could be directed at ground targets or scanned in a manner to follow spacecraft until overheating occurs, and/or until electronic failure disables the craft or produces a mission abort. 2.1.2 U.S. Military Preparedness Implications The energy problem of the DOD was defined in the January 1977 U.S. Navy 9/ Energy Plan— as follows: The most serious and pervasive threat to long-term national stability is the growing world inadequacy of assured energy resources to support world needs. National security depends on maintaining a worldwide balance of the distribution of energy resources. National security objectives can be achieved only if the United States is thoroughly prepared to meet essential industrial and military energy requirements. Attaining these objectives, deterring armed conflict, producing modern weapons systems, and maintaining the overall readiness of the U.S. military are all keyed to uninterrupted energy supplies. - a radiation level as high as 1.5 W/crn is permitted for aircraft. High speed aircraft flying at low altitude are able to dissipate radiation loads several times this value. (In space there is no air flow across spacecraft surfaces to cool them. Therefore, the radiant heat of the beam must be rejected by the use of reflective surfaces and/or absorption and reradiation.)
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