effective radiation of waste heat. The strips can be coiled for transport and deployed and installed by construction equipment with little direct labor. Connection of power busses to solar cell blankets is less amenable to automation and may involve more CSE. In summary, construction of the SPS represents a significant technology challenge because the size and operational location have no valid analogies. The number of parameters and options in developing concepts is almost unlimited. Analysis of construction has been concentrated in defining feasible approaches. A technology base must be developed to establish the credibility of construction techniques and of productivity and cost estimates. 2. Rectenna Construction The initial concept of an SPS rectenna advanced by Raytheon utilized a 10 km diameter rectenna with its groundplane perpendicular to the microwave beam. This was accomplished by segmenting the groundplane into a series of tilted (relative to the ground) panels. An in-house study (ref. 2) was conducted at JSC to further define the Raytheon concept so that materials requirements and costs could be analyzed. Primary ground rules for the study were: (1) groundplane must be perpendicular to the microwave beam, (2) maintenance of the entire area is required, (3) land must be available for other purposes, (4) terrain is flat, and (5) location is near the Houston area. The preliminary design selected was a very simple conventional structural concept and no attempt was made to optimize the structure as to concept, weight, constructability, or cost. Material selected for the structure was basically structural aluminum shapes. The unit cost for a 5 GW rectenna system was $0.60/ft based on structural materials, construction labor, and site preparation 1975 cost indexes. The quantities of aluminum required to construct the number of rectennas projected for the year 2000 would result in a 7 percent increase in the projected annual United States aluminum demand for the year 2000. Also, the energy required to produce the aluminum would require a longer payback time than steel. Because of this high aluminum usage, a small study contract was initiated
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