SPS Feasability Study SD76SA0239-2

4.4 PAYLOADS INTEGRATION Delivery of cargo for SPS assembly must be phased properly with the demand rates for construction materials. The problem is made more difficult by the volume and mass constraints of any ELV inasmuch as certain hardware elements are of some minimum irreducible size and others of very low density. Analysis of the SPS components point immediately to the microwave (MW) antenna subarray panels with a packaging density of 4 kg/m3 ( 0.25 lb/ft^). For the MW antenna concept described in Section 3, each 30-m by 30-m subarray section is comprised of nine 10-m by 10-m subarrays panels, and each subarray contains fifty 1-m by 2-m RCR's. For purposes of minimizing on-orbit installation, assembly and checkout operations, every attempt should be pursued in integrating the largest dimension possible of the MW antenna panels. This was the approach taken in sizing the cargo bay for the selected reference ELV. Figure 4.4-1 illustrates the dimensions chosen as representative of the reference ELV payload compartment. For a payload of 91,000 kg, a packaging density of 50.5 kg/m3 (3.2 lb/ft3) results. Calculations were made of the MW antenna subarray panels with amplitrons attached and an average payload packaging arrangement could be achieved as shown. This, of course, is a "mixed" cargo integrated with either structures materials or with 25-m long rolls of solar blankets and reflectors. Of the 300 OTV cargo flights required, 240 required different cargo materials to be integrated with the low-density MW antenna elements. This is reflected in Figure 4.4-2, which shows the cumulative cargo delivered over the 75-day period starting with activation of the structures base. Many iterations were required between construction sequencing and cargo traffic models before acceptable results were obtained. In terms of supply and demand of cargo materials, the traffic model shown in Figure 4.4-3 ultimately evolved. It should be noted that the supply lines exceed the demand with sufficient margin to account for operational delays as they occur. i Figure 4.4-1. Payload Integration 151