Figure 1.2-1. SPS Reference Configuration In-depth studies had been conducted by Raytheon for NASA of the microwave power transmission system (MPTS), and Rockwell proposed to use those concepts, weights, and cost data for this study. Design concepts for the MW antenna structure, however, were studied in two other NASA-funded efforts by Grumman Aerospace Corporation and the Martin Marietta Corporation. Both studies had developed a concept for a box-grid matrix-type structure to be assembled in orbit using relatively short-length beams that were fabricated either with on-orbit automated modules (Grumman) or pre-fabricated on the ground (Martin-Marietta). In both cases, on-orbit assembly times appeared as an area where significant reductions could be made by taking a different design approach. The reference structural concept proposed was a compression frame-tension web configuration which was under company-sponsored investigation. The compression frame structure would be roll-formed in orbit with a continuous-beam fabricator concept that was also being studied at Rockwell. Within the stated study guidelines, ground rules and assumptions, two variations occurred during the study; both resulting in added data. The first of these is an investigation conducted by the Autonetics Division of Rockwell to develop alternative approaches to the microwave power transmission system. This is discussed in Section 2.3. The second study addition was introduced when considering the transportation system requirements for SPS. An earth launch vehicle (ELV) concept new to SPS studies has been selected for its performance potential and operational versatility (Section 4.1). It should be noted that each of these alternatives represents major design challenges and needs considerable in-depth study. They are included in the study, however, because of the highly significant advantages to an SPS program should future efforts prove them feasible.