Figure 1.1-1. Study Overview crews needed for assembly. As indicated in the figure, constant iteration was required between these tasks throughout the study. Finally, in the fourth task, cost were compiled, a representative program schedule was developed, and the technical disciplines polled to define critical technology advancements required. 1.2 STUDY GROUND RULES AND ASSUMPTIONS NASA has analyzed potential SPS configurations and systems both in-house and utilizing contractor support. The reference configurations provided conceptual approaches to SPS that were judged to be within a cost-competitive regime. These configurations are called reference concepts as opposed to baseline concepts since the latter designation implies that a relatively firm set of design requirements has been established. Rather than duplicate analyses of existing concepts, Rockwell proposed to study alternatives which offered unique design and operations features not yet pursued in other studies. These alternative features and the rationale behind their choice were described in the proposal. In each case, the alternative feature proposed by Rockwell appeared to offer added cost-effectiveness over the present reference concepts. Further, they represented appropriate alternatives which would be analyzed to generate requirements, resolve design, operational, and developmental issues, and identify problems common to establishing the technical feasibility and economic viability of all concepts. The alternatives adopted for study are tabulated in Table 1.2-1.