5. Space Transportation System Configuration, Staging and Performance

In all space missions, the main objective during the design phase is to define a suitable STS configuration which has the needed capability to inject the defined spacecraft into the specified orbit. To achieve these objectives, STS is configured with suitable propulsion systems to impart the required equivalent velocity to the satellite, after accounting for the various velocity losses the vehicle encounters during its mission. This chapter discusses the STS configuration, selection criteria to provide the required energy to inject the satellite into the orbit, while meeting the various other subsystems requirements. The optimum STS configuration has to provide the maximum performance with respect to the vehicle size, maximum reliability, reduced unit cost for the vehicle, minimum cost for design and development and a reasonable schedule for the realization of the vehicle. To arrive at an optimum vehicle sizing and configuration, exhaustive trade-off studies are required. The studies have to address existing technologies and advanced new technologies with respect to performance improvements, performance requirements, demonstrations, process technologies, advanced technology developments, overall vehicle reliability, unit cost of the vehicle, technology risks, increased development cost and schedule, limitations on the realization of the systems, etc. The selection methodology for STS configuration, design guidelines and the various processes involved in the design of an optimum configuration are discussed in this chapter. Design strategies for various vehicle subsystems which influence the vehicle performance and the vehicle configuration are highlighted. The constraints imposed by the existing technology limitations and the possible future technology improvements are explained. The requirements of multi-staging and their relative merits and demerits are highlighted. The optimum staging aspects, the design sensitivities and various factors which influence the vehicle performance are elaborated, Attention to ground and launch operations while finalising the configuration of the vehicle is of utmost importance because it has large influence on the technology options for the vehicle, schedule and cost. The infrastructure needed for ground operations like launch complex, launch tower, propellant servicing facilities, etc. has to be closely linked to the vehicle configuration. Therefore these aspects are addressed in brief at the end of the chapter.