Strategies for Launch and Assembly of Modular Spacecraft

NASA’s human lunar and Mars exploration program requires a new transportation system between Earth and the Moon or Mars. In recent years, unfortunately, human space exploration programs have faced myriad political, technical, and financial difficulties. In order to avoid such problems, future human space exploration programs should be designed from the start for affordability. This thesis addresses one aspect of affordable exploration programs by tackling the issue of high costs for access to space. While launch vehicle trades for exploration programs are relatively well understood, on-orbit assembly has been given much less attention, but is an equally important component of the infrastructure enabling human access to space. Two separate but related perspectives on in-space assembly of modular spacecraft are provided: first, the coupling between launch vehicle selection, vehicle design, and on-orbit assembly is explored to provide a quantitative understanding of this combined tradespace; and second, a number of on-orbit assembly methods are analyzed in order to understand the potential value of a reusable assembly support infrastructure. Within the first topic, a quantitative enumeration of the launcher-assembly tradespace (in terms of both cost and risk) is provided based on a generalizable process for generating spacecraft modules and launch manifests from a transportation architecture. An optimal module size and launcher capability is found for a sample architecture at 82 metric tons; a 28-mt EELV emerges as another good option. The results show that the spacecraft design, assembly planning, and launcher selection are highly coupled and should be considered together, rather than separately. Within the second topic, four separate assembly strategies involving module self-assembly, tugbased assembly, and in-space refueling are modeled and compared in terms of mass-toorbit requirements for various on-orbit assembly tasks. Results show that the assembly strategy has a significant impact on overall launch mass, and reusable space tugs with inspace refueling can significantly reduce the required launch mass for on-orbit assembly. This thesis thus examines a broad but focused set of issues associated with on-orbit assembly of next-generation modular spacecraft. Thesis supervisor: Olivier L. de Weck Title: Associate Professor of Aeronautics and Astronautics and Engineering Systems