As the Space Shuttle program draws to a close, NASA faces the challenge of developing thetransportation system for future human space exploration. Given current debates on the goals ofthe space program, it is critical to ensure that comprehensive but transparent exploration ofavailable options for future launch vehicle developments is available.Evaluation of launch architectures requires the assessment of options over a range ofdimensions, which can be broadly grouped into technical performance, time to initial capability,cost, and satisfaction of stakeholders' various needs. The challenge is to fairly compare a broadrange of architectures across these dimensions, in a way that empowers high level decisionmakers.This paper describes a tradespace exploration study which provides preliminary design offamilies, by exploring hundreds of concepts using coarse system evaluation metrics. The paperinvestigates the trade-offs associated with stage propellant selection, launch vehicle configurationand other relevant design parameters. Furthermore, the study considers potential LEO-classvehicles derived from the heavy lift vehicle in order to deliver early benefit from the heavy liftvehicle and provide an ongoing affordable LEO service.Architectures are evaluated through a broad set of metrics, including engineering performance,compliance to stakeholder needs and goals, compatibility with existing ground infrastructure andoff-design performance. The technical assessment methodology is validated against existinglaunch vehicles. The paper demonstrates how a field of 192 possible launch vehicles can betransparently reduced to seven possible designs on technical considerations, almost all of whichare represented by particular viewpoints in the current debate, and how further narrowing thedesign space requires weighting competing stakeholder priorities. The preferred conceptsemerging from the study are a 2.5 stage 7/8.4m diameter all-cryogenic vehicle and a 7/8.4mdiameter 2.5 stage LOX/LH2 vehicle with solid boosters as preferred baselines for furtherconceptual study. The paper further shows how conducting this coarse tradespace explorationearly in the process can inform decision-making on the future space transportation infrastructure.The paper closes with some suggestions for future work in the area.
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