Historical accounts depict NASA's interactions with American citizens beyond government agencies and aerospace firms since the 1950s and 1960s as efforts to 'sell' its human space flight initiatives and to position external publics as would-be observers, consumers, and supporters of such activities. Characterizing citizens solely as celebrants of NASA's successes, however, masks the myriad publics, engagement modes, and influences that comprised NASA's efforts to forge connections between human space flight and citizens after Apollo 11 culminated. While corroborating the premise that NASA constantly seeks public and political approval for its costly human space programs, I argue that maintaining legitimacy in light of shifting social attitudes, political priorities, and divided interest in space flight required NASA to reconsider how to serve and engage external publics vis-à-vis its next major human space program, the Space Shuttle. Adopting a sociotechnical imaginary featuring the Shuttle as a versatile technology that promised something for everyone, NASA sought to engage citizens with the Shuttle in ways appealing to their varied, expressed interests and became dependent on some publics' direct involvement to render the vehicle viable economically, socially, and politically. NASA's ability and willingness to democratize the Shuttle proved difficult to sustain, however, as concerns evolved following the Challenger accident among NASA personnel, political officials, and external publics about the Shuttle's purpose, value, safety, and propriety. Mapping the publics and engagement modes NASA regarded as crucial to the Shuttle's legitimacy, this case study exposes the visions of public accountability and other influences -- including changing perceptions of a technology -- that can govern how technoscientific institutions perceive and engage various external publics. Doing so illuminates the prospects and challenges associated with democratizing decisions and uses for space and, perhaps, other technologies managed by U.S. government agencies while suggesting a new pathway for scholarly inquiry regarding interactions between technoscientific institutions and external publics. Expanding NASA's historical narrative, this study demonstrates that entities not typically recognized as space program contributors played significant roles in shaping the Shuttle program, substantively and culturally. Conceptualizing and valuing external publics in these ways may prove key for NASA to sustain human space flight going forward. / Ph. D.