This dissertation examines the debates and discourses surrounding the Korean Astronaut Program (KAP) using the concepts of sociotechnical imaginaries, sociotechnical vanguards, and the construction of expertise. Based on documentary analysis and oral interviews, this research considers KAP as an example of how the visions of sociotechnical vanguards conflict and their failure to construct a unified sociotechnical imaginary. Furthermore, it contends that the expertization of the Korean astronaut failed because of the public openness of KAP. KAP was proposed by the Ministry of Science and Technology (MOST) and run by the Korea Aerospace Research Institute (KARI). These two sociotechnical vanguards, MOST and KARI, provided different visions to the Korean public sphere, which already ascribed to its own image of an astronaut. MOST imagined the future Korea as a science-loving nation in which especially the next generations would have a strong interest in science and technology. Thus, MOST defined KAP as a science popularizing program and the Korean astronaut as a science popularizer. However, imagining a better Korea with better science and technology, KARI defined KAP as a research program that would lead to human space flight technology and considered the Korean astronaut a space expert. However, in the Korean public sphere, the widely shared expectation was a better Korea with a Korean heroic astronaut, because having a hero similar to that in other countries could position Korea on par with other advanced countries. These three visions conflicted in Korean society during KAP, and none of them succeeded in becoming the dominant sociotechnical imaginary. This elicited severe criticism of KAP and the Korean astronaut. KAP was also a good example of expertization with public openness. Credibility is the most important part of modern scientific practice. Without credibility, scientific experts cannot exercise their authority. Credibility rests on social markers such as academic degrees, track records, and institutional affiliation. However, these social markers are not suddenly assigned to an expert, who spends much time and effort attaining them. Rather, experts are made in a continuous process of improvement. Therefore, this research focuses on the process through which a person becomes an expert in emerging science and proposes the new terminology: expertization. Usually, the expertization process is hidden behind a public image. People do not know how experts obtain social markers, despite believing that these verify expertise. However, when the expertization process open to the public, it could be easily destroyed. KARI tried to position the Korean astronaut as a space expert. The first Korean astronaut did not become an expert overnight, but emerged as such to the Korean public through a selection process, training, and spaceflight. However, unlike other expertization, all steps comprising KAP were broadcast, and the expertization of Dr. Soyeon Yi, the first Korean astronaut, was open to the public. Consequently, her expertise was questioned each time the public found an element that did not satisfy their expectations. This research also clarifies the meaning of gender in emerging science. Dr. Soyeon Yi became the first Korean astronaut before any Korean male. In this way, KAP provided an important meaning to women in science, especially in the field of emerging science, which is usually dominated by males. Through these discussions, this research expands the application of sociotechnical imaginary and expert studies. It also enhances understanding of these discourses in Korean society, and stimulates discussions of the negative consequences of research programs. / Doctor of Philosophy / In April 2008, the first Korean Astronaut, Dr. Soyeon Yi, was launched to the International Space Station. The Korean nation welcomed their astronaut and believed this marked Korea's entry into the space age. However, before long, this aspiration changed to severe criticism. This research analyzes the Korean Astronaut Program (KAP) from its proposal to after its spaceflight in terms of its reception by Korean society. The Korean Astronaut Program was proposed by the Ministry of Science and Technology (MOST) to overcome the science and engineering crisis in 2004. As such, MOST defined KAP as a science-popularization program and the Korean astronaut as a science popularizer. However, as the first human space program in Korea, the Korea Aerospace Research Institute (KARI), who ran KAP, considered it a research program to achieve human spaceflight technology and the Korean astronaut a space expert. These two different understandings were communicated to the Korean public sphere. However, the Korean pubic already had its own image of the "heroic" astronaut based on other countries' space programs and popular culture. The public thought that having an astronaut would position the country on par with other countries. Because the visions of MOST, KARI, and the Korean public differed, KAP could not satisfy the expectations of all three actors. In addition, the process through which Dr. Yi became the first Korean astronaut was opened to the Korean public. Consequently, when the public found an element that did not satisfy their expectations, they doubted Dr. Yi as a space expert, bringing about severe criticism of KAP and the concept of the Korean astronaut.