While there has been some aggregate quantitative work on arms races and rivalry, this paper analyzes the space race between the US and the USSR as an in-depth quantitative case study of interstate co mpetition. During the height of the Cold War, the United States and the Soviet Union engaged in a struggle to prevent the other side from dominating space. Here we test the popular notion that after the launch of the first Sputnik the Soviet Union and the U.S. engaged in a race to space, following previous patterns of competition between th e major power rivals. Placing the analysis into the expanding rivalry literature, this pa per employs a time-series analysis of the unfolding space rivalry between the two major power competitors. Using newly collected data on satellite and rocket la unches into space, as well as presidential approval, conflict/cooperation scales, and economic indicators, we are able to illustrate the dynamic interaction between domestic and international competition. Specifically, applying VAR techniques to the data allows for the testing of various hypotheses related to reciprocity and two-level models of interstate interaction. The results show that the space race was fueled in large part by domestic considerations, rather than following a pure action-reacti on sequence. Increased Soviet conflict did not inflate the likelihood of US launches, as one might expect. Instead, US launches followed dips in presidential approval. Historical documents and secondary sources further support the importance of domestic politics, although not to the exclusion of international variables. In total, the findings confirm a two-level logic for rivalry maintenance, whereby increased competition from an enemy is inflated by domestic politics and inflames further competition in the future.