Space-Based Missile Warning: An Opportunity to Deepen U.S.-Japan Security Cooperation

executive summary: This article explores Japan's pursuit of missile-warning satellites and the opportunity this presents for the U.S.-Japanese security partnership in space. main argumentIn recent years, Japan has taken steps toward developing its own missile-warning satellites. Developing a space-based missile-warning system is a challenging feat, one that is complex and expensive, evidenced by the fact that only a few countries operate such systems. Given that the U.S. already shares some missile-warning information with Japan, Tokyo's pursuit of its own satellites reflects, at least in part, the country's push toward achieving a more independent capability. However, this push should not be construed as sudden or a shift away from its longtime ally. Rather, it represents (1) a continuation of latent historical efforts to acquire missile-warning satellites, and (2) a response to technological developments that have made potential adversarial missile systems more threatening and developing missile-warning satellites more feasible. Japan's pursuit of missile-warning satellites fits within the country's broader acceleration as a defense power and contributor to the U.S.-Japan security relationship. It also presents a compelling opportunity for more extensive collaboration between the two allies. policy implications• Japan has had a long-standing interest in space-based missile-warning systems and more broadly in mitigating missile threats using space-based technologies. Even if Japan does not acquire these assets soon, the issue of whether to acquire them will continue to be central to its defense debate. • Japan's development of a space-based missile-warning system, alongside the U.S.'s development of its own next-generation missile-warning capabilities, could offer opportunities for heightened collaboration between the two countries. Partnering on these assets could lead to financial savings and the potential for the alliance to develop a better protected and more capable missile-warning architecture.