Contemporary global governance is increasingly taking place through informal institutions, and the outer space regime is no exception. The institutional foundation of the outer space regime is based on four multilateral treaties adopted in the 1960s and 1970s. However, in the past fifty years, this regime's development has relied heavily on the conclusion of memorandums of understanding (MOUs). This study aims to explore how this emerging informality aligns with the more formal foundation of outer space governance. Relying on a dataset of 582 MOUs related to outer space governance, we investigate both their structural position and normative content. Our findings indicate that MOUs involving powerful states are more likely to serve as substitutes for formal treaties, while those entered by less powerful states tend to complement formal treaties. These results suggest that the normative activism of powerful states plays a crucial role in understanding the intricate relationship between formal and informal governance. In doing so, this paper dialogues with existing literatures on regime complexity, informal lawmaking, forum shopping, and space governance.
