This study describes the development of requirements for a cognitive assistant (CA) for use onboard a space vehicle/station. For missions beyond low Earth orbit (LEO), delayed communication will limit mission control’s ability to support the space crew in real time. During off-nominal situations, where no procedures have been developed prior to missions, crews must develop responses in real time and may increasingly rely on automation. A systematic approach was used to model the domain knowledge of the collaborative decision-making process of current space operations, extrapolate to missions beyond LEO, and develop the design requirements for a CA. Document analysis and interviews were conducted to create an abstraction hierarchy and a decision-action diagram of the cognitive functions currently performed by space crew, mission control, and onboard automation. These domain models were extrapolated to missions beyond LEO by identifying the breakpoints where current decision-making processes would break down due to increased communication delay between mission control and the space crew. Design requirements were identified for future CA systems that offer real-time decision-making support to mitigate the negative effect of limited support in off-nominal situations. The approach developed for this research can be generalized to identify the design requirements for future support systems in domains beyond space operations.