We present a compositional approach to modeling and analyzing space mission operation sequences with steps across multiple viewpoints. We consider different tasks such as communication, science observation, trajectory correction, and battery charging; and separate their interactions across discipline viewpoints. In each sequence step, these tasks are modeled as assume-guarantee contracts. They make assumptions on the initial state of a step, and if these assumptions are satisfied, they guarantee desirable properties of the state at the end of the step. These models are then used in Pacti, a tool for reasoning about contracts. We demonstrate a design methodology leveraging Pacti's operations: contract composition for computing the contract for the end-to-end sequence of steps and contract merging for combining them across viewpoints. We also demonstrate applying Pacti's optimization techniques to analyze the figures of merit of admissible sequences satisfying operational requirements for a CubeSat-sized spacecraft performing a small-body asteroid rendez-vous mission. We show that analyzing tens of thousands of combinations of sequences and operational requirements takes just over one minute, confirming the scalability of the approach. The methodology presented in this paper supports the early design phases, including requirement engineering and task modeling.