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Large (> 1000kg), expensive (> $1bn), monolithic, flagship-class satellites (e.g., Hubble, Chandra, James Webb telescopes) may soon be overshadowed by constellations of many, smaller, cheaper, more agile spacecraft working together as a coordinated system. In this work, we study several important attitude and orbit control problems relevant to the formation and operation of small spacecraft constellations. Our example problems include agile attitude maneuvering for multi-target acquisition in an Earth observation application, a centralized approach to constellation formation in low Earth orbit, a distributed approach to constellation formation in Mars areostationary orbit, and orbital rendezvous with objects in the inner Solar System. Our main tool is trajectory optimization, an approach that is appropriate for spacecraft applications where we often seek solutions that are optimal (e.g., minimum-time, minimum-fuel, minimum-control-effort) in the presence of mission or spacecraft constraints. We employ recent advances in sequential convex programming to efficiently handle the nonlinear dynamics and non-convex constraints that exist in our problem formulations.