In this thesis, a general method was developed to solve the momentum-optimal attitude command trajectory for a given reorientation. The solution method relied on converting a standard two-point boundary-value problem to an unconstrained optimization problem using Lagrange multipliers. This approach was applied to a realistic robotic assembly operation of the International Space Station. Results for the optimization method in this thesis were compared with alternative attitude command strategies. Unlike much of the previous research, the methods developed in this thesis account for spacecraft with arbitrary and/or changing inertia matrices, control torques which do not necessarily coincide with the principal axes of the spacecraft, the full nonlinear rotational dynamics, known external torques that are functions of attitude and changes in angular momentum and mass properties due to repositioning of spacecraft components. Using the methods developed in this thesis, the peak momentum use during a maneuver was minimized. Additionally, optimal maneuvers were able to remove accumulated momentum from the CMG system.