The need for higher level of SIC autonomy is gaining increased importance in future space missions planning. These autonomous capabilities are needed not only to reduce the overall mission life-cycle cost but also to enable a new class of planetary missions (comets, asteroids, moons, etc.) requiring rendezvous and/or sample return. Some of the key candidate technologies identified for such missions include, autonomous approach/rendezvous/descent navigation, autonomous maneuver planning and implementation, and target based pointing and tracking. This paper presents the results of implementation and simulation of on-board maneuver planning, where a high level command is implemented while satisfying mission flight rules and spacecraft constraints. As part of this effort, a candidate spacecraft simulation is developed within a S/W architecture that provides a set of constructs suited for implementation of high level task decomposition and planning as well as on-line constraints checking and exception handling functions. The software architecture allows for future incremental refinements or addition of new autonomous capabilities as mission needs evolve