This paper describes the New Millennium Remote Agent (NMRA) architecture for autonomous spacecraft control systems. This architecture integrates traditional real-time monitoring and control with constraint-based planning and scheduling, robust multi-threaded execution, and model-based diagnosis and reconfiguration. We implemented a prototype autonomous spacecraft agent within the architecture and demonstrated the prototype in the context of a challenging autonomous mission scenario on a simulated spacecraft. As a result of this success, the integrated architecture has been selected to control Deep Space One (DS-1), the first flight of NASA's New Millennium Program (NMP), which will launch in 1998. It will be the first AI system to autonomously control an actual spacecraft.