The advent of requirements for rapid and economical deployment of national space assets in support of Air Force operational missions has resulted in the need for a Manned SpacePlane (MSP) that can perform military missions with minimal preflight preparation and little if any in-orbit support from a mission control center. In this new approach to space operations, successful mission accomplishment will depend almost completely upon the MSP crew and upon the on- board capabilities of the spaceplane. In recognition of the challenges that will be faced by the MSP crew and to begin to address these challenges, the USAF Air Force Research Laboratory (Phillips Laboratory) initiated the Virtual SpacePlane (VSP) project. To support the MSP, the VSP must demonstrate a broad, functional subset of the anticipated missions and capabilities of the MSP throughout its entire flight regime, from takeoff through space operations and on through landing. Additionally, the VSP must execute the anticipated MSP missions in a realistic and tactically sound manner within a distributed virtual environment. Furthermore, the VSP project must also uncover, refine and validate MSP user interface requirements, design and demonstrate an intelligent user interface for the VSP, and design and implement a prototype VSP that can be used to demonstrate Manned SpacePlane missions. To enable us to make rapid progress on the project, we employed portions of the Virtual Cockpit and Solar System Modeler distributed virtual environment applications, and the Common Object Database (CODB) architecture tools developed in our labs. The Virtual Cockpit and Solar System Modeler supplied baseline interface components and tools, 3D graphical models, vehicle motion dynamics models, and VE communication capabilities. We use the CODB architecture to facilitate our use of Rapid Evolutionary and Exploratory Prototyping to uncover application requirements and evaluate solutions. The Information Pod provides the paradigm and architectural framework for the user interface development. To achieve accurate and high fidelity performance for the VSP throughout its operational regime, the system integrates aerodynamics and astrodynamics models into a single seamless high fidelity model of the VSP's dynamics. In this paper we discuss the software architecture and design of the Virtual SpacePlane and describe how it supports the transition between motion models, the design of the dynamics software module, and techniques for employment of multiple dynamics models within a single virtual environment actor. We describe how we used rapid prototyping to refine requirements, improve the implementation, and accommodate new requirements throughout the project. We conclude the paper with a brief discussion of results and present suggestions for additional work.