The Lunar Atmosphere Dust Environment Explorer (LADEE) was a small explorer class spacecraft that was launched on Sept 7, 2013. After completing all of the mission objectives, LADEE was de-orbited and successfully impacted the moon's surface on April 17, 2014.In order to reduce costs and leverage previous research and development, LADEE utilized the "common modular bus" design. The physical con struction utilized a low-cost, rapidly prototyped design and the same philosophy drove the development of the software base. To achieve this goal, a Model Based Design approach was utilized to develop the On-board Flight SoftWare (OFSW), and coincident with this, a model-based multipurpose simulator was created of the LADEE spacecraft and its mission environment. The spacecraft simulator was designed to have sufficient fidelity that it could be used to test the required modes and responses of the OFSW. A faster-than-real-time Workstation SIMulator (WSIM) version of the LA DEE simulator was used to develop and test the software control algorithms in the Simulink environment. The automatic code generation feature in Simulink was used to port the simulation to several real-time environments to support Processor-in-the-Loop (PIL) and Hardware-in-the-Loop (HIL) testing, verification and validation. Since the simulation inter face was designed to be compatible with the command interface employed by the LA DEE mission operation team, the WSIM, PIL and HIL simulators were used for both personnel training (nominal and ofT-nominal operations) prior to the mission and to perform command sequence verification during the mission. This approach resulted in time and budget savings, and allowed changes to the model to be quickly propagated through all the simulation target environments. The mode-based design ap proach also allows the simulation framework to be generalized and reused to model future small-satellite missions.