LIDAR systems are becoming an important tool in many areas of remote data collection. Recently, BATC has applied their integrated modeling toolset, EOSyM (End-to-end Optical System Model), to development of a LIDAR system model. With the recent successful launch and deployment of the Calipso remote sensing instrument, an additional opportunity was present to develop a partially validated model from combined test data and measureables from the flight. The concept was to validate the CALIPSO system model and then use this tool to facilitate the system engineering process for future space-based designs. The system model includes the important physics of a laser, the CALIPSO optical prescription for the transmitter and receiver, thermoelastic disturbances, a simple atmospheric model, detection and signal processing of the data. This paper describes the model development process using EOSyM, some initial results with comparison to flight data and proposed future developments to expand it's use for future missions.