As the complexity of telescope systems have increased, system engineering trades related to cost and performance issues have become correspondingly more difficult. Many of the proposed space-based systems cannot be tested at the system level prior to launch and precursor technology missions are too expensive and do not fully duplicate the actual hardware. Therefore, industry is increasingly reliant upon modeling to predict end-to-end system performance from sub-system validation through laboratory testing. The increase of computational speed has enabled the development of integrated modeling tools which compliments the subsystem design process while facilitating system performance modeling. With integrated modeling, the optical design, structural dynamics, controls, disturbances, and sensor models are contained in a single environment. The challenge is to maintain computational speed and accurate computations while managing the complexity of multiple models, interfaces and hundreds of parameters. This paper discusses the issues involved with system modeling including architectural decisions, integration of subsystem models and disturbance modeling.