The simulation of synthetic data is commonly used by scientist and engineers to consolidate the instrument configuration and to define retrieval strategies. Despite synthetic FLEX data has been generated to develop suninduced fluorescence retrieval algorithms, the propagation of platform and instrument effects on the signal has not been properly incorporated. This paper describes the FLEX End-to-End Mission Performance Simulator (FLEX-E) that couples platform, instrument, synthetic scenes and image processing algorithms for a realistic simulation of the complete mission concept. An overview of FLEX-E design and current status is given in this paper, with a demonstration of some preliminary results. It is expected that FLEX-E will serve to consolidate the mission concept and instrument design as well as it will support the development of retrieval algorithms.