An operational satellite simulator is a digital representation that imitates the behavior of one satellite, the space environment in which it is inserted, and the ground stations with which it communicates. The simulator is organized into a set of virtual models. For satellite, the models reproduce the subsystems functioning, as for example, power supply, signal transmitters and receivers. One of the main functions of such a simulator is to support engineers in defining late operational procedures (i.e, sequence of commands) required when changes in the satellite's behavior occur after its launch. These changes can be foreseen, such as wear and tear of equipment over time, or unforeseen, such as unexpected failures or unplanned use of payload instruments. In these cases, the simulator helps find solutions without exposing the satellite to risks, and test new procedures considering the constraints, which can optimize the use of the satellite's resources, thus extending the mission's lifetime. The core function of simulator is to interpret commands received from the Mission Operations System, execute them considering the context, and produce responses exactly like the telemetry from a real satellite. Although it is mainly developed in software, it can include hardware models. It has a is multidisciplinary development requiring comprehensive knowledge of the areas related to Space Systems, and it can be the most complex software of a mission, depending on the fidelity degree required for the real system representation. The Operational Simulator for CBERS 3&4 satellites (SimSBERS) was developed between 2007 and 2017 by the National Institute for Space Research (INPE) to meet Brazilian operational requirements for this mission, such as facilitating the analysis of unforeseen situations that could occur during the satellite's life. One of the main challenges in the SimCBERS Project was to create a standardized specification of the models for the 15 satellite subsystems, and find a language that faithfully represented the behavior of the subsystems and that could be understood by experts on electrical, mechanical, mathematical, computing, optics, etc. The development of the SimCBERS was supported by the subsystems engineers and by the mission managers to verify the specifications and validate the results of the simulations. The SIMCBERS design solutions and challenges allowed the rapid development of the simulator for the Amazon satellite, as well as research topics such as use of AI techniques in models, interaction and visualization with virtual reality, among others.