Satellite development worldwide has significantly changed within the last decade and has been accelerated and optimized by modern simulation tools. The classic method of developing and testing several models of a satellite and its subsystems with the aim to build a pre-flight and finally a flight model is being replaced more and more by a considerably faster and more inexpensive method. The new approach no longer includes functional test models on entire spacecraft level but a system simulation. Thus overall project runtimes can be shortened. But also significantly more complex systems can be managed and success oriented tests on integration and software level can be realized before the launch. Applying modern simulation infrastructures already during spacecraft development phase, enables the consistent functionality checking of all systems both in detail and concerning their interaction. Furthermore, they enable checks of the system's proper functionality, their reliability and safety / redundancy. But also analysis regarding aging and lifetime issues can be performed by simulation. Project-related simulations of operational scenarios, for example with remote sensing satellites, and the checking of different operational modes are of similar importance. On the whole, risk is reduced significantly and the satellite can be produced in a considerably more cost efficient way, with higher quality and in shorter periods of time. Therefore "Simulating Spacecraft Systems" - the title of the present book - is an important domain of modern system engineering, which meanwhile has successfully established a position in many other sectors of industry and research, too.