This paper introduces a simulation architecture to evaluate the implementation of a va- riety of civil UAS missions with little recon guration time and overhead. This architecture, called Icarus Simulation Integrated Scenario (ISIS), is capable of simulating the behavior of the UAS from the mission point of view, but also is able to include additional aerial/ground vehicles. Additionally, the mutual interaction between vehicles and the interaction with their surrounding environment is modeled. The objective of ISIS is to minimize both the development e ort and risk, as well as to provide a feasible migration of the software from the testbed platform to the real ight platform. The UAS simulator is designed as a distributed simulation architecture in which vehicles and environment are modeled through specialized pieces of software. A service-oriented communication middleware provides the underlying infrastructure to easily implement the inter-vehicle coordination and even the coordination with third party applications providing additional simulated vehicles or simulated environment. A UAS-based forest re monitor- ing application is selected to describe the ISIS capabilities to coordinate the simulation of a multi-vehicle cooperative environment developing a complex mission.