Trajectory simulation is a software module that computes the flight path and flight parameters of munitions. It is used throughout the engineering process, including simulations for studying the design trade-offs, to mission simulations for defended area analysis. In this wide application domain, reuse has always been one of the challenges of the trajectory simulation community. We apply an ontology-based simulation development methodology to fulfil the functional requirements of a trajectory simulation while targeting reuse through interoperability and composability. Trajectory Simulation ONTology (TSONT) has been constructed as a simulation conceptual model for trajectory simulations. Based on the knowledge captured in TSONT, a domain-oriented reuse methodology has been leveraged to develop HLA-compliant trajectory simulations. A trajectory simulation federate was developed by conforming to the simulation object model based on TSONT. This paper demonstrates our approach to achieve composable and interoperable simulations over a case study in which a trajectory simulation federate serves in a variety of federations that have been constructed.