Trajectory simulations can be regarded as computational tools to calculate the flight path and other flight parameters of munitions. They have a wide range of uses from concept formation to training simulator construction throughout the lifecycle of a weapons system. Trajectory simulations differ widely with respect to their performance and fidelity characteristics. From our observations, it is a common practice in the industry that developments of these simulations are carried out as isolated projects although they have lot in common. We envision the Reusable Trajectory Simulation Suite (RTSS) as an infrastructure that enables reuse starting from requirements through high level and low level design, coding and testing for trajectory simulation projects. Adhering to domain engineering principles, we have started with the domain analysis for trajectory simulation. The resulting domain model takes the form of an ontology, designated Trajectory Simulation Ontology. It contains the basic notions and relationships in the trajectory simulation domain. Web Ontology Language (OWL) of World Wide Web Consortium (W3C) is used to represent the ontology.