We apply an ontology based knowledge and software reuse methodology adhering to domain engineering principles. Our domain is trajectory simulation. A trajectory simulation is a piece of software to calculate the flight path and other parameters of a munition, such as its orientation and angular rates, from launch to impact. Trajectory Simulation ONTology (TSONT) has been constructed as part of the domain analysis. Object oriented and function oriented reuse infrastructures have been built based upon TSONT following a model-driven development approach. Use of these infrastructures in simulation development has been demonstrated.