To achieve the goals of effective Attitude Determination and Control subsystem design (ADCS), a methodology of knowledge based system has been proposed in this project. An open-licence knowledge representation software tool, Protégé is used to develop an ontology. This ontology presents the vocabulary for representing and communicating knowledge about the ADCS subsystem design by defining a set of relationships that hold among the terms in that vocabulary. This ontology system is modeled by the preexisting expert’s domain knowledge and concepts, to be used in the early stages of ADCS subsystem design with a goal of improved design. The utility and potential applications of the ontology have been evaluated, and its effectiveness in representing ADCS design knowledge assessed. The ontology is expected to generate a greater understanding of the process of knowledge capture and representation, in the context of ADCS systems, and also to identify the current state-of-the-art and methodologies used in practical field. It is anticipated that the work will be a useful tool that can be used to represent ADCS subsystem knowledge during design processes or training.