One of the main tasks involving the development of a new spacecraft is how to distribute its electronic equipment over its structural panels. This problem is first addressed in the conception phase of the design and is traditionally carried out by a group of system engineers. It is a multidisciplinary task since structural, thermal, dynamics, and integration issues, must all be taken into account simultaneously. Usually, the initial positioning is done based on the engineers' experience, followed by an analysis stage (thermal, structural, etc.) in which the design performance and constraints are verified. This process takes time and hence, as soon as a good feasible design is found, it is taken as the baseline. This precludes a broad exploration of the conceptual design space, which usually leads to a suboptimal layout design. In this paper the main features of a multi-objective methodology are presented which were developed to automatically find solutions for a three-dimensional layout of equipment in spacecraft. It includes mass, inertia, thermal and subsystem requirements and geometric constraints using a multi-objective approach that combines CAD and optimization tools in an integrated environment. As a case study, the methodology was applied to the layout optimization of the Brazilian Multi-Mission Space Platform (MMP) equipment. The main results are presented.