OSE follows Module Based Design
This allows multiple parts of an artifact to be developed in parallel, and it allows these parts to be produced in parallel via a 'barnraising'-style social production model.
To achieve Module Based Design - a machine/artifact first needs to be broken down into modules. These modules must be designed such that they fit together with other modules. For this to happen, a clear interface design must be presented.
Modular Breakdown as Technical Design
Once we have defined Conceptual Design, we can proceed to further refinement of concept towards a technical design. Upon sufficient refinement, there is sufficient information to manifest the technical design in the form of 3D CAD. The Modular Breakdown step is where the concept can be refined further by examining the constituent modules. The Modular Breakdown is the best place to capture the transition from concept to the actual design. Once the actual design (3D CAD) is produced - we can do full Calculations including structural, thermal, fluid, and electromagnetic. Partial calculations can be made at the phase of conceptual design - with back of the envelope calculations just to get an idea of basic feasibility. All of these steps can be done at various levels of product-service system organization: the system, machine, module, and submodule (part) levels.