The Multi-role Capsule as an Example of Function Based Requirement Generation

A "function-based" requirement generation process has been proposed as a superior methodology to the conventional "mission based" approach when dealing with space infrastructure elements. The Excalibur Multi-role capsule is used to illustrate the use of this new methodology on a personnel transport system element. Working from the objective that it should be the most flexible and capable crew space transportation system possible in current circumstances, the core functions that support the objective are identified. Some of these functions and performance parameters are fixed, being either a discrete funcrion or a parameter that has an optimum value. Other performance parameters are unconstrained, having a (normally unachievable) target that the system should move towards. The Excalibur concept was used as a feasibility design to test the technical viability of the fixed parameters and establish the achievable values for the unconstrained parameters. All the technical requirements are derived on the basis of the feasibility design without any reference to any missions it might perform; proving the function based methodology can be made to work.