Conceptual Design of an Aerospace Vehicle Controller Using Axiomatic Theory

Abstract

A EROSPACE systems are extremely involved with complex interdependencies between the attendant subsystems, making their design and engineering quite challenging. Requirements on performance, efficiency, economy, environmental effects, and issues of safety, reliability, ease of maintenance, and other factors, are usually interlinked and may often be in mutual conflict. This has led to the adoption of a systems engineering perspective to many aerospace design problems [1,2], and the development of processes, tools, and methods broadly classed as system of systems engineering [3]. Yet, the design and development of aerospace systems, like any other system design, must follow the natural course of ideate, analyze, check, and revise. The ideation phase is a creative process where the designer must make a coherent problem statement that clearly captures the design requirements, and then come up with one or more concepts that appear to meet the stated requirements. Each conceptmust be realized by one ormore designs (for example, vortex liftconceptmaybe realizedbyacanardora strakeora crankeddeltaor any other design), each of which must then be analyzed and quantitative measures obtained that enable one to judge whether the design solves thegivenproblemand, if so,whichamong thedesigns is the best. Almost every device available to the designermay be seen to be a realization (inverse problem), analysis (modeling & simulation) or a comparison (optimization) tool, with hardly any tool, if at all, to help the designer in the conception phase. This is of concern, especially when the concept is innovative, not merely an improvement, but a radical departure from existing conceptual approaches to the problem.Admittedly, the conception process is highly subjective, depending on the creativepowers of the designer andhis/her ability to integrate knowledge in diverse disciplines. Yet, a systematic basis to help the designer eliminate faulty concepts and narrowdown thefield to good designs will be of immense value in curtailing development time and cost, and in yielding a superior product. Precisely such a systematic approach to design based on a few fundamental axioms, called the axiomatic design theory, has been developed by Suh [4]. In essence, the problem statement is captured in a set of functional requirements (FR) in the functional space, and the design is defined as a mapping from the functional space to the physical spacewhich consists of a set of design parameters (DP). The axioms, and corollaries derived from them, deal with the choice of FRs, the corresponding DPs, and the nature of the mapping between them. Besides applications in several branches of engineering [5], axiomatic design theory also provides a scientific basis for design education [6]. The aim of this paper is to introduce axiomatic design theory to aerospace systems by way of a modest example of conceptual design of an aerospace vehicle controller. As will become clear in the following, this does not refer to “control system design” in the traditional sense; rather, it focusses on concept-level decisions to be made by the system designer before the task of controller realization (followed by analysis) is handed over to the control design team.