Managing uncertainty in space systems conceptual design using portfolio theory

Abstract

One of the most significant challenges in conceptual design is managing the tradespace of potential architectures-choosing which design to pursue aggressively, which to keep on the table and which to leave behind. This thesis provides a framework for managing a tradespace of architectures not through traditional effectiveness measures like cost and performance, but instead through a quantitative analysis of the embedded uncertainty in each potential space system architecture. Cost and performance in this approach remain central themes in decision making, but uncertainty serves as the focal lense to identify potentially powerful combinations of architectures to explore concurrently in further design phases. Presented is an approach to identify, assess, and quantify uncertainty in space system architectures, as well as a means to manage it using portfolio theory and optimization. Perhaps best known to economists and investors, portfolio theory is based around the objective of maximizing return subject to a decision maker's risk aversion. This simple concept, as well as the theoretical rigor that has evolved the theory to practice, is presented as one means of exploring the tradespace of potential architectures around the central theme of uncertainty. The approach presented relies upon previous work to model space system architectures using simulations that capture attributes of performance and cost. The first step in the approach is an analysis of the tradespace of potential architectures, including the bounding of architectural concepts that will be evaluated and the potential uncertainties and scenarios that will be investigated.

(cont.) The second step is to adjust the simulation models to include sources of uncertainty. The third step is to quantify the impact of the uncertainties on the evaluation criteria for each architecture through propagation techniques. Finally, portfolio theory is incorporated as an approach to manage uncertainty effectively. Illustrative cases present the changing shape of the decision process with uncertainty as a focal point. The three cases, a military space based radar mission, a commercial broadband system, and an scientific observing mission, illustrate the this new approach on tradespace exploration and highlight some of the intuitive and non-intuitive characteristics that can be discovered about the tradespace.