Time-expanded decision networks: A framework for designing evolvable complex systems

This paper describes the concept of Time-Expanded Decision Networks (TDNs), a new methodology to design and analyze flexibility in large-scale complex systems. This includes a preliminary application of the methodology to the design of Heavy Lift Launch Vehicles for NASA’s space exploration initiative. Synthesizing concepts from Decision Theory, Real Options Analysis, Network Optimization, and Scenario Planning, TDN provides a holistic framework to quantify the value of system flexibility, analyze development and operational paths, and identify designs that can allow managers and systems engineers to react more easily to exogenous uncertainty. TDN consists of five principle steps, which can be implemented as a software tool: (1) Design a set of potential system configurations; (2) quantify switching costs to create a “static network” that captures the difficulty of switching among these configurations; (3) create a time-expanded decision network by expanding the static network in time, including chance and decision nodes; (4) evaluate minimum cost paths through the network under plausible operating scenarios; and (5) modify the set of initial design configurations to exploit high-leverage switches and repeat the process to convergence. Results can inform decisions about how and where to embed flexibility in order to enable system evolution along various development and operational paths. © 2007 Wiley Periodicals, Inc. Syst Eng 10: 167–186, 2007 Regular Paper * An earlier version of this paper was published and presented as follows: M. Silver and O. de Weck, Time-expanded decision network methodology for designing evolvable systems, AIAA-2006-6964, 11th AIAA/ISSMO Multidisciplinary Analysis Optim Conf, Portsmouth, VA, September 6–8, 2006. †Author to whom all correspondence should be addressed (e-mail: [email protected]). Systems Engineering, Vol. 10, No. 2, 2007 © 2007 Wiley Periodicals, Inc.