Systems Architecting for Survivability: Limitations of Existing Methods for Aerospace Systems

Survivability may be defined as the ability of a system to minimize the impact of a finite disturbance on value delivery. This paper reviews existing methods of specifying, evaluating, and verifying survivability for aerospace systems in order to identify opportunities for improvement. First, the systems architecting methods underlying this research are described. Second, survivability challenges within the domain of space system architecture are analyzed for motivation. Third, five limitations of existing methods are discussed: (1) treatment of survivability as a constraint on design, (2) static system threat assessment reports, (3) assumption of independent disturbance encounters, (4) narrow scope of survivability design and analysis, and (5) lack of a value-centric perspective. In conclusion, prescriptions are offered for improving the practice of systems architecting for survivability. Research Context: System Architecture and Value-Based Design This paper describes ongoing doctoral research for improving the practice of systems architecting for aerospace systems (Richards, Hastings et al. 2007). A standard definition of architecture used by the Department of Defense (2003) is “the structure of components, their relationships, and the principles and guidelines governing their design and evolution over time.” The process of creating and building architectures is referred to as systems architecting and concerns itself most with system conceptualization, objective definition, and certification for use (Maier and Rechtin 2002). Within systems architecting, the research is focused on the application of value-based methods to conceptual design. Value, a subjective measure of benefit from a bundle of consequences that is specified by a stakeholder, provides a fundamental metric for relating system properties to desired stakeholder outcomes (Keeney 1992). Empirical evidence suggests that the lifecycle value delivered by systems is primarily determined at the beginning of development programs (Gruhl 1992), highlighting the criticality of good decision making during conceptual design. Conceptual design includes both concept development (i.e., identification of stakeholders, enumeration and evaluation of design alternatives, and selection of one or more concepts for further development) and system-level design (i.e., definition of the architecture, including subsystem decompositions and functional specifications) (Ulrich and Eppinger 2004). Taking the value-centric perspective during conceptual design empowers decision makers to