Designing and maintaining systems in a dynamic contemporary environment requires a rethinking of how systems provide value to stakeholders over time. Developing either changeable or classically robust systems are approaches to promoting value sustainment. But, ambiguity in definitions across system domains has resulted in an inability to specify, design, and verify to ilities that promote value sustainment. In order to develop domain-neutral constructs for improved system design, the definitions of flexibility, adaptability, scalability, modifiability, and robustness are shown to relate to the core concept of "changeability," described by three aspects: change agents, change effects, and change mechanisms. In terms of system form or function parameter changes, flexibility and adaptability reflect the location of the change agent-system boundary external or internal respectively. Scalability, modifiability, and robustness relate to change effects, which are quantified differences in system parameters before and after a change has occurred. The extent of changeability is determined using a tradespace network formulation, counting the number of possible and decision maker acceptable change mechanisms available to a system, quantified as the filtered outdegree. Designing changeable systems allows for the possibility of maintaining value delivery over a system lifecycle, in spite of changes in contexts, thereby achieving value robustness.

The inability to approach systematically the high level of ambiguity present in the early design phases of space systems causes long, highly iterative, and costly design cycles. A process is introduced and described to capture decision maker preferences and use them to generate and evaluate a multitude of space system designs, while providing a common metric that can be easily communicated throughout the design enterprise. Communication channeled through formal utility interviews and analysis enables engineers to better understand the key drivers for the system and allows for a more thorough exploration of the design tradespace. Multi-attribute tradespace exploration with concurrent design, a process incorporating decision theory into model-and simulation-based design, has been applied to several space system projects at the Massachusetts Institute of Technology. Preliminary results indicate that this process can improve the quality of communication to resolve more quickly project ambiguity and to enable the engineer to discover better value designs for multiple stakeholders. The process is also integrated into a concurrent design environment to facilitate the transfer of knowledge of important drivers into higher fidelity design phases. Formal utility theory provides a mechanism to bridge the language barrier between experts of different backgrounds and differing needs, for example, scientists, engineers, managers, etc. Multi-attribute tradespace exploration with concurrent design couples decision makers more closely to the design and, most important, maintains their presence between formal reviews. Nomenclature K= multi-attribute utility normalization constant k i = multi-attribute utility scaling factor for attribute i N = number of attributes U (X) = multi-attribute utility function U i (X i ) = single attribute utility function i X = set of multiple attributes 1, . . . , N X i = single attribute i Introduction SPACE system engineers have been developing effective systems for about 50 years, and their accomplishments are a testament to human ingenuity. In addition to tackling the complex technical challenges in building these systems, engineers must also cope with the changing political and economic context for space system design and development. The history, scope, and scale of space systems results in a close tie with government and large budgets. The postCold War era has resulted in much smaller budgets and a space industry that needs to do more with less. Time and budget pressures can result in corner cutting (such as the Mars program) and careless accounting (such as the International Space Station program).Space system design often starts with needs and a concept. Engineers perform trade studies by setting baselines and making minor changes to seek improvement in performance, cost, schedule, and risk. The culture of an industry that grew through an Apollo race to the moon and large defense contracts in the 1970s and 1980s is slow to adapt a better way to design systems to ensure competitiveness in a r...

Abstract. Over the past five years, researchers working on a number of system design projects in the Space Systems, Policy, and Architecture Research Consortium (SSPARC) at the Massachusetts Institute of Technology (MIT) have developed a process of value-focused, broad tradespace exploration for the development of space systems. The broad tradespace framework has provided insights into communicating and quantifying the impact of changing requirements, uncertainty, and system properties such as flexibility and robustness. Additionally, insights have been made in applications to more complex cases, such as analyzing policy effects on system cost and performance, as well as understanding the time-dependent effects of architecture and design choices for spiral development. The tradespace exploration paradigm both broadens the perspective of designers in conceptual design to better understand the "physics" of the proposed solutions relative to one another, and focuses the designer on delivering systems of value to key system stakeholders.

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Abstract.A traditional approach to system design is to optimize the system with regard to a set of system objectives, as defined in a given context. This approach falls short when designing systems that are capable of delivering sustained value to stakeholders in the face of a rapidly changing world. In order to achieve this value robustness, systems should be designed using natural value-centric time scales, as defined by their contexts, for conceptualizing system timelines. Epoch-Era Analysis is an approach that provides for visualization and a structured way to think about the temporal system value environment. This paper discusses Epoch-Era Analysis as central to a tradespace exploration process for system design comparison and selection, invoking passive or active value robustness design strategies. The analysis can also serve as a socio-technical bridge, integrating the tradespace exploration activities of architects and engineers, which may be traditionally independent efforts in contemporary engineering programs.

Often shifts in context, such as changes in budgets, administrations, and warfighter needs, occur more frequently than high-cost space-based system development timelines. In order to ensure the successful development and operation of such systems, designers must balance between anticipating future needs and meeting current constraints and expectations. This paper describes the application of Multi-Epoch Analysis on a previously introduced satellite radar system program case study, quantitatively analyzing the impact of changing contexts and preferences on "best" system designs for the program. Each epoch characterizes a fixed set of context parameters, such as available technology, infrastructure, environment, and mission priorities. For each epoch, several thousand design alternatives are parametrically assessed in terms of their ability to meet imaging, tracking, and programmatic expectations using Multi-Attribute Tradespace Exploration. While insights on tradeoffs are discovered within a particular epoch, further dynamic insights become apparent when comparing tradespaces across multiple epochs. The Multi-Epoch Analysis reveals three key insights: 1) the ability to quantitatively investigate the impact of "requirements" across many systems and contexts, 2) the ability to quantitatively identify value "robust" systems, including both passively robust and changeable systems, and 3) the ability to quantitatively identify key system tradeoffs and compromises across stakeholders and missions.

A framework for assessing changeability in the context of dynamic Multi-Attribute Tradespace Exploration (MATE) is proposed and applied to three aerospace systems. The framework consists of two parts. First, changeability concepts such as flexibility, scalability, and robustness are defined in a value-centric context. These system properties are shown to relate "real-space to value-space" dynamic mappings to stakeholder-defined subjective "acceptable cost" thresholds. Second, network analysis is applied to a series of temporally linked tradespaces, allowing for the quantification of changeability as a decision metric for comparison across system architecture and design options. The quantifiable is defined as the filtered outdegree of each design node in a tradespace network formed by linking design options through explicitly defined prospective transition paths. Each of the system application studies are assessed in the two part framework and within each study, observations are made regarding the changeability of various design options. The three system applications include a hypothetical low Earth orbit satellite mission, a currently deployed weapon system, and a proposed large astronomical on-orbit observatory. Preliminary cross-application observations are made regarding the embedding of changeability into the system architecture or design. Results suggest that the low Earth orbit satellite mission can increase its changeability by having the ability to readily change its orbit. The weapon system can increase its changeability by continuing to embrace modularity, use of commercial off-the-shelf parts (COTS), and simple, excess capacity interfaces. The large astronomical observatory can increase its potential changeability by having the ability to reconfigure its physical payloads and reschedule its observing tasks. The analysis approach introduced in this paper is shown to be a powerful concept for focusing discussion, design, and assessment of the changeability of aerospace systems.

Abstract. Engineering systems is a field of scholarship focused on developing fundamental theories and methods to address the challenges of large-scale complex systems in context of their sociotechnical environments. The authors describe facets of their recent and ongoing research within the field of engineering systems to develop constructs and methods for architecting enterprises engaged in system-of-systems (SoS) engineering,. The ultimate goal of the research is to develop a framework for characterizing, designing, and evaluating SoS enterprise architectures throughout the system lifespan as various forces result in entering/exiting of constituent systems, changing environment, and shifting enterprise profile. The nature of systems-of-systems demands constructs for multi-dimensional architectural descriptions, as well as methods for design and evaluation that employ dynamic approaches. In this paper, two important elements in an emerging framework are described, including a holistic enterprise architecting framework and an epoch-based analysis method for examining possible futures of the SoS enterprise.