Adam M. Ross

Multi-Attribute Tradespace Exploration as Front End for Effective Space System Design

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.

Assessing Changeability in Aerospace Systems Architecting and Design Using Dynamic Multi-Attribute Tradespace Exploration

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.

A Framework for Incorporating "ilities" in Tradespace Studies

Non-traditional design criteria such as flexibility, robustness, survivability and others (collectively referred to as the “ilities”) are increasingly recognized as critical system properties for the success of aerospace programs. While most decision makers would agree that the ilities are important system properties, they are neither well-defined nor easily evaluated in isolation. While some evaluation methodologies do exist (e.g., real options for flexibility), there is a need for a holistic framework for describing systems with these properties. This paper will explore the use of these “ilities” properties as selection criteria in tradespace studies. A framework is described that can be used to incorporate ilities into conceptual design and tradespace studies in a systematic way. The framework is based on describing ilities in terms of changes in three dimensions: changes in the context, changes in the needs, and changes in the systems itself. The ilities are then interpreted as methods of navigating changes in this space. Quantitative analysis can be accomplished through Epoch/Era Analysis linking multiple discrete tradespace studies into a coherent timeline. An extended example is presented to demonstrate an analysis and visualization of the survivability of a space tug system to LEO orbital debris over a ten year lifetime. The results indicate that passive shielding for satellites in LEO provides only marginal benefit, at best, given the debris distribution. The smaller satellite designs in the tradespace display an unfavorable tradeoff of cost versus survivability. The example case study is a simple application of the framework, and points out the potential challenges of displaying multidimensional, non-aggregate data in “ilities” dynamic tradespace studies. The framework and case study suggest that using Epoch/Era Analysis, “ilities” will emerge as properties describing how systems change across epochs, and can be prescribed as visual and quantitative strategies that can be traded in terms of benefit and cost over time.

Architecting the system of systems enterprise: Enabling constructs and methods from the field of engineering systems

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 socio-technical 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.

Multi-attribute tradespace exploration for survivability

Multi-attribute tradespace exploration for survivability is a system design and analysis methodology that incorporates survivability considerations into the tradespace exploration process (i.e., a solution-generating and decision-making framework that applies decision theory to model-based design). During the concept-generation phase of tradespace exploration, the methodology applies 17 empirically validated survivability design principles spanning susceptibility reduction, vulnerability reduction, and resilience enhancement. During subsequent concept evaluation, the methodology adds value-based survivability metrics to traditional architectural evaluation criteria of mission utility and life-cycle cost. Applied to a satellite radar mission, the methodology allowed operational survivability to be statistically evaluated across representative distributions of naturally occurring disturbances in the space environment and for survivability to be incorporated as a decision factor earlier in the design process...

Responsive systems comparison method: Dynamic insights into designing a satellite radar system

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.

Responsive Systems Comparison Method: Case Study in Assessing Future Designs in the Presence of Change

In this short paper, the Responsive Systems Comparison (RSC) method is introduced. RSC is a structured method for collecting information and conducting analysis to characterize a wide variety of possible futures in order to enable the comparison of the performance of proposed systems in those futures. A case study uses the RSC to analyze a satellite radar system. The needs and expectations of a user community for such a system, the context it will operate in, and its technical basis are determined both at the present time, and with possible changes over the next 15 years. This information is used to set up an analysis that should be able to highlight systems that will deliver value under a wide variety of future situations. The case study illustrates the practicality of the method, and provides lessons for improvement and implementation.

Using Pareto Trace to determine system passive value robustness

An important role of system designers is to effectively explore the tradespace of alternatives when making design decisions during concept phase. As systems become more complex, formal methods to enable good design decisions are essential; this can be empowered through a tradespace exploration paradigm. This paper demonstrates the use of the Pareto Trace and associated metrics to identify system alternatives across tradespaces with high degrees of passive value robustness—alternatives that continue to deliver value to stakeholders in spite of changes in needs (attributes) or context. A value-driven tradespace approach is used to represent the baseline performance versus cost of a large number of system alternatives. The classical notion of Pareto Set is extended to identify alternatives and their characteristics that lead to their inclusion in Pareto Sets across changing contexts. Using a low-earth orbiting satellite case example, five types of context changes are used to demonstrate this method: 1) addition or subtraction of attributes; 2) change in the priorities of attributes; 3) change in single attribute utility function shapes; 4) change in multi-attribute utility aggregation function; and 5) addition of new decision maker. This approach demonstrates the ability for system designers to pose questions about assessment of alternatives during early conceptual design. Suggestions for application of Pareto Trace beyond the case example are discussed and presented, including application of a “fuzziness” factor and statistical measures. In particular, distinctions from traditional sensitivity analysis are made, as well as linkages to dynamic analysis for discovery of generalized value robust alternatives.

Scenario planning in dynamic multi-attribute tradespace exploration

The long time scales associated with complex system design and operation necessitate front-end systems engineering methodologies that enable consideration of alternative futures. This paper advances scenario planning techniques through a parameterization and ordering of potential future contexts and stakeholder expectations (e.g., articulated system attributes, available technology, funding levels, and supporting infrastructures). After surveying existing approaches for scenario planning, a methodology for specifying and analyzing large numbers of alternative system timelines is presented. A satellite radar case study is used to motivate and illustrate the value of this approach. Benefits of the methodology include: (1) broader and more rigorous consideration of alternative future needs, contexts, and timelines, (2) identification of gaps in traditionally-derived scenario sets, (3) identification of passively value-robust system alternatives, and (4) providing a basis for evaluating system evolution strategies that enable sustainment of value delivery across potential timelines.

Aligning Perspectives and Methods for Value-Driven Design

Recent years have seen a push to use explicit consideration of “value” in order to drive design. This paper conveys the need to explicitly align perspectives on “value” with the method used to quantify “value.” Various concepts of value are introduced in the context of its evolution within economics in order to propose a holistic definition of value. Operationalization of value is discussed, including possible assumption violations in the aerospace domain. A series of prominent Value-Centric Design Methodologies for valuation are introduced, including Net Present Value, Multi-Attribute Utility Theory, and CostBenefit Analysis. These methods are compared in terms of the assumptions they make with regard to operationalizing value. It is shown that no method is fully complete in capturing the definition of value, but selecting the most appropriate one involves matching the particular system application being valued with acceptable assumptions for valuation. Two case studies, a telecommunications mission and a deep-space observation mission, are used to illustrate application of the three prior mentioned valuation methods. The results of the studies show that depending on method used for valuation, very different conclusions and insights will be derived, therefore an explicit consideration of the appropriate definition of value is necessary in order to align a chosen method with desired valuation insights.