Survivability engineering is critical for minimizing the impact of disturbances to the operation of space systems. To improve the evaluation of survivability during conceptual design, metrics are proposed for the assessment of survivability as a dynamic, continuous, and path-dependent system property. Two of these metrics, time-weighted average utility loss and threshold availability, are then incorporated into a tradespace study on the survivability of future space tug vehicles to orbital debris. A value-based design approach, Dynamic Multi-Attribute Tradespace Exploration, is taken to evaluate survivability based on the relationship between stochastic space tug utility trajectories and changing stakeholder expectations across nominal and disturbed environmental states. Results of the tradespace study show that moderate levels of bumper shielding and access to an on-orbit servicing infrastructure benefit space tugs with large exposed cross-sectional areas while active collision avoidance only delivers value to extremely risk-averse decision makers. Timeweighted average utility loss and threshold availability are found to be discriminating metrics for navigating survivability tradespaces of thousands of design alternatives. NomenclatureA T = threshold availability CS = campaign-level survivability ∆V = change in velocity F(t) = failure likelihood as a function of time MoME = measure of mission effectiveness MTAT = mean time above critical value threshold MTBF = mean time between repair MTTR = mean time to repair P K = probability of kill P K|E = probability of kill for multiple-shot engagement P K|SS = probability of kill from single-shot P S = probability of survival P S|E = probability of survival for multiple-shot engagement P H = probability of hit (susceptibility) P K|H = probability of kill given hit (vulnerability) R(t) = reliability as a function of time T dl = time of design life T r = permitted recovery time U ‾ L = time-weighted average utility loss from design utility, U 0 ‾ U t = time-weighted average utility U(t) = utility delivery over time; multi-attribute utility trajectory V e = emergency value threshold V(t) = value delivery over time V x = required value threshold

Survivability engineering is critical for minimizing the impact of disturbances to the operation of space systems. To improve the evaluation of survivability during conceptual design, metrics are proposed for the assessment of survivability as a dynamic, continuous, and path-dependent system property. Two of these metrics, time-weighted average utility loss and threshold availability, are then incorporated into a tradespace study on the survivability of future space tug vehicles to orbital debris. A value-based design approach, Dynamic Multi-Attribute Tradespace Exploration, is taken to evaluate survivability based on the relationship between stochastic space tug utility trajectories and changing stakeholder expectations across nominal and disturbed environmental states. Results of the tradespace study show that moderate levels of bumper shielding and access to an on-orbit servicing infrastructure benefit space tugs with large exposed cross-sectional areas while active collision avoidance only delivers value to extremely risk-averse decision makers. Timeweighted average utility loss and threshold availability are found to be discriminating metrics for navigating survivability tradespaces of thousands of design alternatives. Nomenclature A T= threshold availability CS = campaign-level survivability ∆V = change in velocity F(t) = failure likelihood as a function of time MoME = measure of mission effectiveness MTAT = mean time above critical value threshold MTBF = mean time between repair MTTR = mean time to repair P K = probability of kill P K|E = probability of kill for multiple-shot engagement P K|SS = probability of kill from single-shot P S = probability of survival P S|E = probability of survival for multiple-shot engagement P H = probability of hit (susceptibility) P K|H = probability of kill given hit (vulnerability) R(t) = reliability as a function of time T dl = time of design life T r = permitted recovery time U ¯ L = time-weighted average utility loss from design utility, U 0 Ū t = time-weighted average utility U(t) = utility delivery over time; multi-attribute utility trajectory V e = emergency value threshold V(t) = value delivery over time V x = required value threshold

Abstract. This research examines the underlying rationale of architecture frameworks and their use in acquisition with the goal of identifying best practices to improve system development. Three key questions are addressed: (1) What is the role of artifacts in system design? (2) What are the benefits provided by architecture frameworks? And (3) what are the best measures-ofeffectiveness for assessing the value of architecture frameworks? To address the first question, we review relevant literature on collaborative design and propose a rationale for using artifacts as communicative and illustrative tools. Second, we enumerate the motivations for their use in system design and acquisition.Third, eight measures-of-effectiveness of architecture frameworks are derived from the literature and our experience with the Department of Defense Architecture Framework.

Previous research in satellite constellation designs has focused on Low Earth Orbit (LEO) communication systems that service a global market of uniform demand. This paper addresses the challenge of designing a hybrid satellite system constellation to meet the emerging satellite broadband market while enabling a phased satellite deployment strategy. The broadband market model developed in the paper highlights the highly non-uniform distribution of traffic that future satellite systems must handle. The proposed solution employs a LEO backbone satellite constellation to capture a fraction of the total market demand with additional elliptical satellite constellations to service areas of high and growing demand. By opening up the tradespace to multiple orbital altitudes (Low Earth Orbit, Medium Earth Orbit, and Geosynchronous Orbit) and both circular and elliptical orbits, this paper will search for a lower cost solution to the broadband communication constellation design problem. Lastly, this paper will introduce a novel visualization of the tradespace using convex hulls and conditional Pareto fronts, which enable instant recognition of the impact of design choices on the final design.

The presence of space situational awareness is one approach to mitigating the long-term risks associated with space debris in low Earth orbit (LEO). As the U.S. and other nations continue to develop the space situational awareness mission area, questions arise as to how stakeholders should act to mitigate the effects of resident space objects and how our understanding of the physics of LEO inform the evolution of ground-and space-based sensors. To characterize interactions among international stakeholders, space situational awareness is modeled as a system of systems with technical and social elements. Through the use of game-theoretic cooperation archetypes and System Dynamics modeling, possible futures are explored. Extensions in space situational awareness capabilities are modeled as mechanisms to improve satellite survivability. Finally, general implications for system architecture and systems of systems are elucidated.