Multi-attribute tradespace exploration for survivability

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 235-249).Survivability is the ability of a system to minimize the impact of a finite-duration disturbance on value delivery (i.e., stakeholder benefit at cost), achieved through (1) the reduction of the likelihood or magnitude of a disturbance, (2) the satisfaction of a minimally acceptable level of value delivery during and after a disturbance, and/or (3) a timely recovery. Traditionally specified as a requirement in military systems, survivability is an increasingly important consideration for all engineering systems given the proliferation of natural and artificial threats. Although survivability is an emergent system property that arises from interactions between a system and its environment, conventional approaches to survivability engineering are reductionist in nature. Furthermore, current methods neither accommodate dynamic threat environments nor facilitate stakeholder communication for conducting trade-offs among system lifecycle cost, mission utility, and operational survivability. Multi-Attribute Tradespace Exploration (MATE) for Survivability is introduced as a system analysis methodology to improve the generation and evaluation of survivable alternatives during conceptual design. MATE for Survivability applies decision theory to the parametric modeling of thousands of design alternatives across representative distributions of disturbance environments. To improve the generation of survivable alternatives, seventeen empirically-validated survivability design principles are introduced. The general set of design principles allows the consideration of structural and behavioral strategies for mitigating the impact of disturbances over the lifecycle of a given encounter.(cont.) To improve the evaluation of survivability, value-based metrics are introduced 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 used to evaluate survivability based on the relationship between stochastic utility trajectories of system state and stakeholder expectations across nominal and perturbed environments. Finally, the survivability "tear(drop)" tradespace is introduced to enable the identification of inherently survivable architectures that efficiently balance performance metrics of cost, utility, and survivability. The internal validity and prescriptive value of the design principles, metrics, and tradespaces comprising MATE for Survivability are established through applications to the designs of an orbital transfer vehicle and a satellite radar system.by Matthew G. Richards.Ph.D

On-orbit serviceability of space system architectures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2006.Includes bibliographical references (p. 171-182).On-orbit servicing is the process of improving a space-based capability through a combination of in-orbit activities which may include inspection; rendezvous and docking; and value-added modifications to a satellite's position, orientation, and operational status. As a means to extend the useful life or operational flexibility of spacecraft, on-orbit servicing constitutes one pathway to a responsive space enterprise. Following launch, traditional satellite operations are tightly constrained by an inability to access the orbiting vehicle. With the exception of software upgrades from ground controllers, operators are wedded to supporting payload technologies that become rapidly obsolete and to bus structures that deform during the stress of launch and degrade in the harsh environment of space. On-orbit servicing offers satellite operators an option for maintaining or improving space-based capabilities without launching a new spacecraft. Numerous studies have been performed on on-orbit servicing, particularly regarding the architecture of the servicing provider. Several customer valuation case studies have also been performed to identify the economic case (or lack thereof) for different categories of servicing missions.(cont.) Little work, however, has been done to analyze the tradespace of potential on-orbit servicing customers-a global analysis of operational satellites currently orbiting the Earth. The goal of this research is to develop and test a methodology to assess the physical amenability of satellites currently in operation to on-orbit servicing. As defined here, physical amenability of a target satellite, or "serviceability," refers to the relative complexity required of a teleoperated or autonomously controlled robotic vehicle to accomplish on-orbit servicing. A three-step process is followed to perform serviceability assessments. First, a taxonomy of space systems is constructed to add structure to the problem and to identify satellite attributes that drive servicing mission complexity. Second, a methodology is proposed to assess serviceability across the four servicing activities of rendezvous, acquire, access, and service.(cont.) This includes development of an agent-based model based on orbital transfers as well as a generalized framework in which serviceability is decomposed into four elements: (1) knowledge, (2) scale, (3) precision, and (4) timing. Third, the value of architecture frameworks and systems engineering modeling languages for conducting serviceability assessments is explored through the development of a discrete event simulation of the Hubble Space Telescope. The thesis concludes with prescriptive technical considerations for designing serviceable satellites and a discussion of the political, legal, and financial challenges facing servicing providers.by Matthew G. Richards.S.M

Supreme Court Voting Behavior: 1995 Term

This Article, the eleventh in a series, attempts through statistical analysis to determine whether individual Justices on the United States Supreme Court (as well as the Court as a whole) voted more conservatively, more liberally, or about the same in the 1995 Terms as compared with past terms. The 1995 figures reveal a Court in ideological tension. Although some statistical measures suggest conservatism on the High Bench, there are notable contrary liberal indicators as well (principally in the areas of state criminal cases, federal jurisdiction, and First Amendment claims). Indeed, regression analysis demonstrates that the 1995 liberal movement in state criminal cases by the Court\u27s three most conservative members (the Chief Justice and Justices Scalia and Thomas) is statistically significant. Perhaps the most important (although least surprising) statistics are those that demonstrate the Court\u27s identifiable division into two wings: a liberal coalition composed of Justices Stevens, Souter, Ginsburg and Breyer, and a conservative bloc composed of the Chief Justice and Justices Scalia and Thomas. Justices Kennedy and O\u27Connor remain between these two factions, casting the deciding votes in the most hotly contested cases. The voting behavior of these moderate swing voters has caused the Court to vacillate markedly between liberal and conservative outcomes during the past four Terms. This ideological dynamic is likely to be altered only by resignations and replacements on the Court

Assessing the Challenges to a Geosynchronous Space Tug System

A space tug vehicle is designed to rendezvous and dock with a space object; make an assessment of its current position, orientation, and operational status; and then either stabilize the object in its current orbit or move the object to a new location with subsequent release. A subset of on-orbit servicing, space tug missions in the geosynchronous belt include stationkeeping of satellites which have lost attitude control and repositioning of satellites. Repositioning of spacecraft may be desirable as a means to rescue satellites launched into incorrect orbits, for the retirement of satellites into “graveyard” orbits, and for on-demand maneuvers that support flexible mission requirements. This paper aims to unify the political, legal, operational, and financial aspects of the space tug concept and highlight the challenges that stand in the way of an operational space tug vehicle. U.S. Space Transportation Policy is reviewed, and a space tug operation is recognized as an enabler of emerging national space transportation requirements. Customary international and United States laws are explored as potential constraining forces on future tug missions. A concept of operations in geosynchronous orbit, including parking orbit selection and approach strategies, is analyzed with emphasis placed on safety and reliability. Potential financing models and the issue of insurance for space tugs are discussed and identified as the principal challenges facing implementation of a space tug system. This paper offers a positive forecast for the future of on-orbit servicing and endorses continued government support for proof-of-concept missions

Multi-attributes tradespace exploration for survivability: Application to satellite radar

Multi-Attribute Tradespace Exploration (MATE) for Survivability is introduced as a general methodology for survivability analysis and demonstrated through an application to a satellite radar system. MATE for Survivability applies decision theory to the parametric modeling of thousands of design alternatives across representative distributions of disturbance environments. Survivability considerations are incorporated into the existing MATE process (i.e., a solution-generating and decision-making framework that applies decision theory to model-based design) by applying empirically-validated survivability design principles and value-based survivability metrics to concept generation and concept evaluation activities, respectively. MATE for Survivability consists of eight iterative phases: (1) define system value proposition, (2) generate concepts, (3) specify disturbances, (4) apply survivability principles, (5) model baseline system performance, (6) model impact of disturbances on dynamic system performance, (7) apply survivability metrics, and (8) select designs for further analysis. The application of MATE for Survivability to satellite radar demonstrates the importance of incorporating survivability considerations into conceptual design for identifying inherently survivable architectures that efficiently balance competing performance metrics of lifecycle cost, mission utility, and operational survivability

Managing Complexity with the Department of Defense Architecture Framework: Development of a Dynamic System Architecture Model

Architecture frameworks are tools for managing system complexity by structuring data in a common language and format. By characterizing the form, function, and rules governing systems, architecture frameworks serve as a communication tool to stakeholder communities with different views of the system and facilitate comparative evaluation across architectures. The goal of this research is to explore the applicability of architecture frameworks to the study of emergent properties of satellites. The U.S. Department of Defense Architecture Framework was selected to achieve this goal given its orientation towards technical systems in contrast to the majority of architecture frameworks focused on business enterprises. Although developed by military planners in the 1990’s to support the acquisition of interoperable information systems, the Department of Defense Architecture Framework can be used to connect operational concepts and capabilities to the technical architecture of any system. While the views of the Department of Defense Architecture Framework are well-defined, little guidance is provided on how the views are to be constructed. Vitech Corporation’s software program CORE,® a systems engineering modeling tool with the ability rapidly to produce architecture views from a common data repository, was employed to complete Department of Defense Architecture Frameworks for the Hubble Space Telescope. Upon characterizing Hubble within this common structure, the value of the Department of Defense Architecture Framework for conducting dynamic quantitative analyses of system architectures was explored. A methodology is proposed and tested for evaluating human and robotic architectures for on-orbit servicing—the extension of the useful life of spacecraft through refueling, upgrading, repair, relocation, et al. In particular, a multi-year servicing campaign is modeled for Hubble including behavioral threads that characterize the Orbiting Observatory, servicing architecture, and science customers. Preliminary results indicate that, when coupled with an executable model, the Department of Defense Architecture Framework can be utilized for dynamic quantitative evaluation of space system architectures. The paper concludes with lessons learned from using the Department of Defense Architecture Framework and proposes improvements for the application of its static views to model-based systems engineering

Supreme Court Voting Behavior: 1994 Term

This Article attempts, through statistical analysis, to identify the ideological leanings of the United States Supreme Court during the October 1994 Term. Although generally perceived as a conservative institution, the Court this Term adopted a more liberal stance in its approach to First Amendment, statutory civil rights, jurisdictional and federalism issues, and in litigation involving the federal government. Furthermore, in close cases that were decided by a one-Justice majority, the Court overwhelmingly adopted a more liberal result. Justice Kennedy remained the most influential Justice, his vote determining the outcome in over 80% of these close cases. While some of this liberal movement may be attributed to the nature of the agenda pursued by the Clinton administration, it is too broad-based to be discounted entirely. Regression analysis, moreover, reveals that there are several positive correlations (and one negative correlation) in the voting patterns of the five longest-tenured Justices

“Tuning aggregative versus non-aggregative lectin binding with glycosylated nanoparticles by the nature of the polymer ligand”

Glycan–lectin interactions drive a diverse range of biological signaling and recognition processes. The display of glycans in multivalent format enables their intrinsically weak binding affinity to lectins to be overcome by the cluster glycoside effect, which results in a non-linear increase in binding affinity. As many lectins have multiple binding sites, upon interaction with glycosylated nanomaterials either aggregation or surface binding without aggregation can occur. Depending on the application area, either one of these responses are desirable (or undesirable) but methods to tune the aggregation state, independently from the overall extent/affinity of binding are currently missing. Herein, we use gold nanoparticles decorated with galactose-terminated polymer ligands, obtained by photo-initiated RAFT polymerization to ensure high end-group fidelity, to show the dramatic impact on agglutination behaviour due to the chemistry of the polymer linker. Poly(N-hydroxyethyl acrylamide) (PHEA)-coated gold nanoparticles, a polymer widely used as a non-ionic stabilizer, showed preference for aggregation with lectins compared to poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA)-coated nanoparticles which retained colloidal stability, across a wide range of polymer lengths and particle core sizes. Using biolayer interferometry, it was observed that both coatings gave rise to similar binding affinity and hence provided conclusive evidence that aggregation rate alone cannot be used to measure affinity between nanoparticle systems with different stabilizing linkers. This is significant, as turbidimetry is widely used to demonstrate glycomaterial activity, although this work shows the most aggregating may not be the most avid, when comparing different polymer backbones/coating. Overall, our findings underline the potential of PHPMA as the coating of choice for applications where aggregation upon lectin binding would be problematic, such as in vivo imaging or drug delivery