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Weaving time into system architecture : new perspectives on flexibility, spacecraft design lifetime, and on-orbit servicing

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dc.contributor.advisor Daniel E. Hastings. en_US
dc.contributor.author Saleh, Joseph Homer, 1971- en_US
dc.contributor.other Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. en_US
dc.date.accessioned 2005-08-24T20:23:02Z
dc.date.available 2005-08-24T20:23:02Z
dc.date.copyright 2001 en_US
dc.date.issued 2002 en_US
dc.identifier.uri http://hdl.handle.net/1721.1/8106
dc.description Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, June, 2002. en_US
dc.description Includes bibliographical references (leaves 203-214). en_US
dc.description.abstract A roadmap for a comprehensive treatment of issues of flexibility in system design is developed that addresses the following questions: 1) What are the characteristic features of flexibility in system design? Can one clearly and unambiguously characterize flexibility, and disentangle it from closely related concepts? 2) What drives the need for flexibility in system design, and what are the attributes of an environment in which flexible designs should be sought and fielded? 3) How can one embed flexibility in a system design? 4) What are the trade-offs associated with designing for flexibility? What is the value of flexibility and what are the associated penalties (cost, performance, risk, etc.), if any? These are the fundamental questions around which this thesis revolves. The first part of this work addresses the first two questions: Flexibility of a design is here defined as the property of a system that allows it to respond to changes in its initial objectives and requirements-both in terms of capabilities and attributes-occurring after the system has been fielded, i.e., is in operation, in a timely and cost-effective way. It is argued that flexibility should be sought when: 1) the uncertainty in a system's environment is such that there is a need to mitigate market risks, in the case of a commercial venture, and reduce a design's exposure to uncertainty in its environment, 2) the system's technology base evolves on a time scale considerably shorter than the system's design lifetime, thus requiring a solution for mitigating risks associated with technology obsolescence. en_US
dc.description.abstract (cont.) In other words, flexibility reduces a design's exposure to uncertainty, and provides a solution for mitigating market risks as well as risks associated with technology obsolescence. One way flexibility manifests its criticality to systems architects is in the specification of the system design lifetime requirement. The second part of this work addresses issues of design lifetime, and ways to provide and value flexibility in the particular case of space systems. First, it is shown that design lifetime is a key requirement in sizing various spacecraft subsystems. Second, spacecraft cost profiles as a function of the design lifetime are established and a cost per operational day metric is introduced. It is found that a cost penalty of 30% to 40% is incurred when designing a spacecraft for fifteen years instead of three years, all else being equal. Also, the cost per operational day decreases monotonically as a function of the spacecraft design lifetime. An augmented perspective on system architecture is proposed (diachronic) that complements traditional views on system architecture (synchronic). It is suggested for example that the system's design lifetime is a fundamental component of system architecture although one cannot see it or touch it. Consequently, cost, utility, and value per unit time metrics are introduced and explored in order to identify optimal design lifetimes for complex systems in general, and space systems in particular. Results show that an optimal design lifetime for space systems exists, even in the case of constant expected revenues per day over the system's lifetime ... en_US
dc.description.statementofresponsibility by Joseph Homer Saleh. en_US
dc.format.extent 224 leaves en_US
dc.format.extent 16370827 bytes
dc.format.extent 16370587 bytes
dc.format.mimetype application/pdf
dc.format.mimetype application/pdf
dc.language.iso eng en_US
dc.publisher Massachusetts Institute of Technology en_US
dc.rights M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. en_US
dc.rights.uri http://dspace.mit.edu/handle/1721.1/7582
dc.subject Aeronautics and Astronautics. en_US
dc.title Weaving time into system architecture : new perspectives on flexibility, spacecraft design lifetime, and on-orbit servicing en_US
dc.type Thesis en_US
dc.description.degree Ph.D. en_US
dc.contributor.department Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. en_US
dc.identifier.oclc 51299335 en_US


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