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Saleh,
Joseph H.
Saleh,
Joseph H.
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ItemComparative Reliability of GEO, LEO, and MEO Satellites(Georgia Institute of Technology, 2009-10) Hiriart, Thomas ; Castet, Jean-Francois ; Lafleur, Jarret M. ; Saleh, Joseph H.Reliability has long been a major consideration in the design of space systems, and in recent years it has become an essential metric in spacecraft design trade-space exploration and optimization. The purpose of this paper is to statistically derive and compare reliability results of Earth-orbiting satellites as a function of orbit type, namely geosynchronous orbits (GEO), low Earth orbits (LEO) and medium Earth orbits (MEO). Using an extensive database of satellite launches and failures/anomalies, life data analyses are conducted over three samples of satellites within each orbit type and successfully launched between 1990 and 2008. Because the dataset is censored, the Kaplan-Meier estimator is used to estimate the reliability functions. Plots of satellite reliability as a function of orbit altitude are provided for each orbit type, as well as confidence bounds on these estimates. Using analytical techniques such as maximum likelihood estimation (MLE), parametric fits are conducted on the previous nonparametric reliability results using single Weibull and mixture distributions. Based on these parametric fits, a comparative reliability analysis is provided identifying similarities and differences in the reliability behaviors of satellites in these three types of orbits. Finally, beyond the statistical analysis, this work concludes with several hypotheses for structural/causal explanations of these trends and difference in on-orbit failure behavior.
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ItemStatistical Reliability Analysis of Satellites by Mass Category: Does Spacecraft Size Matter?(Georgia Institute of Technology, 2009-10) Dubos, Gregory F. ; Castet, Jean-Francois ; Saleh, Joseph H.Reliability has long been recognized as a critical attribute for space systems, and potential causes of on-orbit failures are carefully sought for identification and elimination through various types of testing prior to launch. From a statistical or actuarial perspective, several parameters of the spacecraft, such as mission type, orbit, or spacecraft complexity, can potentially affect the probability of failure of satellites. In this paper, we explore the correlation between satellite mass, considered here as a proxy for size, and satellite reliability, and we investigate whether different classes of satellite, defined in terms of mass, exhibit different reliability profiles. To this end, we first conduct nonparametric analysis of satellite reliability based on a sample of 1,444 satellites. The satellites are organized in three main categories defined by satellite mass (Small – Medium – Large). Three nonparametric reliability curves are thus derived. We then provide parametric fits of the reliability curves to facilitate the identification of failure trends. We proceed to the comparative analysis of failure profiles over time and clearly identify different reliability behaviors for the various satellite mass categories. Finally, we discuss possible structural and causal reasons for these trends and failure differences, in particular with respect to design, testing and procurement.
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ItemSurvivability and Resiliency of Spacecraft and Space-Based Networks: a Framework for Characterization and Analysis, Version 2(Georgia Institute of Technology, 2008-09-09) Castet, Jean-Francois ; Saleh, Joseph H.Considerations of survivability and resiliency have always been of importance in the design and analysis of military systems. Over the past two decades, the importance of survivability and resiliency has expanded beyond military systems to include public networks and infrastructure systems. The analysis and assessment of networked systems with respect to survivability has become particularly acute in recent years, as attested to by a growing technical literature on the subject. In this paper, we bring these considerations of survivability and resiliency to bear on spacecraft and space-based networks. We develop a framework for comparing the survivability and resiliency of different space architectures, namely that of a monolithic design and a distributed (or networked) space system architecture. There are multiple metrics along which different space architectures can be benchmarked and compared. We argue that if survivability and resiliency are not accounted for, then the evaluation process is likely to be biased in favor of monolithic spacecraft. We show that if in a given context survivability and resiliency are an important requirement for a particular customer, then a distributed architecture is more likely to satisfy this requirement than a monolithic spacecraft design. We discuss in the context of our framework different classes of threats, as well as the high-frequency and low-frequency system response to (or coping strategies with) these shocks or damaging events. We illustrate the importance of this characterization for a formal definition of survivability and resiliency and a proper quantitative analysis of the subject. Finally, we propose in future work to integrate our framework with a design tool that allows the exploration of the design trade-space of distributed space architecture and show how survivability can be “optimized” or traded against other system attributes.
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ItemSurvivability and Resiliency of Spacecraft and Space-Based Networks: a Framework for Characterization and Analysis, Version 1(Georgia Institute of Technology, 2008-09) Castet, Jean-Francois ; Saleh, Joseph H.Considerations of survivability and resiliency have always been of importance in the design and analysis of military systems. Over the past two decades, the importance of survivability and resiliency has expanded beyond military systems to include public networks and infrastructure systems. The analysis and assessment of networked systems with respect to survivability has become particularly acute in recent years, as attested to by a growing technical literature on the subject. In this paper, we bring these considerations of survivability and resiliency to bear on spacecraft and space-based networks. We develop a framework for comparing the survivability and resiliency of different space architectures, namely that of a monolithic design and a distributed (or networked) space system architecture. There are multiple metrics along which different space architectures can be benchmarked and compared. We argue that if survivability and resiliency are not accounted for, then the evaluation process is likely to be biased in favor of monolithic spacecraft. We show that if in a given context survivability and resiliency are an important requirement for a particular customer, then a distributed architecture is more likely to satisfy this requirement than a monolithic spacecraft design. We discuss in the context of our framework different classes of threats, as well as the high-frequency and low-frequency system response to (or coping strategies with) these shocks or damaging events. We illustrate the importance of this characterization for a formal definition of survivability and resiliency and a proper quantitative analysis of the subject. Finally, we propose in future work to integrate our framework with a design tool that allows the exploration of the design trade-space of distributed space architecture and show how survivability can be “optimized” or traded against other system attributes.
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ItemSurvivability and Resiliency of Spacecraft and Space-Based Networks: a Framework for Characterization and Analysis(Georgia Institute of Technology, 2008-09) Castet, Jean-Francois ; Saleh, Joseph H.Considerations of survivability and resiliency have always been of importance in the design and analysis of military systems. Over the past two decades, the importance of survivability and resiliency has expanded beyond military systems to include public networks and infrastructure systems. The analysis and assessment of networked systems with respect to survivability has become particularly acute in recent years, as attested to by a growing technical literature on the subject. In this paper, we bring these considerations of survivability and resiliency to bear on spacecraft and space-based networks. We develop a framework for comparing the survivability and resiliency of different space architectures, namely that of a monolithic design and a distributed (or networked) space system architecture. There are multiple metrics along which different space architectures can be benchmarked and compared. We argue that if survivability and resiliency are not accounted for, then the evaluation process is likely to be biased in favor of monolithic spacecraft. We show that if in a given context survivability and resiliency are an important requirement for a particular customer, then a distributed architecture is more likely to satisfy this requirement than a monolithic spacecraft design. We discuss in the context of our framework different classes of threats, as well as the high-frequency and low-frequency system response to (or coping strategies with) these shocks or damaging events. We illustrate the importance of this characterization for a formal definition of survivability and resiliency and a proper quantitative analysis of the subject. Finally, we propose in future work to integrate our framework with a design tool that allows the exploration of the design trade-space of distributed space architecture and show how survivability can be "optimized" or traded against other system attributes.