Edward J. Zampino

Reliability Assessment Approach for Stirling Convertors and Generators

Stirling power conversion is being considered for use in a Radioisotope Power System (RPS) for deep space science missions because it offers a multifold increase in the conversion efficiency of heat to electric power. Quantifying the reliability of an RPS that utilizes Stirling power conversion technology is important to develop and demonstrate the capability for long‐term success. A description of the Stirling power convertor is provided, along with a discussion about some of the key components. On‐going efforts to understand component life, design variables at the component and system levels, and related sources and nature of uncertainties is discussed. The requirement for reliability is discussed, and some of the critical areas of concern are identified. A section on the objectives of the overall development of the performance model and computation of reliability is included to highlight the goals of this effort. Also, a viable physics based reliability plan to model the design level variable uncertain...

The potential application of risk assessment to the Breakthrough Propulsion Physics Project

In May of 2001, researchers at the NASA Glenn Research center in Cleveland Ohio began exploring the possibility of applying risk assessment to a frontier propulsion project called Breakthrough Propulsion Physics (BPP). The goals of BPP are the drastic reduction or elimination of propellant mass, the attainment of hyper-fast space travel (approaching or exceeding) the speed of light, and new methods for onboard energy conversion. The BPP challenges transcend mere engineering and forces a re-examination of the fundamental physics from which technology is developed. BPP is at a maturity level of emerging science. The challenge is formidable: to apply risk assessment to a project that will not have conceptual designs for a long time to come. However, we suggest that it still makes a great deal of sense to think about the risks associated with various paths of research. In particular, it is suggested that there are a number of potential areas where risk assessment can be applied even when a project is at the maturity level of emerging science. It is believed that with the concepts and tools of risk assessment, more is possible than assessing potential reliability and maintainability. There is more to the story than the obvious need for greater reliability. We are proposing that risk assessment tools can be applied to guide research success.

Combining System Safety & Reliability to ensure NASA CoNNeCT's success

Hazard Analysis, Failure Modes and Effects Analysis (FMEA), the Limited-Life Items List (LLIL), and the Single Point Failure (SPF) List were applied by System Safety and Reliability engineers on NASAs Communications, Navigation, and Networking reConfigurable Testbed (CoNNeCT) Project. The integrated approach involving cross reviews of these reports by System Safety, Reliability, and Design engineers resulted in the mitigation of all identified hazards. The outcome was that the system met all the safety requirements it was required to meet.

System reliability analysis with the response surface method

The reliability of a simple turbomachinery model was calculated to demonstrate the application of a newly developing system integration tool, Probabilistic Design and Analysis Framework(PRODAF), along with efficient probabilistic methods using a response surface method. The model represents a system consisting of hypothetical turbine components. The parts include a blade, disk, and shaft with an applied angular velocity. All the components were modeled with the properties of the nickel alloy, Inconel 718. A response surface was calculated for the system of components to improve probabilistic computational efficiency. In addition, a fast probability integration method, Advanced First Order Reliability Method (AFORM), was used for the probabilistic analysis in order to provide an efficient analysis as possible. Geometric dimensions, the applied load, and material yield strength were varied for this study. The probability of failure was determined using the maximum first principal stress response and the material yield strength. A simple G function using the difference between strength and loading stress was used to determine failure limits. The probabilistic sensitivity of the failure response relative to the individual variables was determined also with material yield strength having the greatest influence. The model was recreated with every iteration of the probabilistic analysis in order to vary the geometry. As a result, the response surface method has a significant impact on improving computational efficiency and enabling reliability analysis with rapid turnaround.

Reliability quantification of the flexure: a critical Stirling convertor component

The objective of the paper is to present a methodology and quantified results of numerical simulation for the reliability of flexures used in the Stirling convertor for their structural performance. The proposed approach is based on application of finite element analysis method in combination with the random fatigue limit model, which includes uncertainties in material fatigue life. Additionally, sensitivity of fatigue life reliability to the design variables is quantified and its use to develop guidelines to improve design, manufacturing, quality control and inspection design process is described.

International R&M/safety cooperation lessons learned between NASA and JAXA

Presented are a number of important experiences gained and lessons learned from the collaboration of the National Aeronautics and Space Administration (NASA) and the Japanese Aerospace Exploration Agency (JAXA) on the CoNNeCT (Communications, Navigation, and Networking re-Configurable Testbed) project. Both space agencies worked on the CoNNeCT Project to design, assemble, test, integrate, and launch a communications testbed facility mounted onto the International Space Station (ISS) truss. At the 2012 RAMS, two papers about CoNNeCT were presented: one on Ground Support Equipment Reliability & System Safety, and the other one on combined application of System Safety & Reliability for the flight system. In addition to the logistics challenges present when two organizations are on the opposite side of the world, there is also a language barrier. The language barrier encompasses not only the different alphabet, it encompasses the social interactions; these were addressed by techniques presented in the paper. The differences in interpretation and application of Spaceflight Requirements will be discussed in this paper. Although many, but definitely not all, of JAXAs Spaceflight Requirements were inspired by NASA, there were significant and critically important differences in how they were interpreted and applied. This paper intends to summarize which practices worked and which did not for an international collaborative effort so that future missions may benefit from our experiences. The CoNNeCT flight system has been successfully assembled, integrated, tested, shipped, launched and installed on the ISS without incident. This demonstrates that the steps taken to facilitate international understanding, communication, and coordination were successful and warrant discussion as lessons learned.

Potential application of FORM and SORM for PRA

The focus of this paper is two-fold: 1) a discussion of a process by which a probabilistic risk assessments (PRA) system model is used to direct a multi-disciplinary development project. 2) Under this framework, a potential technique for the application of the First-Order Reliability Method (FORM) and Second-Order Reliability Method (SORM) to provide probabilistic failure data for PRA of structural systems. Technique 2) is an elaboration of the analysis techniques described in chapter 14 of [1]. Specifically, the technique relies on the concept of the limit state function in conjunction with varying levels of model fidelity, sound engineering judgment, and expert opinion. This methodology is complementary to the Response Surface Method presented in [2] and is best utilized during the conceptual or preliminary stages of a design project. This technique is beneficial when reliability data is not readily available and/or one is constrained by aggressive development schedules. As the design matures, the events in the system event tree can be systematically re-defined by a process that uses the results of refined physics-based models.

Reliability Quantification of Advanced Stirling Convertor (ASC) Components

The Advanced Stirling Convertor is intended to provide power for an unmanned planetary spacecraft and has an operational life requirement of 17 years. Over this 17 year mission, the ASC must provide power with desired performance and efficiency. The very long mission time intended for the ASC drives a total test time and sample of test units that exceeds the resource constraints of the project. Reliability demonstration must be accompanied by the application of analysis, system and component level testing, and simulation models, taken collectively. Therefore, computer simulation with limited test data verification is a viable approach to assess the reliability of ASC components. This approach is based on understanding the physics-of-failure mechanisms and the relationship among the design variables based on physics, mechanics, material behavior models, interaction of different components. Their respective disciplines such as structures, materials, fluid, thermal, mechanical, electrical, etc. are all applied. In addition, these models are based on the available test data, which can be updated, and analysis refined as more data and information becomes available. Consequently, guidelines to improve design reliability and better operating controls to reduce the probability of failure can be developed. Quantified reliability assessment based on fundamental physical behavior of components and their relationship with other components has demonstrated itself to be a superior technique to conventional reliability approaches based on utilizing failure rates derived from similar equipment or simply expert judgment.

Ideas and possible approaches for ultra-reliability

Ultra-reliability means assured, dependable operation over the required service life with repeatable success. This will be a vital part of any system developed for the NASA space exploration vision. In order to achieve this goal, equipment must be able to survive the stresses of prolonged operation and there has to be a drastic reduction in manufacturing flaws and the human error rate. There will have to be a dedication to the practice of designing in highly robust electrical, mechanical, and electromechanical components into complex systems and special attention to survival of environmental threats such as radiation and micro-meteors. Complex systems present an exceptional challenge because of the large number of potential failure modes as well as the possibilities for system interactions and failure propagation. Failure mode and effects analysis, Event Tree, and fault tree analysis should be applied to the hardware and software as an integrated configuration. In many cases, it will be determined that existing technology has reached its reliability or operating life limit and new technology will be required. Sustained research and development over a period of 20 years or beyond may be needed to develop Ultra-reliable systems on a mass scale. New technology with greater operating life may be able to support the goal of ultra-reliability but that new technology also introduces new reliability problems that will have to be overcome. Resources and established practices for reliability engineering must be strongly maintained as the foundation for achieving ultra-reliability.

Probabilistic risk assessment (PRA) approach for the next generation launch technology (NGLT) program turbine-based combined cycle (TBCC) architecture 6 launch vehicle

The NASA Next Generation Launch Technology (NGLT) Program is evaluating various concepts for less expensive and reduced-risk access to space. Critical to these goals are more reliable and easily maintained vehicles, with high fidelity integrated vehicle health management (IVHM) systems, rapid turn-around time and dual-use technology. The initial application of probabilistic risk assessment (PRA) on the turbine-based combined cycle (TBCC) architecture 6 concept has helped to define key assumptions necessary to make the development of the architecture 6 concept successful. While the final figures of merit (FOMs) will be based on successfully developing and testing the vehicle, preliminary FOMs can be used now for basic trades between propulsion and staging concepts, thus providing a valuable tool to evaluate the overall trade space between highly divergent concepts. Reliability analysis, probabilistic design methods (PDM), and probabilistic risk assessment can be integrated to evaluate overall systems architecture, a complete mission model, and a fleet logistics model. In addition, the PRA may be used to evaluate and compare a high and low energy crew escape system.