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All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Evolving Reliability and Maintainability Allocations for NASA Ground Systems

This paper describes the methodology and value of modifying allocations to reliability and maintainability requirements for the NASA Ground Systems Development and Operations (GSDO) program’s subsystems. As systems progressed through their design life cycle and hardware data became available, it became necessary to reexamine the previously derived allocations. This iterative process provided an opportunity for the reliability engineering team to reevaluate allocations as systems moved beyond their conceptual and preliminary design phases. These new allocations are based on updated designs and maintainability characteristics of the components. It was found that trade-offs in reliability and maintainability were essential to ensuring the integrity of the reliability and maintainability analysis. This paper discusses the results of reliability and maintainability reallocations made for the GSDO subsystems as the program nears the end of its design phase.

allocations↗
NASA NTRS1994

Recommended techniques for effective maintainability. A continuous improvement initiative of the NASA Reliability and Maintainability Steering Committee

This manual presents a series of recommended techniques that can increase overall operational effectiveness of both flight and ground based NASA systems. It provides a set of tools that minimizes risk associated with: (1) restoring failed functions (both ground and flight based); (2) conducting complex and highly visible maintenance operations; and (3) sustaining a technical capability to support the NASA mission using aging equipment or facilities. It considers (1) program management - key elements of an effective maintainability effort; (2) design and development - techniques that have benefited previous programs; (3) analysis and test - quantitative and qualitative analysis processes and testing techniques; and (4) operations and operational design techniques that address NASA field experience. This document is a valuable resource for continuous improvement ideas in executing the systems development process in accordance with the NASA 'better, faster, smaller, and cheaper' goal without compromising safety.

Source record↗
NASA NTRS2016

Evolving Reliability and Maintainability Allocations for NASA Ground Systems

This paper describes the methodology and value of modifying allocations to reliability and maintainability requirements for the NASA Ground Systems Development and Operations (GSDO) programs subsystems. As systems progressed through their design life cycle and hardware data became available, it became necessary to reexamine the previously derived allocations. This iterative process provided an opportunity for the reliability engineering team to reevaluate allocations as systems moved beyond their conceptual and preliminary design phases. These new allocations are based on updated designs and maintainability characteristics of the components. It was found that trade-offs in reliability and maintainability were essential to ensuring the integrity of the reliability and maintainability analysis. This paper discusses the results of reliability and maintainability reallocations made for the GSDO subsystems as the program nears the end of its design phase.

reliability↗
NASA NTRS2011

Reliability and Maintainability Engineering - A Major Driver for Safety and Affordability

The United States National Aeronautics and Space Administration (NASA) is in the midst of an effort to design and build a safe and affordable heavy lift vehicle to go to the moon and beyond. To achieve that, NASA is seeking more innovative and efficient approaches to reduce cost while maintaining an acceptable level of safety and mission success. One area that has the potential to contribute significantly to achieving NASA safety and affordability goals is Reliability and Maintainability (R&M) engineering. Inadequate reliability or failure of critical safety items may directly jeopardize the safety of the user(s) and result in a loss of life. Inadequate reliability of equipment may directly jeopardize mission success. Systems designed to be more reliable (fewer failures) and maintainable (fewer resources needed) can lower the total life cycle cost. The Department of Defense (DOD) and industry experience has shown that optimized and adequate levels of R&M are critical for achieving a high level of safety and mission success, and low sustainment cost. Also, lessons learned from the Space Shuttle program clearly demonstrated the importance of R&M engineering in designing and operating safe and affordable launch systems. The Challenger and Columbia accidents are examples of the severe impact of design unreliability and process induced failures on system safety and mission success. These accidents demonstrated the criticality of reliability engineering in understanding component failure mechanisms and integrated system failures across the system elements interfaces. Experience from the shuttle program also shows that insufficient Reliability, Maintainability, and Supportability (RMS) engineering analyses upfront in the design phase can significantly increase the sustainment cost and, thereby, the total life cycle cost. Emphasis on RMS during the design phase is critical for identifying the design features and characteristics needed for time efficient processing, improved operational availability, and optimized maintenance and logistic support infrastructure. This paper discusses the role of R&M in a program acquisition phase and the potential impact of R&M on safety, mission success, operational availability, and affordability. This includes discussion of the R&M elements that need to be addressed and the R&M analyses that need to be performed in order to support a safe and affordable system design. The paper also provides some lessons learned from the Space Shuttle program on the impact of R&M on safety and affordability.

Safie, Fayssal M.↗
NASA NTRS2015

Proposal for a Comparison of Reliability and Maintainability Activities Across ESA, JAXA, and NASA

NASA has developed an objectives based hierarchy for guiding Reliability and Maintainability activities. This presentation overviews the hierarchy and proposes to the international trilateral partners to formulate a task force to consider the elements of the NASA RM framework, as captured in the hierarchy of RM considerations, to identify commonalities and differences in the way reliability and maintainability is addressed by the flight projects among the partners.

JAXA↗
NASA NTRS1994

Integrating O/S models during conceptual design, part 2

This report documents the procedures for utilizing and maintaining the Reliability & Maintainability Model (RAM) developed by the University of Dayton for the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) under NASA research grant NAG-1-1327. The purpose of the grant is to provide support to NASA in establishing operational and support parameters and costs of proposed space systems. As part of this research objective, the model described here was developed. Additional documentation concerning the development of this model may be found in Part 1 of this report. This is the 2nd part of a 3 part technical report.

Ebeling, Charles E.↗
NASA NTRS2015

Ethernet for Aerospace Applications - Ethernet Heads for the Skies

One of the goals of aerospace applications is to reduce the cost and complexity of avionic systems. Ethernet is a highly scalable, flexible, and popular protocol. The aerospace market is large, with a forecasted production of over 50,000 turbine-powered aircraft valued at $1.7 trillion between 2012 and 2022. Boeing estimates demand for commercial aircraft by 2033 to total over 36,000 with a value of over $5 trillion. In 2014 US airlines served over 750 million passengers and this is growing over 2% yearly. Electronic fly-by-wire is now used for all airliners and high performance aircraft. Although Ethernet has been widely used for four decades, its use in aerospace applications is just beginning to become common. Ethernet is the universal solution in commercial networks because of its high bandwidths, lower cost, openness, reliability, maintainability, flexibility, and interoperability. However, when Ethernet was designed applications with time-critical, safety relevant and deterministic requirements were not given much consideration. Many aerospace applications use a variety of communication architectures that add cost and complexity. Some of them are SpaceWire, MIL-STD-1553, Avionics Full Duplex Switched Ethernet (AFDX), and Time-Triggered Ethernet (TTE). Aerospace network designers desire to decrease the number of networks to reduce cost and effort while improving scalability, flexibility, openness, maintainability, and reliability. AFDX and TTE are being considered more for critical aerospace systems because they provide redundancy, failover protection, guaranteed timing, and frame priority and are based on Ethernet IEEE 802.3. This paper explores the use of AFDX and TTE for aerospace applications.

Ethernet↗
NASA NTRS2020

The New NASA Approach to Reliability and Maintainability

In 2017, after 20 years, NASA issued a major revision of its reliability and maintainability (R&M) policy, NASA-STD- 8729.1A. Formerly NASA required certain specific R&M activities during each succeeding phase of project development. Now NASA requires a project to start by including the initial development of R&M requirements and the devising of strategies to implement and verify them. Rather than resolving all the requirements first and then designing the system, as has been usual in systems design, the design process now is to work top down by layers. It begins by first identifying the top level requirements and suggesting top level design strategies for those, then making these higher strategies the basis for a lower level set of requirements, and so on down to the lowest components. This approach is intended to ensure that R&M is designed in from the beginning rather than added later with difficulty to a completed design concept. The new R&M standard uses an innovative and effective top-down system design approach intended to effectively implement R&M.

Jones, Harry W.↗
NASA NTRS2020

The New NASA Approach to Reliability and Maintainability

In 2017, after 20 years, NASA issued a major revision of its reliability and maintainability (R&M) policy, NASA-STD-8729.1A [1]. Formerly NASA required certain specific R&M activities during each succeeding phase of project development. Now NASA requires a project to start by including the initial development of R&M requirements and the devising of strategies to implement and verify them. Rather than resolving all the requirements first and then designing the system, as has been usual in systems design, the design process now is to work top down by layers. It begins by first identifying the top level requirements and suggesting top level design strategies for those, then making these higher strategies the basis for a lower level set of requirements, and so on down to the lowest components. This approach is intended to ensure that R&M is designed in from the beginning rather than added later with difficulty to a completed design concept. The new R&M standard uses an innovative and effective top-down system design approach intended to effectively implement R&M.

Jones, Harry W.↗
NASA NTRS2018

Improving Reliability and Maintainability (R&M) in Space Life Support

This paper considers how to improve the reliability and maintainability (R&M) of future NASA space life support systems. If these systems are procured under an industry contract, defining the R&M requirements would take precedence over providing technical guidance on designing the system. Imposing a specific R&M design could be over constraining. However, the mission may define the overall R&M approach, as the International Space Station (ISS) did by requiring Orbital Replacement Units (ORUs). Before defining the R&M requirements for the next mission, the life support research program should understand and plan the R&M approach. The recent NASA technical standard on R&M has moved away from requiring specific R&M activities during each of the traditional project phases to instead developing and planning to implement the R&M requirements to meet the top level project R&M objectives. The emphasis is on providing the evidence to show that the R&M requirements are met, rather than on conducting specific prescribed R&M activities. The technical standard on R&M defines a comprehensive hierarchy of specific R&M objectives and identifies particular strategies to implement them at each level. That is, the top level R&M objective is defined and then one or more design strategies to implement it are developed immediately, before the next lower objectives are defined and the strategies to achieve those are designed. This step-by-step, top-down approach is similar to the axiomatic design method. The objectives are the R&M requirements, and the strategies are the hardware designs or operations plans developed to meet these requirements. The new R&M process is aligned with the systems design process and helps ensure that the methods to meet the R&M requirements are built into the design.

Jones, Harry W.↗
NASA NTRS2013

Reliability and Maintainability Analysis of a High Air Pressure Compressor Facility

This paper discusses a Reliability, Availability, and Maintainability (RAM) independent assessment conducted to support the refurbishment of the Compressor Station at the NASA Langley Research Center (LaRC). The paper discusses the methodologies used by the assessment team to derive the repair by replacement (RR) strategies to improve the reliability and availability of the Compressor Station (Ref.1). This includes a RAPTOR simulation model that was used to generate the statistical data analysis needed to derive a 15-year investment plan to support the refurbishment of the facility. To summarize, study results clearly indicate that the air compressors are well past their design life. The major failures of Compressors indicate that significant latent failure causes are present. Given the occurrence of these high-cost failures following compressor overhauls, future major failures should be anticipated if compressors are not replaced. Given the results from the RR analysis, the study team recommended a compressor replacement strategy. Based on the data analysis, the RR strategy will lead to sustainable operations through significant improvements in reliability, availability, and the probability of meeting the air demand with acceptable investment cost that should translate, in the long run, into major cost savings. For example, the probability of meeting air demand improved from 79.7 percent for the Base Case to 97.3 percent. Expressed in terms of a reduction in the probability of failing to meet demand (1 in 5 days to 1 in 37 days), the improvement is about 700 percent. Similarly, compressor replacement improved the operational availability of the facility from 97.5 percent to 99.8 percent. Expressed in terms of a reduction in system unavailability (1 in 40 to 1 in 500), the improvement is better than 1000 percent (an order of magnitude improvement). It is worthy to note that the methodologies, tools, and techniques used in the LaRC study can be used to evaluate similar high value equipment components and facilities. Also, lessons learned in data collection and maintenance practices derived from the observations, findings, and recommendations of the study are extremely important in the evaluation and sustainment of new compressor facilities.

Safie, Fayssal M.↗
NASA NTRS1991

ETARA PC version 3.3 user's guide: Reliability, availability, maintainability simulation model

A user's manual describing an interactive, menu-driven, personal computer based Monte Carlo reliability, availability, and maintainability simulation program called event time availability reliability (ETARA) is discussed. Given a reliability block diagram representation of a system, ETARA simulates the behavior of the system over a specified period of time using Monte Carlo methods to generate block failure and repair intervals as a function of exponential and/or Weibull distributions. Availability parameters such as equivalent availability, state availability (percentage of time as a particular output state capability), continuous state duration and number of state occurrences can be calculated. Initial spares allotment and spares replenishment on a resupply cycle can be simulated. The number of block failures are tabulated both individually and by block type, as well as total downtime, repair time, and time waiting for spares. Also, maintenance man-hours per year and system reliability, with or without repair, at or above a particular output capability can be calculated over a cumulative period of time or at specific points in time.

Hoffman, David J.↗