Towards Efficacy Hypotheses for Safety Cases
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Leveling Arguments: Easier Said Than Done
The aerospace industry’s current desire to rapidly adopt new technologies is inconsistent with the traditional approach to creating new aerospace certification standards. To address this, an FAA-sponsored international Overarching Properties Working Group comprising industry representatives and certifying agencies has introduced the concept of Overarching Properties (OPs). OPs provide a foundation for proposing alternative Means of Compliance (MoC) by demonstrating a product's possession of the Intent, Correctness, and Innocuity properties. Handling criticality levels with the OPs is in its infancy but still required to integrate alternative MoC into the existing aerospace certification infrastructure. This paper examines the impact of criticality levels on the creation and evaluation of OP-related arguments (OPRAs), specifically focusing on the Auxiliary Power Unit (APU) system. The study highlights the need for tailored OPRA creation based on assigned criticality levels and proposes self-assessment techniques to strengthen arguments. This research serves as a stepping stone in exploring criticality levels for OPs and bridging the gap in aerospace certification practices.
argument↗
SMA for Highly Constrained Projects
This is a collection of presentation elements into a consolidated presentation on overall safety and mission assurance practices for highly constrained projects, such as Class D, 7120.8, or Do No Harm.
safety and mission assurance↗
Evaluation of Agency Non-Code Layered Pressure Vessels (LPVs)
In coordination with the Office of Safety and Mission Assurance and the respective Center Pressure System Managers (PSMs), the NASA Engineering and Safety Center (NESC) was requested to formulate a consensus draft proposal for the development of additional testing and analysis methods to establish the technical validity, and any limitation thereof, for the continued safe operation of facility non-code layered pressure vessels. The PSMs from each NASA Center were asked to participate as part of the assessment team by providing, collecting, and reviewing data regarding current operations of these vessels. This report contains the outcome of the assessment and the findings, observations, and NESC recommendations to the Agency and individual NASA Centers.
Prosser, William H.↗
Evaluation of Agency Non-Code Layered Pressure Vessels (LPVs) : Appendices - Volume 2
In coordination with the Office of Safety and Mission Assurance and the respective Center Pressure System Managers (PSMs), the NASA Engineering and Safety Center (NESC) was requested to formulate a consensus draft proposal for the development of additional testing and analysis methods to establish the technical validity, and any limitation thereof, for the continued safe operation of facility non-code layered pressure vessels. The PSMs from each NASA Center were asked to participate as part of the assessment team by providing, collecting, and reviewing data regarding current operations of these vessels. This document contains the appendices to the main report.
Prosser, William H.↗
Evaluation of Agency Non-Code Layered Pressure Vessels (LPVs)
In coordination with the Office of Safety and Mission Assurance and the respective Center Pressure System Managers (PSMs), the NASA Engineering and Safety Center (NESC) was requested to formulate a consensus draft proposal for the development of additional testing and analysis methods to establish the technical validity, and any limitation thereof, for the continued safe operation of facility non-code layered pressure vessels. The PSMs from each NASA Center were asked to participate as part of the assessment team by providing, collecting, and reviewing data regarding current operations of these vessels. This report contains the outcome of the assessment and the findings, observations, and NESC recommendations to the Agency and individual NASA Centers.
Prosser, William H.↗
Test plan and report for Space Shuttle launch environment testing of Bergen cable technology safety cable
Bergen Cable Technology (BCT) has introduced a new product they refer to as 'safety cable'. This product is intended as a replacement for lockwire when installed per Aerospace Standard (AS) 4536 (included in Appendix D of this document). Installation of safety cable is reportedly faster and more uniform than lockwire. NASA/GSFC proposes to use this safety cable in Shuttle Small Payloads Project (SSPP) applications on upcoming Shuttle missions. To assure that BCT safety cable will provide positive locking of fasteners equivalent to lockwire, the SSPP will conduct vibration and pull tests of the safety cable.
Ralph, John↗
Adaptive Mission Assurance (AMA) – A Conceptual Guide for NASA Missions
NASA is well acquainted with and skilled in conducting Risk Class A Safety and Mission Assurance (SMA). Class A missions are characterized as having highly specific performance with an ultra-low risk tolerance for risk and mission failure. But space is rapidly changing, and the space enterprise is challenged to pursue faster more agile mission developments with fewer resources and directed schedules. To meet this demand mission development teams face accepting more risk and trading performance within strict cost and schedule constraints. In responding to this challenge, The Aerospace Corporation has evolved the Adaptive Mission Assurance (AMA) approach. The benefit of an “adaptive” approach is most realized for smaller Research and Development (R&D), or Science and Technology (S&T) demonstration missions constrained by significantly smaller budgets and directed schedules. The challenge for these “risk tolerant, constraints-driven” missions is how to identify the most valuable mission assurance tasks that will fit within strict budgetary and schedule constraints for “gracefully” accepting risk that still achieves an agreeable expectation of mission success. AMA can respond to this challenge with little to no impact to team staffing or existing workload. This conceptual guide introduces AMA as a potential implementation for NASA Risk Class D and Sub-Class D missions.
Douglas A. Harris↗
Technical Reference Suite Addressing Challenges of Providing Assurance for Fault Management Architectural Design
Research into complexities of software systems Fault Management (FM) and how architectural design decisions affect safety, preservation of assets, and maintenance of desired system functionality has coalesced into a technical reference (TR) suite that advances the provision of safety and mission assurance. The NASA Independent Verification and Validation (IV&V) Program, with Software Assurance Research Program support, extracted FM architectures across the IV&V portfolio to evaluate robustness, assess visibility for validation and test, and define software assurance methods applied to the architectures and designs. This investigation spanned IV&V projects with seven different primary developers, a wide range of sizes and complexities, and encompassed Deep Space Robotic, Human Spaceflight, and Earth Orbiter mission FM architectures. The initiative continues with an expansion of the TR suite to include Launch Vehicles, adding the benefit of investigating differences intrinsic to model-based FM architectures and insight into complexities of FM within an Agile software development environment, in order to improve awareness of how nontraditional processes affect FM architectural design and system health management. The identification of particular FM architectures, visibility, and associated IV&V techniques provides a TR suite that enables greater assurance that critical software systems will adequately protect against faults and respond to adverse conditions. Additionally, the role FM has with regard to strengthened security requirements, with potential to advance overall asset protection of flight software systems, is being addressed with the development of an adverse conditions database encompassing flight software vulnerabilities. Capitalizing on the established framework, this TR suite provides assurance capability for a variety of FM architectures and varied development approaches. Research results are being disseminated across NASA, other agencies, and the software community. This paper discusses the findings and TR suite informing the FM domain in best practices for FM architectural design, visibility observations, and methods employed for IV&V and mission assurance.
Fitz, Rhonda↗
Technical Reference Suite Addressing Challenges of Providing Assurance for Fault Management Architectural Design
Research into complexities of software systems Fault Management (FM) and how architectural design decisions affect safety, preservation of assets, and maintenance of desired system functionality has coalesced into a technical reference (TR) suite that advances the provision of safety and mission assurance. The NASA Independent Verification and Validation (IVV) Program, with Software Assurance Research Program support, extracted FM architectures across the IVV portfolio to evaluate robustness, assess visibility for validation and test, and define software assurance methods applied to the architectures and designs. This investigation spanned IVV projects with seven different primary developers, a wide range of sizes and complexities, and encompassed Deep Space Robotic, Human Spaceflight, and Earth Orbiter mission FM architectures. The initiative continues with an expansion of the TR suite to include Launch Vehicles, adding the benefit of investigating differences intrinsic to model-based FM architectures and insight into complexities of FM within an Agile software development environment, in order to improve awareness of how nontraditional processes affect FM architectural design and system health management.
Fitz, Rhonda↗
Querying Safety Cases
Querying a safety case to show how the various stakeholders' concerns about system safety are addressed has been put forth as one of the benefits of argument-based assurance (in a recent study by the Health Foundation, UK, which reviewed the use of safety cases in safety-critical industries). However, neither the literature nor current practice offer much guidance on querying mechanisms appropriate for, or available within, a safety case paradigm. This paper presents a preliminary approach that uses a formal basis for querying safety cases, specifically Goal Structuring Notation (GSN) argument structures. Our approach semantically enriches GSN arguments with domain-specific metadata that the query language leverages, along with its inherent structure, to produce views. We have implemented the approach in our toolset AdvoCATE, and illustrate it by application to a fragment of the safety argument for an Unmanned Aircraft System (UAS) being developed at NASA Ames. We also discuss the potential practical utility of our query mechanism within the context of the existing framework for UAS safety assurance.
Safety Case↗
System Safety Analysis of Complex NASA Systems with Model-Based Engineering (REV B)
The emergence of model-based engineering is transforming design and analysis methodologies. A recognized benefit of model-based engineering is the existence of a “single source of truth” about the system that becomes the authoritative source of data and information for designers, analysts, and developers. This promotes consistency and efficiency as the design emerges and can be used to further optimize the design. Integrating System Safety Engineers to the “single source of truth” will ensure that the outputs of their assessments and analyses are relevant to the design as it evolves. Use of an integrated system model enables near immediate evaluation of a design change as well as development of operational processes for risk assessment and communication. Such models can enable efficient and timely analysis of system hazards (e.g., hazard fault tree analysis and procedure simulations) and produce complete, accurate, and more consistent products (e.g., hazard reports and safety requirement evaluations). Therefore, an agency-sponsored team at Goddard Space Flight Center (GSFC) recently completed a System Safety Study of modeling and testing capabilities as part of a Model-Based Safety and Mission Assurance Initiative (MBSMAI). Using an existing model developed for reliability analyses, GSFC modeling and system safety experts performed system safety analysis/modeling and produced safety products. The team evaluated model-based feasibility to support System Safety Engineering, developed safety analysis modeling processes, and identified tool capability advancement/development needs. These study results indicate model-based engineering is valid and useable for System Safety Engineering for NASA if adequate modeling processes and environment are established.
NASA↗
CST: A Tool for Optimizing the Efficiency and Effectiveness of Static-Code Analysis Tools
Static Code Analysis (SCA) is a vital component of NASA IV&V’s mission assurance for safety-critical software as it reduces the likelihood of software-induced hazards impacting mission success. Static Code Analysis achieves this by identifying hazards that may not have been otherwise detectable by typical code reviews or other testing. Using SCA tools, however, can be intimidating due to steep learning curves, especially considering tool performance and defect coverage varies greatly. Because of this variation amongst SCA tools, understanding which tools support certain defects and which do not, as well as understanding how to run an analysis based on steps that are unique to each tool, can be difficult to both new and experienced analysts alike. To mitigate this, the SCAWG or the IV&V Static Code Analysis Working Group, created the SCA Checker Taxonomy and Starting Point Profiles. The Checker Selection Tool (CST) incorporates these two SCAWG products into an interactive tool which allows the user to: select organized categories of defects they would like the SCA tools to discover, select default checkers depending on their mission type (e.g. flight), and configure multiple SCA tools at once. C/C++, Java, and Python defect checkers from four common SCA tools were utilized in this iteration of the CST. This iteration also includes the addition of training, SCA tool specific help, and taxonomy guide links, into its design to help users new to Static Code Analysis learn how to perform SCA more efficiently. The CST has been subject to beta testing by experienced static code analysts from the SCAWG to ensure a usable and accurate final product. The implications of the CST in the mission assurance of NASA safety-critical software are profound, as the CST can help identify and reduce false positives and false negatives, fundamentally improving overall SCA efficiency and accuracy.
static code analysis↗
Challenges in High-Assurance Runtime Verification
Safety-critical systems are growing more complex and becoming increasingly autonomous. Runtime Verification (RV) has the potential to provide protections when a system cannot be assured by conventional means, but only if the RV itself can be trusted. In this paper, we proffer a number of challenges to realizing high-assurance RV and illustrate how we have addressed them in our research. We argue that high-assurance RV provides a rich target for automated verification tools in hope of fostering closer collaboration among the communities.
Goodloe, Alwyn E.↗
Safety of hydrogen pressure gauges.
Study of the relative safety afforded an operator by various hydrogen-pressure gauge case designs. It is shown that assurance of personnel safety, should a failure occur, requires careful selection of available gauge designs, together with proper mounting. Specific gauge case features and mounting requirements are recommended.
Voth, R. O.↗
[MaRS Project]
The Space Exploration Division of the Safety and Mission Assurances Directorate is responsible for reducing the risk to Human Space Flight Programs by providing system safety, reliability, and risk analysis. The Risk & Reliability Analysis branch plays a part in this by utilizing Probabilistic Risk Assessment (PRA) and Reliability and Maintainability (R&M) tools to identify possible types of failure and effective solutions. A continuous effort of this branch is MaRS, or Mass and Reliability System, a tool that was the focus of this internship. Future long duration space missions will have to find a balance between the mass and reliability of their spare parts. They will be unable take spares of everything and will have to determine what is most likely to require maintenance and spares. Currently there is no database that combines mass and reliability data of low level space-grade components. MaRS aims to be the first database to do this. The data in MaRS will be based on the hardware flown on the International Space Stations (ISS). The components on the ISS have a long history and are well documented, making them the perfect source. Currently, MaRS is a functioning excel workbook database; the backend is complete and only requires optimization. MaRS has been populated with all the assemblies and their components that are used on the ISS; the failures of these components are updated regularly. This project was a continuation on the efforts of previous intern groups. Once complete, R&M engineers working on future space flight missions will be able to quickly access failure and mass data on assemblies and components, allowing them to make important decisions and tradeoffs.
Aruljothi, Arunvenkatesh↗
System Safety Analysis of Complex NASA Systems with Model Based Engineering
The emergence of model-based engineering is transforming design and analysis methodologies [5]. A recognized benefit of model-based engineering is the existence of a “single source of truth” about the system that becomes the authoritative source of data and information for designers, analysts, and developers. This promotes consistency and efficiency as the design emerges and can be used to further optimize the design. Integrating System Safety Engineers to the “single source of truth” will ensure that the outputs of their assessments and analyses are relevant to the design as it evolves. Use of an integrated system model enables near immediate evaluation of a design change as well as development of operational processes for risk assessment and communication. Such models can enable efficient and timely analysis of system hazards (e.g., hazard fault tree analysis and procedure simulations) and produce complete, accurate, and more consistent products (e.g., hazard reports and safety requirement evaluations). Therefore, an agency-sponsored team at Goddard Space Flight Center (GSFC) recently completed a System Safety Study of modeling and testing capabilities as part of a Model-Based Safety and Mission Assurance Initiative (MBSMAI). Using an existing model developed for reliability analyses [1], GSFC modeling and system safety experts performed system safety analysis/modeling and produced safety products. The team evaluated model-based feasibility to support System Safety Engineering, developed safety analysis modeling processes, and identified tool capability advancement/development needs. These study results indicate model-based engineering is valid and useable for System
Model Based Engineering↗
Verification and Implementation of Operations Safety Controls for Flight Missions
There are several engineering disciplines, such as reliability, supportability, quality assurance, human factors, risk management, safety, etc. Safety is an extremely important engineering specialty within NASA, and the consequence involving a loss of crew is considered a catastrophic event. Safety is not difficult to achieve when properly integrated at the beginning of each space systems project/start of mission planning. The key is to ensure proper handling of safety verification throughout each flight/mission phase. Today, Safety and Mission Assurance (S&MA) operations engineers continue to conduct these flight product reviews across all open flight products. As such, these reviews help ensure that each mission is accomplished with safety requirements along with controls heavily embedded in applicable flight products. Most importantly, the S&MA operations engineers are required to look for important design and operations controls so that safety is strictly adhered to as well as reflected in the final flight product.
Smalls, James R.↗