Single-point Failure Modes Research Articles

On-Orbit Implementation of Discrete Isolation Schemes for Improved Reliability of Serial Communication Buses

Serial communication buses are used in electronic systems to interconnect sensors and other devices, but two of the most widely used protocols, i.e., interintegrated circuit (I2C) and serial peripheral interface (SPI), are vulnerable to bus-wide failure if even one device on the bus malfunctions. For aerospace applications demanding increasingly more distributed processing and sensing capability, the compounding risk to system reliability as device count scales becomes a limiting factor in mission scope, performance, and lifetime. We propose a simple external circuit to be added to each node on a communication bus that automatically isolates the node in the event of device failure. By automatically isolating failed devices, the integrity of the bus is preserved without requiring additional signals or processing overhead from the host controller. In this article, I2C and SPI isolation circuits are simulated, fabricated, and experimentally verified to be effective at preserving bus integrity in the event of peripheral device failure. The isolation circuits were integrated into three spacecraft for the successful NASA V-R3x mission and found to significantly improve system reliability by eliminating single-point failure modes of the I2C and SPI buses. The developed protection schemes are a valuable tool for decoupling system reliability from serial bus device count and can readily be integrated into the existing aerospace systems.

Fatigue life cycle estimation and reliability analysis of hydraulic plumbing of a launch vehicle control actuator

One of the single point failure modes identified for the electro hydraulic control actuators of launch vehicles, is the fatigue failure of the hydraulic plumbing and its joints due to severe vibration environments. This paper presents a case study of the fatigue analysis on the hydraulic plumbing with flared coupling joint, subjected to high vibration levels. An evaluation of the vibration response of the system is made through analysis and experimentation. A finite element model of the plumbing is made to capture the dynamic behaviour of the system. The alternating stresses are assessed by dynamic stress analysis using the validated model. Fatigue life cycle estimation and reliability of the joint are determined pragmatically through stress life methods, based on the local peak stress, the corresponding local strength, and their statistical distribution. Based on the study, a simple design solution is suggested to improve the robustness of the critical control actuator of the launch vehicle.

Failure Mode Avoidance of Solid Rocket Motor Pressure Monitoring Joint Seals

The sealing joints used for pressure monitoring of solid propellant rocket motors (SRMs) of launch vehicles are very critical, as they are large in number, and leak through any of them is a single point failure mode. Identification of failure modes and its prevention is the key for reliable performance of an SRM. Failure modes are identified and the failure mechanisms of different seals in the pressure monitoring system studied through investigative tests with deliberately induced variations in the design parameters and nonconformance. Systematic analysis is carried out for the proposed designs through a failure mode effects analysis (FMEA), failure modes ranked in accordance with Risk Priority Number (RPN) and reliability of the joints worked out from the data. Design concerns are analyzed, alternate designs explored and innovative design solutions evolved. The effectiveness of the final design is brought out quantitatively by reduced RPN ratings and quantum jump in the reliability. Critical design, process and quality control parameters were identified, and procedures to ensure them evolved for failure mode avoidance.

Failure Analysis of AISI 304 Stainless Steel Sleeve Used in High-Pressure Hose Assembly of Actuation System of a Satellite Launch Vehicle

Hydraulic control actuation systems in launch vehicles use flexible hoses for transmission of forces to actuators at different locations. The hose ends are connected to the interface adapters by AISI 304 stainless steel sleeves. These sleeves are assembled to nipple end fittings of the high-pressure hose by a swaging operation to obtain leak-proof hose assemblies. The swaging operation is carried out at room temperature by a hydraulically operated swaging machine. Performance of the system as a whole requires strict adherence to the quality standards maintaining the critical interface dimensions within specified tolerances and ensuring the compression given to the swaged joint through the sleeve. If the joining forces are less, this can result in loose joints and gross leakage, whereas excessive compression can cause damage to the parts of the system namely the sleeve, stainless steel braid, PTFE or the adapter. The swaged joint is a single-point failure mode, indicating that a failure in the joint can lead to mission failure. It has to withstand harsh environments such as high pressure, low and high temperature extremes, fatigue loading due to pressure cycling as well as vibration. Therefore, as part of design verification, a detailed qualification plan has been prepared and the hoses were tested as per the plan. As per the test plan, these hoses undergo acceptance tests which include pneumatic and hydraulic pressure testing. During acceptance testing of hoses, one of the hose sleeves was found to be cracked. The cracking was observed after carrying out the pneumatic test when the assembly was being prepared for hydraulic pressure set-up. This paper describes the detailed metallurgical investigation carried out to understand the cause of failure and actions taken to avoid similar failures.

Reliability analysis for thermal cutting method based non-explosive separation device

In order to increase the reliability of a separation device for a small satellite, a new non-explosive separation device is invented. This device is activated using a thermal cutting method with a Ni-Cr wire. A reliability analysis is carried out for the proposed non-explosive separation device by applying the Fault tree analysis (FTA) method. In the FTA results for the separation device, only ten single-point failure modes are found. The reliability modeling and analysis for the device are performed considering failure of the power supply, the Ni-Cr wire burns failure and unwinds, the holder separation failure, the balls separation failure, and the pin release failure. Ultimately, the reliability of the proposed device is calculated as 0.999989 with five Ni-Cr wire coils.

Reliability and Quality Assurance Experience in Launcher Hold and Release System used in GSLV

The launcher hold and release system (LHRS) was successfully used, for the first time, for GSLV-DI mission after thorough test and evaluation, in line with reliability and quality assurance (R&QA) requirements. Various R&QA techniques are applied to make LHRS failure-free. Failure mode effect and criticality analysis (FMECA) was used as a tool for identifying critical failure modes. Single-point failure modes (SPFMs) identified from FMECA are strengthened by design modifications and the same are verified by testing. Testing philosophy is tailored to have more number of tests at the system level. Capability demonstration tests and failure mode simulation tests were carried out during system qualification phase. Acceptance tests are done on the flight hardware at launch pad to demonstrate better confidence on the system. This paper illustrates how R&QA techniques complimented and added value at different stages in the development cycle of LHRS, by means of few case studies. Testing methodologies adopted and problems encountered during the development and qualification phases are described in brief. Various problems surfaced during preparation for flight are also discussed.

A distributed media access protocol for packet radio networks and performance analysis. Part 1: Network capacity

AbstractA distributed time‐slot assignment protocol is developed for a mobile multi‐hop broadcast packet radio network, using time division multiple access channel access and virtual circuit switching. The protocol eliminates the single point failure mode of centralized network management and the delays of centralized processing. It is applicable to the user‐to‐user communications functions of such systems as the U. S. Army's enhanced position location and reporting system (EPLRS). The important functions of the distributed protocol, including time‐slot assignment, virtual circuit set‐up, and network synthesis, are identified, and implementing algorithms are presented and verified. The performance analysis of the protocol is divided into two parts. In this paper, Part 1 of the performance analysis, the capacity of a network using this protocol is studied and a tool is developed to design the network capacity by trading off among the network area, the transmission range, and the number of packet radio units. Since these results are not in closed form, numerical results provide insight into these parameters. In Part 2 the network set‐up time and network data rate are analysed and a hierarchical architecture for the distributed protocol is proposed and analysed.

A manufacturing capacity planning experiment through functional workload decomposition

In this paper, we describe an experiment to evaluate a distributed architecture via functional database workload decomposition. A workload in a circuit pack assembly environment was decomposed and mapped onto a frontend/backend distributed computer architecture. To evaluate this distributed architecture, an operational model for capacity planning was devised, and performance and cost-effectiveness measures were chosen. Model parameters were estimated through benchmark experiments in a distributed system consisting of various super-microcomputers connected by a CSMA/CD local area network with INGRES as the database management system. The frontend/backend architecture consists of a backend data repository and analysis computer system and a few frontend computer systems dedicated for data collection and manufacturing process verification. Because of the significant software overhead in communication protocol and database processing, information exchange was batched between the backend and frontend systems to amortize such cost to improve overall system performance. Results of the experiments were analyzed to gain quantitative insight on the feasibility of such decomposition and its mapping onto the proposed architecture. With sufficient batching, the proposed distributed architecture not only has more overall system capacity, but also is more cost-effective than the typical centralized architecture. The approach described is applicable in more general contexts. Advantages of such distributed systems include the relative robustness of the distributed architecture under single point failure mode and the ease of capacity growth by upgrading the computer systems and/or by increasing the number of frontend systems.