This page features a series of short (4 to 8-page) summaries of reliability design and test practices which have contributed to the success of NASA spaceflight missions. Practices within the categories of natural space environment, reliability design, reliability analysis, and hardware test are provided for viewing and downloading in PDF format. Over 100 preferred practice summaries are available (including those published by the other NASA centers). Each summary defines the practice and discusses its benefits, spacecraft applications, implementation method, technical rationale, impact of non-performance, and lists references and related practices.
|The reliability practices published by the other NASA field installations may be accessed from the NASA HQ practices home page.|
NASA Technical Memorandum 4322
1101: Environmental Factors
Practice: At the onset of the design process, identify the operating conditions that will be encountered during the life of the equipment.
Benefits: Each of the identified environmental factors requires consideration in the design process. This assures that adequate environmental strength is incorporated into the design to ensure reliability.
1102: Meteoroids/Space Debris
Practice: Design spacecraft external surfaces to ensure 95 percent probability of no mission-critical failures from particle impact.
Benefit:Reliability is greatly enhanced because the likelihood of serious mission degradation or spacecraft loss is significantly reduced.
1103: Ni-CdConventional Spacecraft Battery Handling and Storage
Practice: Flight projects develop and implement handling and storage procedures for Ni-Cd flight batteries when applicable to minimize deterioration and irreversible effects on flight performance due to improper handling and storage.
The procedures described in this practice are specifically for Conventional Ni-Cd batteries and are not necessarily applicable to Super Ni-Cd batteries.
Benefit:Ni-Cd batteries are perishable and their ability to satisfactorily complete mission life is directly related to prudent handling and storage procedures. The development and implementation of appropriate project-unique procedures based on a set of proven guidelines assure that the optimum performance of Ni-Cd batteries is not degraded due to inappropriate handling and storage.
1104: Monitoring Spacecraft Exposure to Magnetic Fields
Practice: This reliability practice provides a read out of magnetic field exposures which could adversely affect the magnetic cleanliness of the spacecraft. When transporting a spacecraft or flight instrument to a launch site or other facility, monitor the D.C. magnetic field peak exposure with a "tell tale" sensor. This practice is also applicable to flight hardware placed in storage for extended periods.
Benefit: The "telltale" device will provide an indication of the peak D.C. magnetic field intensity to which the transported (or stored) system has been exposed. High residual fields are sometimes caused by nearby lightning strikes, power system faults or exposure to strong permanent magnets. Compliance with the peak magnetic field exposure, as defined in the Magnetic Control Plan document, assures that the flight hardware is in its lowest magnetic state, thereby minimizing any adverse effects on the integrity of science data.
1105: Solar Flare Proton & Heavy Ion Modeling for Single Event Effects
Operational spacecraft can experience adverse effects from impinging high energy radiation. A single event upset (SEU) occurs when a single particle, usually a heavy ion or proton, deposits enough charge at a sensitive node in a microcircuit to cause that circuit to change state. In general, these effects are temporary and appear as "soft failures" such as anomalous bit flips or spurious commands. In extreme cases, latch-up can occur and result in the destructive failure of the part.
The practice is to formulate an energetic particle environment model for calculating single event effect rates by utilizing the JPL statistical models for solar proton, alpha particle and heavy ion fluence. This predicted rate, which is a function of cumulative probability, is a useful measure when specifying shielding thickness to protect susceptible components, employing mitigating software, or both to reduce the risk to an acceptable level. Note that this assessment does not consider concentration of particle radiation due to the Earth's magnetic field, (ref. 1), and factors which are not influenced by shielding thickness, such as GCR (Galactic Cosmic Rays).
Shielding thickness can be realistically assessed by considering the cumulative probability of component failure due to radiation of solar particles.
1106: Plasma Noise in EMI Design
Practice: Missions with payloads that can interact strongly with the ambient plasma, such as a high power electron beam, a high power RF source, or an ion engine, may require a structural current test for conducted susceptibility and higher radiated susceptibility test levels. The practice is to perform an analysis early in such a program to estimate the amplitude of plasma noise induced electromagnetic interference (EMI). This may identify potential adverse effects on operational reliability.
Benefits:Potential EMI sources are identified in time so that appropriate measures can be incorporated into the electromagnetic compatibility (EMC) program. If the high predicted levels turn out to be a problem, the early identification allows time to develop a solution.
1107: Micrometeorite Protection
Provide protection for the spacecraft structure and instruments to minimize damage from micrometeoroid1 penetration. Typical reliability engineering measures range from structural positioning to protect sensitive hardware to placement of protective blankets on the spacecraft exterior. The extent of the protective measures is based on estimates of the meteoroid environment for the flight profile, the ability of micrometeoroids to penetrate the external skin, and the likelihood of critical damage from a penetration.
Micrometeoroid protection minimizes the risk of impacts that can damage spacecraft systems and jeopardize flightworthiness. Sources of meteoroids include planetary ejecta and particles of asteroidal and cometary origin. Impacts on spacecraft can cause partial penetration, perforation, spalling, local deformation, or secondary fractures, any of which can result in failure of a critical system. Typical failure modes include:
- Catastrophic rupture.
- Vaporific flash.
- Reduced structural strength.
1 For the purpose of environmental modeling, a micrometeoroid is defined as being in the range of 10-18 to 1.0 grams in mass.
1108: Super Ni-Cd Spacecraft Battery Handling and Storage Practice
Practice: Flight projects assure reliable operation of Super Ni-Cd flight batteries through the implementation of appropriate handling and storage procedures. Such procedures minimize deterioration and irreversible effects.
Benefit: Super Ni-Cd batteries are perishable and their reliability is directly related to prudent handling and storage procedures. The development and implementation of appropriate project-unique procedures based on a set of proven guidelines assure that the optimum performance of Super Ni-Cd batteries is not degraded due to inappropriate handling and storage.
1109: Ni-H2 Spacecraft Battery Handling and Storage Practice
Practice: Develop and implement handling and storage procedures to ensure reliable operation, minimize deterioration, and prevent irreversible effects on the flight performance of Ni-H2 flight batteries due to improper handling and storage.
Benefit:Ni-H2 batteries will significantly deteriorate, principally due to capacity fading, if the proper storage and handling procedures are not followed in a number of stages in the cell/battery lifetime. A set of proven guidelines is followed by flight projects in the preparation and utilization of project unique handling and storage procedures in order to minimize these deterioration effects and ensure the reliable performance of Ni-H2 batteries.
1110: Optical Fiber Cable Terminations Techniques and Procedures
Practice: Apply approved requirements and assembly techniques and procedures in the termination of optical fiber cables used in spaceflight applications.
Benefits:This practice ensures the performance reliability of optical fiber cable assemblies by requiring the selection of optical fiber cable components that have been tested and approved for spaceflight use and by specifying approved assembly and acceptance inspection and test procedures
1201: EEE Parts Derating
Practice: Derate applied stress levels for electrical, electronic, and electromechanical (EEE) part characteristics and parameters with respect to the maximum stress level ratings of the part. The allowed stress levels are established as the maximum levels in circuit applications.
Benefits:Derating lowers the probability of failures occurring during assembly, test, and flight. Decreasing mechanical, thermal, and electrical stresses lowers the possibility of degradation or catastrophic failure.
1202: High Voltage Power Supply Design and Manufacturing Practices
Practice: Thoroughly test high voltage power supply packaging on flight configured engineering models, in a simulated space flight environment, to evaluate corona effects.
Benefits:Process controls on design, manufacturing, and testing operations reduce component failure rates and improve reliability. The goal is production of power supplies that will operate in space for the mission duration.
1203: Class S Parts in High Reliability Applications
Practice: Use Class S and Grade 1 or equivalent parts in all applications requiring high reliability or long life1 to yield the lowest possible failure rates.
Benefits: Low parts failure rates in typical circuit applications result in significant system reliability enhancement. For space systems involving serviceability, the mean-time-between-failure (MTBF) is greatly extended, which significantly reduces maintenance requirements and crew time demands.
1 Long life is defined as a requirement to perform the defined function without sacrifice to the primary mission objectives for a period longer than 3 years. Criticality of a function may require high reliability for any period of time and is not necessarily coupled to long life. However, when high reliability is coupled with long life, increased attention to the best reliability design practices is appropriate.
1204: Part Junction Temperature
Practice: Maintain part junction temperatures during flight below 60 C. (Short-term mission excursions associated with transient mission events are permissible.)
Benefit:Reliability is greatly increased because the failure rate is directly related to the long-term flight temperature.
1205: Welding Practices for 2219 Aluminum and Inconel 718
Practice: Gas Tungsten Arc Welding and Variable Polarity Plasma Arc Welding are preferred for joining 2219 Aluminum, and Electron Beam Welding is preferred for joining Inconel 718 in critical aerospace flight applications.
Benefit:Adhering to proven design practices and processing techniques for 2219 Aluminum and Inconel 718 will result in high performance joints, reduced weld defects, reduced weld repair costs, and reduced inspection costs. These practices, if conscientiously applied, will reduce the potential for galvanic corrosion, hot cracking, imperfect bead shape, inclusions, lack of fusion, lack of penetration, microfissuring, mismatch, peaking, porosity, residual stresses, start/stop defects, and stress corrosion cracking.
1206: Power Line Filters
Practice: Power line filters are designed into power lines (power buses) at the inputs to payloads, instruments, subsystems, and components.
Benefits: Power line filters minimize the flow of conducted noise currents on power buses emanating from hardware that could interfere with the proper operation of other hardware also operating on the same power buses. Additionally, power line filters minimize the flow of noise currents on power buses into hardware which could interfere with the proper operation of that hardware.
1207: Magnetic Design Control for Science Instruments
Practice: Design flight subsystems with low residual dipole magnetic fields to maintain the spacecrafts total static and dynamic magnetic fields within science requirements.
Benefit:Provides for a magnetically clean spacecraft, which increases the quality and accuracy of interplanetary and planetary magnetic field data gathered during the mission.
1208: Static Cryogenic Seals for Launch Vehicle
Practice: Deflection actuated, pressure assisted coated metal seals, or spring energized TeflonŽ seals, along with prudent flange joint designs, should be used for high pressure static cryogenic sealing applications in launch vehicle engines and related propulsion system components.
Benefit: Leak-free joints can be achieved in cryogenic lines, joints, valves, and pumps for launch vehicles through the use of proven, state-of-the-art static cryogenic seals. These seals adapt to wide ranges of temperature and continue to seal when subjected to high pressures, in-flight static stresses, and in-flight dynamic loads.
1209: Ammonia-Charged Aluminum Heat Pipes with Extruded Wicks
Use heat pipes, preferably aluminum heat pipes charged with anhydrous ammonia, in spacecraft
and instrument thermal control applications. This practice enhances the control and flow of heat
generated within the spacecraft.
Benefit:Heat pipes use the latent heat of vaporization of a working fluid to transfer heat efficiently at a nearly constant temperature. This characteristic can be used to control the temperature of spacecraft components and systems. The Goddard Space Flight Center (GSFC) has chosen ammonia-charged aluminum heat pipes for most near-room temperature (200 K to 350 K) applications. The axial groove aluminum pipe is the design of choice, because it is easy to design and relatively easy to fabricate. The aluminum container and axial grooves are extruded in one process. At the operating temperature of unmanned spacecraft, ammonia has the most favorable thermodynamic properties that make it an excellent heat pipe working fluid. Anhydrous ammonia is compatible with the aluminum heat pipe body and wick if proper care is taken in the manufacturing process.
1210: Assessment and Control of Electrical Charges
Practice: Provide protection against electrostatic charges, discharges, and lightning strikes by shielding and bonding space systems, structures, and their components in accordance with Standard Payload Assurance Requirements (SPAR-3) for GSFC Orbital Projects. This reliability practice does not cover Electrostatic Discharge (ESD) control due to an energetic space plasma environment.
Benefit: The Earth's space environment (geospace) is uniquely comprised of dynamic and complex regions of interacting plasmas, ionized particles, magnetic fields and electrical currents. Proper grounding/bonding of the space vehicle's shell and its electronic equipment can provide protection against lightning strikes in geospace, and also can eliminate or control most of its internal electrical and electrostatic hazards. This results in lower failure rates and significant reliability and safety enhancement of space systems and space vehicles.
1211: Combination Methods for Deriving Structural Design Loads
Design primary and secondary structural components to accommodate loads which include steady-state, transient dynamic, and vibro-acoustic contributions at liftoff.
Benefit:The probability of structural failure during launch and landing is significantly reduced.
1212: Design & Analysis of Circuits for Worst Case Environments and Part Variations
Practice: Design all circuits to perform within defined tolerance limits over a given mission lifetime while experiencing the worst possible variations of electronic piece parts and environments.
Benefit:The probability of mission success is maximized by assuring that all assemblies meet their mission electrical performance requirements at all times.
1213: Electrical Shielding of Power, Signal, and Control Cables
Practice: All wiring harnesses, cables, and wires on payloads, instruments, subsystems, and components are well shielded, including the use of connector types that provide tight EMI back shells or other means for attaching shields. This practice assumes that all efforts have been made to develop a design which requires minimum shielding.
Benefit: High performance shielding on wiring harnesses, cables and wires minimizes radiated emissions from hardware that could be picked up by itself or other hardware and interfere with proper operation. Shielding also minimizes the sensitivity of hardware to radiated emissions, from itself or other hardware, that could interfere with proper operation.
1214: Electrical Grounding Practices for Aerospace Hardware
Practice: Electrical grounding procedures must adhere to a proven set of requirements and design approaches to produce safe and trouble-free electrical and electronic circuits. Proper grounding is fundamental for reliable electronic circuits.
Benefits:Grounding procedures used in the design and assembly of electrical and electronic systems will protect personnel and circuits from hazardous currents and damaging fault conditions. Benefits are prevention of potential damage to delicate space flight systems, subsystems and components, and protection of development, operations, and maintenance personnel.
1215-1: Preliminary Design Review
Practice: Conduct a formal Preliminary Design Review (PDR) at the system and subsystem levels prior to the start of subsystem detail design, to assure that the proposed design and associated implementation approach will satisfy the system and subsystem functional requirements.
Benefits:The PDR will provide for increased assurance that the proposed design approach, and the manufacturing and test implementation plans, will result in an acceptable product, with minimal project risk.
1215-2: Hardware Review / Certification Requirement
Practice: A Hardware Review/Certification Requirement (HR/CR) Review is conducted prior to the delivery of flight hardware and associated software to evaluate and certify that the hardware is ready for delivery and that it is acceptable for integration with the spacecraft.
Benefit:The HR/CR provides a structured review process for assessing the status of flight hardware and screening for unresolved defects prior to delivery for integration.
1215-3: Critical Design Review for Unmanned Missions
Practice: Conduct a formal Critical Design Review (CDR) of hardware, software, and firmware at the subsystem and system levels. Schedule the review prior to the start of subsystem fabrication and assembly to assure that the design solutions satisfy the performance requirements established in the development specifications. Establish this review as a standard reliability engineering practice for flight hardware.
Benefits:The CDR provides increased assurance that the proposed design, and the planned manufacturing and test methods and procedures, will result in an acceptable product, with minimal project risk.
1215-4: Common Review Methods
Practice: Conduct technical reviews to validate engineering designs using a common, consistent approach which has been proven to lead to reliable and quality products. A technical review is an evaluation of the engineering status of products and processes by an independent group of knowledgeable people. Although major technical reviews for a project differ in their content and timing, there are practices common to most reviews which may be defined to assure review success. These practices provide a common framework for planning, conducting, documenting, and evaluating the review process.
Benefits:Standards established for common review methods are presently supporting reliability assurance by emphasizing early detection and correction of deficiencies through the increased use of working level, peer reviews (detailed technical reviews) in preparation for major design reviews. The standards also assure that reviews are scaled in accordance with criticality, complexity, and risk, and that the review process is optimized to produce results of value to the mission.
1215-5: Pre-Ship Review
Practice: Prior to shipment of hardware or software, conduct a pre-ship review at the completion of the fabrication or build and testing of the item to be shipped. This review is scheduled as part of the overall technical review program as defined in a project review plan. Pre-ship review is held at the supplier or NASA facility where the item was made and tested.
Benefits: Pre-ship review ensures the completeness and readiness of each item of hardware and, if applicable, any associated software or firmware, prior to release for shipment to another facility. By imposing this requirement, any discrepancies or unresolved problems may be identified and corrected while the item remains under supplier purview. This review is beneficial because it provides an independent assessment of product readiness by knowledgeable people not directly involved in the fabrication and test activity.
1216: Active Redundancy
Practice: Use active redundancy as a design option when development testing and reliability analysis show that a single component is not reliable enough to accomplish the function. Although active redundancy can be applied to various types of mechanical and electrical components and systems, the application detailed in this practice illustrates an approach using a Traveling Wave Tube amplifier in a space flight application.
Benefits:Provides multiple ways of accomplishing a function to improve mission reliability.
1217: Structural Laminate Composites for Space Applications
Practice: The creation of reliable structural laminate composites for space applications requires precision design and manufacturing using an integrated, concurrent engineering approach. Since the final material characteristics are established at the same time the part or subassembly is fabricated, part design, fabrication development, and material characterization must proceed concurrently. Because composite materials are custom-tailored to meet structural requirements of the assembly, stringent in-process controls are required to arrive at a configuration with optimum physical and material properties.
Benefits: Conscientious adherence to proven procedures in the design, manufacture, and test of aerospace structural composites will result in low rejection rates and high product integrity. In specific applications, successful composite design provides design flexibility, increased strength to weight ratio, dimensional stability under thermal loading, light weight, ease of fabrication and installation, corrosion resistance, impact resistance, high fatigue strength (compared to metal structures with the same dimensions), and product simplicity when compared to conventional fabricated metal structures.
1218: Application of Ablative Composites to Nozzles for Reusable Solid Rocket Motors
Practice: Fabrication of ablative composite materials for solid rocket motor nozzles requires a precision, integrated, multi-disciplinary, multivendor approach to design and manufacture. Creation of the material requires stringent process controls during manufacture of the rayon fiber, weaving the rayon fiber into cloth, carbonizing the rayon cloth, impregnation of carbon cloth with resin and filler, wrapping the carbon-phenolic onto a mandrel to the proper thickness, curing, nondestructive inspection and final machining to the designed configuration. Environmental conditions and cleanliness levels must be closely monitored when bonding the ablative material to the metal housing. The critical material properties for acceptance of carbon cloth-phenolic prepreg material are cloth content, dry resin solids content, volatile content, carbon filler content, and resin flow. Use of certified and highly skilled tape wrapping operators, bonding technicians, machinists, and destructive and nondestructive testing personnel, is a must.
Benefits:Adhering to proven design practices and process controls during manufacture of ablative composite nozzle components will result in a high quality product with few rejects. Successful design and manufacturing of ablative composite materials for solid motor nozzles provides for proper transfer of the combustion gases from the burning propellant surface through the nozzle without damage to the metal structure. Use of a properly controlled manufacturing process will result in the proper density, percent resin content, compressive strength, interlaminar shear strength, thermal conductivity, coefficient of thermal expansion, and tensile strength.
1219: Vehicle Integration/Tolerance Build-up Practices
Practice: Use master gauges, tooling, jigs, and fixtures to transfer precise dimensions to ensure accurate mating of interfacing aerospace hardware. Calculate overall worst-case tolerances using the root sum square method of element tolerances when integrating multiple elements of aerospace hardware.
Benefits:Using prudent and carefully planned methods for specifying tolerances and for designing, manufacturing and mating major elements of aerospace hardware, will result in a cost-effective program with minimal rejects and waivers, and will avoid costly schedule delays due to potential mismatching or misfitting of major components and assemblies.
1220: Demagnetization of Ferromagnetic Parts
Practice: In those cases where spacecraft science requirements or attitude control systems impose constraints on the magnetic characteristics of components and the use of ferromagnetic material cannot be avoided, perform a complete demagnetization of the ferromagnetic parts, individually, prior to assembly.
Benefit:In an unassembled state, ferromagnetic parts can be exposed to stronger AC demagnetizing fields, as high as 60 mT (600 Gauss), thus assuring a lower level of remanent magnetization than can be achieved after the parts are mounted on assemblies. Attaining a low level of remanent magnetization minimizes the adverse effects of unwanted fields. In those cases where magnetic compensation may be required, the ability to apply high level fields to an unmounted part enables the utilization of techniques to stabilize the magnetic moment of the part.
1221: Battery Selection Practice for Aerospace Power Systems
Practice: When selecting batteries for space flight applications, the following requirements should be considered: ampere-hour capacity, rechargeability, depth of discharge (DOD), lifetime, temperature environments, ruggedness, and weight. Many batteries have been qualified and used for space flight, enhancing the ease of selecting the right battery.
Benefits:Selection of the optimum battery for space flight applications results in a safe, effective, efficient, and economical power storage capability. The optimum battery also enhances launch operations, minimizes impacts to resources, supports contingency operations, and meets demand loads.
1222: Magnetic Field Restraints for Spacecraft Systems and Subsystems
Practice: Control magnetic field disturbance of spacecraft systems by avoiding the use of components and sub-assemblies with significant magnetic dipole moments.
Benefit:Limits magnetic field interference at flight sensor positions and minimizes magnetic dipole moments that can increase magnetic torquing effects that place additional loads on attitude control systems.
1223: Vacuum Seals Design Criteria
Practice: Well made, clamped, and temperature stabilized circular O-rings should be used in the design of reliable, reusable and long life seals in vacuum sealing applications.
Benefits: Leak free flanges as well as low/undetectable outgassing of the elastomeric materials can be achieved at pressure levels as low as 10-8 Torr by using well made O-rings in a static vacuum seal environment. The use of O-rings has provided ease for running environmental tests on the ground using space simulation chambers.
1224: Design Considerations for Fluid Tubing Systems
Practice: The following practice delineates basic criteria for use in the design of fluid tubing systems for use on space flight equipment. These criteria are meant to enhance reliability and maintainability of these systems through standardized practices in design.
Benefits: By using standard military and industry-accepted tubing design criteria, the overall design of a system consisting of tubing will achieve maximum reliability, producibility, and safety at a minimum cost.
1225: Conducted and Radiated Emissions Design Requirements
Practice: Initially, the design requirements for each subsystem are established so that all non-functional emissions will be at least 9 Db below the emission specification limit.
Benefits:By initially selecting a 9 Db margin, the probability of complying with the electromagnetic compatibility (EMC) specification during system test is high.
1226: Thermal Design Practices for Electronic Assemblies
Practice: Insure that thermal design practices for electronic assemblies will meet the requirements of the combined ground and flight environmental conditions defined by the spacecraft mission. Special emphasis should be placed on limiting the junction temperature of all active components. Proper thermal design practices take into consideration the need for ease of operation and repairability to enhance overall system reliability. The environmental conditions that the spacecraft encounters, both on the ground and in flight, are designed to include adequate margin. The use of proper thermal design practices ensures that the assemblies will survive the expected environmental conditions.
Benefit:Constraining the electronic component junction temperature through proper design practices will ensure that the assemblies can withstand the mission's environmental conditions.
1227: Controlling Stress Corrosion Cracking in Aerospace Applications
Practice: This practice presents considerations that should be evaluated and applied concerning stress corrosion and subsequent crack propagation in mechanical devices, structural devices, and related components used in aerospace applications. Material selection, heat treat methods, fabrication methodology, testing regimes, and loading path assessments are presented as methods to reduce the potential for stress corrosion cracking (SCC) in a material's operational environment.
Benefits:Selection of materials, heat treating methods, fabrication methodologies, testing regimes, and loading paths that are not susceptible to stress corrosion cracking will promote fewer failures due to SCC and will eliminate downtime due to the change-out of components.
1228: Independent Verification and Validation of Embedded Software
Practice: To produce high quality, reliable software, use Independent Verification and Validation (IV&V) in an independent, systematic evaluation process throughout the software life cycle. Using the IV&V process; locate, identify, and correct software problems and errors early in the development cycle.
Benefit:The use of IV&V processes ensures that computer software is developed in accordance with original specifications, that the software performs the functions satisfactorily in the operational mission environment for which it was designed, and that it does not perform unintended functions. Identification and correction of errors early in the development cycle are less costly than identification and correction of errors in later phases, and the quality and reliability of software are significantly improved.
1229: Selection of Electric Motors for Aerospace Applications
Practice: Careful attention is given to the specific application of electric motors for aerospace applications when selecting motor type. The following factors are considered in electric motor design: application, environment, thermal, efficiency, weight, volume, life, complexity, torque, speed, torque ripple, power source, envelope, duty cycle, and controllability. Brushless direct current motors have been proven to be best all-around type of motors for aerospace applications because of their long life, high torque, high efficiency, and low heat dissipation.
Benefit:Selection of the optimum electric motor for space flight operations results in a safe, reliable, effective, efficient and economical electric motor power source for space flight. Brushless direct current motors provide the lightest weight alternative for most applications.
1230: System Design Analysis Applied to Launch Vehicle Configuration
Practice: Use design management improvements such as matrix methods, quality techniques, and life cycle cost analyses in a systematic approach to systems analysis.
Benefit:The use of advanced design management methods in each program phase of major launch vehicle developments will maximize reliability and minimize cost overruns. Significant improvements in user satisfaction, error-free performance, and operational effectiveness can be achieved through the use of these methods.
1231: Design Considerations for Lightning Strike Survivability
Practice: Implement lightning survivability in the design of launch vehicles to avoid lightning induced failures.
Benefits:Experience learned from the Atlas/Centaur and Space Shuttle flights serve to emphasize the importance of the implementation of the proper protection/design enhancements to avoid and survive natural or triggered lightning for all launches.
1232: Spacecraft Orbital Anomaly Report (SOAR) Systems
Practice: Implement a positive feedback system for reporting, documenting, collecting, analyzing, and closing orbital anomaly information on spacecraft. An example of such a system is currently managed by Goddard Space Flight Center.
Benefit:Provides a single uniform, effective, and efficient computer data base for in-orbit reliability studies to identify performance trends for use in design reviews, flight readiness reviews, and in the evaluation of test, reliability, and quality assurance policies.
1233: Contamination Control Program
Practice: Apply a Contamination Control Program to those spacecraft projects involving scientific instruments which have stringent cleanliness level requirements.
Benefits:This practice enables spacecraft to meet these stringent cleanliness level requirements of state-of-the-art scientific instruments. It also serves to maintain the inherent efficiency and reliability of the instrument by minimizing degradation of critical surfaces and sensors due to undesired condensation of molecular and accumulation of particulate contamination layers.
1234: Global Positioning System (GPS) Timing System
Practice: Use of the Global Positioning System (GPS) to provide a timing system with improved reliability and accuracy over the previous system.
Benefits:In addition to improving the timing system's overall reliability by utilizing multiple timing sources, the upgrade from the previous Apollo-era designed system (using LORAN and WWV) provides improvements in the accuracy, monitoring and feedback capabilities. The timing system is used to provide timing commonality between instrumentation systems so data can be referenced with respect to time. Improving the reliability and accuracy of this system improves the time reference capabilities.
1235: Over-Speed Protection System for DC Motor Driven Cranes
Practice: DC drive motor over-speed detection using a voltage sensing relay.
Benefits:This design employs a simple method of providing protection against the effects of a crane operating at a higher than commanded speed while not introducing unwanted nuisance trips to the crane control system. This improves the reliability of the crane control system by preventing the crane from reacting to unwanted commands that are not operator initiated. The improvement allows the crane to be used with a higher degree of confidence that a critical failure will not result in damage to the load suspended from the load hook.
1236: EEE Parts Selection Guidelines for Flight Systems
Practice: Use highest reliability EEE parts available, consistent with functional requirements, program cost, and schedule constraints, for spaceflight systems.
Benefit: One of the most important considerations in designing reliable flight hardware is selection and use of the highest quality possible components. Proper selection, application, and testing of EEE components will generally contribute to mission success and provide long term program cost savings. An effective EEE parts program has helped many projects in achieving optimum safety, reliability, maintainability, on-time delivery, and performance of program hardware. The resulting reduction in parts and part-related failures saves program resources through decreased failure investigation and maintenance costs.
1238: Spacecraft Electrical Harness Design Practice
Practice: Design and fabricate space flight electrical harnesses to meet the minimum requirements of the GSFC Design and Manufacturing Standard for Electrical Harnesses.
Benefit:Designing and testing flight harnesses in accordance with the requirements of the GSFC Design and Manufacturing Standard (Ref. 1) for Electrical Harnesses enhances the probability of mission success (Reliability) by ensuring that harnesses meet high standards of quality as well as the electrical and environmental requirements of space flight missions. The occurrence of early failures is minimized.
1239: Spacecraft Thermal Control Coatings Design and Application Procedures
Practice: Select and apply thermal coatings for control of spacecraft and scientific instrument temperatures within required ranges and for control of spacecraft charging and RF emissions.
Benefit:This practice enhances the probability of mission success by controlling temperatures of flight hardware as well as spacecraft charging and RF emissions over the life of the mission.
1240: Identification, Control, and Management of Critical Items
Practice: Initiate the preparation of Critical Items Lists (CILs) early in programs to identify and potentially eliminate critical items before the design is frozen and as an input to hardware and software design, testing, and inspection planning activities. Utilize CILs during the operational portion of the life cycle to manage failures and ensure mission success.
Benefits:Early identification, tracking, and control of critical items through the preparation, implementation, and maintenance of CILs will provide valuable inputs to a design, development, and production program. From the CIL activity, critical design features, tests, inspection points, and procedures can be identified and implemented that will minimize the probability of failure of a mission or loss of life.
1241: Contamination Budgeting for Space Optical Systems
Practice: Use preplanned contamination budgeting for each manufacturing/assembly, testing, shipping, launch, and flight operation and meticulously test optical systems using witness samples throughout the process to track actual contamination against total and incremental allocations.
Benefit: Budgeting of a specific amount of the established allowable contamination to the major elements and operations during fabrication, assembly, testing, transportation launch support, and launch and on orbit operations of space optical systems will preclude jeopardizing the scientific objectives of the mission. Budgeting of contamination to major elements will ensure that the cleanliness of the optics and instruments will remain within designated optical requirements for operations in space. Reliability of the scientific objectives are increased by limiting the contamination allowed to the optical systems during each operation, which ensures that contamination during orbital operations is within specification.
1242: Design Considerations for Space Trusses
Practice: Use the PSAM (Probabilistic Structural Analysis Methods) contained in the computer code NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) to identify and quantify the reliability of space structures.
Benefits: This practice can be used to determine an optimum truss configuration (e.g. minimum number of members) for a given loading condition and specified reliability. PSAM provides a formal and systematic way to evaluate structural performance reliability or risk at minimal time and low cost.
1243: Fault Protection
Practice: Fault protection is the use of cooperative design of flight and ground elements (including hardware, software, procedures, etc.) to detect and respond to perceived spacecraft faults. Its purpose is to eliminate single point failures or their effects and to ensure spacecraft system integrity under anomalous conditions.
Benefits:Fault protection design maximizes the probability of spacecraft mission success by avoiding possible single failure points through the use of autonomous, short-term compensation for failed hardware.
1244: Design Practice to Control Interference from Electrostatic Discharge (ESD)
Practice: Minimize the adverse effects of electrostatic discharge (ESD) on spacecraft by implementing the following three design practices:
- Make all external surfaces of the spacecraft electrically conductive and grounded to the main structure.
- Provide all internal metallic elements and other conductive elements with an "ESD conductive" path to the main structure.
- Enclose all sensitive circuitry in an electrically conductive enclosure-- a "Faraday cage".
Benefit:The first two practices should dissipate most electric charges before a difference in potential can become high enough to cause an ESD. If a discharge occurs, the third practice lowers the coupling to sensitive circuits, reducing the probability or severity of the interference.
1245: Magnetic Dipole Allocation
Practice: Magnetic dipole allocation is an empirical method for initiating control of spacecraft magnetic contamination. The practice is necessary for missions which incorporate instruments to measure low level magnetic fields.
Benefit:Control of the net magnetic dipole of the spacecraft will assure the integrity of magnetic field measurements made during the mission. Measurement of the individual contributions from various assemblies, subassemblies, and components allows the identification of the major dipole sources. The major contributors can then be evaluated for corrective action, and they can be monitored individually to assure that they are at the lowest level of magnetization at the time of installation on the spacecraft.
1246: Fault Tolerant Design
Practice: Incorporate hardware and software features in the design of spacecraft equipment which tolerate the effects of minor failures and minimize switching from the primary to the secondary string. This increases the potential availability and reliability of the primary string.
Benefits:Fault tolerant design provides a means to achieve a balanced project risk where the cost of failure protection is commensurate with the program resources and the mission criticality of the equipment. By providing compensation for potential hardware failures, a fault tolerant design approach may achieve reliability objectives without recourse to non-optimized redundancy or overdesign.
1247: Spacecraft Lessons Learned Reporting System
Practice: Develop a Spacecraft Lessons Learned File (LLF)-- a quick, but formal record of significant occurrences during design, implementation, and operation of spacecraft and support equipment. Provide fast and convenient traceability for knowledge capture of significant events to guide future spacecraft managers and engineers in recognizing and avoiding critical design problems. Maintain the system as a living problem avoidance database for all flight project activities.
Benefits:The Spacecraft LLF is a quick reference document that preserves the NASA knowledge base, providing engineers and scientists with brief summaries of meaningful events that offer valuable lessons. Within the LLF, lessons of interest can be accessed through a keywords search, with more detailed information accessible from the referenced problem/failure report or alert documentation. The LLF serves as a repository of valuable information, including lessons which were learned at great expense, which would otherwise be lost following personnel turnover. The JPL LLF activity is performed in coordination with the NASA headquarters LLF program.
1248: Spacecraft Data Systems (SDS) Hardware Design Practices
Practice: Use a standard SDS in spacecraft where possible which utilizes a standard data bus and space flight qualified versions of widely used hardware and operating software systems.
Benefit:This practice enhances reliability of the SDS and the probability of mission success by simplifying the design and operation of the SDS system and providing capability to work-around spacecraft and instrument problems.
1249: Electrostatic Discharge (ESD) Control in Flight Hardware
Practice:Apply an Electrostatic Discharge (ESD) Control Program to all spaceflight projects to ensure that ESD susceptible hardware is protected from damage due to ESD.
Benefit:This ESD Control Practice significantly enhances mission reliability by protecting susceptible flight and critical flight support electronic parts and related hardware from damage and/or degradation caused by ESD and Induction Polarization Charge (IPC) during the prelaunch phases of the mission.
1250: Pre-Flight Problem / Failure Reporting Procedures
PRACTICE: A formal procedure is followed in the reporting and documentation of problems/failures occurring during test, pre-launch operations, and launch operations for both hardware and software. A separate system, the "Spacecraft Orbital Anomaly Report (SOAR)", is used for the reporting, evaluation and correction of problems occurring on-orbit (see Practice No. PD-ED-1232).
BENEFIT:This practice significantly enhances the probability of mission success by ensuring that problems/failures occurring during ground test are properly identified, documented, assessed, tracked and corrected in a controlled and approved manner. Another benefit of the PFR procedure is to provide data on problem/failure trends. Trend data may then be analyzed so that errors are not repeated on future hardware and software.
1251: Instrumentation System Design and Installation for Launch Vehicles
Practice: Instrumentation systems and related sensors (transducers), particularly those designed for use in reusable and refurbishable launch systems and subsystems, are analyzed, designed, fabricated and tested with meticulous care in order to ensure system and subsystem reliability.
Benefits:The benefits of implementing these reliability practices for instrumentation system and related sensors are: (1) consistent performance and measurement results, (2) minimum need for continuous or periodic calibration, (3) avoidance of and resistance to contamination, and (4) reduced necessity for repair or replacement in repeated usage.
1252: Material Selection Practices
Practice: Aerospace systems designers must ensure that the most reliable material is used to meet the design requirements for aerospace systems. Test results regarding corrosion resistance, susceptibility to stress corrosion cracking, flammability, toxicity, thermal vacuum stability, and compatibility with rocket engine fuels, oxidizers, and hydraulic fluids; as well as extensive chemical and physical properties data; are included in the Materials and Processes Technical Information System (MAPTIS). This information is used to assist the aerospace designer in identifying the most reliable material candidates for space systems.
Benefits:Reliable materials can be selected for aerospace applications by choosing those materials that have demonstrated reliability in carefully controlled laboratory testing and in operational space flights. Use of the MAPTIS data base by system designers will ensure that materials that have demonstrated reliable performance in flight and test experience are the first to be considered in new or revised designs. Engineers will then have the confidence in their selections, knowing that the data on which their decisions have been made have been thoroughly validated.
1253: Arcjet Thruster Design Considerations for Satellites
Practice: Use flight proven arcjet thrusters in the design of satellites and as a lightweight reliable propulsion maneuvering system to lower propellant mass, increase orbital lifetime, and use smaller less costly launch vehicles.
Benefit:Long-term spacecraft and propulsion system compatibility in near earth orbital environment has been demonstrated by several experimental test flights. This thruster system is currently being incorporated into the new series of Martin Marietta satellites as well as a new series of military reconnaissance satellites. The benefits are a decrease in propulsion system weight, a potential reduction in mission cost, and an increase in orbital lifetime and satellite reliability.
1254: Design Reliable Ceramic Components with CARES Code
Practice: Use the Ceramics Analysis and Reliability Evaluation of Structures (CARES) computer program to calculate the fast-fracture reliability or failure probability of macroscopically isotropic ceramic components.
Benefits: The increasing importance of ceramics as structural materials places high demand on assuring component integrity while simultaneously optimizing performance and cost. Components using ceramics can be designed for high reliability in service if the contributing factors that cause material failure are accounted for. This design methodology must combine the statistical nature of strength controlling flaws with fracture mechanics to allow for multiaxial stress states and concurrent flaw populations. CARES uses results from MSC/NASTRAN or ANSYS finite-element analysis programs to evaluate how inherent surface and/or volume type flaws affect component reliability.
1255: Problem Reporting and Corrective Action System
Practice: A closed-loop Problem (or Failure) Reporting and Corrective Action System (PRACAS or FRACAS) is implemented to obtain feedback about the operation of ground support equipment used for the manned spaceflight program.
Benefits:The information provided by PRACAS allows areas in possible need of improvement to be highlighted to engineering for development of a corrective action, if deemed necessary. With this system in place in the early phases of a program, means are provided for early elimination of the causes of failures. This contributes to reliability growth and customer satisfaction. The system also allows trending data to be collected for systems that are in place. Trend analysis may show areas in need of design or operational changes.
1256: Automatic Transfer Switch (ATS) in Critical Applications
Practice: This practice provides proven techniques for enhancing the reliability of Automatic Transfer Switches (ATS) used in critical applications. Systems which require the use of ATS may be optimized for fail-safe operation using worst-case design techniques and good maintainability/preventive maintenance practices. The probability of internal ATS failures which could result in loss of power to the load can be minimized by giving particular attention to the ATS transfer methods, power-switch types used, and regular attention to the health of the equipment.
Benefits:The major benefit of these design considerations is the greater assurance that loss of power to critical loads and the resulting consequences will not occur. Achieving optimum reliability is of paramount importance in systems that protect life and property. Along with the increase in the reliability of the ATS that is achieved, usually little or no additional design cost is required.
1257: Solid Rocket Motor Joint Reliability
Practice: Critical design features that reduce joint rotation, improve seal features, provide close tolerances, provide for leak checks, and provide venting are used to improve the reliability of case-to-case and case-to-nozzle field joints for large solid propellant rocket motors. Principal design drivers are the combustion chamber pressure vs. time profile, segment stacking and assembly tolerances, insulation and sealing configurations, launch dynamic loads, flight dynamic loads, and environmental temperatures.
Benefit:Proper design of solid rocket motor case-to-case field joints reduces joint rotation and potential leakage during ignition and operation. With detailed dynamic loads analyses, thermal analyses, careful insulation design, and suitable "o"-ring sealing, the leakage of hot combustion gasses through field joints is eliminated. This prevents potentially catastrophic burning or melting of the solid rocket motor and adjacent metal components. Similar benefits are obtained by using improved design practices for case-to-nozzle joints and factory joints between case segments.
1258: Space Radiation Effects on Electronic Components in Low-Earth Orbit
Practice: During system design, choose electronic components/devices which will provide maximum failure tolerance from Space Radiation Effects. The information below provides guidance in selection of radiation hardened (rad-hard) solid state devices and microcircuits for use in space vehicles which operate in low-earth orbits.
Benefit: This practice provides enhanced reliability and availability as well as improved chances for mission success. Failure rates due to space radiation effects will be significantly lower, and thus system down time will be much lower, saving program cost and resources.
1259: Acoustic Noise Requirements
Practice: Impose an acoustic noise requirement on spacecraft hardware design to ensure the structural integrity of the vehicle and its components in the vibroacoustic launch environment. Acoustic noise results from the propagation of sound pressure waves through air or other media. During the launch of a rocket, such noise is generated by the release of high velocity engine exhaust gases, by the resonant motion of internal engine components, and by the aerodynamic flow field associated with high speed vehicle movement through the atmosphere. This environment places severe stress on flight hardware and has been shown to severely impact subsystem reliability.
Benefit: The fluctuating pressures associated with acoustic energy during launch can cause vibration of structural components over a broad frequency band, ranging from about 20 Hz to 10,000 Hz and above. Such high frequency vibration can lead to rapid structural fatigue. The acoustic noise requirement assures that flight hardware-- particularly structures with a high ratio of surface area to mass-- is designed with sufficient margin to withstand the launch environment. Definition of an aggressive acoustic noise specification is intended to mitigate the effects of the launch environment on spacecraft reliability. It would not apply to the Space Station nor to the normal operational environment of a spacecraft.
1260: Radiation Design Margin Requirement
Practice: Design spacecraft hardware assemblies with the required radiation design margin (RDM) to assure that they can withstand ionization effects and displacement damage resulting from the flight radiation environment. The term "margin" does not imply a known factor of safety but rather accommodates the uncertainty in the radiation susceptibility predictions. The reliability requirement to survive for a period of time in the anticipated mission radiation environment is a spacecraft design driver.
Benefits:The RDM requirement is imposed on assemblies or subsystems to assure reliable operation and to minimize the risk, especially in mission critical applications. The general use of an RDM connotes action to overcome the inevitable uncertainties in environmental calculations and part radiation hardness determinations.
1261: Characterization of RF Subsystem Susceptibility to Spurious Signals
Practice: Reliable design of spacecraft radios requires the analysis and test of hardware responses to spurious emissions which may degrade communications performance. Prior to hardware integration on the spacecraft, receivers and transmitters are tested to verify their compatibility with respect to emissions of conducted radio frequency (RF) signals and susceptibility to these signals. This reliability practice is applied to receivers and transmitters located in the same subsystem and to those installed in different subsystems on the same spacecraft. This early test to identify and resolve radio compatibility problems reduces the risk of uplink/downlink degradation which might threaten mission objectives.
Benefits:This practice validates the compatibility of spacecraft receivers and transmitters. If electromagnetic compatibility problems are identified early in radio design, solutions can be developed, implemented, and verified prior to the integration of the hardware on the spacecraft.
1262: Subsystem Inheritance Review
Practice: Conduct a formal design inheritance review at the system, subsystem, or assembly level prior to, or in conjunction with, the corresponding subsystem Preliminary Design Review (PDR). The purpose of the inheritance review is to identify those actions which will be required to establish the compatibility of the proposed inherited design, and any inherited hardware or software, with the subsystem functional and design requirements.
Benefit: Use of inherited flight hardware or software may reduce cost and allow a spacecraft designer to avoid the risk of launching unproven equipment. However, the designer often lacks full information on the many design decisions made during development, including some which may cause incompatibility with current spacecraft requirements. Subsystem inheritance review (SIR) probes inheritance issues to help assure that the proposed inherited item will result in an acceptable and reliable product with minimal mission risk.
1263: Contamination Control of Space Optical Systems
Practice: Contamination of space optical systems is controlled through the use of proper design techniques, selection of proper materials, hardware/component precleaning, and maintenance of cleanliness during assembly, testing, checkout, transportation, storage, launch and on-orbit operations. These practices will improve reliability through avoidance of the primary sources of space optical systems particulate and molecular contamination.
Benefit:Controlling contamination of space optical systems limits the amount of particulate and molecular contamination which could cause performance degradation. Contamination causes diminished optical throughput, creates off-axis radiation scattering due to particle clouds, and increases mirror scattering. Controlling molecular contaminates minimizes performance degradation caused by the deposition of molecular contaminants on mirrors, optical sensors and critical surfaces; improves cost-effectiveness of mission results; and improves reliability.
1264: Integrated Optical Performance Modeling of X-Ray Systems
Guideline: To ensure that high resolution mirror assemblies for grazing incidence x-ray optical systems meet their requirements, image quality must be predicted during design and verified during fabrication by modeling the system for in-orbit and x-ray test configurations. Computer based modeling programs should be used to verify that both the initial design and the as-built configurations will reliably produce the required image quality.
Benefits:The use of computer-based models for integrated x-ray optical performance modeling will provide an independent check of optical systems design and will ensure high quality optical systems by providing in-process verification of the fabrication process. These models can save time and money in optical systems design and development, and should result in highly reliable x-ray imaging.
1265: Precision Diamond Turning of Aerospace Optical Systems
Guideline: Meticulous control of vibration, environmental factors, and machining parameters are required to produce precision diffractive, refractive, reflective and hybrid optical components for aerospace applications.
Benefits:Highly reliable diffractive, refractive, reflective, and hybrid aerospace optical systems can be produced by a meticulously controlled and protected diamond turning process. The result can be rugged, temperature-compensating achromatic precision optical elements suitable for a wide variety of applications.
1266: Binary and Hybrid Optics for Space Applications
Guideline: Binary (diffractive) optics combined with conventional (refractive) optics offer a significant potential for space optics reliability improvement.
Benefits:Improved ruggedness, reduced size, and greater opportunity for redundancy are the potential benefits of using binary and hybrid optical systems for space applications. Hybrid optical systems can be designed that are less sensitive to color (or chromatic variations) and to temperature variations. When combined with conventional optics, binary optical systems can correct for spherical aberrations.
1267: Check Valve Reliability in Aerospace Applications
Practice: In check valve design for aerospace applications examine all design features, materials, and tolerances to evaluate the effects of contamination and exposure to cryogenic or hypergolic propellants. Conduct long term compatibility tests simulating the operational environment to assess material suitability for each unique application.
Benefits:The benefits of using special design and test procedures for aerospace check valves are long life, consistent operation, and trouble-free performance during prelaunch, launch, and orbital operations.
1268: High Performance Liquid Hydrogen Turbopumps
Practice: Understanding and addressing the design environment, component interactions, and potential failure modes are the keys to high reliability in high performance liquid hydrogen turbopumps for launch vehicle engines. Designing and using a combination of unique sealing, cooling, processing, material selection, and balancing techniques in response to engine design requirements will permit the development, production, and reliable flights of hydrogen turbopumps.
Benefit: Use of precision design; manufacturing; and advanced material selection, fabrication, and treatment techniques will ensure reliable operation of large, high performance liquid hydrogen turbopumps. Many of these practices will also lengthen the operational life of the turbopump, increasing the number of uses before teardown, inspection, refurbishment, and re-assembly for subsequent flights. In addition to higher reliability, lower costs and continued assurance of high performance are resulting benefits.
1269: High Performance Liquid Oxygen Turbopumps
Practice: Unique cooling, sealing, draining, and purging methods, along with precision interference fits and vibration damping methods are used in high performance liquid oxygen turbopumps. Coatings and dry lubricants are used to provide protection against cracking, fretting, and generation of contamination. Silicon nitride bearings resist wear and provide long life.
Benefits: The use of special design features, materials, and coatings in high pressure liquid oxygen turbopumps will prevent inadvertent overheating and combustion in the liquid oxygen environment. Special sealing, draining, and purging methods prevent contact between the oxygen in the pump section and the hydrogen rich gasses that drive the turbine. These precision design and manufacturing procedures prevent latent or catastrophic failure of the LOX turbopump Silicon nitride bearings, coupled with other bearing enhancements, prevent bearing wear in advanced LOX turbopumps.
1272: Manned Space Vehicle Battery Safety
Practice: This practice is for use by designers of battery-operated equipment flown on space vehicles. It provides such people with information on the design of battery-operated equipment to result in a design which is safe. Safe, in this practice, means safe for ground personnel and crew to handle and use; safe for use in the enclosed environment of a manned space vehicle and safe to be mounted in adjacent unpressurized spaces.
Benefit: There have been many requests by the Space Shuttle Payload customers for a practice which describes all the hazards associated with the use of batteries in and on manned space flight vehicles. This practice is prepared for designers of battery-operated equipment so that designs can accommodate these hazard controls. This practice describes the process that a design engineer should consider in order to verify control of hazards to personnel and the equipment. Hazards to ground personnel who must handle battery-operated equipment are considered, as well as hazards to space crew and vehicles.
1273: Quantitative Reliability Requirements Used as Performance-Based Requirements for Space Systems
Practice: Develop performance-based reliability requirements by considering elements of system performance in terms of specific missions and events and by determining the requisite system reliability needed to achieve those missions and events. Specify the requisite reliability in the system specifications in quantitative terms, along with recommended approaches to verify the requirements are met. Require the system provider to demonstrate adherence to the reliability requirements via analysis and test.
Benefits:Quantitative reliability requirements provide specific design goals and criteria for assuring that the system will meet the intended durability and life. Early in the design process, the system developer will be required to consider how the design will provide the requisite reliability characteristics and must provide analyses to verify that the delivered hardware will meet the requirements. Assessment of the early design's ability to meet quantitative reliability requirements will support design trades, component selection, and maintainability design, and help assure that appropriate material strengths are used as well as the appropriate levels and types of redundancy.
1301: Surface Charging / ESD Analysis
Practice: Considering the natural environment, perform spacecraft charging analyses to determine that the energy that can be stored by each nonconductive surface is less than 3 mJ. Determine the feasibility of occurrence of electrostatic discharges (ESD). ESD should not be allowed to occur on surfaces near receivers/antenna operating at less than 8 GHz or on surfaces near sensitive circuits. For this practice to be effective, a test program to demonstrate the spacecraft's immunity to a 3 mJ ESD is required.
Benefit:Surfaces that are conceivable ESD sources can be identified early in the program. Design changes such as application of a conductive coating and use of alternate materials can be implemented to eliminate or reduce the ESD risk. Preventive measures such as the installation of RC filters on sensitive circuits also can be implemented to control the adverse ESD effects.
1302: Independent Review of Reliability Analyses
Practice: Establish a mandatory closed-loop system for detailed, independent, and timely technical reviews of all analyses performed in support of the reliability/design process.
Benefit:This process of peer review serves to validate both the accuracy and the thoroughness of analyses. If performed in a timely fashion, it can correct design errors with minimal program impact.
1303: Part Electrical Stress Analyses
Practice: Every part in an electrical design is subjected to a worst-case part stress analysis performed at the anticipated part temperature experienced during the assembly qualification test (typically 75 °C). Every part must meet the project stress derating requirements or be accepted by a formal project waiver.
Benefit:Part failure rates are proportional to their applied electrical and thermal stresses. By predicting the stress through analysis, and applying conservative stresses, the probability of mission success can be greatly enhanced.
1304: Problem/Failure Report Independent Review and Approval
Practice: Problem/Failure (P/F) Reports are reviewed independently and approved by reliability engineering specialists to ensure objectivity and integrity in the closure process. This practice assures that the analysis realistically bounds the extent of the P/F, and the corrective action and its verification are successfully accomplished. The key elements are:
- Analysis must address the problem.
- Corrective action must address the analysis and the problem.
- Analysis must address the effect on other items.
- Corrective action must have been implemented.
- Item must have passed the gate that caused the P/F - the hardware/software must be successfully retested.
Benefit:Any independent review process increases the level of compliance of the subject process. It also broadens the scope and depth of experience available for each individual issue without the need for a large supporting staff at each supplier organization. Also, an in-place independent review structure improves the rate of data flow for a given level of effort.
1305: Risk Rating of Problem/Failure Reports
Practice: Problem/failure (P/F) reports are assigned a two-factor set of ratings: a failure effect rating and a failure cause/corrective action rating. The composite rating is used to assess the hardware/software residual launch and mission risk. The high risk P/F reports are labeled "Red Flag".
Benefit:Risk rating enables management to focus on the issues with the highest probability of impacting mission success. Project management is provided with visibility to a concise subset (< 5 percent) of a large information base focusing on the key problematic areas in a timely fashion.
1306: Thermal Analysis of Electronic Assemblies to the Piece Part Level
Practice: Perform a piece part thermal analysis that includes all piece parts in support of the part stress analysis. Also include fatigue sensitive elements of the assembly such as interconnects (solder joints, bondlines, wirebonds, etc.).
Benefit:Allows the thermally overstressed parts to be identified and assessed for risk (instead of just the electrically overstressed parts). Allows the design life requirements of the thermal fatigue sensitive elements (solder joints, bondlines, wirebonds, etc.) to be quantified.
1307: Failure Modes, Effects And Criticality Analysis (FMECA)
Practice: Analyze all systems to identify potential failure modes by using a systematic study starting at the piece part or circuit functional block level and working up through assemblies and subsystems. Require formal project acceptance of any residual system risk identified by this process.
Benefit:The FMECA process identifies mission critical failure modes and thereby precipitates formal acknowledgment of the risk to the project and provides an impetus for design alteration.
1308: Electromagnetic Interference Analysis of Circuit Transients
Practice: Network circuit analysis programs are valuable tools in the analysis of switching circuit transients which are capable of generating conducted and radiated electromagnetic interference (EMI). The analysis is performed to insure that disruptions or degradations due to EMI do not occur. EMI is capable of disrupting the normal operating environment of an electronic circuit or degrading the performance of such a circuit.
Benefits:Circuit analysis for the purpose of evaluating the conducted and radiated EMI from a switching circuit has resulted in the proper design of switching circuit electronics. The devices connected to electronic switching circuits will not be adversely affected by transient currents and associated radiated fields generated by such currents.
1309: Analysis of Radiated EMI From ESD Events Caused by Space Charging
Practice: Modeling is utilized for the analysis of conducted and radiated electromagnetic interference (EMI) caused by an electrostatic discharge (ESD) event. The modeling requires the combined use of a SPICE, or other circuit analysis code and a wire antenna code based on the method of moments, and is primarily applicable to wires, cables, and connectors.
Benefit:The use of a combined SPICE circuit analysis code and a method of moments code for the study of possible conducted and radiated EMI resulting from an ESD event, allow the assessment of EMI noise coupling onto electronic circuit interfaces.
1310: Spurious Radiated Interference Awareness
Practice: Unexpected interference in receivers can be avoided in a complex system of transmitters and receivers by performing an intermodulation analysis to identify and solve potential problems. Various emitters may be encountered during system test, launch, boost, separation and flight. There are a large number of these harmonics and intermodulation products from which potential sources of spurious radiated interferences are identified by a computer aided analysis and corrective measures evaluated.
Benefit:Spurious radiated interference can be identified and evaluated during the design phase of the project. Solutions can be proposed and implemented in the design phase with far less impact on cost and schedule than when changes are required later.
1311: System Reliability Assessment Using Block Diagraming Methods
Practice: Use high-speed, computer-based computational fluid dynamics analytical techniques, verified by test programs to establish propulsion and launch vehicle hardware designs for optimum performance and high reliability. These procedures will validate designs and provide an early assurance of operational viability.
Benefits:The use of computer-based computational fluid dynamics methods will accelerate the design process, reduce preliminary development testing, and help create reliable, high-performance designs of space launch vehicles and their components. In addition to design verification and optimization, CFD can be used to simulate anomalies that occur in actual space vehicle tests or flights to more fully understand the anomalies and how to correct them. The result is a more reliable and trouble-free space vehicle and propulsion system.
1312: The Team Approach to Fault-Tree Analysis
Practice: Use a multi-disciplinary approach to investigations using fault-tree analysis for complex systems to derive maximum benefit from fault-tree methodology. Adhere to proven principles in the scheduling, generation, and recording of fault-tree analysis results.
Benefits:The use of the team approach to fault-tree analysis permits a rapid, intensive, and thorough investigation of space hardware and software anomalies. This approach is specifically applicable when the solution of engineering problems is urgent and when they must be resolved expeditiously to prevent further delays in program schedules. The systematic, focused, highly participative methodology permits quick and accurate identification, recording, and solution of problems. The resulting benefits of the use of this methodology are reduction of analysis time, and precision in identifying and correcting deficiencies. The ultimate result is improved overall system reliability and safety.
1313: System Reliability Assessment Using Block Diagraming Methods
Practice: Use reliability predictions derived from block diagram analyses during the design phase of the hardware development life cycle to analyze design reliability; perform sensitivity analyses; investigate design trade-offs; verify compliance with system-level requirements; and make design and operations decisions based on reliability analysis outputs, ground rules, and assumptions.
Benefit:Reliability block diagram (RBD) analyses enable design and product assurance engineers to (1) quantify the reliability of a system or function, (2) assess the level of failure tolerance achieved, (3) identify intersystem disconnects as well as areas of incomplete design definition, and (4) perform trade-off studies to optimize reliability and cost within a program. Commercially available software tools can be used to automate the RBD assessment process, especially for reliability sensitivity analyses, thus allowing analyses to be performed more effectively and timely. These assessment methods can also pinpoint areas of concern within a system that might not be obvious otherwise and can aid the design activity in improving overall system performance.
1314: Sneak Circuit Analysis Guideline for Electromechanical Systems
Practice: Sneak circuit analysis is used in safety critical systems to identify latent paths which cause the occurrence of unwanted functions or inhibit desired functions, assuming all components are functioning properly. It is based upon the analysis of engineering and manufacturing documentation. Because of the high cost of a sneak circuit analysis, it should be conducted only in areas where there is a high potential for a hazard.
Benefit:Identification of sneak circuits in the design phase of a project prior to manufacture can improve reliability; eliminate costly redesign and schedule delays; and eliminate problems in test, launch, on-orbit, and protracted space operations. Sneak circuit analysis can also be beneficial in identifying drawing errors and design concerns.
1315: Redundancy Switching Analysis
Practice: To verify that the failure of one of two redundant functions does not impair the ability to transfer to the second function, a rigorous failure modes, effects, and criticality analysis (FMECA) at the piece part-level is performed for all interfacing circuits.
Benefits:By using a systematic method to assure the switching functionality of designed-in redundancy, the long-term performance of complex systems can be assured.
1316: Thick Dielectric Charging/Internal Electrostatic Discharge (IESD)
Practice: Dielectric compositions used in such spacecraft materials as circuit boards, cable insulation and thermal blankets will build up an imbedded charge when exposed to a natural space environment featuring energetic electrons. If the electric field resulting from the imbedded charge exceeds the breakdown threshold for the dielectric, an arc will occur, damaging the dielectric and producing an electromagnetic pulse which can couple into subsystem electronics. Enhance hardware reliability in an energetic electron environment by conducting a materials inventory, resistivity analysis, and shielding assessment. Ascertain material susceptibility to deep dielectric charging and explosive discharge when the material:
- Is exposed to an energetic electron flux exceeding 2x105 electrons/(cm2-s), and
Achieves an imbedded charge density greater than a threshold of 1011 electrons/cm2.
Benefit:Materials and design structures which represent possible internal electrostatic discharge (IESD) sources can be identified early in the program. Risk to hardware may be reduced through design changes which substitute materials having sufficient conductivity to permit charge bleed-off. Sensitive cable runs may be rerouted or shielded to reduce exposure to energetic electrons. Grounding schemes may be changed to ensure that otherwise isolated conductors are grounded and that grounds are designed to maximize the opportunity to bleed-off the charge from dielectric materials.
1317: Flight Load Analysis as a Spacecraft Design Tool
Practice: The determination of accurate spacecraft loads via coupled flight loads analysis is used throughout the entire spacecraft development cycle, from conceptual design to final verification loads calculations.
Benefit:Flight loads analysis, when used throughout the spacecraft development cycle, will 1) provide a mission specific set of loads, 2) provide a balanced structural design, 3) reduce conservatism inherent in bounding quasi-static design load calculations, 4) provide early problem definition, and 5) reduce surprises at the final verification loads cycle.
1318: Structural Stress Analysis
Practice: This paper describes the general methodology for performing stress analysis for structures used in space applications.
Benefit:Reliability of spacecraft structural components is greatly increased, and their cost and weight reduced by the systematic and rigorous application of sound stress analysis principles as an integral part of the design process.
Redundancy Verification Analysis
Not yet available
1401: EEE Parts Screening
Practice: Implement a 100% nondestructive screening test on EEE parts prior to assembly, which would prevent early-life failures (generally referred to as infant mortality).
Benefits:A lower rework cost during manufacturing and lower incident of component failures during flight.
1402: Thermal Cycling
As a minimum, run eight thermal cycles over the approximate temperature range for hardware that cycles in flight over ranges greater than 20°C. The last three thermal cycles should be failure-free.
Benefit:Demonstrates readiness of the hardware to operate in the intended cyclic environment. Precipitates defects from design or manufacturing processes that could result in flight failures.
1403: Thermographic Mapping of PC Boards
Practice: Use thermographic mapping methods to locate hot spots on operating PC boards.
Benefit:Quick find of electronic components operating at or above recommended temperatures. Also, this technique can validate the derating factors and thermal design via low cost testing versus analysis.
1404: Thermal Test Levels & Durations
Practice: Perform thermal dwell test on protoflight hardware over the temperature range of +75 °C/-20 °C (applied at the thermal control/mounting surface or shearplate) for 24 hours at the cold end and 144 to 288 hours at the hot end.
Benefit:This test, coupled with rigorous design practices, provides high confidence that the hardware design is not marginal during its intended long life high reliability mission.
1405: Powered-On Vibration
Practice: Supply power to electronic assemblies during vibration, acoustics, and pyroshock and monitor the electrical functions continuously while the excitation is applied.
Benefit:Aids in the detection of intermittent or incipient failures in electronic circuitry not otherwise found. This reliability practice benefits even those electronics not powered during launch.
1406: Sinusoidal Vibration
Practice: Subject assemblies and the full-up flight system to swept sinusoidal vibration.
Benefit:Certain failures are not normally exposed by random vibration. Sinusoidal vibration permits greater displacement excitation of the test item in the lower frequencies.
1407: Assembly Acoustic Tests
Practice: Subject selected (large surface area, low mass) assemblies, in addition to the full-up flight system, to acoustic noise. It is imperative on missions with fixed launch windows that acoustic problems on assemblies not be deferred to system level tests.
Benefit:Acoustic noise tests subject potentially susceptible hardware to a significant launch environment, revealing design and workmanship inadequacies which might cause problems in flight.
1408A: Pyrotechnic Shock Testing (revised to reflect "powered" test mode)
Practice: Subject potentially sensitive flight assemblies that contain electronic equipment or mechanical devices, as well as entire flight systems, to pyrotechnic shock (pyroshock) as part of a development, acceptance, protoflight, or qualification test program. Perform visual inspection and functional verification testing before and after each pyroshock exposure. Where feasible, perform assembly-level and system-level pyroshock tests with the test article powered and operational to better detect intermittent failures.
Benefit:Early assembly-level pyroshock testing can often reduce the impacts of design and manufacturing/assembly deficiencies upon program cost and schedule prior to system-level test. Such testing can provide a test margin over flight pyroshock conditions which cannot be achieved in system testing. Conversely, system-level shock testing can be used to verify system performance under pyroshock exposure, thus providing increased confidence in mission success and verifying the adequacy of the assembly-level tests.
1409: Thermal-Vacuum Versus Thermal-Atmospheric Tests of Electronic Assemblies
Practice: Perform all thermal environmental tests on electronic spaceflight hardware in a flight-like thermal vacuum environment (i.e., do not substitute an atmospheric pressure thermal test for the thermal/vacuum test). Moreover, if a compromise is thought to be necessary for nontechnical reasons, then an analysis is required to quantify the reduction in test demonstrated reliability.
Benefit: Assembly-level thermal vacuum testing is the most perceptive test for uncovering design deficiencies and workmanship flaws in spaceflight hardware. The margin beyond flight conditions is demonstrated, as is reliability. However, substituting an atmospheric pressure thermal test for the thermal/vacuum test can effectively reduce electronic piece part temperatures by 20 °C or more, even for low power density designs. The net result of this is that the effective test temperatures may be reduced to the point where there is zero or negative margin over the flight thermal environment.
1410: Selection of Spacecraft Materials and Supporting Vacuum Outgassing Data
Practice: Each flight project provides requirements for defining and implementing a contamination control program applicable to the hardware for the program. The program consists first in defining the specific cleanliness requirements and setting forth the approaches to meeting them in a Contamination Control Plan. One significant part of the Contamination Control Plan is a comprehensive Materials and Process Program beginning at the design stage of the hardware. This program helps ensure the safety and success of the mission by the appropriate selection, processing, inspection, and testing of the materials employed to meet the operational requirements for the application. The following potential problem areas are considered when selecting materials: radiation effects, thermal cycling, stress corrosion cracking, galvanic corrosion, hydrogen embrittlement, lubrication, contamination of cooled surfaces, composite materials, atomic oxygen, useful life, vacuum outgassing, toxic offgassing, flammability, and fracture toughness. The practice described here for the collection and compilation of vacuum outgassing data is used in conjunction with a number of other processes in the selection of materials. Vacuum outgassing tests are conducted on materials intended for space flight use, and a compilation of outgassing data, Reference 1, is maintained and constantly updated as new materials are tested. This includes materials used in the manufacture of parts intended for space applications.
Benefit:These test data provide outgassing information on a wide variety of materials and should be used as a guide by engineers in selecting materials with low outgassing properties.
1411: Heat Sinks for Parts Operated in Vacuum
Practice: Perform a thermal analysis of each electronic assembly to the piece-part level. Provide a heat conduction path for all parts whose junction temperature rise exceeds 35 °C above the cold plate.
Benefits: Controlling the operating temperature of parts in a vacuum flight environment will lower the failure rate, improve reliability and extend the life of the parts.
1412: Environmental Test Sequencing
Practice: Perform dynamic tests prior to performing thermal-vacuum tests on flight hardware.
Benefit:Experience has shown that until the thermal-vacuum tests are performed, many failures induced during dynamics tests are not detected because of the short duration of the dynamics tests. In addition, the thermal-vacuum test on flight hardware at both the assembly level and the system level provides a good screen for intermittent as well as incipient hardware failures.
1413: Random Vibration Testing
Practice: Define an appropriate random vibration test, and subject all assemblies and selected subsystems to the test for design qualification and workmanship flight acceptance.
Benefit:This practice assists in identifying existing and potential failures in flight hardware so that they can be rectified before launch.
1414: Electrostatic Discharge (ESD) Test Practices
Practice: Test satellites for the ability to survive the effects of electrostatic discharges (ESDs) caused by a space charging environment. Such environments include Earth equatorial orbits above 8000 km and virtually all orbits above 40 degrees latitude, Jupiter encounters closer than 15 Rj (Jupiter radii), and possibly other planets.
Benefit: Proper implementation of this practice will assure that satellites will operate in the space charging environment without failure or awkward ground controller operations.
1415: Power System Corona Testing
Practice: Test power system components for corona to ensure that their insulation system will meet the design requirements imposed on the equipment and to verify that the gas discharges are not deteriorating the insulation system. The acceptable corona levels are verified in power system components.
Benefits: Knowledge of the presence or absence of corona discharge will help in controlling the reliability of high voltage components/systems. Corona testing can reveal potential and unaccounted-for corona discharges that may shorten the service-life of electrical insulating systems, seriously interfere with high voltage system operation and communication links, and result in failure and loss of mission objectives.
1416: Radiated Susceptibility System Verification
Practice: Verify that a flight vehicle or system is hardened to the launch, boost, and flight electromagnetic radiation environment by radiating simultaneously, during system checkout, on all major emission frequencies that are known to exist during vehicle operations. Monitor all critical systems for erroneous performance while the spacecraft or system is stepped through all operating modes.
Benefit:Spurious interferences and responses can be identified during system checkout. After the spurious responses are evaluated, solutions can be proposed, and remedial action taken, if necessary, prior to the actual flight.
1417: Electrical Isolation Verification (DC)
Practice: Direct current (DC) electrical isolation verification tests are made as part of the EMC test of hardware prior to final spacecraft assembly. Flight acceptance isolation retest is required after any hardware rework of subsystems with electrical interfaces that utilize system wiring.
Benefit:Inadvertent grounds of isolated circuits and ground loops are detected directly by this test. In some cases, such grounds may pass other tests with no apparent degradation. Failure may not occur until the vehicle is subjected to high level electromagnetic radiation. Since this test requires minimal test equipment and can be performed in a short time, its benefits are achieved at low cost.
1418: Qualification of Non-Standard EEE Parts in Spaceflight Applications
Practice: The source for selection of acceptable flight quality EEE parts for use on Goddard projects is GSFC Preferred Parts List (PPL-20) . PPL-20 complements NASA Standard Electrical, Electronic, and Electromechanical (EEE) Parts List (NSPL)(MIL-STD-975) by listing additional part types and part categories not included in MIL-STD-975. Recognizing that it is neither possible nor desirable to include all parts in the GSFC PPL and in the NSPL, the GSFC parts requirements make provision that limited numbers of parts not included in the PPL or the NSPL may be used if it is demonstrated that the parts are acceptable . The acceptability of (5, section 5) nonstandard parts is enhanced by use of the part procurement specifications provided in Appendix E of PPL-20. The acceptability of these nonstandard parts must be demonstrated prior to commitment to design or use. Requests for approval to use nonstandard parts with supporting documentation are forwarded to the appropriate GSFC Project Office for review and approval. The practice described herein is used for demonstrating and documenting the acceptability of nonstandard parts for space flight use.
Benefits:The practice of using approved nonstandard parts that have been appropriately demonstrated to be acceptable for the applications provides for a wider range of parts selection than are available with standard parts. These parts are at a quality level equal to that of Grades 1 or 2 standard parts.
1419: Vibroacoustic Qualification Testing of Payloads, Subsystems, and Components
Practice: Perform acoustic and random vibration testing supplemented with additional sine vibration testing as appropriate to qualify payload hardware to the vibroacoustic environments of the mission, particularly the launch environment and to demonstrate acceptable workmanship.
Benefit:Adherence to the practice alleviates vibroacoustic-induced failures of structural stress and fatigue, unacceptable workmanship, and performance degradation of sensitive subsystems including instruments and components. Implementation of this practice assures that minimal degradation of "design reliability" has occurred during prior fabrication, integration and test activities.
1420: Sine-Burst Load Test
Practice: The sine-burst test is used to apply a quasi-static load to a test item in order to strength qualify the item and its design for flight.
Benefits:The sine-burst test is a simple method to apply a quasi-static load using a vibration shaker and shock testing software. Depending on the complexity of the test item, it often can be used in lieu of , and is more economical than, acceleration (centrifuge) or static tests. For components and subsystems, the fixture used for vibration testing often can also be used for sine-burst strength testing. For this reason, strength qualification and random vibration qualification can often be performed during the same test session which saves time and money.
1421: Eddy Current Testing of Aerospace Materials
Practice: Eddy Current Testing (ECT) can be used on electrically conductive material for detecting and characterizing defects such as surface and near surface cracks, gouges, and voids. It can also be used to verify a material's heat treat condition. In addition, wall thickness of thin wall tubing, and thickness of conductive and nonconductive coating on materials can be determined using ECT.
Benefits:Eddy Current Testing is a fast, reliable, and cost effective nondestructive testing (NDT) method for inspecting round, flat, and irregularly shaped conductive materials. Specific processes have been developed to determine the usability and integrity of threaded fasteners. In addition, ECT has the capability of being automated. With proper equipment and skilled test technicians readout is instantaneous.
1422: Ultrasonic Testing of Aerospace Materials
Practice: Three general methods of ultrasonic testing can be used singly or in combination with each other to identify cracks, debonds, voids, or inclusions in aerospace materials. Each has its own unique application and all require certain precautions or techniques to identify potentially flawed hardware. This practice describes selected principles that are essential in reliable ultrasonic testing.
Benefit:Careful attention to detail in ultrasonic testing can result in the identification of very small cracks, debonds, voids or inclusions in aerospace hardware that could be detrimental to mission performance. New ultrasonic technologies are enhancing the accuracy, speed, and cost-effectiveness of this method of nondestructive testing.
1423: Radiographic Testing of Aerospace Materials
Practice: Radiographic testing can be used as a nondestructive method for detecting internal defects in thick and complex shapes in metallic and nonmetallic materials, structures, and assemblies.
Benefit:Unlike most other nondestructive testing methods, radiographic testing provides a permanent visual record of the defects for possible future use. It can also be used to determine crack growth for use in fracture mechanics to determine critical flaw size in a particular component.
1424: Leak Testing of Liquid Hydrogen and Liquid Oxygen Propellant Systems
Practice: Leak testing is a nondestructive test method that provides the capability to detect and measure the amount of liquid or gas escaping from a sealed pressure system and to locate the individual leaks for possible repair.
Benefit:Leak testing of a Liquid Hydrogen (LH2 ) and a Liquid Oxygen (LO2 ) propellant system prior to flight insures that the flight leakage rate does not exceed allowable leakage established for flight. Leak testing also insures the quality and reliability of a Space Shuttle Element and reduces the probability of system failure. Leak checks also prove that seals and sealing surfaces at joints are defect free and seals are seated correctly.
1425: Magnetic Particle Testing of Aerospace Materials
Practice: Magnetic Particle Testing can be used on all ferromagnetic materials to locate surface and subsurface discontinuities such as cracks, laps, seams, and inclusions.
Benefit:Magnetic particle testing is a cost effective and expedient nondestructive Testing (NDT) method for determining discontinuities in ferromagnetic material. This NDT method can be performed in both the longitudinal and transverse directions.
1426: Penetrant Testing of Aerospace Materials
Practice: Penetrant testing improves hardware reliability by detecting surface flaws and defects in solid materials and structures. The discontinuities must be open to the material surface.
Benefit:Penetrant Testing is a cost effective, nondestructive method for determining cracks, porosity, gouges, laps, seams, and other flaws that are open to the surface of metallics and selected non-metallics.
1427: Rocket Engine Technology Test Bed Practice
Practice: Conduct highly instrumented tests of O2/H2 rocket engine systems to: (1) evaluate and verify new propulsion technologies; (2) validate or modify analytical models; (3) more fully understand the operation of rocket engine systems under varying performance conditions, and (4) ensure engine reliability and operability.
Benefits:Highly instrumented engine system tests of varying configurations under varying conditions provides engine system level validation of advanced propulsion technology concepts prior to incorporation of these concepts into development or production units; provides an opportunity for greater understanding and fine-tuning of analytical tools that characterize engine performance; results in the development and improvement of diagnostic methods; and increases the depth of available knowledge about the inner workings, sensitivities, and detailed performance characteristics of liquid rocket engine systems. The overall benefit are the validation of technology, improved system performance, high system reliability, and mission safety.
1428: Practice of Reporting Parts, Materials, and Safety Problems (Alerts)
Practice: Ensure that potentially significant problems involving parts, materials, and safety discovered during receiving inspection, manufacturing, post-manufacturing inspection, or testing do not affect the safety or the performance of NASA hardware by reporting all anomalies via ALERT systems. ALERTS and SAFE ALERTS pertaining to these problems are quickly disseminated for impact assessment and, if required, corrective action taken or a rationale developed for "flying as is."
Benefit:The benefit of the ALERTS system is the reduction or elimination of duplicate expenditures of time and money by exchanging information of general concern regarding parts, materials, and safety problems within MSFC, between MSFC and other NASA centers, between NASA and other government organizations, and between government and industry to assist in preventing similar occurrences. The use of the ALERTS system avoids future failures, rules out fraudulent hardware, helps enhance reliability, and ensures mission success.
1429: Integration & Test Practices to Eliminate Stresses on Electrical and Mechanical Components
Practice: Use proven GSFC practices during the integration and testing of flight hardware to prevent electrical and mechanical overstressing of flight hardware parts and components, thereby, assuring that the "designed in" reliability is not compromised.
Benefits:These practices prevent the long term degradation and early failure of electrical parts and components due to electrical and mechanical overstressing. Damage due to overstressing may not result in immediate failure and may not be detected by component or assembly level testing but can result in early failures.
1430: Short Circuit Testing for Nickel Hydrogen Battery Cells
Practice: Use Short-Circuit testing method or response characteristics on Nickel/Hydrogen (Ni/H2 ) battery to characterize the battery impedance. This data is necessary for designing power processing equipment and electric power fault protection system.
Benefits: Ni/H2 battery technology is gaining wide acceptance as an energy storage system for use in space applications because of its reliability, weight and long cycle expectancy at deep depths-of-discharge (DOD). When a charged Ni/H2 battery is short-circuited, its short circuit current data can be used to calculate the internal resistance of the cells for the purpose of determining the overall characteristics of the energy storage system. Also, by examining the cell impedance only, a Ni/H2 battery simulation utilizing low cost lead-acid cells can be developed.
1431: Voltage/Temperature Margin Testing
Practice: Voltage and Temperature Margin Testing (VTMT) is the practice of exceeding the expected flight limits of voltage, temperature, and frequency to simulate the worst case functional performance, including effects of radiation and operating life parameter variations on component parts. For programs subject to severe cost or schedule constraints, VTMT has proven an acceptable alternative to conventional techniques such as worst case analysis (WCA). WCA is the preferred approach to design reliability, but VTMT is a viable alternative for flight projects where trade-offs of risk versus development time and cost are appropriate.
Benefits:On spacecraft hardware where risk vs. cost trades permit higher risk (Class C), VTMT is an economical alternative to classical worst case analysis. The major benefits in using VTMT instead of WCA are:
- Assurance of a systematic method for investigation of potential risks where the parameters are not adequately modeled by worst case analysis. An example is RF circuits which have distributed circuit parameters.
- Labor savings for units too complex to simulate and which generally require Monte Carlo or root-sum squares analyses.
- Real-time operation and review of complex circuits, allowing the weighing of alternative design actions.
- Cost savings from expedited risk assessment. Comparative studies have demonstrated that testing may be completed in less than one-third the time required for analyses.
1432: RF Breakdown Characterization
Practice: Tests are performed to verify that radio frequency (RF) equipment, such as receivers, transmitters, diplexers, isolators, RF cables, and connectors, can operate without damage or degradation. Reliability assurance is necessary in both a vacuum environment and at critical pressure with adequate demonstrated margins above the expected operating RF signal levels.
Benefits:Knowledge of the dielectric breakdown characteristics of RF devices at low pressures or in a near vacuum environment can be used to protect sensitive flight equipment. RF breakdown is a concern because of the low, near-vacuum pressures at which spacecraft are tested and operated. RF breakdown testing is conducted to establish hardware resilience to the application of out-of-spec input signal levels, signal reflections due to mismatches at hardware interfaces, inadvertent evacuation of vacuum chambers during RF input, application of RF signals during the ascent phase of the spacecraft launch vehicle, etc.
1433: Mechanical Fastener Inspection System
Practice: Applies a formal Flight Assurance inspection system for mechanical fasteners used in flight hardware and critical applications on ground support equipment (GSE), including all flight hardware/GSE interfaces.
Benefit:This practice significantly enhances flight reliability by ensuring that mechanical fasteners do not fail during the mission due to inadequate integrity requirements or Quality Control inspection procedures.
1434: Battery Verification through Long-Term Simulation
Practice: Conduct highly instrumented real-time long term tests and accelerated testing of space flight batteries using automated systems that simulate prelaunch, launch, mission, and post mission environments to verify suitability for the mission, to confirm the acceptability of design configurations, to resolve mission anomalies, and to improve reliability.
Benefit:Since the operational readiness and future performance of space flight batteries at any point in a mission are strongly dependent upon past power cycles and environments, thoroughly instrumented and analyzed ground testing of space flight batteries identical to flight configurations will ensure predictable performance and high reliability of flight batteries.
1435: Verification of RF Hardware Design Performance
Practice: Analyses are performed early in the design of radio frequency (RF) hardware to determine hardware imposed limitations which affect radio performance. These limitations include distortion, bandwidth constraints, transfer function non-linearity, non-zero rise and fall transition time, and signal-to-noise ratio (SNR) degradation. The effects of these hardware performance impediments are measured and recorded. Performance evaluation is a reliability concern because RF hardware performance is sensitive to thermal and other environmental conditions, and reliability testing is constrained by RF temperature limitations.
Benefits:Identification of hardware-imposed limitations on RF subsystem performance permits designers to evaluate a selected radio technology or architecture against system requirements. In the test phase of the reliability assurance program, it also helps engineers to understand performance characteristics they encounter during testing. RF modeling and verification provides for designed-in reliability in accordance with NASAs project streamlining policy.
1436: Advanced Computed X-Ray Tomography
Practice: Use advanced computed X-ray tomography as a precision method of materials characterization and defect location to ensure high reliability of aerospace hardware and conformance to design requirements. Employ this sophisticated and proven technology for nondestructive evaluation (NDE) of materials and structures. Assure the adherence to established precautionary measures during tomography operations.
Benefits:Advanced computed X-ray tomography can be used to produce both two-dimensional and three-dimensional images of structures, materials, parts, and components. These images are providing information that is useful for inspection, evaluation, and diagnostics of complex hardware.
1437: End to End Compatibility and Mission Simulation Testing
Practice: End-to-End Compatibility and Mission Simulation testing are conducted on all portions of the Ground Data Systems (GDS). These tests are performed to fully demonstrate the operational compatibility and the ability of the entire system to perform as expected during the flight mission.
Benefits:This testing significantly enhances flight reliability by ensuring that all portions of the flight operational system work together as expected. This includes the proper flow of data to the end users.
1438: Reliability Considerations for Launch Vehicle Command Destruct Systems
Practice: Use built-in redundancies, safe and arm provisions, approved and qualified initiators and detonators, shaped charge development testing to collect empirical data for design (empirical testing), and fail-safe designs to achieve reliability in launch vehicle command destruct systems.
Benefits:The benefits of implementing the practices spelled out herein are protection against inadvertent activation of the launch vehicle command destruct system, reliable activation and operation of the command destruct system in the event of vehicle malfunctions, and protection of the mission hardware and personnel prior to and during the launch.
1439: Systems Test Considerations for High Performance Liquid Propellant Rocket Engines
Practice: To achieve high overall liquid rocket fueled propulsion system reliability, conduct a comprehensive test program that verifies and validates the liquid rocket engines operation as it interacts and interfaces with other elements of the propulsion system, (i.e., structures, propellant feed systems, propellant tankage, and control electronics).
Benefit:Experience in systems testing of the Space Shuttle Main Engine has shown that integrated propulsion system testing, (1) provides the necessary test data for "model basing," thus enhancing the reliability of system analysis techniques; (2) integrates vehicle hardware, ground hardware, and procedures for propellant loading, safing, and firing operations; (3) provides a resource for determining stage/engine design margins, establishing redlines, developing procedures and time lines, and confirming extrapolated criteria used in engine development; (4) identifies potential risks for catastrophic flight failure, vehicle hardware damage, and launch complex damage; and (5) identifies potential risks of a delayed initial launch and subsequent launches.
1440: Modal Testing: Measuring Dynamic Structural Characteristics
Practice: Modal testing is a structural testing practice that provides low levels of mechanical excitation to a test structure and measures its response to that excitation. This response is then analyzed to experimentally determine the dynamic structural characteristics of the test subject. Modal testing may be performed on all suitable space structures including those associated with the Orbiter and the Space Station.
Benefit: Specifically, when used in the analysis of Orbiter payloads, the dynamic structural characteristics of a payload created by modal testing can be correlated with finite element models (FEMs) to predict the payloads responses to launch and landing environments as well as any other conditions the spacecraft may encounter. This correlation analysis can also be used to perform coupled loads analyses to ensure that the payload will not have any adverse dynamic effects on the Orbiter.
Similar benefits are also derived through modal testing of other space structures.
1441: Design of an Improved Gas Transfer Valve for Leak Tight Testing
Practice: A needle-point penetration gas transfer valve has been developed at JSC that is leak tight and gives very reliable results in transferring low or high pressure gases from sample containers to laboratory measuring devices such as chromatographs.
Benefit: The reliability benefits of this new valve are that it can be used to transfer gas without risking the loss of the sample or the samples purity. This improved reliability is in comparison to normal refrigeration gas transfer valves which are not leak tight and are not suitable for gas transfer where limited and unique gas samples are available and absolute gas measurements are required.
1442: Design of a Small Apparatus for Improved Vibration / Thermal Testing
Practice: A small test fixture has been specifically designed for conducting vibration/thermal tests on small test specimens such as ignitors and detonators. This test fixture creates much smaller loads and less hostile thermal environments for the vibrator table armature thus creating a more reliable test set up. In addition, this small test fixture provides much more rapid and accurate thermal transfer to a test specimen which results in more data points for the same test times and more accuracy and reliability in the test data.
Benefits: This new environmental fixture is much smaller than other larger, bulky environmental fixture that requires long soaking times for even temperature stability over the entire fixture and sample. The smaller fixture has less weight and requires little temperature soaking time for obtaining fixture and specimen temperature stability. This improves the reliability of the test set up as low, long term soaking temperatures can cause armature brittleness and subsequent failure while long term heat soaking of the armature can cause vibrator shaker shutdown. In addition, more data points can be obtained in a shorter period of time with better thermal resolution.
Reliability Assurance Guidelines for Low Cost/Short Duration Missions
Not yet available
The JPL risk management site also provides guidance on mission success factors. (need to get access)
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