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.
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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-Cd
Conventional 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
Practice: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).
Benefits:
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
Practice: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.
Benefit:
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.
- Leakage.
- Deflagration.
- Vaporific flash.
- Reduced structural strength.
- Erosion.
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 spacecraft’s 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
Practice: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
Practice: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