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. 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. 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.
The use of O-rings has provided ease for running environmental tests on the ground using space simulation chambers. 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. PD-ED 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. PD-ED 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. 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. 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.
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. 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. 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. 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. 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. 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. 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.
The occurrence of early failures is minimized. 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. 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.
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. Benefits : This practice can be used to determine an optimum truss configuration e. PSAM provides a formal and systematic way to evaluate structural performance reliability or risk at minimal time and low cost. PD-ED Practice: Fault protection is the use of cooperative design of flight and ground elements including hardware, software, procedures, etc.
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.
PD-ED 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".
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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. PD-ED 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. 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.
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. 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.
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. Trend data may then be analyzed so that errors are not repeated on future hardware and software.
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. 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.
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.
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. 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. 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. Principal design drivers are the combustion chamber pressure vs. 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. 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. PD-ED 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, 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. PD-ED 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. PD-ED 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. 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. PD-ED 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. 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.
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.
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.
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.
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. 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.
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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.
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. 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. 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. PD-AP 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. 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.
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. 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.
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. 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.
Benefit: Risk rating enables management to focus on the issues with the highest probability of impacting mission success. PD-AP 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.
PD-AP 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. PD-AP 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. 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. PD-AP 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. 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. 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. 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.
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.
PD-AP 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. PD-AP 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. 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.
Acceptability of risk from radiation: Application to human space flight
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. 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.
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. Benefits: A lower rework cost during manufacturing and lower incident of component failures during flight. 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.
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. 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.
PT-TE 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.
Benefit: Certain failures are not normally exposed by random vibration. Sinusoidal vibration permits greater displacement excitation of the test item in the lower frequencies. PT-TE 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. PT-TEA 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. 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. PT-TE Practice: Perform all thermal environmental tests on electronic spaceflight hardware in a flight-like thermal vacuum environment i. 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. 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. 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. 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. PT-TE 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.
PT-TE 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.
Such environments include Earth equatorial orbits above 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.
The acceptable corona levels are verified in power system components. 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.
PT-TE 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.
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. The acceptability of 5, section 5 nonstandard parts is enhanced by use of the part procurement specifications provided in Appendix E of PPL 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. 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. 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. 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. Each has its own unique application and all require certain precautions or techniques to identify potentially flawed hardware. Use of the electronic publication constitutes agreement with these terms.
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