Search NASA⌕ Search

SEARCH · Search NASA

Results for “Leakage Risk Assessment”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Effect of Compressive Stresses on Leakage Currents in Microchip Tantalum Capacitors

Microchip tantalum capacitors are manufactured using new technologies that allow for production of small size capacitors (down to EIA case size 0402) with volumetric efficiency much greater than for regular chip capacitors. Due to a small size of the parts and leadless design they might be more sensitive to mechanical stresses that develop after soldering onto printed wiring boards (PWB) compared to standard chip capacitors. In this work, the effect of compressive stresses on leakage currents in capacitors has been investigated in the range of stresses up to 200 MPa. Significant, up to three orders of magnitude, variations of currents were observed after the stress exceeds a certain critical level that varied from 10 MPa to 180 MPa for capacitors used in this study. A stress-induced generation of electron traps in tantalum pentoxide dielectric is suggested to explain reversible variations of leakage currents in tantalum capacitors. Thermo-mechanical characteristics of microchip capacitors have been studied to estimate the level of stresses caused by assembly onto PWB and assess the risk of stress-related degradation and failures. Keywords: tantalum capacitors, leakage current, soldering, reliability, mechanical stress.

Teverovsky, Alexander↗
NASA NTRS2015

NASA Manufacturing and Test Requirements for Normally Closed Pyrovalves for Hazardous Flight Systems Applications

Pyrovalves (figure 1, Basic Pyrovalve Design and Features,) are typically lighter, more reliable, and in most cases less expensive than other types of valves. They also consume less electrical power. They are single-use devices that are used in propulsion systems to isolate propellants or pressurant gases. These fluids may be hazardous because of their toxicity, reactivity, temperature, or high pressure. Note that in the simplified block diagram below not all detail features are shown so that those of major interest are more prominent. The diagram is provided to point out the various features that are discussed in this Specification. Features of some NC parent metal valve designs may differ. In 2013, the NESC concluded an extensive study of the reliability and safety of NC parent metal valves used in payloads carried aboard ELVs. The assessment successfully evaluated technical data to determine the risk of NC parent metal valve leakage or inadvertent activation in ELV payloads. The study resulted in numerous recommendations to ensure personnel and hardware/facility safety during ground processing of ELV payloads. One of those recommendations was to establish a NASA specification for NC parent metal valves. This Specification is a result of that recommendation, which is documented in NESC-RP-10-00614.

McDougle, Stephen H.↗
NASA NTRSDate not supplied

Pre-Flight Hazardous Gas Assessment Methodology for the Space Launch System

The complexity of the Artemis I liquid rocket propulsion systems produces many sources of hazards during the operation of the vehicle. Pre-flight hazardous gas leakages pose fire and explosion risks to rocket that could potentially lead to loss of the vehicle, mission, and crew. The National Aeronautics and Space Administration (NASA) uses a probability risk assessment strategy to assess the likelihood of the hazard and the consequence should the hazardous situation occur. For high probability hazards that pose a potentially catastrophic consequence to the vehicle, the most effective strategy for reducing the risk is accomplished by engineering and implementing systems that actively mitigate the hazard. A hazards analysis is completed to determine the likelihood and severity of each hazard. These hazard analyses are informed using relevant empirical data and physics-based analytical models. Time-accurate Computational Fluid Dynamics models used to quantify and understand the risks posed to Artemis I due to expulsions of hazardous gas near the vehicle. Several sources of hazardous gas that posed a risk to Artemis I during nominal pre-flight operations are analyzed in this work. The results of the analyses were used to develop flight rationale and make risk acceptance decisions for the Artemis I launch.

Brian R. Richardson↗
NASA NTRSDate not supplied

Pre-Flight Hazardous Gas Assessment Methodology for the Space Launch System

The complexity of the Artemis I liquid rocket propulsion systems produces many sources of hazards during the operation of the vehicle. Pre-flight hazardous gas leakages pose fire and explosion risks to rocket that could potentially lead to loss of the vehicle, mission, and crew. The National Aeronautics and Space Administration (NASA) uses a probability risk assessment strategy to assess the likelihood of the hazard and the consequence should the hazardous situation occur. For high probability hazards that pose a potentially catastrophic consequence to the vehicle, the most effective strategy for reducing the risk is accomplished by engineering and implementing systems that actively mitigate the hazard. A hazards analysis is completed to determine the likelihood and severity of each hazard. These hazard analyses are informed using relevant empirical data and physics-based analytical models. Time-accurate Computational Fluid Dynamics models used to quantify and understand the risks posed to Artemis I due to expulsions of hazardous gas near the vehicle. Several sources of hazardous gas that posed a risk to Artemis I during nominal pre-flight operations are analyzed in this work. The results of the analyses were used to develop flight rationale and make risk acceptance decisions for the Artemis I launch.

Brian R. Richardson↗
NASA NTRS2015

Leakage Currents and Gas Generation in Advanced Wet Tantalum Capacitors

Currently, military grade, established reliability wet tantalum capacitors are among the most reliable parts used for space applications. This has been achieved over the years by extensive testing and improvements in design and materials. However, a rapid insertion of new types of advanced, high volumetric efficiency capacitors in space systems without proper testing and analysis of degradation mechanisms might increase risks of failures. The specifics of leakage currents in wet electrolytic capacitors is that the conduction process is associated with electrolysis of electrolyte and gas generation resulting in building up of internal gas pressure in the parts. The risk associated with excessive leakage currents and increased pressure is greater for high value advanced wet tantalum capacitors, but it has not been properly evaluated yet. In this work, in Part I, leakages currents in various types of tantalum capacitors have been analyzed in a wide range of voltages, temperatures, and time under bias. Gas generation and the level of internal pressure have been calculated in Part II for different case sizes and different hermeticity leak rates to assess maximal allowable leakage currents. Effects related to electrolyte penetration to the glass seal area have been studied and the possibility of failures analyzed in Part III. Recommendations for screening and qualification to reduce risks of failures have been suggested.

degradation mechanisms↗
NASA NTRS2009

A History of Space Toxicology Mishaps: Lessons Learned and Risk Management

After several decades of human spaceflight, the community of space-faring nations has accumulated a diverse and sometimes harrowing history of toxicological events that have plagued human space endeavors almost from the very beginning. Lessons have been learned in ground-based test beds and others were discovered the hard way - when human lives were at stake in space. From such lessons one can build a risk-management framework for toxicological events to minimize the probability of a harmful exposure, while recognizing that we cannot foresee all events. Space toxicologists have learned that relatively harmless compounds can be converted by air revitalization systems into compounds that cause serious harm to the crew. Our toxic risk management strategy now includes an assessment of the fate of any compound that might be released into the atmosphere. Propellants are highly toxic compounds, yet we have not always been able to thoroughly isolate the crew from exposure to these toxicants. Leakage of fluids from systems has resulted in hazardous conditions at times, and the behavior of such compounds inside a spacecraft has taught us how to manage potentially harmful escapes should they occur. Potential combustion events are an ever-present threat to the wellbeing of the crew. Such events have been sufficiently common that we have learned that one cannot judge the health threat of a given fire by the magnitude of the event. Management of such risks demands monitoring of combustion products. In the category of unpredictable toxic events, if one assumes that fires are predictable, we can place experience with toxic microbial metabolites, upsets during repair operations, and discharges from filters that have accumulated a substantial load of pollutants in their absorption beds. Management of such events requires a broad-spectrum, real-time analytical capability to discern the identity and concentrations of pollutants if they enter the atmosphere. Adverse events are an integral part of any human activity, and the spacefaring community must learn as much as possible from mistakes and near misses.

James, John T.↗
NASA NTRS2014

An Example of Risk Informed Design

NASA Engineering requested a Probabilistic Risk Assessment (PRA) to compare the difference in the risk of Loss of Crew (LOC) and Loss of Mission (LOM) between different designs of a fluid assembly. They were concerned that the configuration favored by the design team was more susceptible to leakage than a second proposed design, but realized that a quantitative analysis to compare the risks between the two designs might strengthen their argument. The analysis showed that while the second design did help improve the probability of LOC, it did not help from a probability of LOM perspective. This drove the analysis team to propose a minor design change that would drive the probability of LOM down considerably. The analysis also demonstrated that there was another major risk driver that was not immediately obvious from a typical engineering study of the design and was therefore unexpected. None of the proposed alternatives were addressing this risk. This type of trade study demonstrates the importance of performing a PRA in order to completely understand a system's design. It allows managers to use risk as another one of the commodities (e.g., mass, cost, schedule, fault tolerance) that can be traded early in the design of a new system.

Banke, Rick↗
NASA NTRS2013

An Evaluation of a High Pressure Regulator for NASA's Robotic Lunar Lander Spacecraft

The Robotic Lunar Lander (RLL) development project office at NASA Marshall Space Flight Center is currently studying several lunar surface science mission concepts. The focus is on spacecraft carrying multiple science instruments and power systems that will allow extended operations on the lunar surface or other air-less bodies in the solar system. Initial trade studies of launch vehicle options indicate the spacecraft will be significantly mass and volume constrained. Because of the investment by the DOD in low mass, highly volume efficient components, NASA has investigated the potential integration of some of these technologies in space science applications. A 10,000 psig helium pressure regulator test activity has been conducted as part of the overall risk reduction testing for the RLL spacecraft. The regulator was subjected to typical NASA acceptance testing to assess the regulator response to the expected RLL mission requirements. The test results show the regulator can supply helium at a stable outlet pressure of 740 psig within a +/- 5% tolerance band and maintain a lock-up pressure less than the +5% above nominal outlet pressure for all tests conducted. Numerous leak tests demonstrated leakage less than 10-3 standard cubic centimeters per second (SCCS) for the internal seat leakage at lock-up and less than 10-5 SCCS for external leakage through the regulator body. The successful test has shown the potential for 10,000 psig helium systems in NASA spacecraft and has reduced risk associated with hardware availability and hardware ability to meet RLL mission requirements.

Burnside, Christopher G.↗
NASA NTRS2013

Composite Crew Module (CCM) Permeability Characterization

In January 2007, the NASA Administrator chartered the NASA Engineering and Safety Center (NESC) to form an Agency team to design and build a composite crew module in 18 months in order to gain hands-on experience in anticipation that future exploration systems may be made of composite materials. One of the conclusions from this Composite Crew Module Primary Structure assessment was that there was a lack of understanding regarding the ability for composite pressure shells to contain consumable gases, which posed a technical risk relative to the use of a metallic design. After the completion of the Composite Crew Module test program, the test article was used in a new program to assess the overall leakage/permeability and identify specific features associated with high leak rates. This document contains the outcome of the leakage assessment.

Kirsch, Michael T.↗
NASA NTRS2011

An Evaluation of Ultra-High Pressure Regulator for Robotic Lunar Landing Spacecraft

The Robotic Lunar Lander Development (RLLD) Project Office at NASA Marshall Space Flight Center (MSFC) has studied several lunar surface science mission concepts. These missions focus on spacecraft carrying multiple science instruments and power systems that will allow extended operations on the lunar surface. Initial trade studies of launch vehicle options for these mission concepts indicate that the spacecraft design will be significantly mass-constrained. To minimize mass and facilitate efficient packaging, the notional propulsion system for these landers has a baseline of an ultra-high pressure (10,000 psig) helium pressurization system that has been used on Defense missiles. The qualified regulator is capable of short duration use; however, the hardware has not been previously tested at NASA spacecraft requirements with longer duration. Hence, technical risks exist in using this missile-based propulsion component for spacecraft applications. A 10,000-psig helium pressure regulator test activity is being carried out as part of risk reduction testing for MSFC RLLD project. The goal of the test activity is to assess the feasibility of commercial off-the-shelf ultra-high pressure regulator by testing with a representative flight mission profile. Slam-start, gas blowdown, water expulsion, lock-up, and leak tests are also performed on the regulator to assess performance under various operating conditions. The preliminary test results indicated that the regulator can regulate helium to a stable outlet pressure of 740 psig within the +/- 5% tolerance band and maintain a lock-up pressure less than +5% for all tests conducted. Numerous leak tests demonstrated leakage less than 10-3 standard cubic centimeters per second (SCCS) for internal seat leakage at lock-up and less than10-5 SCCS for external leakage through the regulator ambient reference cavity. The successful tests have shown the potential for 10,000 psig helium systems in NASA spacecraft and have reduced risk associated with hardware availability and hardware ability to meet RLL mission requirements.

Burnside, Christopher↗
NASA NTRS1981

Evaluation of the CNS and cardiovascular effects of prolonged exposure to bromotrifluromethane (CBrF3)

The proposed use of bromotrifluoromethane (CBrF3) as a fire extinguishant in aircraft, spacecraft and submarines has stimulated increasing interest and research in the toxicological properties of this compound. In a spacecraft, because of its unique recirculating life support system, the introduction of CBrF3 by leakage or intentional discharge, will result in continuous exposure of crewman to low concentrations of this compound for periods of up to 7 days, or possibly even longer. The effects of low concentrations of CBrF3, under continuous exposure conditions, on the CNS and cardiovascular systems of animals to enable an assessment of these risks were investigated.

Geller, I.↗
NASA NTRS1993

Evaluating Risk Of Failure With Limited Information

Report describes probabilistic failure assessment (PFA). Developed for application to spaceflight systems for sufficient testing of hardware to ensure reliability not feasible. However, must be ascertained that critical failure modes extremely unlikely to occur during service. PFA applied to any failure mode described by quantitative models of physics and mechanics of failure phenomena, such as fatigue crack in initiation or propagation in structures, leakage of seals, wear in bearings, and erosion of arcjet thrustor cathodes.

Moore, N. R.↗
NASA NTRS2008

Modeling the Risk of Fire/Explosion Due to Oxidizer/Fuel Leaks in the Ares I Interstage

A significant flight hazard associated with liquid propellants, such as those used in the upper stage of NASA's new Ares I launch vehicle, is the possibility of leakage of hazardous fluids resulting in a catastrophic fire/explosion. The enclosed and vented interstage of the Ares I contains numerous oxidizer and fuel supply lines as well as ignition sources. The potential for fire/explosion due to leaks during ascent depends on the relative concentrations of hazardous and inert fluids within the interstage along with other variables such as pressure, temperature, leak rates, and fluid outgasing rates. This analysis improves on previous NASA Probabilistic Risk Assessment (PRA) estimates of the probability of deflagration, in which many of the variables pertinent to the problem were not explicitly modeled as a function of time. This paper presents the modeling methodology developed to analyze these risks.

Ring, Robert W.↗
NASA NTRS2007

Assessment of SOI Devices and Circuits at Extreme Temperatures

Electronics designed for use in future NASA space exploration missions are expected to encounter extreme temperatures and wide thermal swings. Such missions include planetary surface exploration, bases, rovers, landers, orbiters, and satellites. Electronics designed for such applications must, therefore, be able to withstand exposure to extreme temperatures and to perform properly for the duration of mission. The Low Temperature Electronics Program at the NASA Glenn Research Center focuses on research and development of electrical devices, circuits, and systems suitable for applications in deep space exploration missions and aerospace environment. Silicon-On-Insulator (SOI) technology has been under active consideration in the electronics industry for many years due to the advantages that it can provide in integrated circuit (IC) chips and computer processors. Faster switching, less power, radiationtolerance, reduced leakage, and high temp-erature capability are some of the benefits that are offered by using SOI-based devices. A few SOI circuits are available commercially. However, there is a noticeable interest in SOI technology for different applications. Very little data, however, exist on the performance of such circuits under cryogenic temperatures. In this work, the performance of SOI integrated circuits, evaluated under low temperature and thermal cycling, are reported. In particular, three examples of SOI circuits that have been tested for operation at low at temperatures are given. These circuits are SOI operational amplifiers, timers and power MOSFET drivers. The investigations were carried out to establish a baseline on the functionality and to determine suitability of these circuits for use in space exploration missions at cryogenic temperatures. The findings are useful to mission planners and circuit designers so that proper selection of electronic parts can be made, and risk assessment can be established for such circuits for use in space missions.

Elbuluk, Malik↗
NASA NTRS2011

Interstage Flammability Analysis Approach

The Interstage of the Ares I launch platform houses several key components which are on standby during First Stage operation: the Reaction Control System (ReCS), the Upper Stage (US) Thrust Vector Control (TVC) and the J-2X with the Main Propulsion System (MPS) propellant feed system. Therefore potentially dangerous leaks of propellants could develop. The Interstage leaks analysis addresses the concerns of localized mixing of hydrogen and oxygen gases to produce deflagration zones in the Interstage of the Ares I launch vehicle during First Stage operation. This report details the approach taken to accomplish the analysis. Specified leakage profiles and actual flammability results are not presented due to proprietary and security restrictions. The interior volume formed by the Interstage walls, bounding interfaces with the Upper and First Stages, and surrounding the J2-X engine was modeled using Loci-CHEM to assess the potential for flammable gas mixtures to develop during First Stage operations. The transient analysis included a derived flammability indicator based on mixture ratios to maintain achievable simulation times. Validation of results was based on a comparison to Interstage pressure profiles outlined in prior NASA studies. The approach proved useful in the bounding of flammability risk in supporting program hazard reviews.

Little, Jeffrey K.↗
NASA NTRS2017

Susceptibility to Cracking of Different Lots of CDR35 Capacitors

On-orbit flight anomalies that occurred after several months of operation were attributed to excessive leakage currents in CDR35 style 0.47 microF 50 V capacitors operating at 10 V. In this work, a lot of capacitors similar to the lot that caused the anomaly have been evaluated in parallel with another lot of similar parts to assess their susceptibility to cracking under manual soldering conditions and get insight into a possible mechanism of failure. Leakage currents in capacitors were monitored at different voltages and environmental conditions before and after terminal solder dip testing that was used to simulate thermal shock during manual soldering. Results of cross-sectioning, acoustic microscopy, and measurements of electrical and mechanical characteristics of the parts have been analyzed, and possible mechanisms of failures considered. It is shown that the susceptibility to cracking and failures caused by manual soldering is lot-related. Recommendations for testing that would help to select lots that are more robust against manual soldering stresses and mitigate the risk of failures suggested.

cracking↗
NASA NTRS2024

Evaluation of Cleaning Methods for Dust Mitigation of Lunar Docking and Hatch Seals

Low-leakage seals are an enabling technology for future lunar surface systems, and they must be kept clean to ensure that crews have sufficient breathable air for extended lunar surface missions. Previous testing on representative state-of-the-art seals showed that while seals can tolerate some level of lunar simulant dust contamination, dust can degrade seal performance to a point at which seal leak rates exceed maximum allowable values. The ability to clean simulant from seals had not been thoroughly studied, and the effectiveness and potential complications of using different cleaning methods for lunar seals were not well understood. To address this knowledge gap, researchers at the NASA Glenn Research Center executed a multiphase study to better understand and mitigate seal dust-exposure risks. The focus of this report is on the second phase of that study, in which tests were conducted to evaluate the viability of seal cleaning methods for use in the lunar environment. Multiple methods for cleaning seals contaminated with lunar simulant were assessed for cleaning effectiveness and viability for use in the lunar environment. Leak tests were performed on seals after they were cleaned to determine whether leak rates could be brought back to acceptable levels, and cleaned seals were examined to determine whether their surfaces had been damaged by the cleaning processes. This phase of the study also investigated changes in the seals’ adhesion forces as a result of contamination and cleaning.

Dust Mitigation↗
NASA NTRS2009

Effects of Hypervelocity Impacts on Silicone Elastomer Seals and Mating Aluminum Surfaces

While in space silicone based elastomer seals planned for use on NASA's Crew Exploration Vehicle (CEV) are exposed to threats from micrometeoroids and orbital debris (MMOD). An understanding of these threats is required to assess risks to the crew, the CEV orbiter, and missions. An Earth based campaign of hypervelocity impacts on small scale seal rings has been done to help estimate MMOD threats to the primary docking seal being developed for the Low Impact Docking System (LIDS). LIDS is being developed to enable the CEV to dock to the ISS (International Space Station) or to Altair (NASA's next lunar lander). The silicone seal on LIDS seals against aluminum alloy flanges on ISS or Altair. Since the integrity of a seal depends on both sealing surfaces, aluminum targets were also impacted. The variables considered in this study included projectile mass, density, speed, incidence angle, seal materials, and target surface treatments and coatings. Most of the impacts used a velocity near 8 km/s and spherical aluminum projectiles (density = 2.7 g/cubic centimeter), however, a few tests were done near 5.6 km/s. Tests were also performed using projectile densities of 7.7, 2.79, 2.5 or 1.14 g/cubic centimeter. Projectile incidence angles examined included 0 degrees, 45 degrees , and 60 degrees from normal to the plane of the target. Elastomer compounds impacted include Parker's S0383-70 and Esterline's ELA-SA-401 in the as received condition, or after an atomic oxygen treatment. Bare, anodized and nickel coated aluminum targets were tested simulating the candidate mating seal surface materials. After impact, seals and aluminum plates were leak tested: damaged seals were tested against an undamaged aluminum plate; and undamaged seals were placed at various locations over craters in aluminum plates. It has been shown that silicone elastomer seals can withstand an impressive level of damage before leaking beyond allowable limits. In general on the tests performed to date, the diameter of the crater in either the elastomer, or the aluminum, must be at least as big as 80% to 90% of width of the bulb of the seal before significant leakage occurs.

deGroh, Henry C., III↗