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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

QM-8 final performance evaluation report: SEALS, volume 4

The Space Shuttle Redesigned Solid Rocket Motor (RSRM) static test of Qualification Motor-8 (QM-8) was conducted. The QM-8 test article was the fifth full-scale, full-duration test, and the third qualification motor to incorporate the redesigned case field joint and nozzle-to-case joint. This was the second static test conducted in the T-97 test facility, which is equipped with actuators for inducing external side loads to a 360 degree external tank (ET) attach ring during test motor operation, and permits heating/cooling of an entire motor. The QM-8 motor was cooled to a temperature which ensured that the maximum propellant mean bulk temperature (PMBT) of 40 F was achieved at firing. All test results are not included, but rather, the performance of the metal case, field joints, and nozzle-to-case joint is addressed. The involvement is studied of the Structural Applications and Structural Design Groups with the QM-8 test which includes: assembly procedures of the field and nozzle-to-case joints, joint leak check results, structural test results, and post-test inspection evaluations.

Nelsen, L. V.↗
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 NTRS2016

CryoCart Restoration and Vacuum Pipe Construction

Propulsion systems that utilize hypergolic propellants have been used to power space vehicles since the beginning of the space program. Liquid methane and oxygen propulsion systems have emerged as an alternative and have proven to be more environmentally friendly. The incorporation of liquid methane/liquid oxygen (LOX) into the propulsion system has demonstrated an increase in engine performance, as well as a reduction in the volume, size and complexity of the system. Consequently, reducing the total mass of the vehicle which is a crucial aspect that is considered when planning space missions to both the Moon and Mars [1]. Project Morpheus has made significant advancements in liquid oxygen/liquid methane propulsion system technologies by incorporating a LOX/methane propulsion system to a vertical test bed. The vehicle consisted of a 5,000 lb main engine and four 20 lb remote control system (RCS) engines that utilize liquid methane/LOX as its propellant [1]. The vehicle completed successful flight testing at Kennedy Space Center in 2014 which marked the completion of the Morpheus project. Subsequent projects utilizing Morpheus' vertical test bed have been developed to make further advancements. One of the subsequent projects consisted of the addition of a smaller 2,000 lb main engine and a cold helium heat exchanger which would make it possible for a pressurant tank systems to be send to Mars or the Moon by significantly decreasing the overall mass and volume of the pressurant tank. The hot fire tests of the integrated system with the smaller main engine and cold helium heat exchanger were successful at sea level, but further studies are being conducted to better understand how the vertical test bed will behave under thermal-vacuum conditions. For this reason, the integrated vehicle will be taken to Plum Brook to be tested in a chamber capable of simulating these conditions. To ensure that the vehicle will function properly under vacuum conditions, testing will be first completed at the component level. During this process, the igniter of the main engine and the RCS thrusters will be tested under a vacuum. To complete the testing of the components, the test setup first needed to be finalized. The CryoCart is being used to feed the propellants to the test article. The CryoCart is a movable test set-up that was developed in 2009 to provide a mobile platform for testing oxygen/methane systems with hot-fire capability up to 100 lbf. The CryoCart consists of three different systems: Oxygen, Methane, and liquid Nitrogen. The Oxygen and Methane systems are placed into two different carts while the liquid nitrogen system is mainly located in the methane cart. Over the years, the CryoCart has been utilized for different projects and has undergone deterioration. For this reason, a new phase has been developed to rebuild it to working conditions once again. During my internship, I was aiding in the construction and restoration of the CryoCart. In the initial stages of the process, I updated the fluid and electrical schematics for the oxygen, methane, and test article systems. The original CryoCart consisted of an electrical panel that utilized electromechanical relays and a terminal to drive the igniter power and signal, as well as the main fuel and oxygen valves. This electrical panel connected to the CryoCart through various wire harnesses that could be found exiting from the CryoCart. First, it was determined how these harnesses connected to the electromechanical relays so that they worked correctly. Once the electrical system was understood, an alternative for the electromechanical relays and the Molex connectors used throughout the system was sought since these components can often prove to be unreliable. Solid State relays and MIL connectors were purchased to serve as replacements. Upon arrival of the parts, crimping and wiring was completed to install the new solid state relays and MIL connectors. During the replacement of the relays and connectors, system checks of the electrical system were ran to ensure that the system was working correctly. While completing system checks, the pressure transducers that were not functioning properly were also replaced and any issue with the wiring or signal was addressed. Once the electrical components were replaced, the restoration of the fluid system began. Parts of the tubing in the CryoCart had to be rebuild and often consisted of sizing, cutting, bending, filing, and sanding the tubing to prepare it to be flared. Many components had to be proof-tested to bring their certifications up to date, and several components had to be replaced. Various flex hoses, valves, and fittings were send to the Clean Lab because they were new, dirty, or had gone through proof-testing. Once they arrived from the cleaning lab they had to be put back to the system and leak checks and functional tests were conducted. In the Nitrogen system, the copper tubing located in the Oxygen cart was rebuild and Aerogel insulation was added to this section. A new gaseous nitrogen system was added to the CryoCart to purge the vacuum tube which will serve as the test chamber. Once the CryoCart was completed, construction of parts of the vacuum tube began. A flange was manufactured with welded fittings to hold the line of the vacuum pump as well as some extra fittings which will serve as extra inlets used to introduce fluid lines to the vacuum tube. Stress analysis was ran in this flange to ensure that it would not fail under vacuum conditions. The fluid lines leading from the air side of the vacuum to the test article were also constructed and added to the mount that had already been manufactured. Three different sets of tubing were constructed to accommodate the seven different RCS thruster and the main engine igniter that are going to be tested. Full electrical system checks were completed to ensure that all the wire harnesses and valves were functioning. Upon the completion of the CryoCart and the vacuum tube, hot fire testing for the RCS thrusters and the main engine igniter are going to begin. During this time any issues encountered with the engines or igniter will be addressed to ensure that the components function under vacuum conditions. After successful completion of testing, the vertical test bed, Morpheus, will be rebuilt and prepared to be sent to Plum Brook. In Plum Brook, the vehicle will be tested in the thermal-vacuum chamber to demonstrate that integrated lox-methane propulsion system operation in space-like conditions. This internship has allowed me the opportunity to gain valuable hands on experience and to develop skills that will aid in my education as well as in the workforce, while at the same time helping me determine that I would like to further pursue a career in propulsion engineering.

Chaidez, Mariana↗
DOE OSTI2022

Predicting Rupture Pressure and Leak Rate of Alloy 600 U-bend Tubes with PWSCC and Comparing with Test Results (Technical Letter Report)

This report summarizes structural integrity work performed for the US NRC that predicts the structural integrity of steam generator (SG) tubes with flaws in the U-bend. The work covers model development and validation for U-bend tubes containing lab-induced primary water stress corrosion cracks (PWSCC). Limit load models for plastic collapse predicting ligament rupture pressure and leak rate of cracked U-bend tubes were developed and validated with pressure tests and finite element analyses (FEAs). Failure pressure and leak rate tests were conducted at room temperature on Alloy 600 U-bend tubes containing flaws located at various locations around the U-bend. Existing models for predicting structural integrity of straight tubes with well defined, rectangular, electro-discharge-machined (EDM) flaws were modified and used to predict the ligament rupture and unstable burst pressures as well as leak rates for the PWSCC flaws in the U-bend section.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2014

Green Applications for Space Power Project

Spacecraft propulsion and power for many decades has relied on Hydrazine monopropellant technology for auxiliary power units (APU), orbital circularization, orbit raising/lowering and attitude control. However, Hydrazine is toxic and therefore requires special ground handling procedures to ensure launch crew safety. The Swedish Company ECAPS has developed a technology based upon the propellant Ammonium Dinitramide (ADN) that offers higher performance, higher density and reduced ground handling support than Hydrazine. This blended propellant is called LMP-103S. Currently, the United States Air Force (USAF) is pursuing a technology based on Hydroxyl Ammonium Nitrate (HAN, otherwise known as AF-M315E) with industry partners Aerojet and Moog. Based on the advantages offered by these propellants, MSFC should explore powering APU's with these propellants. Due to the availability of space hardware, the principal investigator has found a collection of USAF hardware, that will act as a surrogate, which operates on a Hydrazine derivative. The F-16 fighter jet uses H-70 or 30% diluted Hydrazine for an Emergency Power Unit (EPU) which supplies power to the plane. The PI has acquired two EPU's from planes slated for destruction at the Davis Monthan AFB. This CIF will include a partnership with 2 other NASA Centers who are individually seeking seed funds from their respective organizations: Kennedy Space Center (KSC) and Dryden Flight Research Center (DFRC). KSC is preparing for future flights from their launch pads that will utilize green propellants and desire a low-cost testbed in which to test and calibrate new leak detection sensors. DFRC has access to F-16's which can be used by MSFC & KSC to perform a ground test that demonstrates emergency power supplied to the jet. Neither of the green propellant alternatives have been considered nor evaluated for an APU application. Work has already been accomplished to characterize and obtain the properties of these 2 propellants. However, the spacecraft are using existing leak detection sensors that are typically used for Hydrazine. Using these green propellants for the APU application requires decrementing their TRL down to 3. This task would aim to establish a TRL of 4 at conclusion by showing a proof of concept with a KSC-instrumented EPU asset at the MSFC Component Development Area (CDA). The task to accomplish this is called Green Application for Space Power or GRASP.

Robinson, Joel↗
DOE OSTI2023

Heat Exchanger Intensification Through Powder Processing and Enhanced Design (HIPPED)

High intensity, supercritical CO 2 heat exchangers capable of operating at temperatures between 800 and 1100 ˚C and pressures greater than 80 bar are considered a critical component for high efficiency power generation and a range of next-generation industrial processes. A novel heat exchanger concept was proposed in this project. The proposed concept involved a plate-type architecture with three-dimensional fins, called twisted s-shaped fins, that capitalize on additive manufacturing. Four manufacturing processes were studied to realize the complex envisioned design: press and sinter of metallic powders, directed energy deposition, laser powder bed fusion, and a novel powder bed process involving a photoreactive polymer called SEAM (scalable expeditious additive manufacturing), that later was developed at MSU. The team was able to manufacture subscale heat exchangers using laser powder bed fusion (LPBF) and SEAM. The team settled on using SEAM as a final manufacturing approach due to its very low cost. The SEAM-manufactured heat exchanger, however, when tested under pressure, exhibited leaks and the process still requires further development beyond the timeline of the project. To support the heat exchanger design and testing, the team developed a new high temperature flow loop allowing testing under high temperature and pressure. Computational modeling of the heat exchanger was also performed for the twisted s-shaped fins and the computations were validated with experimental data. The new twisted fins resulted in enhanced heat transfer and reduced pressure drop. To further minimize pressure drop in the plate heat exchanger, the team also developed a simplified model for flow maldistribution in the manifolds, providing a new tool for designers that eliminates the need for complex CFD calculations. A technoeconomic analysis was also developed to contrast SEAM with LPBF, this tool indicated that SEAM is several times less costly and offer significant promises as a rapid low cost additive manufacturing process for metallic systems.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2001

Polymer Matrix Composite Lines and Ducts

Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, a task was undertaken to assess the feasibility of making cryogenic feedlines with integral flanges from polymer matrix composite materials. An additional level of complexity was added by having the feedlines be elbow shaped. Four materials, each with a unique manufacturing method, were chosen for this program. Feedlines were to be made by hand layup (HLU) with standard autoclave cure, HLU with electron beam cure, solvent-assisted resin transfer molding (SARTM), and thermoplastic tape laying (TTL). A test matrix of fill and drain cycles with both liquid nitrogen and liquid helium, along with a heat up to 250 F, was planned for each of the feedlines. A pressurization to failure was performed on any feedlines that passed the cryogenic cycling testing. A damage tolerance subtask was also undertaken in this study. The effects of foreign object impact to the materials used was assessed by cross-sectional examination and by permeability after impact testing. At the end of the program, the manufacture of the electron beam-cured feedlines never came to fruition. All of the TTL feedlines leaked heavily before any cryogenic testing, all of the SARTM feedlines leaked heavily after one cryogenic cycle. Thus, only the HLU with autoclave cure feedlines underwent the complete test matrix. They passed the cyclic testing and were pressurized to failure.

Nettles, A. T.↗
NASA NTRSDate not supplied

On the Equivalence of Gas and Liquid Leak Flow Rates for Application to Propulsion and Propellant Transfer Systems

The equivalence of leak rates for gas flow and liquid flow through an arbitrary small leak size in pressurized systems has been investigated theoretically and experimentally. Measurements were taken for gaseous helium (GHe) rates and water flow issuing from the same leak configuration. The predictions for the correlation of GHe leak rates to water leak rates have been satisfactorily compared with present test data and those of other investigators over a wide range leak flow rates (many orders of magnitude) corresponding to a wide range of leak sizes (0.1 m to 0.1 mm). The results show that at extremely small leak sizes (sub-micron range), the effects of Knudsen number in the free molecular regime (rarefied gases) become important. By a proper scaling procedure, the measured flow rate for water could be applied to equivalent propellant leaks in flight operations. In the present tests the micro-channel range of the leak size is satisfactorily simulated by repeatable precision set needle position valve. Test results show that in general the theoretical model predicts the data reasonably well for GHe flow rates in the range of 0.001 to 1 sccs. Outside this range of GHe flow rates some adjustments (improvements) to the analytical model are required along with further testing.

Max Kandula↗
NASA NTRS1967

Portable fixture facilitates pressure testing of instrumentation fittings

Portable fixture facilitates pressure testing to detect possible leaks in instrumentation fittings mounted on tank bulkheads. It uses a vacuum cup which seals a pressure regulator adapter around one side of the fitting to be pressure tested. Leakage is detected with a gas sniffer.

Olson, G. A.↗
NASA NTRS2019

Oro-Nasal Mask Versus Two-Way Non-Rebreathing Valves for Maximal Aerobic Capacity Testing in Astronauts

Astronauts complete maximal aerobic capacity (VO2pk) testing as part of their annual fitness assessment (AFA) as well as several times once assigned to an International Space Station mission. Historically, the 2-Way T-Shape Non-Rebreathing valve with a mouthpiece and nose clip (“Mouthpiece”) has been used in these tests. The testing procedure was updated to use the oro-nasal mask (“Mask”) for the AFA starting in June 2017. Astronauts who used the mask during their AFA requested it be certified to be used for all mission associated tests. Considering the criticality of the data and the schedule constraints of astronauts, it is imperative that the requested hardware change provide data with equivalent reliability and repeatability as provided by the mouthpiece. PURPOSE: To assess the reliability and validity of mask vs. mouthpiece by comparing submaximal and VO2pkdata within subjects (approximately 1 year apart). METHODS: Each of 17 active astronauts completed a VO (sub 2pk) test with the mouthpiece (first) and the mask (second) for their AFA. The VO (sub 2pk) test was conducted on a cycle ergometer with a metabolic cart. The nominal protocol started with a 3-minute warm-up at 50 Watts (W) and increased 25W every minute until volitional fatigue (Light: 45W start; 15W increase). The VO (sub 2pk)s were compared between tests and the expected day-to-day variation (plus or minus 5 percent) was used as the threshold for determining agreement between tests. Submaximal values were plotted and evaluated visually for deviations between mask and mouthpiece. RESULTS: VO (sub 2pk) values were more than 5 percent different, despite similar test times, between mouthpiece and mask in 6 of 17 comparisons, 3 of which were higher with the mask (9.0 plus or minus 5.9 percent) while 3 were lower (minus10.8 plus or minus 2.0 percent) with the mask. The submaximal data did not indicate a leak in either apparatus during these tests. An Astronaut Strength & Conditioning Rehabilitation specialist confirmed that the measured differences in VO (sub 2pk) of these 6 astronauts was consistent with observed changes in exercise habits during the year that separated the two tests. CONCLUSION: After being presented with the results of this data mining effort the mask was accepted for use in all tests, excepting that, if a leak is detected without resolve, the test will be repeated (if schedule allows) and remaining tests will be completed with the mouthpiece.

Buxton, R.↗
NASA NTRS2007

Portable Microleak-Detection System

The figure schematically depicts a portable microleak-detection system that has been built especially for use in testing hydrogen tanks made of polymer-matrix composite materials. (As used here, microleak signifies a leak that is too small to be detectable by the simple soap-bubble technique.) The system can also be used to test for microleaks in tanks that are made of other materials and that contain gases other than hydrogen. Results of calibration tests have shown that measurement errors are less than 10 percent for leak rates ranging from 0.3 to 200 cm3/min. Like some other microleak-detection systems, this system includes a vacuum pump and associated plumbing for sampling the leaking gas, and a mass spectrometer for analyzing the molecular constituents of the gas. The system includes a flexible vacuum chamber that can be attached to the outer surface of a tank or other object of interest that is to be tested for leakage (hereafter denoted, simply, the test object). The gas used in a test can be the gas or vapor (e.g., hydrogen in the original application) to be contained by the test object. Alternatively, following common practice in leak testing, helium can be used as a test gas. In either case, the mass spectrometer can be used to verify that the gas measured by the system is the test gas rather than a different gas and, hence, that the leak is indeed from the test object.

Rivers, H. Kevin↗
NASA NTRS2010

Full-Scale System for Quantifying Loads and Leak Rates of Seals for Space Applications

NASA is developing advanced space-rated vacuum seals in support of future space exploration missions to low-Earth orbit and other destinations. These seals may be 50 to 60 in. (127 to 152 cm) in diameter and must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions to the International Space Station or the Moon. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them during docking or mating, and seal adhesion forces must be low to allow two mated systems to separate when required. NASA Glenn Research Center has developed a new test apparatus to measure leak rates and compression and adhesion loads of candidate full-scale seals under simulated thermal, vacuum, and engagement conditions. Tests can be performed in seal-on-seal or seal-on-flange configurations at temperatures from -76 to 140 F (-60 to 60 C) under operational pressure gradients. Nominal and off-nominal mating conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features of the test apparatus as well as techniques used to overcome some of the design challenges.

Dunlap, Patrick H., Jr.↗
NASA NTRS1973

Gas flow analysis during thermal vacuum test of a spacecraft.

The pressures indicated by two tubulated ionization gages, one pointing to a spinning spacecraft undergoing thermal vacuum test and the other the walls of the chamber, have been used in a computer program to calculate important parameters of flow kinetics in the vacuum chamber. These parameters calculated as a function of time are: the self-contamination of the spacecraft (defined as the return of outgassed molecules on its critical surfaces either in orbit or while undergoing vacuum test); the spacecraft outgassing including leaks from sealed compartments; and the gas pumping performance of the vacuum chamber. The test indicated the feasibility of this type of evaluation and the improvements in instrumentations and arrangements needed for future tests.

Scialdone, J. J.↗
DOE OSTI2020

Accelerated Aging Humidity Chamber for Nuclear Grade HEPA Filter Media

A unique accelerated aging humidity chamber for simulating the natural aging process of nuclear grade high efficiency particulate air (HEPA) filter media is being designed, implemented, and tested. The nuclear industry currently lacks information regarding the shelf life and service life of HEPA filter media. The Department of Energy recommends disposing of HEPA filters 10 years after the manufacture date for filters operated under dry conditions. Studies have shown the tensile strength and water repellency of HEPA filter media diminish with age. The chamber's principal function is to sustain an elevated relative humidity condition for an extended duration specified by the Arrhenius aging model. To accomplish this, various design parameters were established: (1) consistently achieve uniform humidity conditions within the chamber to equally expose media sheets, (2) ensure the chamber is sufficiently sealed to mitigate the uncontrolled infiltration of air, (3) confidently secure the media sheets to avert the introduction of unnecessary stressing/creasing, (4) fabricate the chamber from clear polycarbonate material to allow inspection of the media sheets, (5) provide a safe and ergonomic design for personnel, (6) ensure the chamber design is replicable and relatively easy to fabricate/assemble. A humidity source, fan, PID controller, humidity and temperature transmitters, and data loggers are required for proper operation and control of the chamber. The humidity source must accommodate target values up to 95% relative humidity throughout the chamber. The three humidity and temperature transmitters are strategically spaced throughout the chamber to ensure uniform conditions. The 10 cubic feet per minute (CFM) fan selected intends to accomplish the desired air change rate inside the chamber of approximately 20 air changes per hour (ACH). The 2 plenums on the upper and lower portions of the chamber utilize a perforated design to uniformly distribute air, promote air mixing, and control the air velocity entering the chamber. Industrial blueprint hanging clamps are being retrofitted to be seated within the chamber drawers and firmly secure the nuclear grade filter media. The aged media will be evaluated using autopsy methodology, and the results obtained intend to help clarify the useful life of nuclear grade HEPA filters. Nuclear grade high efficiency particulate air (HEPA) filters are defined as disposable, extended-media, dry-type filters with a rigid casing enclosing the full depth of the pleats and have a minimum particle removal efficiency of 99.97%. [1] - HEPA filters are constantly exposed to stressors and subsequently have been shown to degrade as the filter ages. Properties such as tensile strength and water repellency, along with others, are negatively impacted. [2] - Due to the scarcity of naturally aged HEPA filters available, it is crucial to develop accelerated aging methods which effectively mimic the natural degradation effects. - After accelerated aging, the filters are subject to testing in the Axial Flow Large Scale Test Stand (ALSTS) and other analysis techniques such as the same qualification tests performed directly after being manufactured. - Quality data is necessary for future decisions regarding the lifetime of nuclear grade HEPA filters. - The objective is to develop a prototype accelerated aging humidity chamber for nuclear grade HEPA filter media. The chamber should expose the media to commonly occurring stressors to expedite the degradation process caused by aging. PID yields reliable and reproducible results: - CFD model correlates well with actual performance; - Further analysis is needed to complete characterization; - Future work for the chamber is still to be completed. The data shown in Figure 5 and Table 1 indicate the system is functioning as designed. As can be determined from the system response evaluation in Table 1, the PID controller is yielding reliable and reproducible results at each set point. As the set point increases, the time constant and 20% settling time increase accordingly. From the results in Table 1, it stands to reason that the CFD model correlates well with the actual performance of the system. Each system response parameter for the 90%RH* CFD model is slightly lower than the parameters collected from the physical model tested at an equivalent set point. This is to be expected considering the inlet in the CFD model is a constant supply of water vapor, whereas the physical model uses a PID controller to monitor the amount of water vapor needed and reacts accordingly. More analysis is still to be done on the prototype chamber. A pressure test will be conducted in order to determine the hourly leak rate of the chamber. This test will involve constant air flow into the chamber until the desired pressure is reached. A uniformity test will also be conducted in order to ensure each filter medium is being exposed to equivalent relative humidity levels. This test will involve an array of humidity meters strategically oriented inside the chamber to record any possible gradients. Future work for the chamber includes dehumidification abilities, tests while fully loaded with filters, and temperature control. Once completed, the autopsy team at Institute of Clean Energy Technology will conduct necessary accelerated aging studies as needed.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1984

Viscous flow effects on hydrogen leaks from cracks in the Orbiter Challenger main engines

An analytical model was developed to provide additional insight and understanding of the factors that influence the simulation and prediction of leak rates from small cracks in pressurized containers. Specifically, the analysis was aimed at developing an analytical model capable of predicting the hydrogen leak rates from a crack in the combustion chamber coolant discharge manifold on main engine 1 of the Orbiter Challenger that was discovered during flight readiness firings 1 and 2. This model was based on viscous pipe flow analyses and calibrated for the crack geometry by using helium leak-rate data obtained from both low- and high-pressure tests used to simulate the flight readiness firing test conditions. In addition, this model includes the effects of crack width changes caused by different working stresses associated with the different test conditions. Because of the combination of the small crack dimensions and the wide range of pressures used for the test conditions, either laminar or turbulent viscous effects dominated the flows at all test conditions. This model was used to illustrate the sensitivity of the predicted leak rates to considerations of test conditions, viscous flow effects, and geometric features of the crack. In addition, the model was certified by comparing the hydrogen leak-rate prediction for the flight readiness firing test condition to the actual measured leak rate. The prediction was within 9 percent of the measured value.

Goodrich, W. D.↗