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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.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

High Energy Cutting and Stripping Utilizing Liquid Nitrogen

The Aerospace Industry has endeavored for decades to develop hybrid materials that withstand the rigors of mechanized flight both within our atmosphere and beyond. The development of these high performance materials has led to the need for environmentally friendly technologies for material re-work and removal. The NitroJet(TM) is a fluid jet technology that represents an evolution of the widely used, large-scale water jet fluid jet technology. It involves the amalgamation of fluid jet technology and cryogenics technology to create a new capability that is applicable where water jet or abrasive jet (water jet plus entrained abrasive) are not suitable or acceptable because of technical constraints such as process or materials compatibility, environmental concerns and aesthetic or legal requirements. The NitroJet(TM) uses ultra high-pressure nitrogen to cut materials, strip numerous types of coatings such as paint or powder coating, clean surfaces and profile metals. Liquid nitrogen (LN2) is used as the feed stream and is pressurized in two stages. The first stage pressurizes sub cooled LN2 to an intermediate pressure of between 15,000 and 20,000 psi at which point the temperature of the LN2 is about -250 F. The discharge from this stage is then introduced as feed to a dual intensifier system, which boosts the pressure from 15,000 - 20,000 psi up to the maximum operating pressure of 55,000 psi. A temperature of about -220 F is achieved at which point the nitrogen is supercritical. In this condition the nitrogen cuts, strips and abrades much like ultra high-pressure water would but without any residual liquid to collect, remove or be contaminated. Once the nitrogen has performed its function it harmlessly flashes back into the atmosphere as pure nitrogen gas. The system uses heat exchangers to control and modify the temperature of the various intake and discharge nitrogen streams. Since the system is hydraulically operated, discharge pressures can be easily varied over a very wide range providing considerable flexibility for various operations. The NitroJet(TM) is an advance on the nitrogen fluid jet technology initially developed at the Idaho National Engineering Laboratory in Idaho Falls, Idaho. NitroCision(R) first introduced the NitroJet(TM) into a commercial setting in 2003 and there has been considerable interest from many diverse sectors of government and industry since then. While the current system is an industrial system with the size and mass normally associated with industrial applications, a smaller system that is much more compact is being contemplated for those applications that do not need the full capabilities of the larger system. The NitroJet(TM) can be deployed as a fixed or mobile system with multiple end effectors capable of cutting, stripping, cleaning, and surface profiling either in robotic or manual applications.

Hume, Howard↗
NASA NTRS2012

Constraining the High-Energy Emission from Gamma-Ray Bursts with Fermi

We examine 288 GRBs detected by the Fermi Gamma-ray Space Telescope's Gamma-ray Burst Monitor (GBM) that fell within the field-of-view of Fermi's Large Area Telescope (LAT) during the first 2.5 years of observations, which showed no evidence for emission above 100 MeV. We report the photon flux upper limits in the 0.1-10 GeV range during the prompt emission phase as well as for fixed 30 s and 100 s integrations starting from the trigger time for each burst. We compare these limits with the fluxes that would be expected from extrapolations of spectral fits presented in the first GBM spectral catalog and infer that roughly half of the GBM-detected bursts either require spectral breaks between the GBM and LAT energy bands or have intrinsically steeper spectra above the peak of the nuF(sub v) spectra (E(sub pk)). In order to distinguish between these two scenarios, we perform joint GBM and LAT spectral fits to the 30 brightest GBM-detected bursts and find that a majority of these bursts are indeed softer above E(sub pk) than would be inferred from fitting the GBM data alone. Approximately 20% of this spectroscopic subsample show statistically significant evidence for a cut-off in their high-energy spectra, which if assumed to be due to gamma gamma attenuation, places limits on the maximum Lorentz factor associated with the relativistic outflow producing this emission. All of these latter bursts have maximum Lorentz factor estimates that are well below the minimum Lorentz factors calculated for LAT-detected GRBs, revealing a wide distribution in the bulk Lorentz factor of GRB outflows and indicating that LAT-detected bursts may represent the high end of this distribution.

Gehrels, Neil↗
NASA NTRS1972

Life prediction of expulsion bladders through fatigue test and fold strain analysis

Cycle life data are presented in terms of true maximum strain for four metals, two plastics, and two elastomers. The Coffin-Manson fatigue theory was applied for metals and plastics, and cut-growth fatigue theory for elastomers. The data are based on measurements made at room and elevated temperatures. It was found that double folds give rise to far severer folding strains than do simple folds. It was also found that, except for the elastomers, all the bladder materials develop surface cracks due to double folds after only one cycle. The findings indicate that metals, which are bets for premeation resistance, are worst for fatigue resistance, and vice versa for elastomers. The intermediate plastics were found to be unsatisfactory for both permeation and fatigue resistance for missions of extended duration.

Chu, H. N.↗
NASA NTRS1986

Characterization of InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

High-performance pseudomorphic In(y)Ga(1-y)As/Al0.15-Ga0.85As y = 0.05-0.2 MODFET's grown by MBE have been characterized at dc (300 and 77 K) and RF frequencies. Transconductances as high 310 and 380 mS/mm and drain currents as high as 290 and 310 mA/mm were obtained at 300 and 77 K, respectively, for 1-micron gate lengths and 3-micron source-drain spacing devices. Lack of persistent trapping effects, I-V collapse, and threshold voltage shifts observed with these devices are attributed to the use of low mole fraction Al(x)Ga(1-x)As while still maintaining two-dimensional electron gas concentrations of about 1.3 x to the 12th per sq cm. Detailed microwave S-parameter measurements indicate a current gain cut-off frequency of 24.5 GHz when y = 0.20, which is as much as 100 percent better than similar GaAs/AlGaAs MODFET structures, and a maximum frequency of oscillation of 40 GHz.

Ketterson, Andrew A.↗
NASA NTRS2017

The Effects of Vegetative Type, Edges, Fire History, Rainfall and Management in Fire-Maintained Ecosystems

The combined effects of repeated fires, climate, and landscape features (e.g., edges) need greater focus in fire ecology studies, which usually emphasize characteristics of the most recent fire and not fire history. Florida scrub-jays are an imperiled, territorial species that prefer medium (1.2-1.7 m) shrub heights. We measured short, medium, and tall habitat quality states annually within 10 ha grid cells that represented potential territories because frequent fires and vegetative recovery cause annual variation in habitat quality. We used multistate models and model selection to test competing hypotheses about how transition probabilities between states varied annually as functions of environmental covariates. Covariates included vegetative type, edges, precipitation, openings (gaps between shrubs), mechanical cutting, and fire characteristics. Fire characteristics not only included an annual presenceabsence of fire covariate, but also fire history covariates: time since the previous fire, the maximum fire-free interval, and the number of repeated fires. Statistical models with support included many covariates for each transition probability, often including fire history, interactions and nonlinear relationships. Tall territories resulted from 28 years of fire suppression and habitat fragmentation that reduced the spread of fires across landscapes. Despite 35 years of habitat restoration and prescribed fires, half the territories remained tall suggesting a regime shift to a less desirable habitat condition. Measuring territory quality states and environmental covariates each year combined with multistate modeling provided a useful empirical approach to quantify the effects of repeated fire in combinations with environmental variables on transition probabilities that drive management strategies and ecosystem change.

Breininger, David R.↗
NASA NTRS1972

High voltage transmission microscopy of Surveyor 3 camera shrouds

The internal structure of painted and unpainted aluminum alloy sheet samples from the TV camera shrouds were examined by high-voltage transmission electron microscopy. No clear-cut evidence of radiation damage effects was observed. Noticeable differences in microstructures between the upper visor and the sides and bottom of the lower shroud suggest different thermal histories, and the maximum temperatures due to solar heating are estimated to be between 164 and 319 C. Some correlation between microstructures and maximum estimated temperature is noted. It is felt that the apparent temperature rise due to solar heating will not affect the structural integrity of spacecraft components except possibly for very long periods of exposure. However, substantial thermal diffusion could affect interpretation of solar wind rare gas studies.

Fisher, R. M.↗
NASA NTRS2000

Development and Testing of a High Level Axial Array Duct Sound Source for the NASA Flow Impedance Test Facility

In this report both a frequency domain method for creating high level harmonic excitation and a time domain inverse method for creating large pulses in a duct are developed. To create controllable, high level sound an axial array of six JBL-2485 compression drivers was used. The pressure downstream is considered as input voltages to the sources filtered by the natural dynamics of the sources and the duct. It is shown that this dynamic behavior can be compensated for by filtering the inputs such that both time delays and phase changes are taken into account. The methods developed maximize the sound output while (i) keeping within the power constraints of the sources and (ii) maintaining a suitable level of reproduction accuracy. Harmonic excitation pressure levels of over 155dB were created experimentally over a wide frequency range (1000-4000Hz). For pulse excitation there is a tradeoff between accuracy of reproduction and sound level achieved. However, the accurate reproduction of a pulse with a maximum pressure level over 6500Pa was achieved experimentally. It was also shown that the throat connecting the driver to the duct makes it difficult to inject sound just below the cut-on of each acoustic mode (pre cut-on loading effect).

Johnson, Marty E.↗
NASA NTRSDate not supplied

Rolling Horizon with K-Position Search Method for Strategic Deconfliction of Package Delivery UAS

In this research, the strategic deconfliction of unmanned aircraft systems for an urban package delivery environment with two depots and multiple drop-off locations is studied. This research aims to formulate a mathematical model to compute both the departure sequence and scheduled time of departure for each unmanned aircraft system at a depot, considering temporal constraints at en-route crossing waypoints and depots for strategic deconfliction. However, the problem formulation results in an NP-hard mixed-integer nonlinear programming problem for the global optimal solution, so instead, a "rolling horizon with𝑘-position search"heuristic method is developed. The simulation studies show that an increase in the value of𝑘(the parameter used to determine the size of the local neighborhood) reduces the average ground delay at the cost of an increase in the computation time for a given problem size. The study also shows an order of magnitude increase in the maximum number of flights scheduled with the integration of rolling horizon (time decomposition) compared to those without the integration of rolling horizon in the heuristic algorithm for a given computation time cut off.

UTM↗
NASA NTRS1988

Friction of ice

Frictional sliding experiments were performed on saw-cut samples of laboratory-made polycrystalline water ice, prepared in the same way as the material used by Kirby et al. (1987) in ice deformation experiments. The data show that the maximum frictional stress is a function of the normal stress but is not measurably dependent on temperature or sliding rate over the ranges covered in these experiments (77-115 K and 0.0003-0.03 mm/s, respectively). The sliding behavior was invariably stick slip, with the sliding surfaces exhibiting only minor gouge development. In samples with anomalously low strength, a curious arrangement of densely packed short vertical fractures was observed. The results of these experiments were applied to a model of near-surface tectonic activity on Ganymede, one of Jupiter's icy moons. The results indicate that a global expansion on Ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 + or - 3 km.

Beeman, M.↗
NASA NTRS1994

Microstructurally based variations on the dwell fatgue life of titanium alloy IMI 834

An experimental study was undertaken to determine the role of microstructure on the fatigue life reduction observed in titanium alloy IMI 834 under dwell loading conditions. The wave forms compared were a trapezoid with 15 and 30 second hold times at the maximum test load and a baseline, 10 Hertz, haversine. The stress ratio for both loading wave forms was 0.10. The fatigue loading of each specimen was conducted in a vacuum within a scanning electron microscope chamber which minimized the possibility that the laboratory environment would adversely affect the material behavior. Two microstructural conditions were investigated in the experimental program. The first involved standard 'disk' material with equiaxed alpha in a transformed beta matrix. The second material was cut from the same disk forging as the first but was heat treated to obtain a martensitic alpha prime microstructure. Tensile tests were performed prior to the onset of the fatigue loading portion of the study, and it was determined that the yield strengths of the specimens from both material conditions were within ten percent. The maximum fatigue loads were chosen to be 72 percent of the average yield strength for both materials as determined from the tensile tests. It was found that the cycles to failure from the 10 Hertz loading wave form were reduced by a factor of approximately five when the loading was changed to the trapezoidal wave form for the standard 'disk' material. The fatigue life reduction for the martensitic structure under identical test conditions was approximately 1.75. The improvement observed with the martensitic structure also was accompanied by an increase in overall fatigue life for the wave forms tested. This paper will review the results and conclusions of this effort.

Thomsen, Mark L.↗
NASA NTRS1974

Spinning mode sound propagation in ducts with acoustic treatment

A detailed theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts is described. The suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. The theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. Some interesting results of the analysis are that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number. For annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. The above results help explain why suppressors with splitter rings were quite effective in spite of the lack of detailed information on the noise source modal structure.

Rice, E. J.↗
NASA NTRS1974

Spinning mode sound propagation in ducts with acoustic treatment

Recent acoustic data have shown larger noise attenuations than predicted for acoustically treated aircraft engine inlets without splitter rings. These data have stimulated a more detailed theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts. In addition, the suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. The theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. It is found that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number. For annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. The results help explain why suppressors with splitter rings have been quite effective in spite of the lack of detailed information on the noise-source modal structure. Conversely, effective use of outer-wall treatment alone will require expanded knowledge of the noise-source structure. Approximate solutions are presented to help interpret the more exact theoretical results.

Rice, E. J.↗
NASA NTRS1984

Big Savings from Smart Motors

Chesebrough-Pond's operates 32 plants across the nation and in those plants are more than 10,000 electric motors. In an effort to cut down on waste of electrical power used by these motors, Chesebrough organized a Corporate Advanced Technology Group to devise ways of improving productivity and cut manufacturing costs. Chesebrough used NASA's Marshall Space Flight Center's Power Factor Controller technology as a departure point for development of their own computerized motor controller that enables motors to operate at maximum efficiency regardless of the motor's applications or operating condition.

Source record↗
NASA NTRS1975

Spinning mode sound propagation in ducts with acoustic treatment

Recent acoustic data show larger noise attenuations than predicted for acoustically treated aircraft engine inlets without splitter rings. A theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts is presented, and a suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. Theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. Results of the analysis indicate that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number, and for annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. These results explain why suppressors with splitter rings were quite effective in spite of the lack of detailed information on the noise source modal structure. Conversely, effective use of outer wall treatment alone will require expanded knowledge of the noise source structure. Approximate solutions are presented to help interpret the more exact theoretical results.

Rice, E. J.↗
NASA NTRS1987

Strength of a thick graphite/epoxy rocket motor case after impact by a blunt object

The National Aeronautics and Space Administration is developing graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The membrane region is about 36 mm thick. A study was made to determine the reduction in strength of the FWC due to accidental damage caused by low-velocity impacts. Two 76.2 cm diameter by 30.5 cm long cylinders were impacted every 5 cm of circumference with 1.27 cm radius impacters of various mass. The impacters represented tools and equipment dropped from various heights. One cylinder was empty and the other was filled with inert propellant. Five cm wide test specimens were cut from the cylinder. Each was centered on an impact sight. The specimens were X-rayed and loaded to failure in uniaxial tension. The strengths and depths of impact damage were analyzed in terms of maximum impact force. Rigid body mechanics and the Hertz law were used to derive an equation for impact force in terms of kinetic energy and the masses of the impacter and target. The depth of damage was predicted in terms of impact force using Love's solution of pressure applied on part of the boundary of a semi-infinite body.

Poe, C. C., Jr.↗
NASA NTRS1989

Strength of a thick graphite/epoxy rocket motor case after impact by a blunt object

The National Aeronautics and Space Administration is developing graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The membrane region is about 36 mm thick. A study was made to determine the reduction in strength of the FWC due to accidental damage caused by low-velocity impacts. Two 76.2 cm diameter by 30.5 cm long cylinders were impacted every 5 cm of circumference with 1.27 cm radius impacters of various mass. The impacters represented tools and equipment dropped from various heights. One cylinder was empty and the other was filled with inert propellant. Five cm wide test specimens were cut from the cylinder. Each was centered on an impact site. The specimens were X-rayed and loaded to failure in uniaxial tension. The strengths and depths of impact damage were analyzed in terms of maximum impact force. Rigid body mechanics and the Hertz law were used to derive an equation for impact force in terms of kinetic energy and the masses of the impacter and target. The depth of damage was predicted in terms of impact force using Love's solution of pressure applied on part of the boundary of a semi-infinite body.

Poe, Clarence C., Jr.↗
NASA NTRS1953

Summary of Rocket-Model Tests at Zero Lift of the Northrop MX-775B Missile Configuration from Mach Numbers of 0.9 to 1.8

Flight tests were conducted between Mach numbers of 0.9 and 1.8 over a Reynolds number range of 9(exp 6) to 30(exp 6) to determine the zero-lift drag and some rolling-effectiveness characteristics of the Northrop MX -775B missile with small and large body. The MX-775B is a proposed long range, supersonic, ground-to-ground missile having an arrow wing with 67.5 degree leading-edge sweep, 15 deg trailing-edge sweep, and a modified NACA 0004 airfoil section. The configuration has no horizontal tail but has wing trailing-edge elevons which serve a dual purpose as elevators and ailerons. The ratio of body frontal area to wing plan-form area is 0.0127 for the small-body configuration and 0.0330 for the large-body configuration. Five 1/4-scale models were flown permitting determination of the drag coefficient for the basic small-body configuration, the incremental drag due to the large body, the incremental drag resulting from a blunt wing trailing edge, the wing-plus-interference drag, and some rolling-effectiveness data. Results indicated that the MX-775B has low supersonic zero-lift drag, the maximum zero-lift drag coefficients being respectively 0.0125 and 0.0155 at a Mach number of M = 1803 for the small- and large-body configurations. The effect of a blunt wing trailing edge, obtained by cutting off 10 percent of the wing chord, was to increase the zero-lift drag by 13 to 21 percent. Wing-plus-interference drag accounted for 78 percent of the total drag at M = 0.9 and 70 percent at M = 195 for the small-body configuration. The ailerons produced positive rolling effectiveness for the wing stiffness of the test models and the dynamic pressures of the test.

Arbic, Richard G.↗
NASA NTRS2006

Mechanisms for Diurnal Variability of Global Tropical Rainfall Observed from TRMM

The behavior and various controls of diurnal variability in tropical-subtropical rainfall are investigated using Tropical Rainfall Measuring Mission (TRMM) precipitation measurements retrieved from the three level-2 TRMM standard profile algorithms for the 1998 annual cycle. Results show that diurnal variability characteristics of precipitation are consistent for all three algorithms, providing assurance that TRMM retrievals are producing consistent estimates of rainfall variability. As anticipated, most ocean areas exhibit more rainfall at night, while over most land areas, rainfall peaks during daytime; however, important exceptions are noted. The dominant feature of the oceanic diurnal cycle is a rainfall maximum in late-evening-early-morning (LE-EM) hours, while over land the dominant maximum occurs in the mid- to late afternoon (MLA). In conjunction with these maxima are pronounced seasonal variations of the diurnal amplitudes. Amplitude analysis shows that the diurnal pattern and its seasonal evolution are closely related to the rainfall accumulation pattern and its seasonal evolution. In addition, the horizontal distribution of diurnal variability indicates that for oceanic rainfall, there is a secondary MLA maximum coexisting with the LE-EM maximum at latitudes dominated by large-scale convergence and deep convection. Analogously, there is a preponderancy for an LE EM maximum over land coexisting with the stronger MLA maximum, although it is not evident that this secondary continental feature is closely associated with the large-scale circulation. Neither of the secondary maxima exhibit phase behavior that can be considered semidiurnal in nature. Diurnal rainfall variability over the ocean associated with large-scale convection is clearly an integral component of the general circulation. Phase analysis reveals differences in regional and seasonal features of the diurnal cycle, indicating that underlying forcing mechanisms differ from place to place. This is underscored by the appearance of secondary ocean maxima in the presence of large-scale convection, along with other important features. Among these, there are clear-cut differences between the diurnal variability of seasonal rainfall over the mid-Pacific and Indian Ocean Basins. The mid-Pacific exhibits double maxima in spring and winter but only LE-EM maxima in summer and autumn, while the Indian Ocean exhibits double maxima in spring and summer and only an LE-EM maximum in autumn and winter. There are also evident daytime maxima within the major large-scale marine stratocumulus regions off the west coasts of continents. The study concludes with a discussion concerning how the observational evidence either supports or repudiates possible forcing mechanisms that have been suggested to explain diurnal rainfall variability.

Yang, Song↗