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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Photodiode-Based, Passive Ultraviolet Dosimeters

Simple, passive instruments have been developed for measuring the exposure of material specimens to vacuum ultraviolet (VUV) radiation from the Sun. Each instrument contains a silicon photodiode and a coulometer. The photocharge generated in the photodiode is stored in the coulometer. The accumulated electric charge measured by use of the coulometer is assumed to be proportional to the cumulative dose of VUV radiation expressed in such convenient units as equivalent Sun hours (ESH) [defined as the number of hours of exposure to sunlight at normal incidence]. Intended originally for use aboard spacecraft, these instruments could also be adapted to such terrestrial uses as monitoring the curing of ultraviolet-curable epoxies. Each instrument includes a photodiode and a coulometer assembly mounted on an interface plate (see figure). The photodiode assembly includes an aluminum housing that holds the photodiode, a poly(tetrafluoroehylene) cosine receptor, and a narrow-band optical filter. The cosine receptor ensures that the angular response of the instrument approximates the ideal angular response (proportional to the cosine of the angle of incidence). The filter is chosen to pass the ultraviolet wavelength of interest in a specific experiment. The photodiode is electrically connected to the coulometer. The factor of proportionality between the charge stored in the coulometer and ultraviolet dosage (in units of ESH) is established, prior to use, in calibration experiments that involve the use of lamps and current sources traceable to the National Institute of Standards and Technology.

Vaughn, Jason A.↗
NASA NTRS1962

PROGRESS REPORT ON THE DEVELOPMENT OF PROTECTED CONSTRUCTION FOR HYPERSONIC VEHICLES

The structural problems of re-entry occasioned by aerodynamic heating are now generally well known. Typical of these heating problems is the environment experienced by the manned lifting vehicle re-entering from a low altitude orbit. Figure 1 shows typical curves of lower surface temperature as a function of time for a wing loading of 25 Ibs/ft(exp 2), and a lift-drag ratio of 2.5. The two curves cover a practical range of re-entry angles, the lower curve representing an ideal re-entry path with zero dive angle and the upper curve assuming a 2° error in the re-entry angle. Maneuvers for course change or correction are also added to the upper curve. Significant factors from this curve are the relationship between the maximum temperatures and the capabilities of available metallic material, and also the long re-entry time and its effect on total heat load. If a very shallow re-entry is made, maximum lower surface temperatures reach 2000°F which is just within the range of conventional superalloys. To accommodate practical re-entry angles and maneuvers, however, the temperature capability must reach about 2500°F which requires refractory metals. The re-entry time may be as high as 100 minutes, which gives total heat loads of approximately 40,000 BTU/ft(exp 2). A heat load of this magnitude, with equilibrium surface temperatures of the values shown, suggests that a lighter airframe can be constructed by dissipating the heat by radiation from the surface, rather than by absorbing it with a heat sink, or surface cooling, or ablation. Air Force programs to provide airframes for this type of environment have involved the parallel development of a number of different structural concepts. The development to be discussed here was carried out by Bell Aerosystems Company for the Fabrication Branch, Manufacturing Technology Laboratory, Directorate of Materials and Processes, Aeronautical Systems' Division, Wright-Patterson Air Force Base, Ohio, under Contract AF33(600)-40100 (Double-Wall Cooled Structure).

Reentry vehicle↗
NASA NTRS1990

Observing soft X-ray line emission from the interstellar medium with X-ray calorimeter on a sounding rocket

For an X-ray calorimeter working at 0.1 K, the energy resolution ideally can be as good as one eV for a practical detector. A detector with a resolution of 17 eV FWHM at 6 keV has been constructed. It is expected that this can be improved by a factor of two or more. With X-ray calorimeters flown on a sounding rocket, it should be possible to observe soft X-ray line emission from the interstellar medium over the energy range 0.07 to 1 keV. Here, a preliminary design for an X-ray calorimeter rocket experiment and the spectrum which might be observed from an equilibrium plasma are presented. For later X-ray calorimeter sounding rocket experiments, it is planned to add an aluminum foil mirror with collecting area of about 400 sq cm to observe line features from bright supernova remnants.

Zhang, J.↗
NASA NTRS1974

Viewing-angle effects in radar images

A quantitative determination of the effect of viewing angle on the detectability of topographic linears in radar imagery is presented. Variations of azimuth and aspect angles of an imaging radar antenna relative to a topographic linear were simulated using low-angle illumination of controlled linear features on polystyrene sheets. The several model surfaces represented idealized versions of surface types that may be expected in areas of geologic interest. Fourier transform spectra of the radar image simulations were obtained using a coherent-optics system. These spectra were found to correlate with a detectability factor obtained directly from the radar image simulations. Fourier transform spectra of a linear feature observed from multiple viewing angles by a K-band imaging radar were also obtained and a detectability factor was estimated which agreed closely with theoretical predictions.

Eppes, T. A.↗
NASA NTRS1973

A coronal hole and its identification as the source of a high velocity solar wind stream

X-ray images of the solar corona showed a magnetically open structure in the low corona which extended from N20W20 to the south pole. Analysis of the measured X-ray intensities shows the density scale heights within the structure to be typically a factor of two less than that in the surrounding large scale magnetically closed regions. The structure is identified as a coronal hole. Wind measurements for the appropriate period were traced back to the sun by the method of instantaneous ideal spirals. A striking agreement was found between the Carrington longitude of the solar source of a recurrent high velocity solar wind stream and the position of the hole.

Krieger, A. S.↗
NASA NTRS1984

Acoustic pressures emanating from a turbomachine stage

A knowledge of the acoustic energy emission of each blade row of a turbomachine is useful for estimating the overall noise level of the machine and for determining its discrete frequency noise content. Because of the close spacing between the rotor and stator of a compressor stage, the strong aerodynamic interactions between them have to be included in obtaining the resultant flow field. A three dimensional theory for determining the discrete frequency noise content of an axial compressor consisting of a rotor and a stator each with a finite number of blades are outlined. The lifting surface theory and the linearized equation of an ideal, nonsteady compressible fluid motion are used for thin blades of arbitrary cross section. The combined pressure field at a point of the fluid is constructed by linear addition of the rotor and stator solutions together with an interference factor obtained by matching them for net zero vorticity behind the stage.

Ramachandra, S. M.↗
NASA NTRS1984

Acoustic pressures emanating from a turbomachine stage

A knowledge of the acoustic energy emission of each blade row of a turbomachine is useful for estimating the overall noise level of the machine and for determining its discrete frequency noise content. Because of the close spacing between the rotor and stator of a compressor stage, the strong aerodynamic interactions between them have to be included in obtaining the resultant flow field. This paper outlines a three-dimensional theory for determining the discrete frequency noise content of an axial compressor consisting of a rotor and a stator each with a finite number of blades. The lifting surface theory and the linearized equation of an ideal, nonsteady compressible fluid motion are used for thin blades of arbitrary cross section. The combined pressure field at a point of the fluid is constructed by linear addition of the rotor and stator solutions together with an interference factor obtained by matching them for net zero vorticity behind the stage.

Ramachandra, S. M.↗
NASA NTRS2017

Development and Validation of NDE Standards for NASA’s Advanced Composites Project

The adoption of composite materials in aircraft manufacturing for use in structural applications continues to increase but is still relatively new to the industry. Composite components have large development and certification costs in comparison to metallic structures. Traditional methods of nondestructive evaluation (NDE) used for isotropic materials such as metals may not be adequate for composite applications and therefore is a contributing factor to the cost and complexity of developing new structural composites. Additionally, the defects of interest in composite materials are significantly different from metals. Thus, good quality composite reference standards are essential to obtaining reliable and quantifiable NDE results. Ideally, reference standards contain flaws or damage whose NDE indications most closely represent those created by actual flaws/damage. They should also be easy to duplicate and inexpensive to manufacture. NASA’s Advanced Composites Project, working with industry partners, developed a set of composite standards that contain a range of validated defects representing those typically found in aerospace composite materials. This paper will provide an overview of the standards fabricated, the manufacturing plans used to fabricate them, the types of defects included, and validation testing that has performed. Also discussed is an inter-laboratory “round-robin” test that is being performed on these standards. The paper will describe a guidance document being compiled to outline relevant inspection procedures for challenging and critical defects unique to composites where conventional techniques may not be appropriate.

Cramer, K. Elliott↗
NASA NTRS2016

Options for Staging Orbits in Cis-Lunar Space

NASA has been studying options to conduct missions beyond Low Earth Orbit, but within the Earth‐Moon system, in preparation for deep space exploration including human missions to Mars. Referred to as the Proving Ground, this arena of exploration activities will enable the development of human spaceflight systems and operations to satisfy future exploration objectives beyond the cis‐lunar environment. One option being considered includes the deployment of a habitable element or elements, which could be used as a central location for aggregation of supplies and resources for human missions in cis‐lunar space and beyond. Characterizing candidate orbit locations for this asset and the impacts on system design and mission operations is important in the overall assessment of the options being considered. The orbits described in this paper were initially selected by taking advantage of previous studies conducted by NASA and the work of other authors. In this paper orbits are assessed for their relative attractiveness based on various factors. A set of constraints related to the capability of the combined Orion and SLS system to deliver humans and cargo to and from the orbit are evaluated. Deployed assets intended to spend multiple years in the Proving Ground would ideally require minimal station keeping costs to reduce the mass budget allocated to this function. Additional mission design drivers include eclipse frequency, potential for uninterrupted communication with deployed assets, thermal, attitude control, communications, and other operational implications. Also the ability to support potential lunar surface activities and excursion missions beyond Earth‐Moon space is considered. The results of the characterization and evaluation of the selected orbits indicate a Near Rectilinear Orbit (NRO) is an attractive candidate as an aggregation point or staging location for operations. In this paper, the NRO is further described in terms which balance a number of key attributes that favor a variety of mission classes to meet multiple, sometimes competing, constraints.

Martinez, Roland↗
NASA NTRSDate not supplied

Feasibility of using Low-Cost COTS Sensors for Particulate Monitoring in Space Missions

Real-time measurement of particles suspended in the spacecraft cabin is of great importance to verify that maximum allowable dust concentrations are not exceeded. This is primarily to protect astronaut health, but also has implications for dust-sensitive equipment. Recently, there is growing interest in low-cost commercial off-the-shelf (COTS) particle sensors by air quality researchers for their ability to map concentrations of airborne particulate matter in various terrestrial settings. In addition to low cost (< $2,000), the compact size and minimal weight of these sensors make them a potential choice for space missions. The detection mechanism for these aerosol sensors is typically measurement of light scattered by particles as they flow through a sensing volume. The amount of scattered light for detection depends on the particle size, shape, density, and refractive index of the particle material. Ideally, particle instruments should be calibrated with reference instruments for each different type of aerosol measurement. In this study we review multiple parameters that may impact the performance of state-of-the-art low-cost aerosol sensors. Environmental factors such as temperature, relative humidity, low ambient pressure, radiation and charge environment, partial-gravity and microgravity can affect the accuracy of particle measurements. Characteristics of the dust aerosols including particle size distribution, aerosol composition, refractive index, morphology and concentration levels also affect the measurement accuracy. Finally, we look at these parameters and issues with respect to an example COTS low-cost aerosol sensor. Instrument performance specifications are evaluated, and experiments are performed to measure real-time concentrations of Arizona Road Dust (a terrestrial reference test dust) and lunar dust simulant in a laboratory chamber. Overall, this study provides insight for evaluating spacecraft particulate monitoring technologies and raises questions to be answered before incorporating low-cost COTS sensors in future space missions to dusty destinations.

lunar dust↗
NASA NTRSDate not supplied

Satellite Tracking of Shallow Cumulus during CAMP2Ex: The Aerosol and Organization Connection

Shallow moist convection is ubiquitous throughout the tropics and represents a key player in boundary layer processes. Shallow clouds come in many forms, from scattered, short-lived cumulus to organized features that include cold pool boundaries and lines reaching O(100 km) scale lasting several hours. In this study, we explore how cloud morphology and environmental aerosol affect shallow cumulus lifecycle properties. Measuring such influences requires a broad, detailed view of these cloud fields as they grow and decay. Geostationary satellites provide a means to follow the clouds with enhanced spatiotemporal sampling from space. We apply a cloud-tracking tool to study lifecycle properties of shallow cumulus sampled during the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) field campaign of 2019. The mission conducted airborne and shipborne operations over the West Pacific Ocean, in tandem with Rapid Scan imagery from the Advanced Himawari Imager (AHI) on the Japan Meteorological Agency’s (JMA) Himawari-8 satellite. We segment shallow cumulus on AHI 0.5-km visible reflectance during the daylit hours of several research flights that exhibited ideal atmospheric conditions for tracking. We collect the resulting cloud tracks by regions containing airborne sampling of the cloud environments and by two specific segmentation techniques: one optimized for small, disorganized cumulus and the other for larger, organized clouds using suitable thresholds for reflectance and blurring. We present an analysis of cloud lifecycle properties using our dual segmentation approach for various sampled environments of CAMP2Ex. A total of 7 research flights (RFs) exhibited ideal conditions for generating cloud-track ensembles under similar thermodynamic and kinematic profiles but with varying aerosol load. We consider lifetime, track-achieved metrics, and ensemble-fitted growth rates to evaluate the aerosol effect. Cloud elongation, a factor in cloud morphology, is also considered for any potential influence in observed shifts in growth rates. The results suggest that aerosol affects cloud lifecycles more significantly for clouds with larger areas and independent of the elongation factor.

Cloud Tracking↗
NASA NTRS1976

Crack problems in cylindrical and spherical shells

Standard plate or shell theories were used as a starting point to study the fracture problems in thin-walled cylindrical and spherical shells, assuming that the plane of the crack is perpendicular to the surface of the sheet. Since recent studies have shown that local shell curvatures may have a rather considerable effect on the stress intensity factor, the crack problem was considered in conjunction with a shell rather than a plate theory. The material was assumed to be isotropic and homogeneous, so that approximate solutions may be obtained by approximating the local shell crack geometry with an ideal shell which has a solution, namely a spherical shell with a meridional crack, a cylindrical shell with a circumferential crack, or a cylindrical shell with an axial crack. A method of solution for the specially orthotropic shells containing a crack was described; symmetric and skew-symmetric problems are considered in cylindrical shells with an axial crack.

Erdogan, F.↗
NASA NTRS1998

Current concepts in the pathophysiology, evaluation, and diagnosis of compartment syndrome

This article reviews present knowledge of the pathophysiology and diagnosis of acute compartment syndromes. Recent results using compression of legs in normal volunteers provide objective data concerning local pressure thresholds for neuromuscular dysfunction in the anterior compartment. Results with this model indicate that a progression of neuromuscular deficits occurs when IMP increases to within 35 to 40 mm Hg of diastolic blood pressure. These findings provide useful information on the diagnosis and compression thresholds for acute compartment syndromes. Time factors are also important, however, and usually are incompletely known in most cases of acute compartment syndrome. Although the slit catheter is a very good technique for monitoring IMP during rest, these catheters and their associated extracorporeal transducer systems are not ideal. Recently developed miniature transducer-tipped catheters and, perhaps, future development of noninvasive techniques may provide accurate recordings of IMP in patients with acute compartment syndromes.

NASA Discipline Cardiopulmonary↗
NASA NTRS2019

Spatiotemporal Monitoring of Hydrilla [Hydrilla verticillata (L. f.) Royle] to Aid Management Actions

Hydrilla is an invasive aquatic plant that has rapidly spread through many inland water bodies across the globe by outcompeting native aquatic plants. Drinking water supply, power generation, and recreational use of lakes are threatened by the spread of this invasive species. Moreover, hydrilla serves as a host for an epiphytic, toxic cyanobacteria known to be the causative agent of the neurodegenerative disease called avian vacuolar myelinopathy, which affects waterfowl, raptors, and amphibians. The early detection of hydrilla infestation is very important to reduce the costs associated with control and removal efforts of this invasive species. Therefore, this study was aimed at developing a rapid, frequent, and large-scale tool for monitoring and predicting spatial extent of hydrilla habitat. This was achieved by integrating in situ and Landsat 8 OLI satellite data for Lake J. Strom Thurmond, the largest US Army Corps of Engineers Lake east of the Mississippi River located on the Georgia/South Caroline border. The predictive model incorporated remote sensing reflectance, Secchi disk depth (SDD), light attenuation coefficient (Kd), maximum depth of colonization (Zc), and percentage of light available through water column (PLW). The model predicted ideal habitat for hydrilla featuring high SDD, low values of Kd, high Zc and PLW. Final analysis showed that hydrilla starts growing in April, reaches peak around October, begins retreating in the following months, and disappears in February. Additionally, physical meteorological factors were analyzed and were found to be closely associated with hydrilla extent. Management agencies can use these results to not only to plan future removal efforts, but also evaluate and adapt their current mitigation efforts.

Percentage of light available through the water co↗
NASA NTRS1985

Lubrication of nonconformal contacts

Minimum film thickness results for piezoviscous-rigid regime of lubrication are developed for a compressible Newtonian fluid with Roelands viscosity. The results provide a basis for the analysis and design of a wide range of machine elements operating in the piezoviscous-rigid regime of lubrication. A new numerical method of calculating elastic deformation in contact stresses is developed using a biquadratic polynomial to approximate the pressure distribution on the whole domain analyzed. The deformation of every node is expressed as a linear combination of the nodal pressures whose coefficients can be combined into an influence coefficient matrix. This approach has the advantages of improved numerical accuracy, less computing time and smaller storage size required for influence matrix. The ideal elastohydrodynamic lubrication is extended to real bearing systems in order to gain an understanding of failure mechanisms in machine elements. The improved elastic deformation calculation is successfully incorporated into the EHL numerical scheme. Using this revised numerical technique and the flow factor model developed by Patir and Cheng (1978) the surface roughness effects on the elastohydrodynamic lubrication of point contact is considered. Conditions typical of an EHL contact in the piezoviscous-elastic regime entrained in pure rolling are investigated. Results are compared with the smooth surface solutions. Experiments are conducted to study the transient EHL effects in instrument ball bearings.

Jeng, Y. R.↗
NASA NTRS1944

The theory of propellers IV : thrust, energy, and efficiency formulas for single and dual rotating propellers with ideal circulation distribution

Simple and exact expressions are given for the efficiency of single and dual rotating propellers with ideal circulation distribution as given by the Goldstein functions for single-rotating propellers and by the new functions for dual-rotating propellers from part I of the present series. The efficiency is shown to depend primarily on a defined load factor and, to a very small extent, on an axial loss factor. Tables and charts are included for practical use of the results.

Theodorsen, Theodore↗
NASA NTRSDate not supplied

21st century trends in stratosphere-to-troposphere transport

One of the key questions in the air quality and climate sciences is how will tropospheric ozone concentrations change in the future. This will depend on two factors: changes in stratosphere-to-troposphere transport (STT) and changes in tropospheric chemistry. Here we aim to identify robust changes in STT using simulations from the Chemistry Climate Model Initiative (CCMI) under a common climate change scenario (RCP6.0). We use two idealized stratospheric tracers implemented in the models to examine changes in transport. We find that the strengthening of the shallow branch of the Brewer-Dobson circulation (BDC) in the lower stratosphere and of the upper part of the Hadley cell in the upper troposphere lead to enhanced STT in the subtropics. The acceleration of the deep branch of the BDC in the NH and changes in eddy transport contribute to increase STT at high latitudes. In the SH, the deep branch does not accelerate due to the dynamical effects of the ozone hole recovery.

stratosphere-to-troposphere transport↗