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At least 937 records · Page 52

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NASA NTRS1988

Multilevel calculation of the Ne IV solar spectrum

A calculation of the atomic parameters of the seven-electron ion Ne IV yields radiative rates A(ki) and distorted-wave collision strengths Omega (ki) between 72 levels of the six configurations 2s2 2p3, 2s2p4, 2p5, 2p2 3s, 2p2 3p, and 2p2 3d. These are used to obtain expected line intensities for quiet, active, and flare solar conditions. Comparisons are made with available solar observations. Good agreement is found, including observed density-sensitivity in the case of the multiplet at 469.8 A. The atomic radiative rates are separately compared with laboratory beam-foil measurements and are shown to be in reasonable agreement with the latter.

Bhatia, A. K.↗

NASA NTRS1990

The perfectly ideal accelerometer

Given here is a condensed version of the results and conclusions that developed during the Workshop. Upper limits of residual accelerations that can be tolerated during materials processes, presented as acceptable and as desirable limits, are shown. Designs and capabilities of various accelerometers, and their inherent problems, are compared. Results of acceleration measurements on Spacelab flights are summarized, and expected acceleration levels on the Space Station under various conditions are estimated.

Stuhlinger, Ernst↗

NASA NTRS1992

The effect of H2O gas on volatilities of planet-forming major elements. I - Experimental determination of thermodynamic properties of Ca-, Al-, and Si-hydroxide gas molecules and its application to the solar nebula

The vapor pressures of Ca(OH)2(g), Al(OH)3(g), and Si(OH)4(g) molecules in equilibrium with solid calcium-, aluminum, and silicon-oxides, respectively, were determined, and were used to derive the heats of formation and entropies of these species, which are expected to be abundant under the currently postulated physical conditions in the primordial solar nebula. These data, in conjunction with thermodynamic data from literature, were used to calculate the relative abundances of M, MO(x), and M(OH)n gas species and relative volatilities of Fe, Mg, Si, Ca, and Al for ranges of temperature, total pressure, and H/O abundance ratio corresponding to the plausible ranges of physical conditions in the solar nebula. The results are used to explain how Ca and Al could have evaporated from Ca,Al-rich inclusions in carbonaceous chondrites, while Si, Mg, and Fe condensed onto them during the preaccretion alteration of CAIs.

Hashimoto, Akihiko↗

NASA NTRS1993

A mechanism for the reduction in risk of decompression sickness in microgravity environment

There is an apparent reduction in the incidence of decompression sickness reported by astronauts (from both the USA and the USSR) during extravehicular activity (EVA). The expected incidence, based on studies conducted under unit gravity conditions in Earth-based laboratories, is greater than that encountered during EVA. A biophysical explanation has been proposed for this difference based upon the mechanism of stress-assisted nucleation. Since the partial pressure ratio at which this gas phase forms is considerably smaller in living systems that in quiescent in vitro models, it was proposed that mechanical forces are involved. In that the lower extremities of astronautics are not gravitationally loaded in microgravity, it is possible that tissue gas micronuclei are but minimally regenerated. Most likely, gas micronuclei formed on Earth (by ambulation under 1 g conditions) would be eventually depleted. In a crossover study, 20 individuals were decompressed--from 1 ATA to 0.43 ATA for 3 hours--following either being fully ambulatory at unit gravity or following being hypokinetic and adynamic (simulated microgravity of 3-day bed rest). The subjects were monitored for gas phase formation by means of precordial Doppler monitoring. The results indicate a reduction in whole body gas phase formation in individuals who were bed rested as compared with themselves when fully ambulatory (p = 0.02). In hypokinetic individuals, the protection conferred was equivalent to an extra 175 minutes of oxygen prebreathe. These results are compatible with a hypothesis relating stress-assisted nucleation to the continual formation of tissue gas micronuclei and their gradual depletion with hypokinesia.

Powell, Michael R.↗

NASA NTRS1993

Application of a two-stream radiative transfer model for leaf lignin and cellulose concentrations from spectral reflectance measurements, part 2

We used the Kubelka-Munk theory of diffuse spectral reflectance in layers to analyze influences of multiple chemical components in leaves. As opposed to empirical approaches to estimation of plant chemistry, the full spectral resolution of laboratory reflectance data was retained in an attempt to estimate lignin or other constituent concentrations from spectral band positions. A leaf water reflectance spectrum was derived from theoretical mixing rules, reflectance observations, and calculations from theory of intrinsic k- and s-functions. Residual reflectance bands were then isolated from spectra of fresh green leaves. These proved hard to interpret for composition in terms of simple two component mixtures such as lignin and cellulose. We next investigated spectral and dilution influences of other possible components (starch, protein). These components, among others, added to cellulose in hypothetical mixtures, produce band displacements similar to lignin, but will disguise by dilution the actual abundance of lignin present in a multicomponent system. This renders interpretation of band positions problematical. Knowledge of end-members and their spectra, and a more elaborate mixture analysis procedure may be called for. Good observational atmospheric and instrumental conditions and knowledge thereof are required for retrieval of expected subtle reflectance variations present in spectra of green vegetation.

Conel, James E.↗

NASA NTRS1997

Soot Volume Fraction Maps for Normal and Reduced Gravity Laminar Acetylene Jet Diffusion Flames

The study of soot particulate distribution inside gas jet diffusion flames is important to the understanding of fundamental soot particle and thermal radiative transport processes, as well as providing findings relevant to spacecraft fire safety, soot emissions, and radiant heat loads for combustors used in air-breathing propulsion systems. Compared to those under normal gravity (1-g) conditions, the elimination of buoyancy-induced flows is expected to significantly change the flow field in microgravity (O g) flames, resulting in taller and wider flames with longer particle residence times. Work by Bahadori and Edelman demonstrate many previously unreported qualitative and semi-quantitative results, including flame shape and radiation, for sooting laminar zas jet diffusion flames. Work by Ku et al. report soot aggregate size and morphology analyses and data and model predictions of soot volume fraction maps for various gas jet diffusion flames. In this study, we present the first 1-g and 0-g comparisons of soot volume fraction maps for laminar acetylene and nitrogen-diluted acetylene jet diffusion flames. Volume fraction is one of the most useful properties in the study of sooting diffusion flames. The amount of radiation heat transfer depends directly on the volume fraction and this parameter can be measured from line-of-sight extinction measurements. Although most Soot aggregates are submicron in size, the primary particles (20 to 50 nm in diameter) are in the Rayleigh limit, so the extinction absorption) cross section of aggregates can be accurately approximated by the Rayleigh solution as a function of incident wavelength, particles' complex refractive index, and particles' volume fraction.

Greenberg, Paul S.↗

NASA NTRS1999

Selected Performance Measurements of the F-15 ACTIVE Axisymmetric Thrust-Vectoring Nozzle

Flight tests recently completed at the NASA Dryden Flight Research Center evaluated performance of a hydromechanically vectored axisymmetric nozzle onboard the F-15 ACTIVE. A flight-test technique whereby strain gages installed onto engine mounts provided for the direct measurement of thrust and vector forces has proven to be extremely valuable. Flow turning and thrust efficiency, as well as nozzle static pressure distributions were measured and analyzed. This report presents results from testing at an altitude of 30,000 ft and a speed of Mach 0.9. Flow turning and thrust efficiency were found to be significantly different than predicted, and moreover, varied substantially with power setting and pitch vector angle. Results of an in-flight comparison of the direct thrust measurement technique and an engine simulation fell within the expected uncertainty bands. Overall nozzle performance at this flight condition demonstrated the F100-PW-229 thrust-vectoring nozzles to be highly capable and efficient.

Orme, John S.↗

NASA NTRS1998

Selected Performance Measurements of the F-15 Active Axisymmetric Thrust-vectoring Nozzle

Orme, John S.↗

NASA NTRS2001

Radar Sounding of Mars: A Focus on MARSIS

Radar has the unique capability of looking under the dry and cold surfaces of Mars. The depth of penetration of radio waves depends on a number of surface and subsurface parameters such as surface topography, subsurface geological structure, and surface and subsurface electromagnetic properties. Among these parameters, the surface topography is known best largely due to valuable data provided by Mars Global Surveyor's MOLA (Mars Orbiter Laser Altimeter) instrument. However, little information is available on the electromagnetic properties and subsurface characteristics of Mars. In addition to dispersion, the ionosphere will also attenuate the radio wave. The level of attenuation depends on the ionosphere's electron density and its profile shape and the electron-neutral collision frequency. Fortunately, information from past missions can provide some information on the expected level of attenuation. A figure shows expected total radio wave attenuation under three different ionospheric conditions. Additional information is contained in the original extended abstract.

Safaeinili, A.↗

NASA NTRS2002

CERT: Center of Excellence in Rotorcraft Technology

The research objectives of this effort are to understand the physical processes that influence the formation of the tip vortex of a rotor in advancing flight, and to develop active and passive means of weakening the tip vortex during conditions when strong blade-vortex-interaction effects are expected. A combined experimental, analytical, and computational effort is being employed. Specifically, the following efforts are being pursued: 1. Analytical evaluation and design of combined elastic tailoring and active material actuators applicable to rotor blade tips. 2. Numerical simulations of active and passive tip devices. 3. LDV Measurement of the near and far wake behind rotors in forward flight.

Source record↗

NASA NTRS2002

Impact Testing and Analysis of Composites for Aircraft Engine Fan Cases

The fan case in a jet engine is a heavy structure because of its size and because of the requirement that it contain a blade released during engine operation. Composite materials offer the potential for reducing the weight of the case. Efficient design, test, and analysis methods are needed to efficiently evaluate the large number of potential composite materials and design concepts. The type of damage expected in a composite case under blade-out conditions was evaluated using a subscale test in which a glass/epoxy composite half-ring target was impacted with a wedge-shaped titanium projectile. Fiber shearing occurred near points of contact between the projectile and target. Delamination and tearing occurred on a larger scale. These damage modes were reproduced in a simpler test in which flat glass/epoxy composites were impacted with a blunt cylindrical projectile. A surface layer of ceramic eliminated fiber shear fracture but did not reduce delamination. Tests on 3D woven carbon/epoxy composites indicated that transverse reinforcement is effective in reducing delamination. A 91 cm (36 in.) diameter full-ring sub-component was proposed for larger scale testing of these and other composite concepts. Explicit, transient, finite element analyses indicated that a full-ring test is needed to simulate complete impact dynamics, but simpler tests using smaller ring sections are adequate when evaluation of initial impact damage is the primary concern.

Roberts, Gary D.↗

NASA NTRS2004

Category 3: Sound Generation by Interacting with a Gust

The cascade-gust interaction problem is solved employing a time-domain approach. The purpose of this problem is to test the ability of a CFD/CAA code to accurately predict the unsteady aerodynamic and aeroacoustic response of a single airfoil to a two-dimensional, periodic vortical gust.Nonlinear time dependent Euler equations are solved using higher order spatial differencing and time marching techniques. The solutions indicate the generation and propagation of expected mode orders for the given configuration and flow conditions. The blade passing frequency (BPF) is cut off for this cascade while higher harmonic, 2BPF and 3BPF, modes are cut on.

Scott, James R.↗

NASA NTRS1953

Low-Speed Investigation of the Static Lateral Stability and Control Characteristics of a 1/6-Scale Model of the Republic XF-84H Airplane with the Propeller Operating

An investigation was made to determine the static lateral stability and control characteristics of a l/6-scale model of the Republic XF-84H airplane with the propeller operating. The model had a 40deg swept wing of aspect ratio 3.45 and had a thin 3-blade supersonic-type propeller. Many modifications to the basic configuration were investigated in attempts to alleviate lateral and directional trim problems which appeared to be associated with propeller slipstream rotation. Although significant benefits were realized with several modifications, none of those tested would be expected to afford satisfactory behavior for all normal flight conditions. A marked left-wing roll-off tendency was indicated at high angles of attack for the basic model configuration. Projection of only the left slat was the most effective remedy found for this problem with the propeller operating. The use of differential wing-flap deflection also appeared to offer a promising means for reducing the roll-off tendency with power on. The large sidewash over the vertical tail, associated with slip- stream rotation, severely restricted the conditions for which directional , trim could be maintained. A small triangular dorsal fin, oriented opposite to the slipstream rotation, was found very effective in reducing the adverse sidewash flow at the tail.

Sleeman, William C., Jr.↗

NASA NTRS2012

HyDE Framework for Stochastic and Hybrid Model-Based Diagnosis

Hybrid Diagnosis Engine (HyDE) is a general framework for stochastic and hybrid model-based diagnosis that offers flexibility to the diagnosis application designer. The HyDE architecture supports the use of multiple modeling paradigms at the component and system level. Several alternative algorithms are available for the various steps in diagnostic reasoning. This approach is extensible, with support for the addition of new modeling paradigms as well as diagnostic reasoning algorithms for existing or new modeling paradigms. HyDE is a general framework for stochastic hybrid model-based diagnosis of discrete faults; that is, spontaneous changes in operating modes of components. HyDE combines ideas from consistency-based and stochastic approaches to model- based diagnosis using discrete and continuous models to create a flexible and extensible architecture for stochastic and hybrid diagnosis. HyDE supports the use of multiple paradigms and is extensible to support new paradigms. HyDE generates candidate diagnoses and checks them for consistency with the observations. It uses hybrid models built by the users and sensor data from the system to deduce the state of the system over time, including changes in state indicative of faults. At each time step when observations are available, HyDE checks each existing candidate for continued consistency with the new observations. If the candidate is consistent, it continues to remain in the candidate set. If it is not consistent, then the information about the inconsistency is used to generate successor candidates while discarding the candidate that was inconsistent. The models used by HyDE are similar to simulation models. They describe the expected behavior of the system under nominal and fault conditions. The model can be constructed in modular and hierarchical fashion by building component/subsystem models (which may themselves contain component/ subsystem models) and linking them through shared variables/parameters. The component model is expressed as operating modes of the component and conditions for transitions between these various modes. Faults are modeled as transitions whose conditions for transitions are unknown (and have to be inferred through the reasoning process). Finally, the behavior of the components is expressed as a set of variables/ parameters and relations governing the interaction between the variables. The hybrid nature of the systems being modeled is captured by a combination of the above transitional model and behavioral model. Stochasticity is captured as probabilities associated with transitions (indicating the likelihood of that transition being taken), as well as noise on the sensed variables.

Narasimhan, Sriram↗

NASA NTRS2011

Nocturnal Aerosol Optical Depth Measurements with a Small-Aperture Automated Photometer Using the Moon as a Light Source

A method is described that enables the use of lunar irradiance to obtain nighttime aerosol optical depth (AOD) measurements using a small-aperture photometer. In this approach, the U.S. Geological Survey lunar calibration system was utilized to provide high-precision lunar exoatmospheric spectral irradiance predictions for a ground-based sensor location, and when combined with ground measurement viewing geometry, provided the column optical transmittance for retrievals of AOD. Automated multiwavelength lunar measurements were obtained using an unmodified Cimel-318 sunphotometer sensor to assess existing capabilities and enhancements needed for day/night operation in NASA s Aerosol Robotic Network (AERONET). Results show that even existing photometers can provide the ability for retrievals of aerosol optical depths at night near full moon. With an additional photodetector signal-to-noise improvement of 10-100, routine use over the bright half of the lunar phase and a much wider range of wavelengths and conditions can be achieved. Although the lunar cycle is expected to limit the frequency of observations to 30%-40% compared to solar measurements, nevertheless this is an attractive extension of AERONET capabilities.

Berkoff, Timothy A.↗

NASA NTRS2012

Role of MODIS Vegetation Phenology Products in the ForWarn System for Monitoring of Forest Disturbances in the Conterminous United States

This presentation discusses MODIS vegetation phenology products used in the ForWarn Early Warning System (EWS) tool for near real time regional forest disturbance detection and surveillance at regional to national scales. The ForWarn EWS is being developed by the USDA Forest Service NASA, ORNL, and USGS to aid federal and state forest health management activities. ForWarn employs multiple historical land surface phenology products that are derived from MODIS MOD13 Normalized Difference Vegetation Index (NDVI) data. The latter is temporally processed into phenology products with the Time Series Product Tool (TSPT) and the Phenological Parameter Estimation Tool (PPET) software produced at NASA Stennis Space Center. TSPT is used to effectively noise reduce, fuse, and void interpolate MODIS NDVI data. PPET employs TSPT-processed NDVI time series data as an input, outputting multiple vegetation phenology products at a 232 meter resolution for 2000 to 2011, including NDVI magnitude and day of year products for seven key points along the growing season (peak of growing season and the minima, 20%, and 80% of the peak NDVI for both the left and right side of growing season), cumulative NDVI integral products for the most active part of the growing season and sequentially across the growing season at 8 day intervals, and maximum value NDVI products composited at 24 day intervals in which each product date has 8 days of overlap between the previous and following product dates. MODIS NDVI phenology products are also used to compute nationwide NRT forest change products refreshed every 8 days. These include percent change in forest NDVI products that compare the current NDVI from USGS eMODIS products to historical MODIS MOD13 NDVI. For each date, three forest change products are produced using three different maximum value NDVI baselines (from the previous year, three previous years, and all previous years). All change products are output with a rainbow color table in which forests with the most severe NDVI decreases are assigned hot colors (yellow to red) and forests with prominent NDVI increases are assigned cold colors (blue tones). All mentioned products have been integrated as data layers into ForWarn s geospatial data viewer known as the U.S. Forest Change Assessment Viewer (FCAV). The latter is used to view and assess the context of the mentioned forest change products with respect to ancillary data layers, such as land cover, elevation, hydrologic features, climatic data, storm data, aerial disturbance surveys, fire data, and land ownership. The FCAV also includes a temporal NDVI profiler for viewing phenological change in multi-year NDVI associated with known or suspected regionally apparent forest disturbances (e.g., from fire and insects). ForWarn forest change products have been used to detect, track, and assess several biotic and abiotic regional forest disturbance events across the country, including ephemeral and longer lasting damage from storms, drought, and insects. Such change products are most effective for viewing severe disturbances affecting multiple MODIS pixels. MODIS vegetation phenology products contribute vital current information on forest conditions to the ForWarn system and this role is expected to grow as these products are refined and derivative products are added.

Spruce, Joseph P.↗

NASA NTRS2014

An Experimental Study of Launch Vehicle Propellant Tank Fragmentation

In order to better understand launch vehicle abort environments, Bangham Engineering Inc. (BEi) built a test assembly that fails sample materials (steel and aluminum plates of various alloys and thicknesses) under quasi-realistic vehicle failure conditions. Samples are exposed to pressures similar to those expected in vehicle failure scenarios and filmed at high speed to increase understanding of complex fracture mechanics. After failure, the fragments of each test sample are collected, catalogued and reconstructed for further study. Post-test analysis shows that aluminum samples consistently produce fewer fragments than steel samples of similar thickness and at similar failure pressures. Video analysis shows that there are several failure 'patterns' that can be observed for all test samples based on configuration. Fragment velocities are also measured from high speed video data. Sample thickness and material are analyzed for trends in failure pressure. Testing is also done with cryogenic and noncryogenic liquid loading on the samples. It is determined that liquid loading and cryogenic temperatures can decrease material fragmentation for sub-flight thicknesses. A method is developed for capture and collection of fragments that is greater than 97 percent effective in recovering sample mass, addressing the generation of tiny fragments. Currently, samples tested do not match actual launch vehicle propellant tank material thicknesses because of size constraints on test assembly, but test findings are used to inform the design and build of another, larger test assembly with the purpose of testing actual vehicle flight materials that include structural components such as iso-grid and friction stir welds.

Richardson, Erin↗

NASA NTRS2016

Meal Replacement Mass Reduction and Integration Acceptability Study

NASA, in planning for long duration missions, has an imperative to provide a food system with the necessary nutrition, acceptability, and safety to ensure sustainment of crew health and performance. The Orion Multi-Purpose Crew Vehicle (MPCV) and future exploration missions are mass constrained; therefore we are challenged to reduce the mass of the food system by 10% while maintaining safety, nutrition, and acceptability for exploration missions. Food bars have previously been used to supplement meals in the Skylab food system, indicating that regular consumption of bars will be acceptable. However, commercially available products do not meet the requirements for a full meal replacement in the spaceflight food system. The purpose of this task is to develop a variety of nutritionally balanced breakfast replacement bars, which meet spaceflight nutritional, microbiological, sensorial, and shelf-life requirements, while enabling a 10% food mass savings. To date, six nutrient-dense meal replacement bars have been developed, using both traditional methods of compression as well as novel ultrasonic compression technologies developed by Creative Resonance Inc. (Phoenix, AZ). All bars will be prioritized based on acceptability and the four top candidates will be evaluated in the Human Exploration Research Analog (HERA) to assess the frequency with which actual meal replacement options may be implemented. Specifically, overall impact to mood, satiety, dietary discomfort, and satisfaction with food will be analyzed to inform successful implementation strategies. In addition, these bars will be evaluated based on final product sensory acceptability, nutritional stability, qualitative stability of analytical measurements (i.e. water activity and texture), and microbiological compliance over two years of storage at room temperature and potential temperature abuse conditions to predict long-term acceptability. It is expected that this work will enable a successful meal replacement strategy to be implemented that maintains crew food consumption and health, while informing exploration missions with appropriate mass savings expectations.

Sirmons, T.↗