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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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

NASCAP modelling of high-voltage power system interactions with space charged-particle environments

The NASA Charging Analyzer Program (NASCAP), an engineering tool capable of analyzing the impact of the charged particle environment on spacecraft surfaces and systems, is described. NASCAP is a quasi-static computational program which analyzes the charging of a 3-dimensional complex body as a function of time and system-generated voltages for given space environmental conditions. The material properties of the surfaces are taken into account; the surface potentials, low energy sheath, potential distribution in space and particle trajectories are calculated. An application of NASCAP to a simple space solar power station consisting of two 6 m by 18 m solar array wings surrounding a central body is presented. Each solar array wing is considered to be divided into three regions operating at 2000 volts. Results of NASCAP analysis of the system for a normal environment and a moderate geomagnetic substorm environment are discussed.

Stevens, N. J.↗
NASA NTRS1980

Observations of electron gyroharmonic waves and the structure of the Io torus

Narrow-banded emissions were observed by the Planetary Radio Astronomy experiment on the Voyager 1 spacecraft as it traversed the Io plasma torus. These waves occur between harmonics of the electron gyrofrequency and are the Jovian analogue of electrostatic emissions observed and theoretically studied for the terrestrial magnetosphere. The observed frequencies always include the component near the upper hybrid resonant frequency, (fuhr) but the distribution of the other observed emissions varies in a systematic way with position in the torus. A refined model of the electron density variation, based on identification of the fuhr line, is included. Spectra of the observed waves are analyzed in terms of the linear instability of an electron distribution function consisting of isotropic cold electrons and hot losscone electrons. The positioning of the observed auxiliary harmonics with respect to fuhr is shown to be an indicator of the cold to hot temperature ratio. It is concluded that this ratio increases systematically by an overall factor of perhaps 4 or 5 between the inner and outer portions of the torus.

Birmingham, T. J.↗
NASA NTRS1980

Noise adding radiometer performance analysis

The DSN noise adding radiometer (NAR) measurement accuracy is analyzed. The NAR capability is part of the precision power monitor function recently introduced in the DSN. The potential system noise temperature measurement accuracy is estimated to be about 1.5% with the 1 kelvin noise diode. Performance verification requires comparison noise temperature measurements with the manual Y factor method and routine monitoring of critical elements in the NAR system such as system linearity and noise diode calibration. A technique is presented to calibrate and reduce the effects of the receiving system nonlinearity. Unsatisfactory performance or degradation of these critical NAR elements would require appropriate system upgrading.

Stelzried, C.↗
NASA NTRS1980

A compensation mechanism for central Pacific

Geos 3 derived geoid heights and sea floor topography were averaged into 256 square areas (203 km on a side) for a region in the central Pacific containing a large portion of the Hawaiian Island chain. The whole region is about 500 m shallower than normal sea floor of the same age. The major portion of the depth anomaly is the Hawaiian swell. Data were analyzed using a two-dimensional fast Fourier transform. A transfer function was computed to determine the part of the observed geoid height that is coherent and in phase with the topography. Two models were introduced, one compensating short-wavelength topography at a shallow depth (14 km) and the other compensating the longer wavelengths by a deep mechanism. Using the transition wavelength between the two models (1100 km), an estimate is made of the amplitude and shape of the heat anomaly needed to uplift the Hawaiian swell. The peak of the anomaly has an amplitude of 530 mW/sq m and is located 275 km east of Hawaii.

Sandwell, D. T.↗
NASA NTRS1980

P78-2 SCATHA environmental data atlas

The 100 eV to approximately 1 MeV plasma environment encountered by the P78-2 Spacecraft Charging at High Altitudes (SCATHA) satellite during its initial operation period was studied. Forty-four days of 10 minute averages of the four moments of the electron and ion distribution functions calculated from the SC5 and SC9 energetic particle measurements were analyzed to determine occurrence frequency, local time variation, geomagnetic activity variation, and L shell variation. The single and double Maxwellian parameters derived from the four moments were similarly analyzed. The interrelationships between the moments and derived parameters were computed and the results compared with the ATS-5 and ATS-6 atlas. Results of this analysis establish a baseline range for the SCATHA plasma environment.

Mulen, E. G.↗
NASA NTRS1982

Fokker-Planck response of stochastic satellites

The present investigation is concerned with the effects of stochastic geometry and random environmental torques on the pointing accuracy of spinning and three-axis stabilized satellites. The study of pointing accuracies requires a knowledge of the rates of error growth over and above any criteria for the asymptotic stability of the satellites. For this reason the investigation is oriented toward the determination of the statistical properties of the responses of the satellites. The geometries of the satellites are considered stochastic so as to have a phenomenological model of the motions of the flexible structural elements of the satellites. A widely used method of solving stochastic equations is the Fokker-Planck approach where the equations are assumed to define a Markoff process and the transition probability densities of the responses are computed directly as a function of time. The Fokker-Planck formulation is used to analyze the response vector of a rigid satellite.

Huang, T. C.↗
NASA NTRS1982

Crash tests of four low-wing twin-engine airplanes with truss-reinforced fuselage structure

Four six-place, low-wing, twin-engine, general aviation airplane test specimens were crash tested under controlled free flight conditions. All airplanes were impacted on a concrete test surface at a nomial flight path velocity of 27 m/sec. Two tests were conducted at a -15 deg flight path angle (0 deg pitch angle and 15 deg pitch angle), and two were conducted at a -30 deg flight path angle (-30 deg pitch angle). The average acceleration time histories (crash pulses) in the cabin area for each principal direction were calculated for each crash test. In addition, the peak floor accelerations were calculated for each test as a function of aircraft fuselage longitudinal station number. Anthropomorphic dummy accelerations were analyzed using the dynamic response index and severity index (SI) models. Parameters affecting the dummy restraint system were studied; these parameters included the effect of no upper torso restraint, measurement of the amount of inertia-reel strap pullout before locking, measurement of dummy chest forward motion, and loads in the restraints. With the SI model, the dummies with no shoulder harness received head impacts above the concussive threshold.

Williams, M. S.↗
NASA NTRS1981

Ground-truth measurement systems

Ground-truth measurements of precipitation and related weather events are an essential component of any satellite system designed for monitoring rainfall from space. Such measurements are required for testing, evaluation, and operations; they provide detailed information on the actual weather events, which can then be compared with satellite observations intended to provide both quantitative and qualitative information about them. Also, very comprehensive ground-truth observations should lead to a better understanding of precipitation fields and their relationships to satellite data. This process serves two very important functions: (a) aiding in the development and interpretation of schemes of analyzing satellite data, and (b) providing a continuing method for verifying satellite measurements.

Serafin, R.↗
NASA NTRS1984

Development of a global model for atmospheric backscatter at CO2 wavelengths

The effect of aerosol microphysical processes on the backscatter from an aerosol plume undergoing long-range atmospheric transport was studied. A numerical model which examines the effects of coagulation and sedimentation on an aerosol size distribution is under development and the initial results for a single homogeneous layer were obtained. Use was made of the SAGE/SAM II data set to study the global variation of aerosol concentration and, hence, to predict the variation of Beta sub CO2. Computer programs were written to determine the mean, median, and the probability distribution of the measured aerosol extinction as a function of altitude, latitude and geographical conditions. The first data sets analyzed in this way are under study. Data was used to study aerosol behavior over the U.S.A. and the Pacific Ocean.

Kent, G. S.↗
NASA NTRS1987

Example on how to model and simulate turbulence for flight simulators

Analytical developments relative to gust response are discussed. Turbulence length scale, spectral functions, zero crossing values, gust loads analysis, power spectral techniques for analyzing the response of aircraft in turbulence, the spectrum of the rolling moment coefficient, and the spectrum correction factor are among the issues considered.

Houbolt, John C.↗
NASA NTRS1990

Analysis of stratocumulus cloud fields using LANDSAT imagery: Size distributions and spatial separations

Stratocumulus cloud fields in the FIRE IFO region are analyzed using LANDSAT Thematic Mapper imagery. Structural properties such as cloud cell size distribution, cell horizontal aspect ratio, fractional coverage and fractal dimension are determined. It is found that stratocumulus cloud number densities are represented by a power law. Cell horizontal aspect ratio has a tendency to increase at large cell sizes, and cells are bi-fractal in nature. Using LANDSAT Multispectral Scanner imagery for twelve selected stratocumulus scenes acquired during previous years, similar structural characteristics are obtained. Cloud field spatial organization also is analyzed. Nearest-neighbor spacings are fit with a number of functions, with Weibull and Gamma distributions providing the best fits. Poisson tests show that the spatial separations are not random. Second order statistics are used to examine clustering.

Welch, R. M.↗
NASA NTRS1990

Planar Laser Imaging of Sprays for Liquid Rocket Studies

A planar laser imaging technique which incorporates an optical polarization ratio technique for droplet size measurement was studied. A series of pressure atomized water sprays were studied with this technique and compared with measurements obtained using a Phase Doppler Particle Analyzer. In particular, the effects of assuming a logarithmic normal distribution function for the droplet size distribution within a spray was evaluated. Reasonable agreement between the instrument was obtained for the geometric mean diameter of the droplet distribution. However, comparisons based on the Sauter mean diameter show larger discrepancies, essentially because of uncertainties in the appropriate standard deviation to be applied for the polarization ratio technique. Comparisons were also made between single laser pulse (temporally resolved) measurements with multiple laser pulse visualizations of the spray.

Lee, W.↗
NASA NTRS1991

Effects of vegetation on soil moisture distribution and flux with implications for the global hydrologic cycle

Recent climate modeling experiments have identified the critical need for a better understanding of land surface - atmosphere interactions. An important issue in global climate modeling is to be able to relate land surface and atmospheric processes. In the past this link has been inadequately represented due to the lack of understanding of the interaction between the processes and also due to the large spatial variability of the hydrological and soil properties. A project was initiated at the Marshall Space Flight Center (MSFC) in FY-90 under the Center's Directorate Discretionary Fund (CDDF) to study small-scale effects of vegetation on the distribution and fluxes of soil moisture. Installation of a large array of instruments was accomplished during that first year (FY-90). During this second year of the project, the instrumentation and data collection systems were improved and data has begun to be taken. Preliminary analysis of the data show that the equipment has been functioning properly. Some of the preliminary results that have recently been analyzed are given.

Macari, Emir Jose↗
NASA NTRS1992

Design and test hardware for a solar array switching unit

This paper describes the control of a pulse width modulated (PWM) type sequential shunt switching unit (SSU) for spacecraft applications. It is found that the solar cell output capacitance has a significant impact on SSU design. Shorting of this cell capacitance by the PWM switch causes input current surges. These surges are minimized by the use of a series filter inductor. The system with a filter is analyzed for ripple and the control to output-voltage transfer function. Stable closed loop design considerations are discussed. The results are supported by modeling and measurements of loop gain and of closed-loop bus impedance on test hardware for NASA's 120 V Earth Observation System (EOS). The analysis and modeling are also applicable to NASA's 160 V Space Station power system.

Patil, A. R.↗
NASA NTRS1992

Prediction of BVI noise patterns and correlation with wake interaction locations

High resolution fluctuating airloads data were acquired during a test of a contemporary design United Technologies model rotor in the Duits-Nederlandse Windtunnel (DNW). The airloads are used as input to the noise prediction program WOPWOP, in order to predict the blade-vortex interaction (BVI) noise field on a large plane below the rotor. Trends of predicted advancing and retreating side BVI noise levels and directionality as functions of flight condition are presented. The measured airloads have been analyzed to determine the BVI locations on the blade surface, and are used to interpret the predicted BVI noise radiation patterns. Predicted BVI locations are obtained using the free wake model in CAMRAD/JA, the UTRC Generalized Forward Flight Distorted Wake Model, and the UTRC FREEWAKE analysis. These predicted BVI locations are compared with those obtained from the measured pressure data.

Marcolini, Michael A.↗
NASA NTRS1993

ADP Analysis project for the Human Resources Management Division

The ADP (Automated Data Processing) Analysis Project was conducted for the Human Resources Management Division (HRMD) of NASA's Langley Research Center. The three major areas of work in the project were computer support, automated inventory analysis, and an ADP study for the Division. The goal of the computer support work was to determine automation needs of Division personnel and help them solve computing problems. The goal of automated inventory analysis was to find a way to analyze installed software and usage on a Macintosh. Finally, the ADP functional systems study for the Division was designed to assess future HRMD needs concerning ADP organization and activities.

Tureman, Robert L., Jr.↗
NASA NTRS1994

Prediction of particulate contamination on aperture window

This paper presents an analysis to predict the effects of light scattering by surface particles on the sensor window of a missile during ascent flight. The particulate contaminant distribution on the window is calculated by tallying the number of particles in a set of size ranges. The particulate contamination at the end of the mission is predicted by adding the contributions from the events of ground and flight operations. The surface particle redistributions caused by vibroacoustically induced surface acceleration was found to contribute the most of the particulate surface contamination. The analytical surface obscuration calculation with a set of particle counts was compared to the results of image analyzer measurement. The analytical results, which were calculated with a given function of particle shape depending on the size, were more conservative than the measurement. A scattering calculation using a verified BSDF model showed that the scattering was less than 0.001 at 20 off the direction of the incident light in the mid IR wavelength when the surfaces were at Level 300 initially.

Lee, Aleck L.↗
NASA NTRS1961

Development of the Lunar and Solar Perturbations in the Motion of an Artificial Satellite

Problems relating to the influence of lunar and solar perturbations on the motion of artificial satellites are analyzed by an extension of Cayley's development of the perturbative function in the lunar theory. In addition, the results are modified for incorporation into the Hansen-type theory used by the NASA Space Computing Center. The theory is applied to the orbits of the Vanguard I and Explorer VI satellites, and the results of detailed computations for these satellites are given together with a physical description of the perturbations in terms of resonance effects.

Musen, P.↗