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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Study on multi-satellite, multi-measurement of the structure of the earth's bow shock

The pulsation model of the earth's bow shock proposed a nonuniform shock having both perpendicular (abrupt, monotonic) and oblique (oscillatory, multigradient) properties simultaneously, depending on local orientation of the shock surface to the interplanetary field B sub sw in parallel planes defined by B sub sw and solar wind velocity. Multiple, concurrent, satellite observations of the shock and solar wind conditions were used. Twenty-six potentially useful intervals of concurrent Explorer 33 and 35 data acquisition were examined, of which six were selected for closer study. In addition, two years of OGO-5 and HEOS 1 magnetometer data were examined for possible conjunctions to these spacecraft having applicable data. One case of clear nonuniformity and several of field-dependent structure were documented. A computational aid, called pulsation index, was developed.

Source record↗
NASA NTRS1973

Signal conditioning electronics for a laser vector velocimeter.

A type of laser velocimeter termed a laser vector velocimeter (LVV) resolves the 180 deg directional ambiguity problem of the conventional laser velocimeter by exploiting optical frequency translation techniques and frequency division demultiplexing techniques. This paper defines some fundamental LVV system signal characteristics and signal conditioning and data acquisition problems. The signal conditioning electronics for a three velocity component LVV system are described. Data obtained from atmospheric wind velocity measurements using a two velocity component LVV system are presented to illustrate the vector velocity measurement capabilities of the system. The operational status LVV systems presently in use are two orthogonal velocity component units. However, a laboratory status LVV system has been used to make three-dimensional vector velocity measurements.

Crosswy, F. L.↗
NASA NTRS1974

Solar wind three; Proceedings of the Third Conference, Pacific Grove, Calif., March 25-29, 1974

Papers are presented relating to the study of solar abundances, the evolution of the solar wind, solar corona dynamics, solar wind interactions, and stellar winds. Some of the topics covered include the nuclear composition of cosmic rays, the solar wind as deduced from lunar samples, spectral characteristics of flares, numerical simulation of interplanetary shock ensembles, radial gradient of solar wind velocity from 1 to 5 AU, the enhancement of solar wind fluctuations with scale size near the proton gyroradius, solar wind-Venus interaction observed from magnetic field experiment on Mariner 10, and binary stellar winds. Individual items are announced in this issue.

Russell, C. T.↗
NASA NTRS1994

Global circulation, thermal structure, and carbon monoxide distribution in Venus' mesosphere in 1991

Millimeter-wave observations of CO lines have provided a detailed picture of Venus' mesosphere dynamics in 1991 from simultaneous measurements of absolute wind velocities in two layers and of temperature and CO horizontal and vertical profiles at 75-115 km. Venus' circulation at 90-110 km was characterized in 1991 by the superposition of a zonal retrograde flow and a subsolar-to-antisolar flow of approximately equal velocities, increasing from about 40 +/- 15 m/sec at 95 km to 90 +/- 15 m/sec at 105 km altitude. The magnitude of the increase of the SS-AS flow is consistent with Venus thermosphere general circulation models (VTGCM). At 105 km, the data further indicate a cos(latitude) dependence of the zonal flow and marginally suggest the presence of a poleward meridional component of 35 +/- 30 m/sec. No obvious day-to-day variations of the circulation are evident in the data at the 20 m/sec level. Thermal profiles in the low-latitude region appear to be consistent with the Pioneer Venus nightside profile, except above 110 km, where they are somewhat colder. High-latitude warming is still found, but mid-latitudes appear to be colder than the equator. The atmosphere appears to be in cyclostrophic balance up to about 105 km. The horizontal distribution of CO on Venus' nightside is essentially uniform, both in latitude and in local time. This behavior agrees with VTGCM simulations in which the zonal flow velocity is prescribed to match the observations. Comparison with previous wind measurements indicates that the zonal flow experiences dramatic long-term variations. This variability, along with short-term fluctuations of the mesospheric zonal flow (evidenced by the variability in the O2 nightglow emissions), apparently controls the CO and O2 nightglow distributions. Gravity wave activity is a plausible mechanism that can drive these variations.

Lellouch, Emmanuel↗
NASA NTRS1995

Limits on longitudinal asymmetries and deceleration of the solar wind in the outer heliosphere

Between 1980 and 1992 the Pioneer 10, Voyager 2, IMP 8, and Pioneer Venus Orbiter (PVO) spacecraft were in locations that made them were well-suited to search for radial trends and longitudinal asymmetries in solar wind parameters. Pioneer 10 and Voyager 2 travelled between the heliocentric distances of 21- 54 AU and 6 - 36 AU respectively Pioneer 10 was headed down stream with respect to the local interstellar medium (LISM) while Voyager 2 was headed upstream. Meanwhile, IMP 8 and PVO were at 1 AU and 0.72 AU respectively. We use data from these four spacecraft to search for to and set upper limits on possible asymmetries in solar wind velocity and temperature and on possible deceleration of the solar wind as a result of its interaction with the LISM.

Gazis, P. R.↗
NASA NTRS2001

Exploration of Solar Wind Acceleration Region Using Interplanetary Scintillation of Water Vapor Maser Source and Quasars

Single-station observations of interplanetary scintillation (IPS) at three microwave frequencies; 2 GHz, 8 GHz and 22 GHz have been carried out between 1989 and 1998 using a large (34 m farad) radio telescope at the Kashima Space Research Center of the Communications Research Laboratory. The aim of these observations is to explore the near-sun solar wind, which is the key region for the study of the solar wind acceleration mechanism. Strong quasars; 3C279 and 3C273B were used for Kashima IPS observations at 2 GHz and 8 GHz, and a water vapor maser source, IRC20431 was used for the IPS observations at 22 GHz. Solar wind velocities derived from Kashima IPS data suggest that the solar wind acceleration takes place at radial distances between 10 and 30 solar radii (R(sub s)) from the sun. Properties of the turbulence spectrum (e.g. anisotropy, spectral index, inner scale) inferred from Kashima data are found to change systematically in the solar wind acceleration region. While the solar wind in the maximum phase appears to be dominated by the slow wind, fast and rarefied winds associated with coronal holes are found to develop significantly at high latitudes as the solar activity declines. Nevertheless, Kashima data suggests that the location of the acceleration region is stable throughout the solar cycle.

Tokumaru, Munetoshi↗
NASA NTRS1989

Molecule formation in fast neutral winds from protostars

A time-dependent chemical model is used to analyze the processes generating and destroying molecules in very high velocity winds from low-mass protostars. CO and SiO are found to be generated in significant quantities despite the persistence of H in atomic form, consistently with recent protostellar wind detections of CO and H I at velocities in excess of 100 km/sec. A moderate mass-loss rate, in conjunction with a temperature distribution that decreases rather rapidly with distance from the protostar, are the conditions for substantial molecule formation.

Glassgold, A. E.↗
NASA NTRS1984

Relationship of spaced antenna and Doppler techniques for velocity measurements (keynote paper), part 3

The Doppler, spaced-antenna and interferometric methods of measuring wind velocities all use the same basic information, the Doppler shifts imposed on backscattered radio waves, but they process it in different ways. The Doppler technique is most commonly used at VHF since the narrow radar beams are readily available. However, the spaced antenna (SA) method has been successfully used with the SOUSY and Adelaide radars. At MF/HF the spaced antenna method is widely used since the large antenna arrays (diameter 1 km) required to generate narrow beams are expensive to construct. Where such arrays of this size are available then the Doppler method has been successfully used (e.g., Adelaide and Brisbane). In principle, the factors which influence the choice of beam pointing angle, the optimum antenna spacing will be the same whether operation is at MF or VHF. Many of the parameters which govern the efficient use of wind measuring systems have been discussed at previous MST workshops. Some of the points raised by these workshops are summarized.

Vincent, R. A.↗
NASA NTRS1973

Pilot Performance During A Simulated Standard Instrument Procedure Turn With and Without A Predictor Display

A simulator study was conducted to measure the effectiveness of predictor information incorporated into a CRT display of a computer simulated aircraft's horizontal and vertical situation. Professional pilots served as subjects for the task of executing a standard instrument procedure turn at constant altitude in constant crosswinds with and without their predicted ground track displayed. The results show that the display with the predicted ground track was markedly and significantly superior to the display without this information and that the subjects were generally satisfied with this type of information. Mean rms lateral path error was independent of the crosswind velocity with the predictor information, and increased without it with increasing wind velocity. Rms stick activity decreased with the predictor display which also uncoupled aileron and elevator activity.

John G Kreifeldt↗
NASA NTRS1995

Stability Analysis of Bow Shocks

We present a linear stability analysis of bow shocks created by the interaction of a spherical wind moving with respect to its surrounding medium. The bounding shocks are assumed isothermal and with Mach number M = infinity. Following Soker (1990) we study the evolution of short wavelength perturbations. We find that the motion is unstable in this limit. Moreover, the ratio of the wind velocity v(sub w) to the star velocity v(sub *) characterizes the stability properties. Bow shocks with fast winds for which v(sub *)/v(sub w)<<1 are more stable than bow sho with slow winds i.e. v(sub *)/v(sub w)>>1.

Bow Shocks↗
NASA NTRS1974

Low-speed wind tunnel tests of a 50.8-centimeter (20-in.) 1.15-pressure-ratio fan engine model

At a typical STOL aircraft takeoff and landing velocity, wind tunnel aerodynamic and acoustic measurements demonstrated that an inlet lip-area contraction ratio of 1.35 was superior to a ratio of 1.26 at high incidence angles. A 17 percent reduction in net thrust and an increase of 9 decibels in sound pressure level at the blade passing frequency resulted from inlet flow separation at an incidence angle of 50 deg with the 1.26-contraction-ratio inlet. Reverse-thrust forces obtained with blade rotation through the feathered angle were 1.8 times larger than with blade rotation through the flat angle. Reverse-thrust force was reduced from 30 to 50 percent and sound pressure level increased from 3 to 7 decibels at the blade passing frequency between the wind-tunnel-off condition and a typical STOL aircraft landing velocity.

Wesoky, H. L.↗
NASA NTRS2012

Dual-Doppler Feasibility Study

When two or more Doppler weather radar systems are monitoring the same region, the Doppler velocities can be combined to form a three-dimensional (3-D) wind vector field thus providing for a more intuitive analysis of the wind field. A real-time display of the 3-D winds can assist forecasters in predicting the onset of convection and severe weather. The data can also be used to initialize local numerical weather prediction models. Two operational Doppler Radar systems are in the vicinity of Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS); these systems are operated by the 45th Space Wing (45 SW) and the National Weather Service Melbourne, Fla. (NWS MLB). Dual-Doppler applications were considered by the 45 SW in choosing the site for the new radar. Accordingly, the 45th Weather Squadron (45 WS), NWS MLB and the National Aeronautics and Space Administration tasked the Applied Meteorology Unit (AMU) to investigate the feasibility of establishing dual-Doppler capability using the two existing systems. This study investigated technical, hardware, and software requirements necessary to enable the establishment of a dual-Doppler capability. Review of the available literature pertaining to the dual-Doppler technique and consultation with experts revealed that the physical locations and resulting beam crossing angles of the 45 SW and NWS MLB radars make them ideally suited for a dual-Doppler capability. The dual-Doppler equations were derived to facilitate complete understanding of dual-Doppler synthesis; to determine the technical information requirements; and to determine the components of wind velocity from the equation of continuity and radial velocity data collected by the two Doppler radars. Analysis confirmed the suitability of the existing systems to provide the desired capability. In addition, it is possible that both 45 SW radar data and Terminal Doppler Weather Radar data from Orlando International Airport could be used to alleviate any radar geometry issues at the NWS MLB radar, such as the "cone of silence" or beam blockage. In the event of a radar outage at one of the sites, the multi-radar algorithms would provide continuing coverage of the area through use of the data from the remaining operational radar sites. There are several options to collect, edit, synthesize and display dual-Doppler data sets. These options include commercial packages available for purchase and a variety of freeware packages available from the National Center for Atmospheric Research (NCAR) for processing raw radar data. However, evaluation of the freeware packages revealed that they do not have sufficient documentation and configuration control to be certified for 45 SW use. Additionally, a TI data line must be installed/leased from the NWS MLB office and CCAFS to enable the receipt of NWS MLB raw radar data to use in the dual-Doppler synthesis. Integration of the TI data line into the Eastern Range infrastructure that will meet the security requirements necessary for 45 SW use is time-consuming and costly. Overall evaluation indicates that establishment of the dual-Doppler capability using the existing operational radar systems is desirable and feasible with no technical concerns. Installation of such a system represents a significant enhancement to forecasting capabilities at the 45 WS and at NWS MLB. However, data security and cost considerations must be evaluated in light of current budgetary constraints. In any case, gaining the dual-Doppler capability will provide opportunities for better visualization of the wind field and better forecasting of the onset of convection and severe weather events to support space launch operations at KSC and CCAFS.

Huddleston, Lisa L.↗
NASA NTRS1973

Pilot performance during a simulated standard instrument procedure turn with and without a predictor display

A simulator study was conducted to measure the effectiveness of predictor information incorporated into a CRT display of a computer simulated aircraft's horizontal and vertical situation. Professional pilots served as subjects for the task of executing a standard instrument procedure turn at constant altitude in constant crosswinds with and without their predicted ground track displayed. The results showed that the display with the predicted ground track was markedly and significantly superior to the display without this information and that the subjects were generally satisfied with this type of information. Mean rms lateral path error was independent of the crosswind velocity with the predictor information, and increased without it and with increasing wind velocity. Rms stick activity decreased with the predictor display which also uncoupled aileron and elevator activity.

Kreifeldt, J. G.↗
NASA NTRS1981

Verification studies of Seasat-A satellite scatterometer /SASS/ measurements

Two comparisons between Seasat-A satellite scatterometer (SASS) data and surface truth, obtained from the Gulf of Alaska Seasat Experiment and the Joint Air-Sea Interaction program, have been made to determine the behavior of SASS and its algorithms. The performance of SASS was first evaluated irrespective of the algorithms employed to convert the SASS data to geophysical parameters, which was done by separating the backscatter measurements into small bins of incidence and azimuth angles and polarity and regression against wind speed measurements. The algorithms were then tested by comparing their predicted slopes and y intercepts with those derived from the regressions, and by comparing each SASS backscatter measurement with the backscatter derived from the algorithms, and the given wind velocity from the observations. It was shown that SASS was insensitive to winds at high incidence angles for horizontal polarizations. Fairly high correlations were found between backscatter and wind speeds. The algorithms functioned well at mid-ranges of incidence angle and backscattering coefficient.

Halberstam, I.↗
NASA NTRS1984

Magnetospheric energization by interaction between planetary spin and the solar wind

If the solar wind is capable of driving magnetospheric convection, then solar-wind flow past any spinning, magnetized planet with a conducting ionosphere must cause the magnetic field lines in the outer part of its magnetospheric tail to be twisted into a helix. Such a magnetic field configuration requires magnetically field-aligned (Birkeland) currents in the tail that flow in and near the magnetopause and close by driving Pedersen currents through the planetary ionosphere. The strength of the Birkeland currents (and, by current continuity, the Pedersen currents) is, to first order, independent of the angle between the planetary-spin vector and the solar-wind velocity vector. Rather, the total current is a function of the magnetic moment of the planet, the radius of the tail, the angular velocity of planetary spin, the conductivity of the ionosphere, and the solar wind speed. For Jupiter, Saturn, Uranus, and perhaps Neptune, the power these currents deliver to the ionosphere is significant with regard to magnetospheric dynamics, such as the production of aurora and the generation of low-frequency radio emissions. For Mercury, Venus, earth, Mars, and probably Pluto, these currents are relatively small, although observable effects may be marginally detectable for the case of the earth's magnetosphere.

Isbell, J.↗
NASA NTRS1988

Influence of wind shear on the aerodynamic characteristics of airplanes

The aerodynamic effect of shear flow through a series of sensitivity studies of the wind velocity gradients and wing planform geometry parameters is investigated and characterized. The wind shear effect is computed using a modified vortex-lattice computer program and characterized through the formulation of wind shear aerodynamic coefficients. The magnitudes if the aerodynamic effects are demonstrated by computation of the resultant change in the aerodynamics of a conventional wing and horizontal stability configuration on a fixed flight path through a simulated microburst. The results indicate that as much as 20 percent of the control authority of the airplane may be required to counteract the wind-shear-induced forces and moments in the microburst environment.

Vicroy, Dan D.↗
NASA NTRS1991

What maintains the zonal circulation in planetary atmospheres?

The latest Voyager observations have shown large zonal velocities in Neptune's atmosphere, with some indication of alternating jets. Similar wind velocities have also been observed on Venus and are characteristic of planetary atmospheres in general, which is remarkable considering that the available solar or internal heating varies by more than a factor of 1000. A simplified model of the planetary circulation which provides some qualitative understanding is discussed. The basic assumption is that the source driving the circulation is also generating the dissipating eddies which are simulated by diffusion. Thus, the magnitude and structure of the zonal circulation are independent both of the source and the dissipation rate. The zonal velocities are related to the speed of sound and are of comparable magnitude in different atmospheres; although the available heating varies by a large factor, and the planetary parameters vary over a wide range. The alternating jets are described by a convective eigenmode which develops when energy transport out of the planetary interior is important, as is the case on Jupiter, Neptune, and Saturn.

Mayr, H. G.↗