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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Review of specific antenna configurations: An estimate of cost and performance versus frequency for a simple (10 Lambda)-2 clear-air radar antenna array

The building of operational clear air radar wind profilers is discussed. The choice of operating frequency and antenna configuration for these profilers is examined. The cost and performance of a (10 lambda) 2 antenna array versus operating frequency over the range 30 to 400 MHz is compared. To simplify the comparison the array beam will be fixed and the array will be uniformly fed. Yagi and coaxial collinear (COCO) cable antennas are compared, although other configurations may be competitive. It is assumed that the array is driven by a typical 50 kW peak power, 1 kW average, power transmitter located at the array edge when calculating feedline power handling requirements and when system performance is compared. For this comparison an array aperture of (10 lambda) 2 was chosen since a one way beam width of 5 deg or less is desirable to limit beam spreading effects.

Ecklund, W. L.↗
NASA NTRS1984

An experimental investigation of surface pressure measurements on an advanced winged entry vehicle at Mach 10

Surface pressure measurements have been made at Mach 10 in air on an instrumented 0.006-scale model of an advanced (control configured) winged entry vehicle. The tests were conducted in the Langley Continuous Flow Hypersonic Tunnel. Data were obtained at 83 surface pressure stations, which include locations on the lower and upper surface centerlines, spanwise positions along the lower and upper surfaces of the wing, the lower surface of the body flap, and radial locations on the fuselage. Data were obtained for angles of attack ranging from zero to 40 deg, sideslip angles of -2 deg to +5 deg, Reynolds numbers of 0.5, 1.0, and 2.0 million per foot, and body-flap deflections of zero, 10, and 20 deg. Test conditions and orifice locations were chosen to correspond directly with those for the heat transfer measurements previously reported on the same configuration. Comparison of windward symmetry plane data with predictions based upon an approximate engineering method was found to yield reasonable agreement for angles of attack from 20 to 40 deg. The leeward surface pressure data were observed to be roughly an order of magnitude lower than the corresponding windward data. At low angles of attack, regions of high pressure were noted on the windward wing surface. The result is attributed to vortical action or shock impingement. High pressures were also measured on the deflected body flap, a critical region for this type of vehicle. Reynolds number effects were found to be insignificant.

Wurster, K. E.↗
NASA NTRS1984

Fine-cut bluntness effects on the hypersonic static stability of a 10 degree cone

A systematic wind-tunnel investigation has been performed on a series of spherically blunted 10-degree cones to determine Mach number and angle-of-attack effects on the hypersonic static stability. The cones, which range in nose-to-base radius ratios from 0 to 0.5, have been tested from -4 to 20 degrees angle of attack at Mach numbers of 6 and 10 in air and 20 in helium. Relatively large excursions in the center-of-pressure location were observed for small changes in cone nose bluntness. The movement of the center of pressure was also noted to become more pronounced as Mach number increased; increases in angle of attack tended to lessen the magnitude of these excursions. Computational predictions of basic aerodynamic coefficients as well as the center-of-pressure locations using both viscous and inviscid theory compare very well with the experimental data.

Bryan, M. D.↗
NASA NTRS1983

10 micron polarimetry of Ceres

Linear polarimetry of Ceres at 10 micron is presented. These data represent the first published polarization measurements of an asteroid in the thermal infrared. It is found that Ceres is polarized at the 0.2-0.6 percent level. This data set is compared with theoretical models of the linear polarization of emitted radiation from a spherical plane. These models are used to derive the pole position and thermal inertia of Ceres. Ceres is best fit with a thermal inertia of 0.0010 + or 0.0003 cal (sq cm K) per square root of second and a pole orientation of beta(p) = 36 deg + or - 5 deg + or -5, lambda(p) = 270 deg + or - 3. It is concluded that 10 micron polarimetry is a potentially powerful technique for remotely sensing the pole orientation and thermal inertia of asteroids.

Johnson, P. E.↗
NASA NTRS1984

A search for the 10-micron silicate feature in periodic Comet Grigg-Skjellerup

A 10-micron spectrum of periodic Comet Grigg-Skjellerup was obtained on 22 June 1982 with the UCL array spectrometer at the United Kingdom Infrared Telescope, Mauna Kea. No emission feature is obvious in the spectrum. The observed spectrum can be fit equally well by a model of small hot absorbing grains or by a composite model with less than or equal to 30 percent (3sigma) warm, 'dirty' silicate grains. The latter model is consistent with the silicate abundance in Comet Kohoutek, which did display an emission feature at 10 microns.

Hanner, M.↗
NASA NTRS1984

Microstructure, strength, and oxidation of a 10 wt pct zyttrite-Si3N4 ceramic

Hot pressed Si3N4 doped with 10 wt pct zyttrite as a sintering aid was studied. An equiaxed, fine grained microstructure was predominant, with no apparent porosity. Bend strengths were determined at room temperature and high temperatures (up to 1370 C). Oxidation was measured by weight gain at 1370 C in air. The resulting material exhibited very good room temperature strength (755 MPa). The work showed that room temperature strength can be improved significantly by using controlled Si3N4 powder with 10 wt pct zyttrite. High temperature strength (514 MPa) at 1370 C was nearly double that of hot-pressed Si3N4 (NC-132). The oxidation resistance at 1370 C was also higher than that of NC-132.

Dutta, S.↗
NASA NTRS1984

Large scale temporal and radial gradients in the IMF - Helios 1, 2, ISEE-3, and Pioneer 10, 11

Recent investigations using measurements at 1 AU have discovered three types of long term variation in the interplanetary magnetic field: solar minimum decreases, solar maximum enhancements, and small decreases around solar reversal. In this study the 1972-1982 Helios 1, 2, ISEE-3, and Pioneer 10, 11 observations between 0.3 and 12 AU are examined to further investigate these changes. It was found that all three IMF solar cycle effects are also present in the Helios and Pioneer measurements, confirming that these variations occur throughout the low latitude heliosphere. In addition, the comparison of measurements by identical magnetometers on ISEE-3, Pioneer 10 and Pioneer 11 has revealed a more rapid decrease in IMF intensity than predicted by classical Parker theory. Causes and ramifications of both the long term variations and steeper-than-expected radial gradients in the interplanetary magnetic field are discussed.

Slavin, J. A.↗
NASA NTRS1984

Pioneer 10 search for gravitational waves - No evidence for coherent radiation from Geminga

Attempts to identify a periodic gravitational wave signal from the binary Geminga in the reduced Doppler data from the Pioneer 10 spacecraft are reported. The study was performed to examine the possibility that the observed 160 min solar oscillation is driven by a gravitational wave from the binary, which has a period exactly one cycle different from the solar oscillation. Three 12 hr passes of Doppler data from Pioneer 10, now beyond the orbit of Neptune, were subjected to FFT analysis to detect a spectral gravitational wave signature. None was found. Least squares analysis of all low noise data from 1981 to characterize the amplitude and phase of a signal from Geminga also produced a null result. Finally, an upper bound was calculated for the polarization component of the potentially observable gravitational strain.

Anderson, J. D.↗
NASA NTRS1984

Nearby molecular clouds. I - Ophiuchus-Sagittarius, b greater than 10 deg

Observations of a 370-sq-deg area at b = 10-24 deg in the Oph-Sag region at the 115-GHz 1-0 transition of CO, obtained with a 256-channel spectrometer on the 1.2-m mm-wave telescope at Columbia University during winter 1980-1981 are reported. Observing parameters include full beamwidth at half power 8 arcmin, resolution 1 or 0.5 deg, velocity resolution 0.65 km/s, and frequency-shifting-mode shift 5 MHz; the data-processing scheme is described in detail. The results are presented in a map and a diagram and discussed with regard to other observations. An extended complex of molecular clouds near the sun and probably connected with the Aquila Rift, the Rho Oph Cloud, and the Gould Belt is detected. A correlation is found between the CO line intensity and the H I deficiency observed in the region, suggesting H2 formation with H2 column densities up to 1 x 10 to the 21st/sq cm.

Huang, Y.-L.↗
NASA NTRS1984

Experimental heating distributions for biconics at incidence in Mach 10 air and comparison to prediction

Heating distributions were measured on a 1.9 percent scale model of a generic, aeroassisted vehicle proposed for missions to a number of planets and also a candidate as a moderate L/D earth orbital transfer vehicle. This vehicle is a spherically blunted, 13 deg/7 deg biconic with the fore-cone bent upward 7 deg to provide self-trim capability; also tested was a straight biconic with the same noise radius and half angles. These measurements were made in the Langley 31-Inch Mach 10 Tunnel at values of the free-stream Reynolds number, based on model length, equal to 0.2 and 0.9 million. The angle of attack, referenced to the aft cone, was varied from 0 to 20 deg. Heating distributions predicted with a parabolized Navier Stokes (PNS) code are compared to measurement over the present range of Reynolds number and angle of attack. Windward heating was predicted to within 10 percent by the PNS code. Leeward heating distributions were predicted qualitatively for both values of Reynolds number, but quantitative agreement was poorer than on the windward side.

Miller, C. G.↗
NASA NTRS1985

Error Growth in Operational 10-day Forecasts

The rate of growth of forecast errors has been estimated previously, using as data base 100 consecutive 10-day operational forecasts from the European Center for Medium Range Forecasting (ECMWF). The growth of the difference between two model forecasts verifying the same day was parameterized. This parameterization of error growth was extended by including the effect of model deficiencies as well as their scale dependence. In this way the forecaster are able to fit real forecast error growth and determine the scale dependence of the derived parameters (rate of error growth, external error source due to model errors, and saturation levels). This work is a necessary step in the application of the Lagged Average Forecasting (LAF) technique to the ECMWF 10-day forecasts. It is found that for both the analyses and the forecasts, there is an approximate equipartition of energy between all the zonal wavenumbers m corresponding to the same total wavenumber n.

Kalnay, E.↗
NASA NTRS1985

Periodic gamma-ray emissions from Geminga at or = 10(12) eV

Analysis of data from an atmospheric Cerenkov telescope indicated the periodic emission of gamma rays of energy 10 to the 12th power eV, at 60.25 second period, from 2CG 195+4. The gamma ray flux at 99% confidence level is estimated to be 9.5 x 10 to 12 photons/sq cm/s.

Kaul, R. K.↗
NASA NTRS1985

Observations of ultraheavy cosmic ray particles at 10 GV cutoff rigidity

Ultraheavy cosmic ray particles with Z 45 and Fe were observed in two balloon flights at a mean geomagnetic cutoff rigidity of 10 GV. Fluxes of these particles at the top of the atmosphere are presented. A ratio of (Z 45)/(Fe) is compared with other experimental results. The ratio decreases with increasing energy in the energy range from 1 to 10 GeV/amu. A possibility is presented to explain the variation of the ratio with energy.

Yanagimachi, T.↗
NASA NTRS1985

Energy spectrum and arrival direction of primary cosmic rays of energy above 10 to the 18th power eV

The observation of ultra high energy cosmic rays with 20 sq km array has started at Akeno. The preliminary results on energy spectrum and arrival direction of energies above 10 to the 18th eV are prsented with data accumulated for four years with the 1 sq km array, for two years with the 4 sq km array and for a half year with the new array. The energy spectrum is consistent with the previous experiments showing the flattening above 10 to the 18.5 eV.

Teshima, M.↗
NASA NTRS1985

The sidereal anisotropy of cosmic rays around 3 x 10 (15) eV observed at a middle north latitude

The sidereal time variation of cosmic rays (median primary energy : 3 10 to the 15th power eV) is investigated with air shower observations at Akeno, Japan (900 m a.s.l.) which started in September 1981. Air showers are detected by a coincidence requirement on several muon detectors. The result obtained for three years is suggestive of a big semi-diurnal variation (0.37 % in amplitude). On the other hand, the diurnal variation is rather small than the semi-diurnal one. The feature of the sidereal anisotropy supposed from the present result looks quite different from that below 10 to the 14th power eV.

Murakami, K.↗
NASA NTRS1985

Evidence for regions of negligible cosmic-ray modulation in the inner heliosphere ( 10 AU)

Gold and Venkatesan report observations of periods during 1974-1976 when extended regions of heliolongitude that emitted lower than average solar wind velocities at 1 AU also exhibited higher than average cosmic ray intensities as measured by the E 35 MeV CPME anti-coincidence scintillator (28 sq cm omnidirectional geometric factor) on IMP-8. Their observations reproduced by a simple model, based on the observed steady solar wind structure, wherein there is little modulation of cosmic rays in the inner heliosphere until they reach the shocked plasma beyond the stream interactions in the outer heliosphere (similar to 5 to 10 AU). Beyond the interaction boundary, the intensity exhibits a constant radial gradient (similar to 2%/AU). The model also offers an explanation for the irregular behavior of the rotation averaged radial gradients observed by inside 10 AU, as well as the significant, but often ephemeral, latitude gradients observed by Voyagers 1 and 2 and IMP-8.

Roelof, E. C.↗
NASA NTRS1985

A method to improve observations of gamma-ray sources near 10 (15) eV

Now that sources of gamma rays near 10 to the 15th power eV have been identified, there is a need for telescopes which can study in detail the high energy gamma ray emissions from these sources. The capabilities of a Cerenkov detector which can track a source at large zenith angle (small elevation angle) are analyzed. Because the observed showers must then develop far from the detector, the effective detection area is very large. During a single half-hour hot phase of Cygnus X-3, for example, it may be possible to detect 45 signal showers compared with 10 background showers. Time structure within the hot phase may then be discernible. The precise capabilities of the detector depend on its mirror size, angular acceptance, electronic speed, coincidence properties, etc. Calculations are presented for one feasible design using mirrors of an improved Fly's Eye type.

Sommers, P.↗