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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The high-latitude winter F region at 300 km - Thermal plasma observations from AE-C

Results are presented for a comprehensive survey of thermal ion composition and electron temperature (Te) variations in the southern high-latitude winter F region near 300-km altitude. The data are obtained from the Atmosphere Explorer (AE-C) satellite during a magnetically quiet period centered on the June 1976 solstice. Prominent ionospheric features, including the nightside main trough, a high-latitude ionization hole, and the dayside auroral zone-cusp region, are characterized in terms of composition and Te variations. The structures under study are qualitatively interpreted in terms of known processes.

Brinton, H. C.↗
NASA NTRS1977

Development and testing of advanced redundancy management methods for the F-8 DFBW aircraft

A reliable aircraft sensor failure detection and identification (FDI) technique is presented. The technique exploits the kinematic and dynamic relationships that exist between variables measured by dissimilar sensors to identify failures in the sensors. The method is applied to management of dual redundant sensors on the NASA F-8 digital fly-by-wire (DFBW) research aircraft.

Deyst, J.↗
NASA NTRS1979

Reynolds number, scale and frequency content effects on F-15 inlet instantaneous distortion

An inlet instantaneous distortion study program sponsored by NASA was recently completed using an F-15 fighter aircraft. Peak distortion data from subscale inlet model wind tunnel tests are shown to be representative of full-scale flight test peak distortion. The effects on peak distortion are investigated for engine presence, Reynolds number, scale and frequency content. Data are presented which show that: (1) the effect of engine presence on total pressure recovery, peak distortion, and turbulence is small but favorable, (2) increasing the Reynolds number increases total pressure recovery, decreases peak distortion, and decreases turbulence, and (3) increasing the filter cutoff frequency increases the calculated values of both peak distortion and turbulence.

Stevens, C. H.↗
NASA NTRS1979

Preliminary flight and wind tunnel comparisons of the inlet/airframe interaction of the F-15 airplane

Preliminary flight and wind tunnel comparison data are presented for the F-15 inlet/airframe interactions program. Test conditions and instrumentation for both the model and the aircraft are described. Flight and wind tunnel inlet drag data (for a 0-deg angle of attack and Mach numbers of 0.6, 0.9, and 1.2), derived by using nearly identical pressure integration equations, are compared. The effects of a movable cowl, movable ramps, and other system components on pressure flow fields along the airframe are discussed. Excellent agreement between wind tunnel and flight pressure-integrated drags is found at all three Mach numbers. The wind tunnel data show good agreement for pressure-integrated and force-balance-measured inlet drag, except at Mach 0.6. Flight-measured pressure-integrated inlet lift is lower than that measured in the wind tunnel.

Webb, L. D.↗
NASA NTRS1979

Total electron content and F-region electron density distribution near the magnetic equator in India

Total electron content derived from the group delay measurements of ATS-6 radio beacons received at Ootacamund (India) are compared with the electron-density vs height distributions derived from the ionosonde data of the nearby station Kodaikanal. The daily variation of equivalent vertical total electron content does not show the midday bite out which is so prominently present in the corresponding daily variation of the maximum F-region electron density. The topside electron content continues to increase from sunrise to a maximum value around 1500 LT, while the bottomside electron content reaches a maximum value around 0500 LT. Daily variations of these as well as other parameters, e.g. the vertical slab thickness, the bottomside semi-thickness, the height of the F2 peak have been also studied for a geomagnetically quiet and a disturbed day.

Rastogi, R. G.↗
NASA NTRS1979

Water tunnel visualization of the vortex flows of the F-15

Flow visualization studies were conducted in a diagnostic water tunnel to provide details of the wing, glove, and forebody vortex flow fields of the F-15 aircraft over a range of angles of attack and sideslip. Both the formation and breakdown of the vortex flow as a function of angle of attack and sideslip are detailed for the basic aircraft configuration. Additional tests showed that the wing upper surface vortex flows were sensitive to variations in an inlet mass flow ratio and an inlet cowl deflection angle. Two lengthened forebodies, one with a modified cross-sectional shape, were tested in addition to the basic forebody. Asymmetric forebody vortices were observed at zero sideslip and high angles of attack on each forebody. A large nose boom was added to each of the three forebodies, and it was observed that the turbulent wake shed from the boom disrupted the forebody vortices.

Lorincz, D. J.↗
NASA NTRS1972

Boundary-Layer Edge Conditions and Transition Reynolds Number Data for a Flight Test at Mach 20 (Reentry F)

A flight experiment, designated Reentry F, was conducted to measure heat-transfer rates for laminar, transitional, and turbulent boundary layers on a 5 deg half-angle cone 3.962 m (13 ft) long with a preflight nose radius of 2.54 mm (0.10 in.). Data were obtained over an altitude range from 36.58 to 18.29 km (120 000 to 60 000 ft) at a flight velocity of about 6.096 km/sec (20 000 ft/sec). The nominal values of the free-stream total enthalpy, sharp-cone Mach number, and the wall-to-total enthalpy ratio were 18 MJ/kg (8000 Btu/lb), 15, and 0.03, respectively. Calculated boundary-layer edge conditions that account for effects of the entropy layer and corresponding local transition Reynolds numbers are reported in the present paper. Fully developed turbulent flow occurred with essentially constant boundary-layer edge conditions near the sharp-cone values. Transition data were obtained with local edge Mach numbers ranging from about 5.55 to 15. Transition Reynolds numbers, based on local condition, were as high as 6.6 x 10(exp 7) with an edge Mach number of about 14.4 at an altitude of 24.38 km (80 000 ft). The transition could be correlated with previous flight data taken over a Mach number range from 3 to 12 in terms of parameters including the effects of local unit Reynolds number, boundary-layer wall-to-edge enthalpy ratio, and local Mach number.

Johnson, Charles B.↗
NASA NTRS1980

F-5F Shark Nose radome lightning test

A unique F-5F radome wtih a geometry similar to a Shark Nose profile was tested with a high voltage Marx generator, 1,200,000 volts in order to demonstrate the effectiveness of the lightning protection system with currents from 5,000 amperes or greater. An edge discontinuity configuration is a characteristic feature in the forward region of the radome and occasionally serves as an attachment point. The results of nineteen attachment tests at various aspect angles with an air gap of one meter indicated that no damage occurred to the dielectric material of the radom. The test proved the effectiveness of the lightning protection system.

Scott, G. W.↗
NASA NTRS1979

High-latitude E and F region ionospheric predictions

The physical processes and morphology of the high latitude E and F layers are discussed. The existence and adequacy of models, and features to be included are examined, as well as reliability of ionospheric predictions.

Hunsucker, R. D.↗
NASA NTRS1980

A continuation of base-line studies for environmentally monitoring space transportation systems at John F. Kennedy Space Center. Executive summary

Studies conducted in and around John F. Kennedy Space Center, Merrit Island, Florida were designed to establish baseline conditions for various attributes of the biotic and abiotic environment. Features were described and quantitatively measured. Certain condition were found to be appropriate for the detection and assessment of possible environmental perturbations caused by future NASA activities. These include plant communities, mammal populations, rainfall chemistry, fish populations, and the status of rare and endangered species. On the basis of statistical analysis of quantitative data and logistic considerations, it was possible to refine the kinds and amounts of measurements needed to evaluate perturbations in selected environmental components.

Stout, I. J.↗
NASA NTRS1980

Composition of the nighttime ionospheric F 1 region near the magnetic equator

The effects of vertical E x B transport on NO(+), O2(+) and O(+) densities in the nighttime equatorial ionospheric F 1 region are investigated. Ion densities are calculated as functions of altitude, latitude and local time by the numerical solution of coupled, time-dependent ion continuity equations, taking into account production, loss by charge exchange and dissociative recombination and transport by diffusion and E x B drift. The results of the calculations are compared with measurements of NO(+), O2(+) and O(+) ion densities obtained at low altitudes by a mass spectrometer on board the Atmospheric Explorer C satellite, and are found to be consistent with the observations, suggesting that in the equatorial region, vertical transport by E x B drift is primarily responsible for producing the observed NO(+), O2(+) and O(+) density profiles. In addition, the reaction of O2(+) with N(4S) is found to be an important sink for O2(+) and a source of NO(+) ions. Implications of the observed and calculated near constancy of electron and ion densities with altitude when NO(+) is the dominant ion on the growth of large-scale irregularities are also considered

Anderson, D. N.↗
NASA NTRS1980

Causes of the F region winter anomaly

Measurements made by the Atmosphere Explorer satellites are used to determine the causes of the F-region winter anomaly, i.e., seasonal variations which result in peak electron densities which are larger in winter than in summer. It is found that for the data examined there are three causes of the winter anomaly: (1) seasonal changes in neutral composition; (2) an increase in the vibrational temperature of N2 and hence in the rate coefficient for the reaction O(+)(4S) + N2 yields NO(+) + N; (3) an increase in winter in the production of O(+)(4S) due to enhanced electron quenching of O(+)(2D). The presence of vibrational excitation is inferred from an increase in the rate coefficient for the reaction O(+) + N2 yields NO(+) + N from winter to summer at heights above 260 km. It is demonstrated quantitatively that the initial increase in electron density produced in winter by causes (1) and (2) results in an increase in the quenching of O(+)(4S), thereby enhancing the source of O(+)(4S) ions. It is estimated that causes (1) to (3) account for approximately 55%, 20% and 25% respectively of the seasonal change in O(+)(4S) from summer to winter at solar minimum.

Torr, D. G.↗
NASA NTRS1980

Interhemispheric transport induced by neutral zonal winds in the F region

Reliable measurements of the interhemispheric ion transport velocity have shown a large longitudinal variability at equinox. The roles of zonal and meridional F region neutral winds have been evaluated in a simple way to account for the observed longitude dependence. The magnetic declination and relative displacement of the geographic and geomagnetic equators are both important considerations. It is shown that the zonal wind makes a strong contribution to the observed interhemispheric transport velocities near equinox.

Heelis, R. A.↗
NASA NTRS1980

Granulation in a main-sequence F-type star

The modal approach developed by Nelson and Musman (1977) is used to investigate convection in an F-type main-sequence star (effective temperature of 7300 K, g = 10,000 cm per sec per sec). The convective velocities and intensity contrasts are found to be larger than in the sun. Even though the convective flux is less than 1% of the total flux at a mean optical depth of unity, the spectral-energy distribution is strongly reddened as a result of the fluctuating opacity. This has important implications in the conversion scale from observed colors to effective temperature. The scale of the surface granulation is expected to be in the range 1000-5000 km. Calculations of the combined H-He I and He II convection zones support the prediction of Toomre et al. (1976) that the stable region between the zones is well mixed

Nelson, G. D.↗
NASA NTRS1980

F region above Kauai - Measurement, model, modification

Results of the Lagopedo II experiment conducted from Kauai, Hawaii to investigate the ionospheric modification that occurs when rocket combustion products are introduced into the O(+)-rich F region are presented. The experiment involved the detonation of a chemical explosion in the F2 peak accompanied by rocket-borne measurements of ion composition and electron content in the vicinity of the explosion. The experimental data is found to be in good agreement with the predictions of a model of the nighttime ion densities in the midlatitude laminar ionosphere, with the exception of N2(+) densities before the explosion. H2O(+) and H3O(+) currents produced by considerable H2O outgassing from the rocket are used to determine a H3O(+)/H2O(+) dissociative recombination rate averaging 1.6 to 1.08, depending on model assumptions. At the time of the explosion, an ionic void 1 km in radius is observed, the boundary of which is characterized by a steep gradient in ionic densities. Evidence of variations in the concentrations of ambient ion species, new reactant species and ionic depletion by sweeping is also obtained.

Johnson, C. Y.↗
NASA NTRS1981

IUE spectra of F and late A stars

The International Ultraviolet Explorer (IUE) spectra of alpha CMi (F5 IV-V), beta Cas (F2 IV), alpha Car (F0 Ib), and gamma Boo (A7 III) in the context of the question as to whether chromospheres disappear in the early F late A portions of the Hertzsprung-Russell diagram. Both alpha CMi (Procyon) and beta Cas show bright emission line spectra indicative of chromospheres and transition regions, but neither alpha Car (Canopus) nor gamma Boo show any evidence of emission in their SWP spectra or at the Mg II lines, despite very deep exposures. Alpha CMi has emission line fluxes roughly 6 times those of the quiet Sun, but the rapidly rotating delta Scuti type variable beta Cas has surface fluxes 10 to 50 times those of the quiet Sun. Upper limits on emission line fluxes for alpha Car are 4 to 20 and for gamma Boo 15 to 80 times the quiet Sun. It is concluded that the apparent absence of emission lines in the spectra of alpha Car and gamma Boo should not be interpreted as due to the absence of nonradiatively heated outer atmospheres in stars hotter than spectral type F0, but rather to the inability to see emission lines with IUE against a background of scattered light and a bright photospheric absorption line spectrum either in low or high dispersion.

Linsky, J. L.↗