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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Collisionless effects on the spectrum of secondary auroral electrons at low altitudes

A common feature of all rocket measurements of the differential flux of primary and secondary electrons under auroral activity is that between 30 and 85 eV, where the measurements overlap in energy, the electron flux data can be fitted by a certain power law. In the present paper, it is shown that the existence of plasma waves even in a region where they are nonresonant with the ambient particles can significantly modify the observed flux power law.

Papadopoulos, K.↗
NASA NTRS1979

Current leakage for low altitude satellites - Modeling applications

To simulate the behavior of a high voltage solar cell array in the ionospheric plasma environment, the large (90 ft x 55 ft diameter) vacuum chamber was used to measure the high-voltage plasma interactions of a 3 ft x 30 ft conductive panel. The chamber was filled with Nitrogen and Argon plasma at electron densities of up to 1,000,000 per cu cm. Measurements of current flow to the plasma were made in three configurations: (a) with one end of the panel grounded, (b) with the whole panel floating while a high bias was applied between the ends of the panel, and (c) with the whole panel at high negative voltage with respect to the chamber walls. The results indicate that a simple model with a constant panel conductivity and plasma resistance can adequately describe the voltage distribution along the panel and the plasma current flow. As expected, when a high potential difference is applied to the panel ends more than 95% of the panel floats negative with respect to the plasma.

Konradi, A.↗
NASA NTRS1951

Meteorological Analysis of Icing Conditions Encountered in Low-Altitude Stratiform Clouds

Liquid-water content, droplet size, and temperature data measured during 22 flights in predominatly stratiform clouds through the 1948-49 and the 1949-50 winters are presented. Several icing encounters were of greater severity than those previously measured over the same geographical area, but were within the limits of similar measurements obtained over different terrain within the United States. An analysis of meteorological conditions existing during the 74 flights conducted for four winters indicated an inverse relation of liquid-water concentration to maximum horizontal extent of icing clouds. Data on the vertical extent of supercooled clouds are also presented. Icing conditions were most likely to occur in the southwest and northwest quadrants of a cyclone area, and least likely to occur in the southeast and northeast quadrants where convergent air flow and lifting over the associated warm frontal surface usually cause precipitation. Additional data indicated that, icing conditions were usually encountered in nonprecipitating clouds existing at subfreezing temperatures and were unlikely over areas where most weather observing stations reported the existence of precipitation. Measurements of liquid-water content obtained during 12 flights near the time and location of radiosonde observations were compared with theoretical values. The average liquid-water content of a cloud layer, as measured by the multicylinder technique, seldom exceeded two-thirds of that which could be released by adiabatic lifting. Local areas near the cloud tops equaled or occasionally exceeded the calculated maximum quantity of liquid water.

Kline, D. B.↗
NASA NTRS1982

Attitude and translation control of a low-altitude Gravsat

Dynamic simulation of the Gravsat's attitude and translation control system is used to provide an upper bound for the fuel supply and test the feasibility of the preliminary design. A preliminary design is made for the disturbance compensation system (DISCOS) sensor, the thruster control laws, reaction wheel control laws, and the onboard state estimators. The sensor analysis and noise measurements show no problems in scaling the Triad navigation satellite sensor design up to meet the Gravsat requirements, except for proof mass center-of-mass offset. A promising technique is proposed to measure and eliminate this error. The covariance analysis confirms that a sophisticated post-flight data fit will be necessary to reconstruct a scientifically useful proof mass state. The DISCOS sensor will have to be continuously calibrated from the inflight data to achieve this reconstruction.

Ray, J. C.↗
NASA NTRS1983

Evidence for a low-altitude origin of lightning on Venus

Radio emissions attributed to lightning on Venus have been recorded by Venera 11 and 12 and by the Pioneer Orbiter. The Venera descent records are compared to patterns of radio propagation within the Venusian atmosphere and an explanation is found for some timing trends that, if correct, indicates the lightning was below 33 km in altitude.

Croft, T. A.↗
NASA NTRS1983

Comparison of low-altitude wind-shear statistics derived from measured and proposed standard wind profiles

Wind shear statistics were calculated for a simulated set of wind profiles based on a proposed standard wind field data base. Wind shears were grouped in altitude in altitude bands of 100 ft between 100 and 1400 ft and in wind shear increments of 0.025 knot/ft. Frequency distributions, means, and standard deviations for each altitude band were derived for the total sample were derived for both sets. It was found that frequency distributions in each altitude band for the simulated data set were more dispersed below 800 ft and less dispersed above 900 ft than those for the measured data set. Total sample frequency of occurrence for the two data sets was about equal for wind shear values between +0.075 knot/ft, but the simulated data set had significantly larger values for all wind shears outside these boundaries. It is shown that normal distribution in both data sets neither data set was normally distributed; similar results are observed from the cumulative frequency distributions.

Usry, J. W.↗
NASA NTRS1984

Low altitude wind shear statistics derived from measured and FAA proposed standard wind profiles

Wind shear statistics were calculated for a simulated data set using wind profiles proposed as a standard and compared to statistics derived from measured wind profile data. Wind shear values were grouped in altitude bands of 100 ft between 100 and 1400 ft, and in wind shear increments of 0.025 kt/ft between + or - 0.600 kt/ft for the simulated data set and between + or - 0.200 kt/ft for the measured set. No values existed outside the + or - 0.200 kt/ft boundaries for the measured data. Frequency distributions, means, and standard deviations were derived for each altitude band for both data sets, and compared. Also, frequency distributions were derived for the total sample for both data sets and compared. Frequency of occurrence of a given wind shear was about the same for both data sets for wind shears, but less than + or 0.10 kt/ft, but the simulated data set had larger values outside these boundaries. Neglecting the vertical wind component did not significantly affect the statistics for these data sets. The frequency of occurrence of wind shears for the flight measured data was essentially the same for each altitude band and the total sample, but the simulated data distributions were different for each altitude band. The larger wind shears for the flight measured data were found to have short durations.

Dunham, R. E., Jr.↗
NASA NTRS1985

Low altitude, one centimeter, space debris search at Lincoln Laboratory's (M.I.T.) experimental test system

The majority of work performed by the Lincoln Laboratory's Space Surveillance Group, at the request of NASA, to define the near-earth population of man-made debris is summarized. Electrooptical devices, each with a 1.2 deg FOV, were employed at the GEODSS facility in New Mexico. Details of the equipment calibration and alignment procedures are discussed, together with implementation of a synchronized time code for computer controlled videotaping of the imagery. Parallax and angular speed data served as bases for distinguishing between man-made debris and meteoroids. The best visibility was obtained in dawn and dusk twilight conditions at elevation ranges of 300-2000 km. Tables are provided of altitudinal density distribution of debris. It is noted that the program also yielded an extensive data base on meteoroid rates.

Taff, L. G.↗
NASA NTRS1985

Observations of magnetospheric convection from low altitudes

The high-latitude ionosphere is considered as a convenient 'viewing screen' for deducing magnetospheric convection, since the footprints of the immense volume of the magnetospheric flux tubes map to a considerably more manageable surface area. This area is, however, still very large, and an instantaneous measurement of the flow pattern over the entire high latitude region is presently not feasible. Therefore, much effort has been made in synthesizing many passes of polar orbiting spacecraft into convection patterns. The present investigation follows the development of a description of the global convection pattern and its dependence on the interplanetary magnetic field (IMF). The convection pattern is described in terms of the plasma flow speed and direction. Attention is given to the southward interplanetary magnetic field and the northward interplanetary magnetic field.

Heelis, R. A.↗
NASA NTRS1985

Analysis of low-altitude wind speed and direction shears

Horizontal wind profile measurements recorded at the NASA 150-Meter Ground Winds Tower Facility at the Kennedy Space Center, Fla., are analyzed to evaluate wind shears known to be hazardous to the ascent and descent of conventional aircraft and the Space Shuttle. Twenty 5-s intervals of high (between 10 and 18 m/s) and gale force (18 to 33 m/s) surface winds provided instantaneous recordings every 0.1 s per speed, direction, and tower level from 3-150 m. Mathematical (maximum, mean, standard deviation) and graphical (percentage frequency distribution) descriptions of absolute, positive, and negative speed and direction shears with altitude (six vertical layers) and along flight path (one horizontal distance) are presented as functions of the intensity categories and significant values.

Alexander, M. B.↗
NASA NTRS1984

Evidence of magnetic merging from low-altitude spacecraft and ground-based experiments

Magnetic-reconstruction models of magnetospheric phenomena and the airborne and ground-based measurement data supporting such models are reviewed and illustrated with diagrams and graphs. The primary emphasis is on the correlation of east-west flows on the dayside with the y component of the interplanetary magnetic field (IMF), and consideration is given to z-component IMF effects, magnetospheric convection for a northward IMF, and evidence based on particle distributions.

Reiff, P. H.↗
NASA NTRS1985

Low-altitude field-aligned electrons

Earlier measurements of field-aligned electrons are reexamined in the light of the more recent and comprehensive data available from both rocket and satellite observations. It is found that: (1) field aligned electrons are associated with evening, midnight, and cusp auroras; (2) rocket data associate the field aligned electrons with active auroral forms and on the edges of moving discrete arcs, predominantly the leading edge; and (3) the spatial/temporal scale of the field-aligned events seen by satellites is a few seconds or tens of kilometers, while the rocket time scale extends from seconds to hundreds of seconds. Recent acceleration mechanisms involving turbulence are discussed.

Arnoldy, R. L.↗
NASA NTRS1985

Simulation evaluation of display/FLIR concepts for low-altitude, terrain-following helicopter operations

Trials were run on a six degree of freedom combat helicopter simulator to evaluate head-down displays with integrated FLIR imagery for terrain-following, course-steering, and transition to approach and hover helicopter pilot tasks. Three display formats were tested, providing varying levels of symbology for, e.g., the flight path angle, pitch-attitude data, vertical speed, altitude, etc. The pilots were also furnished flight director guidance, i.e., terrain-following, course steering, airspeed hold, and approach to hover. All the displays permitted the pilots to fly satisfactory mission in the CGI scenarios. The results revealed that the pilots preferred a nonconformal FLIR display superposition.

Swenson, H. N.↗
NASA NTRS1986

Lightning strikes to a NASA airplane penetrating thunderstorms at low altitudes

The NASA Storm Hazards program was dedicated during the 1984 storm season to a study of lightning strikes on an instrumented F-106B aircraft, during penetrations of thunderstorms at altitudes lower than the 6-8 km center of lightning flash density. These altitudes coincide with the negative charge region of thunderstorms. An analysis of the correlation between the UHF band radar data obtained and TV images of lightning strikes indicates that, with a known aircraft position relative to the radar, the lightning channel motion can be adequately interpreted on the basis of radar echo evolution.

Mazur, V.↗