SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Altimetry and radar scattering data for Venus, obtained from 10 of the first 13 orbits of the Pioneer Venus orbiter, have disclosed what appears to be a rift valley having vertical relief of up to 7 kilometers, as well as a neighboring, gently rolling plain. Planetary oblateness appears unlikely to exceed 1/2500 and may be substantially smaller.
Results are reported for extensive spectrophotometric observations, over the wavelength range from 3800 to 7800 A, of the peculiar 14th-mag emission-line object Stephenson-Sanduleak (SS) 433, which has been identified with a variable nonthermal radio source and is positionally coincident with the X-ray source A1909+04. It is found that the spectrum is dominated by intense variable Balmer and He I emission, that three of the He I lines have very prominent P Cygni profiles, and that virtually all the emission features undergo changes in equivalent width on a time scale of days. Anomalous emission features are described which consist of three previously unreported, very strong, broad emission lines at unfamiliar wavelengths in the green, red, and IR, and which vary nightly in intensity, profile, and wavelength. SS 433 is inferred to be a luminous object with an absolute visual magnitude of -3.1 or brighter.
Eleven different methods for accelerating convergence of sequences and series have been tested and compared on a wide range of test problems, including both linearly and logarithmically convergent series, monotone and alternating series. All but one of these methods are already in the literature, and they include both linear and nonlinear methods. The only methods found to accelerate convergence across the board were the u and v transforms of Levin and the theta algorithm of Brezinski. The paper gives detailed comparisons of all the tested methods on the basis of number of correct digits in the answer as a function of number of terms of the series used. A theorem of Germain-Bonne states that methods of a certain form which are exact on geometric series will accelerate linear convergence. The theorem applies to theta sub 2, and we have extended it to apply to Levin's transforms. No corresponding theorem is known for logarithmic convergence, but u, v, and theta are exact on certain large classes of logarithmic series, and all tested methods lacking this property failed to accelerate some logarithmically convergent series.
Three large Venus surface features, identified previously in images obtained from earth-based radar observations, are shown by the Pioneer Venus radar mapper to be elevated 5 to 10 km above the surrounding terrain. Two of these features, one bright and the other dark, lie adjacent to each other astride the 65 N parallel between longitudes 310 E and 10 E. The combined region forms a huge tectonically uplifted plateau, surmounted by radar-bright ridges that may have either a volcanic or tectonic origin. The third feature, located at 30 N, 283 E, is radar-bright and may consist of volcanic material extruded along a fault zone. A first radar-scattering image, compiled from data obtained by the mapper in its imaging mode, shows a region north of the equator; several circular depressions seen in this area may result from meteoritic impact.
Satellite digital data from Landsat and NOAA satellites is often marred by striping or streaking errors due to variations in the response of the radiometric sensors. In this paper, we discuss the equalization of the digital data as a preprocessing step, prior to image enhancement or automatic classification. The methods described make use of statistics of the data itself to generate nonlinear or linear memory-less equalization algorithms. These algorithms, by contrast to multidimensional filtering, do not result in a loss of spatial resolution. Examples of applications to Landsat and NOAA-3 thermal infrared data are given and illustrated.
Two hydrogen-maser clocks, one at Haystack Observatory and one at the National Radio Astronomy Observatory, were synchronized by means of observations of several extragalactic radio sources on March 28, and again on September 23, 1977. Observations were made sequentially in eight 360-kHz bands distributed between about 8.4 and 8.5 GHz with spacings designed to enable the group-delay difference between the signals received at the two observatories from a given source to be estimated unambiguously, within an uncertainty of less than 1 ns set by receiver noise. The epoch and the rate differences between the observatories' clocks for each experiment were estimated by analysis of observations that spanned several hours. The application of corrections for the contributions to the delays of the antennas, feeds, receiver systems, and recorders yielded absolute determinations of the clock epoch differences. During each experiment, portable cesium clocks were flown from the U.S. Naval Observatory to the observatories and back. The traveling-clock data, analyzed in each case after the VLBI synchronization had been completed, confirmed the VLBI results to within 18 and 14 ns for the first and second experiments, respectively.
Structured programming language has been given new features and some limitations are removed. Language runs more efficiently, and concepts of top down development and modularity are extended to task management.
A laser-optical measurement system was developed to measure single blade tip clearances and average blade tip clearances between a rotor and its gas path seal in rotating component rigs and complete engines. The system is applicable to fan, compressor and turbine blade tip clearance measurements. The engine mounted probe is particularly suitable for operation in the extreme turbine environment. The measurement system consists of an optical subsystem, an electronic subsystem and a computing and graphic terminal. Bench tests and environmental tests were conducted to confirm operation at temperatures, pressures, and vibration levels typically encountered in an operating gas turbine engine.
The development of an engineering data base for aerospace batteries is discussed.
The paper presents the Faint Object Spectrograph (FOS) for the Space Telescope to provide a digitized spectra of faint astronomical objects over the 115 to 700 nm wavelength range at resolving powers of 1000 and 100. A variety of concave gratings and prisms is employed to form nearly stigmatic spectra on one of the two Digicon photon counting detectors which are optimized for two different but overlapping ranges. The scientific goals associated with quasars, active galaxies, and objects within our solar system are discussed, and the FOS optical design features, including detectors, electronics, signal processing, power supplies, and data handling are examined. The FOS structural system, mechanism, and controls are described, along with the predicted performance capabilities in the spectral and spectropolarimetry modes. Finally, system performance parameters, including spatial resolution, time resolution, noise, and efficiency are discussed.
A simple, yet effective procedure for the geometric correction of partial Landsat scenes is described. The procedure is based on the acquisition of actual and virtual control points from the line printer output of enhanced curvilinear features. The accuracy of this method compares favorably with that of the conventional approach in which an interactive image display system is employed.
Particle creation due to field interactions in an expanding Robertson-Walker universe is investigated. A model in which pseudoscalar mesons and photons are created as a result of their mutual interaction is considered, and the energy density of created particles is calculated in model universes which undergo a bounce at some maximum curvature. The free-field creation of non-conformally coupled scalar particles and of gravitons is calculated in the same space-times. It is found that if the bounce occurs at a sufficiently early time the interacting particle creation will dominate. This result may be traced to the fact that the model interaction chosen introduces a length scale which is much larger than the Planck length.
An operational procedure for use by the Corps of Engineers to acquire land use information for hydrologic planning purposes is described. The operational constraints preclude the use of dedicated, interactive image processing facilities. The procedure combines manual interpretation techniques and the batch-mode computer analysis of Landsat digital data. An example of the application of the procedure to an urban watershed is described.
The need for blade tip clearance instrumentation has been intensified recently by advances in technology of gas turbine engines. A new laser-optical measurement system has been developed to measure single blade tip clearances and average blade tip clearances between a rotor and its gas path seal in rotating component rigs and complete engines. The system is applicable to fan, compressor and turbine blade tip clearance measurements. The engine mounted probe is particularly suitable for operation in the extreme turbine environment. The measurement system consists of an optical subsystem, an electronic subsystem and a computing and graphic terminal. Bench tests and environmental tests were conducted to confirm operation at temperatures, pressures, and vibration levels typically encountered in an operating gas turbine engine.
The terrain-surface features of the Appalachian Valley and Ridge province were analyzed using Seasat synthetic aperture radar imagery. Particular attention was given to determining the efficiency and capability of this microwave imaging system for geologic mapping.
Forty-one digitally correlated Seasat synthetic-aperture radar images of land areas in North America, the Caribbean, and Western Europe are presented to demonstrate this microwave orbital imagery. The characteristics of the radar images, the types of information that can be extracted from them, and certain of their inherent distortions are briefly described. Each atlas scene covers an area of 90 X 90 kilometers, with the exception of the one that is the Nation's Capital. The scenes are grouped according to salient features of geology, hydrology and water resources, urban landcover, or agriculture. Each radar image is accompanied by a corresponding image in the optical or near-infrared range, or by a simple sketch map to illustrate features of interest. Characteristics of the Seasat radar imaging system are outlined.
A speed control device is characterized by a reference speed shaft spatially related to a heavy duty shaft, a drive train for driving the reference speed shaft at a constant angular velocity, a drive train for driving the heavy duty shaft at a variable angular velocity and a speed control assembly for continuously comparing the angular velocity of the heavy duty shaft with the angular velocity of the reference speed shaft. A brake assembly is connected to the heavy duty shaft and is adapted to respond to errors in the angular velocity of the heavy duty shaft in order to reduce the angular velocity of the heavy duty shaft to that of the reference speed shaft.
A series of tests was conducted on two 12 ampere hour nickel cadmium batteries under a simulated cycle regime using the multiple voltage versus temperature levels designed into the modular power system (MPS). These tests included: battery recharge as a function of voltage control level; temperature imbalance between two parallel batteries; a shorted or partially shorted cell in one of the two parallel batteries; impedance imbalance of one of the parallel battery circuits; and disabling and enabling one of the batteries from the bus at various charge and discharge states. The results demonstrate that the eight commandable voltage versus temperature levels designed into the MPS provide a very flexible system that not only can accommodate a wide range of normal power system operation, but also provides a high degree of flexibility in responding to abnormal operating conditions.