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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The Apollo 15 regolith - Comparative petrology of drive tube 15010/15011 and drill core section 15003

Two Apollo 15 regolith cores - double drive-tube 15010/15011 and deep drill core section 15003 - were compared. The drive tube was taken from near the edge of Hadley Rille within the mare region and the drill core was taken from the landing site, approximately the same distance as the drive tube from the Apennine Front. Optical modes were done on the two cores, each of which was divided into three stratigraphic units defined by minor differences in grain size and modal abundances. Electron microprobe data were collected on the mineral and glass fragments within each unit. Fused-soil-free bulk chemistries were calculated for each unit by modal recombination, using our modal data and average compositional and density data for soil components. It is found that the drive tube and drill core section are fairly homogeneous units both chemically and modally. Both soils are submature to immature. There are, however, significant differences between the cores. The drill core shows significant enrichments of highland lithic-fragments and highland-derived minerals and glasses relative to the drive tube. These differences are attributed to the fresh nature of the drive tube soil whose major source material is mare basalt ejecta from the shallow bedrock.

Walker, R. J.↗
NASA NTRS1982

The NGC 7538 region - The distribution and dynamics of molecules compared with those of HI and H/+/

CO maps and preliminary H2S and H2CO data for the molecular cloud associated with the HII region NGC 7538 are compared with the distributions of ionized and neutral hydrogen. South of the optical HII region is a ridge of high (C-13)O column density with cold, self-absorbed HI gas just beyond it. A dense clump within thy ridge is found adjacent to the HII region in the southeast. The percentage of the hydrogen in atomic form varies from approximately 0.1% in the dense region to approximately 0.8% in the outskirts. The lower-density region of expanding gas seen next to the HII region in the southwest is attributed to the passage of a molecular dissociation wave.

Dickel, H. R.↗
NASA NTRS1982

Comparative study of subsynchronous rotating flow patterns in centrifugal compressors with vaneless diffusers

A comparative experimental investigation of the unstable operating modes of a centrifugal compressor was made. Impeller and/or diffuser rotating stall was observed, depending on the flow conditions. The measured relative rotational speed of this perturbation is cross checked with other experimental data and it is shown that the rotational speed is strongly dependent on the type of rotating stall. The diffuser absolute inlet flow angle at the onset of diffuser rotating stall agrees well with the value predicted by an existing stability criterion.

Frigne, P.↗
NASA NTRS1983

Systems design and comparative analysis of large antenna concepts

Conceptual designs are evaluated and comparative analyses conducted for several large antenna spacecraft for Land Mobile Satellite System (LMSS) communications missions. Structural configurations include trusses, hoop and column and radial rib. The study was conducted using the Interactive Design and Evaluation of Advanced Spacecraft (IDEAS) system. The current capabilities, development status, and near-term plans for the IDEAS system are reviewed. Overall capabilities are highlighted. IDEAS is an integrated system of computer-aided design and analysis software used to rapidly evaluate system concepts and technology needs for future advanced spacecraft such as large antennas, platforms, and space stations. The system was developed at Langley to meet a need for rapid, cost-effective, labor-saving approaches to the design and analysis of numerous missions and total spacecraft system options under consideration. IDEAS consists of about 40 technical modules efficient executive, data-base and file management software, and interactive graphics display capabilities.

Garrett, L. B.↗
NASA NTRS1983

A comparative study of measurements from radiosondes, rocketsondes, and satellites

Direct comparisons of operational products derived from measurements of radiance by satellites to measurements from conventional in situ sensors are important for the evaluation of satellite systems. However, errors in the in situ measurements themselves complicate such comparisons. Atmospheric temporal and spatial variability are also influential. These issues are investigated by means of a special field program composed of flights of dual radiosondes and multiple radiosondes launched near the time of NOAA-6 overpasses. Satellite derived mean layer temperatures, geopotential heights, and winds are compared with the same quantities determined from the in situ sensors. Of particular interest is the impact of in situ errors on these comparisons. It is shown that the radiosonde provides a precise pressure height relationship and therefore precise data for synoptic type use. Radar tracking of the radiosondes reveals, however, an imprecise pressure measurement which causes large differences between the actual altitude of the radiosonde and the altitude at which it is calculated to be. Radiosondes should be radar tracked and pressures calculated if the data are to be used for purposes other than synoptic use. Evaluation of rocketsonde data reveals a temperature precision of 1 to 2 K below about 55 km. Above 55 km, the precision decreases rapidly; rms differences of up to 11 K are obtained.

Nestler, M. S.↗
NASA NTRS1983

A comparative study of time-marching and space-marching numerical methods

Menees (1981) has conducted an evaluation of three different flowfield codes for the Jupiter entry conditions. However, a comparison of the codes has been made difficult by the fact that the three codes use different solution procedures, different computational mesh sizes, and a different convergence criterion. There are also other differences. For an objective evaluation of the different numerical solution methods employed by the codes, it would be desirable to select a simple no-blowing perfect-gas flowfield case for which the turbulent models are well established. The present investigation is concerned with the results of such a study. It is found that the choice of the numerical method is rather problem dependent. The time-marching and the space-marching method provide both comparable results if care is taken in selecting the appropriate mesh size near the body surface.

Gupta, R. N.↗
NASA NTRS1982

A comparative study of monocot and dicot root development in normal /earth/ and hypogravity /space/ environments

The anatomy and fine structure of roots from oat and mung bean seedlings grown under hypogravity conditions aboard NASA's Space Shuttle were examined and compared to those of roots from ground control plants grown under similar conditions. Oat roots from both sets of plants exhibited normal tissue organization and ultrastructural features, with the exception of cortex cell mitochondria, which characteristically showed a 'swollen' morphology. Flight-grown mung bean roots differed significantly from the controls in that root cap cells were somewhat disorganized and degraded in appearance, especially at the cap periphery. At the EM level, these cells exhibited a loss organelle integrity and a condensed cytoplasm. The potential significance of this finding for the putative gravity-sensing cap cells were noted.

Slocum, R. D.↗
NASA NTRS1983

Comparative analysis of large antenna spacecraft using the ideas system

A Land Mobile Satellite System (LMSS), capable of providing mobile communications for commercial and government applications in nonmetropolitan areas of the continental U.S. and Canada as an augmentation to existing and planned terrestrial systems, is being studied. The satellite system would provide 'narrow band' telecommunications services such as mobile radio, telephone, dispatch, safety, and special radio services, and thin-route fixed telephone and data services in the 806-890 MHz band and continuous emergency beacon monitoring in the 406-406.1 MHz band. A single Shuttle launch with an upper stage orbital transfer system would place the LMSS spacecraft in geosynchronous orbit over the continental U.S. in 1995 with a 10-year lifetime. The present investigation has the objective to evaluate, compare, and rank selected spacecraft concepts, to suggest design improvement to the individual concepts, and to identify technology needs.

Garrett, L. B.↗
NASA NTRS1983

A comparative study of the nonuniqueness problem of the potential equation

The nonuniqueness problem occurring at transonic speeds with the conservative potential equation is reviewed. Additional evidence supporting the idea that the nonuniqueness problem is inherent to the differential equation is given. An extensive, comparative study between potential and Euler calculations is presented. The results of the study indicate that the nonuniqueness problem is not an inviscid phenomenon, but a result of the conservative potential approximate treatment of shock waves. A new bound on the limit of validity of the potential formulation is discussed.

Salas, M. D.↗
NASA NTRS1983

Terrestrial versus Jovian VLF chorus - A comparative study

The relevant parameters of the magnetospheres of Jupiter and earth are investigated based on the wave-particle resonant interactions that are believed to be responsible for the generation of VLF chorus emissions observed on Voyager 1. Expressions are derived for the wave-particle interaction length and the nonlinearity parameter, and the values of these parameters are compared with those calculated for the earth's magnetosphere. It is determined that the typical interaction lengths are at least 2-5 times larger in the Jovian than in the terrestrial magnetosphere, and that the wave intensity necessary to reach the threshold of nonlinearity in the Jovian magnetosphere is 5-100 times lower. Measurements by Voyager 1 show that the inferred wave magnetic field intensities of the Jovian chorus are in the range of reported intensities for terrestrial chorus, probably due to the fact that the fluxes of few keV resonant particles found in the Jovian magnetosphere were typically two orders of magnitude higher. Growth rate measurements on Voyager 1 broadband wave data are employed to confirm that the temporal growth rates of Jovian chorus bursts are higher than for the earth.

Inan, U. S.↗
NASA NTRS1983

On searches for periodic pulsed emission - The Rayleigh test compared to epoch folding

The Rayleigh test has been recently invoked as a method of searching a time series for periodic pulsations. In this paper, this technique is discussed and compared to epoch folding, a technique which has had widespread use in X-ray astronomy. It is found that the Rayleigh test provides a more sensitive approach to the search for periodic pulsations when the pulses are sinusoidal or of broad duty cycle, such as those typical of the pulsing X-ray sources. Epoch folding, on the other hand, is more sensitive to the narrow pulses typical of radio pulsars.

Leahy, D. A.↗
NASA NTRS1982

Horizon sensor errors calculated by computer models compared with errors measured in orbit

Using a computer program to model the earth's horizon and to duplicate the signal processing procedure employed by the ESA (Earth Sensor Assembly), errors due to radiance variation have been computed for a particular time of the year. Errors actually occurring in flight at the same time of year are inferred from integrated rate gyro data for a satellite of the TIROS series of NASA weather satellites (NOAA-A). The predicted performance is compared with actual flight history.

Ward, K. A.↗
NASA NTRS1983

Space shuttle orbiter leading-edge flight performance compared to design goals

Thermo-structural performance of the Space Shuttle orbiter Columbia's leading-edge structural subsystem for the first five (5) flights is compared with the design goals. Lessons learned from thse initial flights of the first reusable manned spacecraft are discussed in order to assess design maturity, deficiencies, and modifications required to rectify the design deficiencies. Flight data and post-flight inspections support the conclusion that the leading-edge structural subsystem hardware performance was outstanding for the initial five (5) flights.

Curry, D. M.↗
NASA NTRS1983

Comparative assessment of LANDSAT-4 MSS and TM data quality for mapping applications in the southeast

The initial objectives of analyses of the MSS data are two-fold: (1) to evaluate the geodetic accuracy of CCT-P data of the test sites; and (2) to improve the geodetic accuracy by additional processing if the original data either do not meet pre-launch specifications or mapping requirements. The location of 45 ground control points (GCP) digitized from 35 U.S. Geological Survey 1:24,000 scale quadrangles (UTM coordinates) were identified in terms of pixel and scan line values. These 46 points are used to establish UTM position error vector distributions in the scene. As an initial check on the geometric reliability of the MSS data, 28 well-distributed GCPs were input to a program which compares the scaled image distances between all possible point pairs with the corresponding map distances and computes the distance differences; that is, the relative positional errors. The relative errors obtained from initial computations averaged about +/- 200 m. These errors could result from a number of sources, including misidentification of GCP locations, UTM coordinate errors introduced by the map digitizing process or errors resulting from data acquisition and geometric processing.

Welch, R.↗
NASA NTRS1984

High stability buffered phase comparator

A low noise RF signal phase comparator comprised of two high stability driver buffer amplifiers driving a double balanced mixer which operate to generate a beat frequency between the two RF input signals coupled to the amplifiers from the RF sources is described. The beat frequency output from the mixer is applied to a low noise zero crossing detector which is the phase difference between the two RF inputs. Temperature stability is provided by mounting the amplifiers and mixer on a common circuit board with the active circuit elements located on one side of a circuit board and the passive circuit elements located on the opposite side. A common heat sink is located adjacent the circuit board. The active circuit elements are embedded into the bores of the heat sink which slows the effect of ambient temperature changes and reduces the temperature gradients between the active circuit elements, thus improving the cancellation of temperature effects. The two amplifiers include individual voltage regulators, which increases RF isolation.

Adams, W. A.↗
NASA NTRS1984

A comparative look at sunspot cycles

On the basis of cycles 8 through 20, spanning about 143 years, observations of sunspot number, smoothed sunspot number, and their temporal properties were used to compute means, standard deviations, ranges, and frequency of occurrence histograms for a number of sunspot cycle parameters. The resultant schematic sunspot cycle was contrasted with the mean sunspot cycle, obtained by averaging smoothed sunspot number as a function of time, tying all cycles (8 through 20) to their minimum occurence date. A relatively good approximation of the time variation of smoothed sunspot number for a given cycle is possible if sunspot cycles are regarded in terms of being either HIGH- or LOW-R(MAX) cycles or LONG- or SHORT-PERIOD cycles, especially the latter. Linear regression analyses were performed comparing late cycle parameters with early cycle parameters and solar cycle number. The early occurring cycle parameters can be used to estimate later occurring cycle parameters with relatively good success, based on cycle 21 as an example. The sunspot cycle record clearly shows that the trend for both R(MIN) and R(MAX) was toward decreasing value between cycles 8 through 14 and toward increasing value between cycles 14 through 20. Linear regression equations were also obtained for several measures of solar activity.

Wilson, R. M.↗