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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

ITOS VHRR on-board data compression study

Data compression methods for ITOS VHRR data were studied for a tape recorder record-and playback application. A playback period of 9 minutes was assumed with a nominal 18 minute record period for a 2-to-1 compression ratio. Both analog and digital methods were considered with the conclusion that digital methods should be used. Two system designs were prepared. One is a PCM system and the other is an entropy-coded predictive-quantization, sometimes called entropy-coded DPCM or just DPCM, system. Both systems use data management principles to transmit only the necessary data. Both systems use a medium capacity standard tape recorder from specifications provided by the technical officer. The 10 to the 9th power bit capacity of the recorder is the basic limitation on the compression ratio. Both systems achieve the minimum desired 2 to 1 compression ratio. A slower playback rate can be used with the DPCM system due to a higher compression factor for better link performance at a given CNR in terms of bandwidth utilization and error rate. The report is divided into two parts. The first part summarizes the theoretical conclusions of the second part and presents the system diagrams. The second part is a detailed analysis based upon an empirically derived random process model arrived at from specifications and measured data provided by the technical officer.

Gray, R. M.↗
NASA NTRS1975

Is there an electrostatic field tangential to the dayside magnetopause and neutral line

Energy considerations are put forward which lead to the conclusion that the magnetopause current does not flow through the magnetospheric potential difference (of 60,000 V), and that the magnetopause is roughly an equipotential surface. Because of the necessary continuity of the tangential component of the electric field, this conclusion implies that no steady-state electric field exists along the neutral line located near the dayside magnetopause (in an open magnetospheric model). Since such an electric field is an essential part of the theory of merging of magnetic lines of force, it is concluded that the merging model does not hold for the electric field.

Heikkila, W. J.↗
NASA NTRS1975

Stabilizer flutter investigated by flight test

Flight flutter tests were conducted on an experimental airplane which resulted in the successful prediction of a limited amplitude stabilizer flutter at supersonic speeds. The flutter obtained was unusual in that fore and aft bending of the stabilizer carry-through structure contributed to the flutter condition. During flight tests the impending flutter condition was observed from force per unit amplitude, damping coefficient, and frequency measurements. A description is given of the physical and operational characteristics of the test equipment and telemetering facilities. A flutter analysis using measured modes and incompressible two-dimensional strip air forces yielded a conservative flutter speed. Sled tests of a similar stabilizer configuration had lead to the conclusion that flutter would not be encountered. Certain overall conclusions are reached regarding this particular flight flutter testing program and the need for a concerted research effort in this field.

Baird, E. F.↗
NASA NTRS1976

No new limit on the size distribution of gamma-ray bursts

The results of a study (Carter et. al.) of gamma ray bursts using long duration balloon exposure are analyzed. Arguments are presented against the conclusion that the size spectrum extrapolates to a power law with index from -1.0 to -0.5, and that therefore the gamma ray bursts are of galactic origin. It is claimed that the data are consistent with an upper limit over 100 times that proposed, and that therefore no conclusion can be drawn from the measurements regarding the nature or origin of gamma ray bursts. The resulting upper limit to the rate of occurrence of small bursts lies above the -1.5 index power law extrapolation of the size spectrum of known events, i.e., greater than the rate expected from an infinitely extended source region.

Cline, T. L.↗
NASA NTRS1975

Tug payload interfaces

Some conclusions reached during the IUS/Tug payload requirements compatibility study are presented. This study is concerned with all prospective Tug-payload interfaces, including detailed analysis of low-earth orbit, geosynchronous, and interplanetary missions. Tug payload requirements are discussed and summarized as to operational requirements, structural/mechanical interface, avionics interfaces, fluids interface, and environment. The shuttle impacts created by Tug/payload interfaces are examined and presented in tabular form. Major conclusions are that all payloads in the mission model can be suitably and inexpensively accommodated by the Tug and the Shuttle if standardized integration equipment is employed, that multiple payloads pose no significant integration challenge, and that a relatively small inventory of integration equipment is required to support all prospective payloads.

Runge, F.↗
NASA NTRS1976

Spectral and spatial energetics of the GISS model atmosphere

A calculation of the spectral and spatial energetics of the Goddard Institute for Space Studies (GISS) 9-level model of the global atmosphere is given. Results are presented from a model simulation of January 1973 and compared with previous model studies and an observational analysis for the Northern Hemisphere. The spectral analysis permits detailed study of those physical processes of scale larger than the grid spacing and allows indirect conclusions concerning unresolved subgrid-scale processes. Major conclusions for larger-than-grid-scale processes are that (1) the GISS model with a relatively coarse resolution of 4 deg latitude by 5 deg longitude produces significant nonlinear energy transfers; and (2) baroclinic conversion is large near planetary wave-number 6, but both the GISS model and another orographic model show a less peaked structure than nonorographic models and observations. A linear fit to the kinetic energy spectrum yields a power law of -2.6 in the wavenumber region 8 to 15. For subgrid-scale processes, the turbulence theory result of very small energy flux cascade is obtained.

Tenenbaum, J.↗
NASA NTRS1976

New vertical geodesy

The paper contains a review of the theoretical difference between orthometric heights and heights labeled geometric which are determined through use of an extraterrestrial frame of reference. The theory is supplemented with examples which portray very long baseline interferometry as a measuring system that will provide estimates of vertical crustal motion which are radically improved in comparison with those obtained from analysis of repeated geodetic levelings. The example of the San Fernando earthquake of 1971 is used to show how much estimates of orthometric and geometric height change might differ. A comment by another author is appended which takes issue with some of the conclusions of this paper. In particular, an attempt is made in the comment to rebut the conclusion that geodetic leveling is less reliable than VLBI measurements for determining relative elevation change of points separated by more than 56 km.

Whitcomb, J. H.↗
NASA NTRS1977

Solar flare activity - Evidence for large-scale changes in the past

An analysis of radar and photographic meteor data and of spacecraft meteoroid-penetration data indicates that there probably has not been a large increase in meteoroid impact rates in the last 10,000 yr. The solar-flare tracks observed in the glass linings of meteoroid impact pits on lunar rock 15205 are therefore reanalyzed assuming a meteoroid flux that is constant in time. Based on this assumption, the data suggest that the production rate of Fe-group solar-flare tracks may have varied by as much as a factor of 50 on a time scale of about 10,000 yr. No independently obtained data are known to require conflict with this interpretation. Confidence in this conclusion is somewhat qualified by the experimental and analytical uncertainties involved, but the conclusion nevertheless remains the present 'best' explanation for the observed data trends.

Zook, H. A.↗
NASA NTRS1977

Composition of the hot plasma near geosynchronous altitude

Although there were no direct measurements of the composition of the hot (keV) plasma at geosynchronous altitudes, the combination of other observations leads to the conclusion that, at least during geomagnetically disturbed periods, there are significant fluxes of ions heavier than protons in this region. Ion composition measurements below 8000 km altitude show upward streaming fluxes of both O(+) and H(+) ions in the L-region of the geosynchronous orbit. These observations are consistent with the conclusion that at least a portion of the total ion fluxes observed at geosynchronous altitude to be highly peaked near the magnetic field lines are heavier than protons and originate in the ionosphere.

Johnson, R. G.↗
NASA NTRS1977

Analysis and design of a refractive virtual image system

The optical performance of a virtual image display system is evaluated. Observation of a two-element (unachromatized doublet) refractive system led to the conclusion that the major source of image degradation was lateral chromatic aberration. This conclusion was verified by computer analysis of the system. The lateral chromatic aberration is given in terms of the resolution of the phosphor dots on a standard shadow mask color cathode ray tube. Single wavelength considerations include: astigmatism, apparent image distance from the observer, binocular disparities and differences of angular magnification of the images presented to each of the observer's eyes. Where practical, these results are related to the performance of the human eye. All these techniques are applied to the previously mentioned doublet and a triplet refractive system. The triplet provides a 50-percent reduction in lateral chromatic aberration which was the design goal. Distortion was also reduced to a minimum over the field of view. The methods used in the design of the triplet are presented along with a method of relating classical aberration curves to image distance and binocular disparity.

Kahlbaum, W. M.↗
NASA NTRS1978

Response to actual and simulated recordings of conventional takeoff and landing jet aircraft

Comparability between noise characteristics of synthesized recordings of aircraft in flight and actual recordings were investigated. Although the synthesized recordings were more smoothly time-varying than the actual recordings and the synthesizer could not produce a comb-filter effect that was present in the actual recordings, results supported the conclusion that annoyance response is comparable to the synthesized and actual recordings. A correction for duration markedly improved the validity of engineering calculation procedures designed to measure noise annoyance. Results led to the conclusion that the magnitude estimation psychophysical method was a highly reliable approach for evaluating engineering calculation procedures designed to measure noise annoyance. For repeated presentations of pairs of actual recordings, differences between judgment results for identical signals ranged from 0.0 to 0.5 db.

Mabry, J. E.↗
NASA NTRS1978

The spiral field inhibition of thermal conduction in two-fluid solar wind models

The paper reports on two-field models which include the inhibition of thermal conduction by the spiraling interplanetary field to determine whether any of the major conclusions obtained by Nerney and Barnes (1977) needs to be modified. Comparisons with straight field line models reveal that for most base conditions, the primary effect of the inhibition of thermal conduction is the bottling-up of heat in the electrons as well as the quite different temperature profiles at a large heliocentric radius. The spiral field solutions show that coronal hole boundary conditions do not correspond to states of high-speed streams as observed at 1 AU. The two-fluid models suggest that the spiral field inhibition of thermal conduction in the equatorial plane will generate higher gas pressures in comparison with flows along the solar rotation axis (between 1 and 10 AU). In particular, massive outflows of stellar winds, such as outflow from T Tauri stars, cannot be driven by thermal conduction. The conclusions of Nerney and Barnes remain essentially unchanged.

Nerney, S.↗
NASA NTRS1979

A critical review of the life sciences project management at Ames Research Center for the Spacelab Mission development test 3

A management study was initiated by ARC (Ames Research Center) to specify Spacelab Mission Development Test 3 activities and problems. This report documents the problems encountered and provides conclusions and recommendations to project management for current and future ARC life sciences projects. An executive summary of the conclusions and recommendations is provided. The report also addresses broader issues relevant to the conduct of future scientific missions under the constraints imposed by the space environment.

Helmreich, R. L.↗
NASA NTRS1978

Titan's atmosphere: Comments on haze content, methane abundance, band shapes, and hydrogen upper limit

The existence of scatterers in Titan's atmosphere was demonstrated in a paper published in the Astrophysical Journal three years ago. This conclusion was not affected by recent laboratory investigations showing that certain CH4 bands are independent of pressure because it was shown that the reflecting layer model failed to explain Titan's CH4 absorptions regardless on which portion of the curve of growth Titan's CH4 lines lie. Saturn's atmosphere was utilized along the central meridian for studies of CH4 absorption, and to show that the conclusion is insensitive to the moderate scattering there. The quite pronounced role of scattering in Titan's atmosphere strongly suggests that Titan's surface is obscured.

Trafton, L.↗
NASA NTRS1978

Integrated orbital servicing study follow-on. Volume 1: Executive summary

Orbital maintenance concepts were investigated and the equipment for one-g demonstrations of axial and radial module exchange was designed in three control modes: manual direct control, supervisory control, and manually augmented control. Significant results obtained and the conclusions drawn are presented and discussed. The overall conclusion is that on-orbit servicing should be established as an ongoing space transportation system capability.

Derocher, W. L., Jr.↗
NASA NTRS1979

A comparison of linear acoustic theory with experimental noise data for a small-scale hovering rotor

Linear acoustic calculations based on full aerodynamic data as input are presented and compared with measured cases reported by Boxwell et al. (1978). The full aerodynamic data are obtained using three programs giving radial loading, chordwise loading, and chordwise position of transition. It is shown that in the theoretical results the most significant noise source mechanism is due to blade thickness. Thus the conclusions of Boxwell et al. as to the importance of nonlinearities around the blades are upheld. These conclusions concern the width, shape and the level of the acoustic pressure calculated from linear acoustic theory. Some of the approximations involved in the application of acoustic analogy using quadrupole sources are discussed. It is necessary that the near- and far-field problems of rotating blades be treated together as shown for the case of an oscillating sphere.

Farassat, F.↗
NASA NTRS1979

IUE observations of the quasar 3C 273

IUE observations indicate that the spectrum of 3C 273 is similar to that of other large-redshift quasars. There is a large excess of flux in the range 2400 A to 5300 A, which encompasses the Balmer jump region but which does not appear to be explainable by Balmer emission. The intensity ratio of Lyman-alpha to H-beta is 5.5, in agreement with other measures and a factor 6 smaller than the recombination value. The only absorption lines in the spectrum are due to our Galaxy. There is marginal evidence for a depression of the continuum shortward of the Lyman-alpha emission line, but the errors are too large to warrant any conclusion that 3C 273 has a rich absorption-line spectrum such as that seen in large-redshift quasars. The absence of emission and absorption lines of Fe II leads to the conclusion that resonance fluorescence probably produces the visual Fe II emission lines.

Boggess, A.↗
NASA NTRS1979

Geophysical observations pertaining to solid-state convection in the terrestrial planets

Observational evidence for solid-state convection in the interiors of the terrestrial planets is reviewed. For the earth, the motion of the lithospheric plates constitutes clear evidence of large-scale convection in the mantle. Although Mars has been found to lack evidence of plate tectonics, the morphology of the Tharsis uplift and the elevation dichotomy between the northern and southern hemispheres may be evidence of mantle convection at one time. Measurements of lunar heat flow and seismic Q imply a convective mechanism limited to the lower mantle. Evidence for internal convection on Mercury consists of its dipole magnetic field and the 3/2 resonance between its rotational motion and its orbital motion, both of which can also be explained by other processes. The limited radar imagery of Venus has not yet provided conclusive evidence of either the presence or absence of convection features. It is concluded that although interior convection in terrestrial planets is implied by rheological, energy and momentum considerations, only on earth is the lithosphere thin enough to provide conclusive evidence of convection.

Phillips, R. J.↗