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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Spacecraft reorientation via slewing about nonorthogonal axes

A mathematical procedure was developed which determines the exact slews relative to any known axes. The axes may be completely arbitrary; their coordinates merely reside on a data base which can be changed at any time without affecting the software. Given the desired reorientation, the procedure then determines all of the two-legged or three-legged slews which will accomplish the reorientation. For example, there are 12 possible permutations of three axes, and if they are orthogonal each always has two solutions. The nonorthogonal case, on the other hand, gives some surprising results, including the nonexistence of a solution: Consider a large reorientation where the three axes are nearly collinear. In this connection, it can be shown that every three-axis reorientation can be accomplished by three successive slews, if and only if the middle axis is perpendicular to the other two.

Davenport, P. B.↗
NASA NTRS1973

ERTS-1 views the Great Lakes

The meteorological content of ERTS images, particularly mesoscale effects of the Great Lakes and air pollution dispersion is summarized. Summertime lake breeze frontal clouds and various winter lake-effect convection patterns and snow squalls are revealed in great detail. A clear-cut spiral vortex over southern Lake Michigan is related to a record early snow storm in the Chicago area. Marked cloud changes induced by orographic and frictional effects on Lake Michigan's lee shore snow squalls are seen. The most important finding, however, is a clear-cut example of alterations in cumulus convection by anthropogenic condensation and/or ice nuclei from northern Indiana steel mills during a snow squall situation. Jet aircraft condensation trails are also found with surprising frequency.

Lyons, W. A.↗
NASA NTRS1973

The velocity structure of the lunar crust.

Seismic refraction data, obtained at the Apollo 14 and 16 sites, when combined with other lunar seismic data, allow a compressional wave velocity profile of the lunar near-surface and crust to be derived. The regolith, although variable in thickness over the lunar surface, possesses surprisingly similar seismic properties. Underlying the regolith at both the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is low-velocity brecciated material or impact derived debris. Key features of the lunar seismic velocity profile are: (1) velocity increases from 100 to 300 m/sec in the upper 100 m to about 4 km/sec at 5 km depth, (2) a more gradual increase from about 4 km/sec to about 6 km/sec at 25 km depth,(3) a discontinuity at a depth of 25 km, and (4) a constant value of about 7 km/sec at depths from 25 km to about 60 km.

Kovach, R. L.↗
NASA NTRS1973

Tektite ablation - Some confirming calculations.

The calculation of tektite ablation has been redone, taking into account transient effects, internal radiation, melting and nonequilibrium vaporization of the glass, and the drag effect of the flanges. It is found that the results confirm the earlier calculations of Chapman and his group and of Adams and his co-workers. The general trend of the results is not sensitive to reasonable changes of the physical parameters. The ablation is predominantly by melting rather than by vaporization at all velocities up to 11 km/sec; this is surprising in view of the lack of detectable melt flow in most tektites. Chemical effects have not been considered.

O'Keefe, J. A., III↗
NASA NTRS1973

Variations in density and chemical composition at 120 km from chemical and dynamical processes.

Atmospheric parameters show both systematic and random patterns of behavior at 120 km altitude. Variations in density, temperature, pressure, and especially atomic oxygen concentration are important. The variations are particularly significant because constant boundary conditions at this altitude have commonly been assumed in atmospheric model making. It is surprising how well the assumption of constant boundary conditions has served over the past decade. However, their use has probably introduced erroneous concepts into the field of atmospheric structure, or at least held off the recognition and introduction of important new concepts. The variations at 120 km are caused by changes in energy input into the upper atmosphere, including internal gravity waves and tidal energy from below, and changes in the transport processes within the atmosphere.

Johnson, F. S.↗
NASA NTRS1973

Magnetospheric plasma motion during a sudden commencement.

A sudden commencement occurred at 2348 UT on Feb. 15, 1967, when the ATS-1 satellite was about 2 hr past local noon at a geocentric distance of 6.6 earth radii. Plasma was observed by the Suprathermal Ion Detector first to flow in the antisolar direction, as expected, but then to flow westward, for about 2 min, at about 50 km/sec. Analysis of ground magnetograms suggests that the surprising westward flow, which must have involved an electric field of about 10 mV/m at 6.6 earth radii, resulted from the ionosphere's reaction to the sudden commencement. Beginning about 2 min before the start of the westward flow at ATS-1, ground magnetometers near the foot of the ATS-1 field line typically recorded magnetic-field deflections of about 70 gamma, to the northeast. Taking the ground observations, assuming a height-integrated Hall conductivity of 1 mho, and a standoff distance of 7.2 earth radii inferred from Explorer 33 solar-wind data, a magnetospheric electric field is derived which agrees in magnitude and direction with that required to produce the observed flow at ATS-1.

Lin, C.-A.↗
NASA NTRS1973

Mapping of the major structures of the African rift system

The author has identified the following significant results. The new fault map of the main Ethiopian rift, based on aerial photo compilations, generally agrees well with the maps produced from ERTS-1 imagery. Characteristically, the ERTS-1 imagery shows some of the major faults to be more extensive than realized from ground studies, though due to the angle of sun illumination some east-facing fault scarps are not easily discernible on the imagery. The Corbetti caldera, shows up surprisingly poor on the imagery, and is shown to be an adjunct to an older, larger caldera now occupied by Lakes Awassa and Shallo. The lithological boundaries mapped by De Paola in the rift are difficult to discern on the ERTS-1 imagery. On the Somalian plateau, east of the rift, a denuded caldera has been identified as the source of much of the lavas of the Batu Mountains. Further south, ERTS-1 imagery amplifies the structural and lithological mapping of the Precambrian rocks of the Shakisso-Arero area, and of the Kenya-Ethiopia border region. For the first time with some certainty, it is now possible to say that on the evidence of the ERTS-1 imagery, the Western Rift does not continue northeast beyond the Sudan-Uganda border, and is thus not to be sought in western Ethiopia.

Mohr, P. A.↗
NASA NTRS1973

Evaluation of ERTS-1 data applications to geologic mapping, structural analysis and mineral resource inventory of South America with special emphasis on the Andes Mountain region

The author has identified the following significant results. Segerstrom delineated many grabens (down-faulted blocks) not shown on published maps of Argentina nor of South America. The faults that border the grabens are better appreciated in ERTS-1 imagery than on air photos or on the ground because of the masking affect of alluvial fill deposits. In frame no. 1188-13545 a change in local prevailing wind direction from east to southeast is noted in sand streams. In frame no. 1188-13551 it was surprising to see that Solar del Hombre Muerto was covered with water. In November 1971 the investigator has driven across the salt pan several times without wetting his wheels. It was also possible to differentiate the following rock and soil classes: Granites, metamorphic, volcanic rocks, Tertiary and Quaternary clastic deposits and salt pans. Portions of railroads and highways as well as small towns were identified. In frame no. 1188-13551 the Incahuasi Gold Mine and the Tincalayu Borax Mine were located.

Carter, W. D.↗
NASA NTRS1974

Geologic and mineral and water resources investigations in western Colorado, using Skylab EREP data

The author has identified the following significant results. Discovery of three major north-trending, throughgoing faults in the Front Range, previously mapped only as isolated segments, demonstrates the utility of space photography and may lead to reinterpretation of the Front Range tectonic style. Faulting and alteration appear to be the most useful indicators of mineralization in central Colorado. These phenomena appear on Skylab photography as tonal lineaments and color anomalies. Twenty-three lineaments have been mapped in the San Juan Mountains, the longest of which is 156 km long. Twelve lineaments intersect or are tangent to calderas. Intrusive domes are aligned along lineaments, but calderas appear to occur at the intersections of major lineaments. Lineaments can be recognized on some EREP passes but not on other passes over the same area. The difference is attributed to solar elevation effects. Bedding attitudes can be photogeologically estimated down to surprisingly low dips, on the order of + or - 1-2 deg, and attitudes can be subdivided easily into quantitative groups. The primary application of Skylab photography to geologic mapping in montane areas is clearly limited to regional mapping at scales smaller than 1:24,000.

Lee, K.↗
NASA NTRS1974

Six-color photometry of Iapetus, Titan, Rhea, Dione and Tethys

The extensive photometric observations of Titan, Iapetus, Rhea, Dione and Tethys have made it possible to separate the solar phase and orbital phase contributions to the observed light variations of these satellites. For Titan, the wavelength dependence of its solar phase coefficient has been obtained. This dependence should prove useful in constructing future model atmospheres. The other four satellites show a surprising array of different photometric behaviors. Despite these differences, all four satellites have similar spectral reflectivities. Clearly Iapetus, Rhea, Dione and Tethys are complex objects, varying substantially from one another in surface structure and/or composition.

Noland, M.↗
NASA NTRS1974

Silicon ions below 100 km: A case for SiO2(+)

Silicon ions are normally detected at altitudes above 100 km and within sporadic E layers. Traces have rarely been observed within the more permanent metallic layer near 93 km. This is surprising since silicon is an important constituent of chondritic meteorites, which ablate material in this region to provide a primary source of the metallic species observed there. Evidence is presented that Si(+)ions form SiO2(+) at the lower altitudes, and exist in this ionic state prior to recombination. A rocket launched from El Arenosillo, Spain on 3 July 1972, at 0743 LMT, during the predicted period of the Beta Taurids meteor shower, passed through a continuous belt of metallic ions that began near 85 km, ended near 115 km, and exhibited an order of magnitude increase in the form of a layer near 114 km. Si(+)was measured in and below the ledge down to 103 km. It showed a rapid decrease below this height. Radiative association is offered as a primary mechanism for SiO2(+) production.

Goldberg, R. A.↗
NASA NTRS1973

Abundances in the Crab Nebula

The bright visual-wavelength emission lines in spectra of filaments in the Crab Nebula cannot be used to derive unique values for the relative abundances of elements there, even under a simplifying assumption that heating is due entirely to photoionization by the Crab's nonthermal continuum. However, a range of possibilities may be estimated. By mass, helium is more abundant than hydrogen; but the mass fraction of heavier elements may be surprisingly small. Such conclusions are subject to modification if a noticeable fraction of the energy density involves fast particles around 1 MeV.

Davidson, K.↗
NASA NTRS1973

Doppler broadening effect on collision cross section functions - Deconvolution of the thermal averaging

The surprising feature of the Doppler problem in threshold determination is the 'amplification effect' of the target's thermal energy spread. The small thermal energy spread of the target molecules results in a large dispersion in relative kinetic energy. The Doppler broadening effect in connection with thermal energy beam experiments is discussed, and a procedure is recommended for the deconvolution of molecular scattering cross-section functions whose dominant dependence upon relative velocity is approximately that of the standard low-energy form.

Bernstein, R. B.↗
NASA NTRS1973

Magnetic properties and granulometry of metallic iron in lunar breccia 14313

Based on a detailed study of time-dependent or viscous remanence (VRM), thermoremanence (TRM) and magnetic granulometry of soil breccia 14313, single-domain particles of iron 100 to 200 A in size are proposed as the major carriers of natural remanence (NRM) in this rock. The VRM of 14313 is unusually intense and exhibits a logarithmic time decrease of VRM which ceases fairly abruptly after a time about equal to the original exposure to the field. The partial TRM spectrum reveals both a high-blocking-temperature fraction, scarcely affected by AF demagnetization to 1000 Oe, and an unusual concentration of blocking temperatures just above room temperature. The former fraction would contribute a very hard and stable component to any NRM of lunar origin, but the latter fraction, which accounts for the pronounced VRM of 14313 and undoubtedly has imparted a large viscous NRM component in the earth's field, is also surprisingly hard. A substantial portion (20 to 40%) is not demagnetized by an 800-Oe field.

Dunlop, D. J.↗
NASA NTRS1974

Coincidence degree and periodic solutions of neutral equations

A study is made of the problem of existence of periodic solutions for some nonautonomous neutral functional differential equations. It is essentially an application of a basic theorem on the Fredholm alternative for periodic solutions of some linear neutral equations recently obtained by Hale (1973) and of a generalized Leray-Schauder theory developed by Mawhin (1972, and to appear). Although their proofs are surprisingly simple, the obtained results are nontrivial extensions to the neutral case of a number of recent existence theorems for periodic solutions of functional differential equations.

Hale, J. K.↗
NASA NTRS1973

Review of Kaufman thruster development at the Lewis Research Center - 1973

Work on Kaufman thruster development completed during the years 1971 and 1972 is reviewed. Thrusters tested have ranged in size from 2.5-cm to 150-cm diameters, in thrust from 0.4 to 4300 mN, and in power from 0.03 to 203 kW. A 2.5-cm thruster was briefly tested and found to have surprisingly high thruster efficiency. Emphasis is placed on thruster system reliability and lifetime as previous work has increased thruster efficiency to a high level. Work also proceeds on definition of thruster-spacecraft interactions. Major R&D efforts are directed at present into two areas of thruster size: a 5-cm to 8-cm diameter thruster to be used for station keeping and attitude control of geosynchronous spacecraft; and a 30-cm diameter thruster to be used for primary propulsion in a 3- to 7-thruster array for solar electric propulsion of interplanetary spacecraft.

Kerslake, W. R.↗
NASA NTRS1974

The reliability of the daily quick look solar wind velocities as indicators of interplanetary activity

It is shown that the daily quick look solar wind velocities based on the Ames Research Center solar wind plasma data obtained on the Pioneer spacecraft are surprisingly reliable indicators of interplanetary activity. These velocities can appropriately be used in correlation studies with an average accuracy of plus or minus 5%. This accuracy reflects the 'jitter' in the solar wind velocity during quiescent intervals and across high-speed streams.

Intriligator, D. S.↗