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All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Structure and variations of the heterosphere

Atmospheric composition is kept almost homogeneous to a height of approximately 90 km (the homosphere) by mixing; above 100 km (the heterosphere), diffusive separation of the atmospheric constituents occurs. The heterosphere is dominated by two energy sources: solar extreme ultraviolet radiation and the solar wind. Many large variations are observed in this region and they can all be related, directly or indirectly, to variations in the intrinsic intensity of these two sources and to variations in the location of the sources relative to the observer. Atmospheric models can be successfully constructed in which the temperature and density variations are empirically related to solar and geomagnetic parameters. Some of the more recent findings concerning the structure and variations in the heterosphere are presented.

Jacchia, L. G.↗
NASA NTRS1971

Back contamination.

Discussion of the concept and implications of back contamination and of the ways and means for its prevention. Back contamination is defined as contamination of the terrestrial biosphere with organisms or materials returned from outer space that are capable of potentially harmful terrestrial activity. Since the question of whether or not life exists on other planets may, in reality, not be answered until many samples are returned to earth for detailed study, requirements for the prevention of back contamination are necessary. A review of methods of microbiologic contamination control is followed by a discussion of the nature of back contamination and its risk levels, contamination sources and locations, and possible defenses against back contamination. The U.S. lunar back contamination program is described and shown to provide a valuable basis for further refining the technology for the control of planetary back contamination.

Phillips, G. B.↗
NASA NTRS1971

X-ray observation of a new soft source in Cygnus.

The location of the new X-ray source, designated Cygnus X-6, is discussed. The polycarbonate window counter detected Cyg X-6 only in the pulse-height interval from 0.5 to 1.3 keV. A total of 44 counts was acquired from the source above a diffuse X-ray and non-X-ray background of 18 plus or minus 3 counts. The polycarbonate pulse-height spectrum for Cyg X-6 is presented together with the calculated counter response to three different model source spectra.

Coleman, P. L.↗
NASA NTRS1972

The extended X-ray source at M87.

It is shown that the X-ray source in Virgo must be intimately associated with the galaxy M87, as evidenced by the coincidence of the source centroid location with the galaxy. Although the presented results do not completely explain the origin of the X rays from the Virgo cluster, they do indicate that the bulk of the emission does not come from the nucleus or the jet, and they also indicate the presence of strong energy processes in a region surrounding M87. One view of the origin of these X rays is that they are due to relativistic electrons ejected from M87, and interacting with magnetic or radiation fields in intergalactic space by the synchrotron of inverse Compton process. The other view holds that the X rays could be due to thermal emission from a hot plasma.

Kellogg, E.↗
NASA NTRS1973

Evaluation of radioisotope tracer and activation analysis techniques for contamination monitoring in space environment simulation chambers

Radioisotope measurement techniques and neutron activation analysis are evaluated for use in identifying and locating contamination sources in space environment simulation chambers. The alpha range method allows the determination of total contaminant concentration in vapor state and condensate state. A Cf-252 neutron activation analysis system for detecting oils and greases tagged with stable elements is described. While neutron activation analysis of tagged contaminants offers specificity, an on-site system is extremely costly to implement and provides only marginal detection sensitivity under even the most favorable conditions.

Smathers, J. B.↗
NASA NTRS1972

Preliminary mapping of the lunar magnetic field

Magnetic field measurements made with the Apollo 15 subsatellite established the existence of remanent magnetization over much of the Moon's surface. The major features of the structure of the measured remanent field are apparently associated with large craters, the most apparent detected to date being that in the vicinity of the Van de Graaff crater. A preliminary contour map of relative magnetic intensity was produced for a limited region of the Moon. A high resolution plot of the Van de Graaff region was constructed from vector data in an attempt to locate the source of the largest feature observed.

Coleman, P. J., Jr.↗
NASA NTRS1974

New theory on the reverberation of rooms

The inadequacy of the various theories which have been proposed for finding the reverberation time of rooms can be explained by an attempt to examine what might occur at a listening point when image sources of determined acoustic power are added to the actual source. The number and locations of the image sources are stipulated. The intensity of sound at the listening point can be calculated by means of approximations whose conditions for validity are given. This leads to the proposal of a new expression for the reverberation time, yielding results which fall between those obtained through use of the Eyring and Millington formulae; these results are made to depend on the shape of the room by means of a new definition of the mean free path.

Pujolle, J.↗
NASA NTRS1974

Direction finding measurements of auroral kilometric radiation

Direction finding measurements with plasma wave experiments onboard the Hawkeye-1 and IMP-8 satellites were used to locate the source region of auroral kilometric radiation. The radiation exhibits peak intensities between about 100 kHz and 300 kHz, and emits intense sporadic bursts lasting for between one half hour to several hours. The total power emitted in this frequency range exceeds 10 to the 9th power watts at peak intensity. The occurrence of the radiation is known to be closely associated with bright auroral arcs which occur in the local evening auroral regions.

Kurth, W. S.↗
NASA NTRS1975

Single- and dual-carrier microwave noise abatement in the deep space network

The NASA/JPL Deep Space Network (DSN) microwave ground antenna systems are presented which simultaneously uplink very high power S-band signals while receiving very low level S- and X-band downlinks. Tertiary mechanisms associated with elements give rise to self-interference in the forms of broadband noise burst and coherent intermodulation products. A long-term program to reduce or eliminate both forms of interference is described in detail. Two DSN antennas were subjected to extensive interference testing and practical cleanup program; the initial performance, modification details, and final performance achieved at several planned stages are discussed. Test equipment and field procedures found useful in locating interference sources are discussed. Practices deemed necessary for interference-free operations in the DSN are described. Much of the specific information given is expected to be easily generalized for application in a variety of similar installations. Recommendations for future investigations and individual element design are given.

Bathker, D. A.↗
NASA NTRS1975

Direction-finding measurements of auroral kilometric radiation

Direction-finding measurements with plasma wave experiments on the Hawkeye 1 and Imp 8 satellites are used to locate the source region of auroral kilometric radiation. This radiation has peak intensities between about 100 and 300 kHz and is emitted in intense sporadic bursts lasting for from half an hour to several hours. At peak intensity the total power emitted in this frequency range exceeds 1 billion W. The occurrence of this radiation is known to be closely associated with bright auroral arcs which occur in the local evening auroral regions. Hawkeye 1 provides direction-finding measurements of kilometric radiation from observations at high latitudes over the northern polar regions, and Imp 8 provides similar observations at large radial distances near the equatorial plane. Results from both satellites place the source of the intense auroral kilometric rdiation in the late local evening at about 22.0 hours LT and at a distance of about 0.75 earth radii from the polar axis of the earth.

Kurth, W. S.↗
NASA NTRS1976

Terrestrial kilometric radiation: 2: Emission from the magnetospheric cusp and dayside magnetosheath

Measurements of the location of sources of terrestrial kilometric radiation obtained with the lunar orbiting Radio Astronomy Explorer-2 satellite have revealed a class of emission associated with the cusp and dayside magnetosheath. At frequencies near 250 kHz this emission is observed at radial distances between 2 and 20 R sub E at magnetic latitudes of 75 deg to 80 deg and is most often detected during periods of auroral activity (AE or approximately = 250) and southward orientation of the interplanetary magnetic field vertical component. During very disturbed times, the emission at the lowest frequencies ( or approximately = 200 kHz) appears to come from the dayside magnetosheath at distances or approximately = 12 R sub E. Whenever the geomagnetic dipole is tilted significantly with respect to the ecliptic pole ( or approximately = 10 deg) the cusp emission is confined to the hemisphere containing the sub solar point. The measurements also suggest that the region of cusp emission is rather narrowly confined in longitude to within + or - a few hours of the noon meridian.

Alexander, J. K.↗
NASA NTRS1976

Lunar seismic profiling experiment natural activity study

The Lunar Seismic Experiment Natural Activity Study has provided a unique opportunity to study the high frequency (4-20 Hz) portion to the seismic spectrum on the moon. The data obtained from the LSPE was studied to evaluate the origin and importance of the process that generates thermal moonquakes and the characteristics of the seismic scattering zone at the lunar surface. The detection of thermal moonquakes by the LSPE array made it possible to locate the sources of many events and determine that they are definitely not generated by astronaut activities but are the result of a natural process on the moon. The propagation of seismic waves in the near-surface layers was studied in a qualitative manner. In the absence of an adequate theoretical model for the propagation of seismic waves in the moon, it is not possible to assign a depth for the scattering layer. The LSPE data does define several parameters which must be satisfied by any model developed in the future.

Duennebier, F. K.↗
NASA NTRS1977

Application of remote sensing in South Dakota to provide accurate inventories of agricultural crops, enhance contrast in photographic products, monitor rangeland habitat loss, map Aspen, and prepare hydrogeologic surveys

The author has identified the following significant results. Digital analysis of LANDSAT CCT's indicated that two discrete spectral background zones occurred among the five soil zone. K-CLASS classification of corn revealed that accuracy increased when two background zones were used, compared to the classification of corn stratified by five soil zones. Selectively varying film type developer and development time produces higher contract in reprocessed imagery. Interpretation of rangeland and cropped land data from 1968 aerial photography and 1976 LANDSAT imagery indicated losses in rangeland habitat. Thermal imagery was useful in locating potential sources of sub-surface water and geothermal energy, estimating evapotranspiration, and inventorying the land.

Myers, V. I.↗
NASA NTRS1977

Terrestrial kilometric radiation. II - Emission from the magnetospheric cusp and dayside magnetosheath

Measurements of the location of sources of terrestrial kilometric radiation obtained with the lunar-orbiting Radio Astronomy Explorer 2 satellite have revealed a class of emission associated with the cusp and dayside magnetosheath. At frequencies near 250 kHz, this emission is observed at radial distances between 2 and 20 earth radii at magnetic latitudes of 75 to 80 deg and is most often detected during periods of auroral activity and southward orientation of the interplanetary magnetic-field vertical component. During very disturbed times, the emission at the lowest frequencies (below about 200 kHz) appears to come from the dayside magnetosheath at distances of at least 12 earth radii. Whenever the geomagnetic dipole is tilted significantly with respect to the ecliptic pole, the cusp emission is confined to the hemisphere containing the subsolar point. The measurements also suggest that the region of cusp emission is rather narrowly confined in longitude to within a few hours of the noon meridian.

Alexander, J. K.↗
NASA NTRS1978

The prediction of fast stream front arrivals at the earth on the basis of solar wind measurements at smaller solar distances

The problems involved in the prediction of the arrival of fast solar wind streams at the earth on the basis of measurements made by space probes in the region between 0.3 and 1 AU are discussed. It is shown that arrival time predictions accurate to within a few hours that can be made at least as long as the large scale conditions on the Sun are relatively stationary as observed near the time of solar minimum. However, the latitudinal extent of the respective high speed streams is found to be important for making quantitative predictions. Coronal data sufficient for locating the sources of high speed streams can improve the precision of these predictions.

Rosenbauer, H.↗
NASA NTRS1979

Algorithms for the determination of the time delays of the signal when using unequal detectors

In treating the recorded results from detectors at different locations in space, the analysis of the time delays of signals is crucial to locating the sources of detected radiation. Because the correlation method requires the manipulation of awkward matrices to evaluate its accuracy, a solution is outlined based on minimizing the sum of the squares of signal deviations, and the algorithms for evaluating the resulting error are presented.

Novak, B. L.↗
NASA NTRS1978

Deformation and failure information from composite materials via acoustic emission

The paper reviews some principles of applying acoustic emission (AE) to the study of fiber-composite materials and structures. This review covers the basics of using AE to monitor the deformation and fracture processes that occur when fiber-composite materials are stressed. Also, new results in some areas of current research interest are presented. The following areas are emphasized: study of couplants for AE testing of composites, evaluation of a special immersion-type AE transducer, and wave propagation complications and the development of techniques for locating AE sources in Kevlar 49/epoxy composite pre

Hamstad, M. A.↗
NASA NTRS1978

The magnetization of the lunar crust as deduced from orbital surveys

A two-dimensional magnetic anomaly map of a region of intense crustal magnetization near Van de Graaff crater has been constructed from Apollo 15 and 16 subsatellite vector magnetometer observations. The mapping method used limits coverage to relatively low altitudes (65-80 km) over the Van de Graaff region along the Apollo 15 track and over the central far side highlands along the Apollo 16 track; a simple differencing technique was used to remove external noise contributions. An approximate inversion of this map using a surface plate model for source region geometry has revealed at least four different sources. No correlation between the lateral locations of these source regions and surface morphology was found; the directions of magnetization seem to be unrelated except for a strong north-south depletion. A rough antipodal correlation of the two most strongly magnetized regions yet mapped on the moon with the Imbrium and Orientale basins gives mild support to the ejecta deposit hypothesis suggested by Strangway et al. (1973) for formation of anomaly source regions.

Hood, L. L.↗