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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

X-ray and radio emission from the compact galaxy III Zw 2

X-rays from the compact galaxy III Zw 2 have been detected with the rotating modulation collimator on board SAS 3. The (2-10-keV) flux is (4.3 + or - 0.5) by 10 to the -11th power erg/sq cm per sec, which corresponds to a luminosity of 1.4 by 10 to the 45th power erg/s at 530 Mpc. Subsequent radio observations between 1.46 and 90 GHz were made at the NRAO Very Large Array and 36-foot (11-m) installations. The radio spectrum rises sharply toward higher frequencies and, below about 100 GHz, is indicative of a self-absorbed synchrotron spectrum from an extremely compact, rapidly evolving object.

Schnopper, H. W.↗
NASA NTRS1978

The 3-dimensional radio mapping experiment /SBH/ on ISEE-C

The SBH experiment on ISEE-C will provide maps of the large scale structure of the interplanetary magnetic field from ten solar radii altitude to the earth orbit, in and out of the ecliptic. The SBH instrument will track type III solar radio bursts at 24 frequencies in the range 30 kHz-2 MHz thus providing the positions of 24 points along the line of force which guides the electrons producing the radio radiation. The antennas are two dipoles: one (90 m long) in the spin plane, the other (15 m long) along the spin axis. The receiver was designed for high sensitivity (0.3 microV in 3 kHz BW), high intermodulation rejection (80 dB/1 microV input for order 2 products), large dynamic range (70 dB), high selectivity (-30-dB response 6.5 kHz away from the center frequency of 10.7 MHz for the 3 kHz BW channels), and high reliability (expected orbital life: 3 years).

Knoll, R.↗
NASA NTRS1977

Measurements of the solar wind using spacecraft radio scattering observations

This paper reviews radio scattering measurements of the solar wind carried out with coherent, monochromatic, and point-source spacecraft signals. The observed phenomena which include spectral and angular broadening, and phase as well as intensity scintillations, have provided measurements of the solar wind previously not available from radio astronomical observations. These cover a wide range of heliocentric distances (as close as 1.7 solar radii), and large- as well as small-scale electron density fluctuations.

Woo, R.↗
NASA NTRS1978

Systems and methods for determining radio frequency interference

The presence, frequency and amplitude of radio frequency interference superimposed on communication links originating from a terrestrial region and including a relay in a geostationary spacecraft are determined by pointing a narrow beam antenna on the satellite at the terrestrial region. The level of noise radiated from the region to the antenna is measured at a terrestrial station that is usually remote from the region. Calibrating radio signals having a plurality of predetermined EIRP's (Effective Isotropic Radiated Power) and frequencies in the spectrum are transmitted from the region through the spacecraft narrow beam antenna back to the station. At the station, the levels of the received calibrating signals are separately measured for each of the frequency bands and EIRP's.

Johannsen, K. G.↗
NASA NTRS1978

Non-thermal radio emission from Saturn

Direct, strong evidence for non-thermal radio emission from Saturn exists in the hectometric data observed by Imp 6. The planet has been tentatively identified as a decametric source, but the most sensitive and most recent data fail to confirm this. At metric or decimetric wavelengths Saturn has no non-thermal emission like Jupiter's synchrotron sources. Finally, a comparative study of Earth and Jupiter radio emissions suggests lightning discharges.

Warwick, J. W.↗
NASA NTRS1978

The radio telescope RATAN 600

A six-meter radio antenna having 900 reflector elements arranged on a 579 -meter diameter circle and located in the northern part of the Caucasian Mountains is described. The elements are about 7.4 m by 2 m resulting in a total reflector surface of about 10,000 sq m. Individual elements can be adjusted by changing 260 screws and can be rotated both horizontally and vertically as well as being moved translationally in the radial direction. The circular area is equipped with a grid of tracks where four asymmetric cylindrical paraboloids serving as subreflectors are located. The directional profile or observational direction of the antenna is achieved by shifting the subreflectors and changing the position of the reflecting elements with respect to the subreflectors. Different radio sources can be observed at the same time by using different subreflectors and their associated reflector sectors. Each subreflector is connected to a receiving station. Capabilities for spectroscopic observation are discussed.

Schwartz, R.↗
NASA NTRS1978

Mobile radio interferometric geodetic systems

Operation of the Astronomical Radio Interferometric Earth Surveying (ARIES) in a proof of concept mode is discussed. Accuracy demonstrations over a short baseline, a 180 km baseline, and a 380 km baseline are documented. Use of ARIES in the Sea Slope Experiment of the National Geodetic Survey to study the apparent differences between oceanographic and geodetic leveling determinations of the sea surface along the Pacific Coast is described. Intergration of the NAVSTAR Global Positioning System and a concept called SERIES (Satellite Emission Radio Interferometric Earth Surveying) is briefly reviewed.

Macdoran, P. F.↗
NASA NTRS1979

Rocket radio measurement of electron density in the nighttime ionosphere

One experimental technique based on the Faraday rotation effect of radio waves is presented for measuring electron density in the nighttime ionosphere at midlatitudes. High frequency linearly-polarized radio signals were transmitted to a linearly-polarized receiving system located in a spinning rocket moving through the ionosphere. Faraday rotation was observed in the reference plane of the rocket as a change in frequency of the detected receiver output. The frequency change was measured and the information was used to obtain electron density data. System performance was evaluated and some sources of error were identified. The data obtained was useful in calibrating a Langmuir probe experiment for electron density values of 100/cu cm and greater. Data from two rocket flights are presented to illustrate the experiment.

Gilchrist, B. E.↗
NASA NTRS1978

Radio observations of asteroids: Results and prospects

Radio observations of the asteroids can provide information on the thermal and dielectric properties of the surface materials and because the radio emission arises somewhat below the surface, the data give some indication of layering. Observational difficulty has limited the investigations to only 6 asteroids: 1 Ceres and 324 Bamberga appear to have a layer of dust covering a more compacted material; the data on 4 Vesta cannot be matched by any current models for the surface; and the results for 18 Melpomene, 31 Euphrosyne and 433 Eros are too incomplete for firm conclusions. Future possibilities include more accurate radiometry of a few selected asteroids of different taxonomic classes and actual resolution of some of the larger objects by aperture synthesis techniques.

Dickel, J. R.↗
NASA NTRS1979

Radio observations of asteroids: Results and prospects

Radio observations of the asteroids can provide information on the thermal and dielectric properties of the surface materials and because the radio emission arises somewhat below the surface, the data give some indication of layering. Observational difficulty limited the investigations to only 6 asteroids:1 Ceres and 324 Bamberga appear to have a layer of dust covering a more compacted material; the data on 4 Vesta cannot be matched by any current models for the surface; and the results for 18 Melpomene, 31 Euphrosyne and 433 Eros are too incomplete for firm conclusions. Future possibilities include more accurate radiometry of a few selected asteroids of different tuxonomic classes and actual resolution of some of the larger objects by aperture synthesis techniques.

Dickel, J. R.↗
NASA NTRS1979

Interim radio spectrum surveillance station

Radio frequency interference at NASA's deep space stations has become a serious problem. A radio spectrum surveillance capability at these stations is needed to determine the sources of interference so that preventative measures can be taken. The first phase of a program to develop this capability was the development of a low-cost surveillance station now in operation at the Goldstone Space Communication Complex near Barstow, California. This interim surveillance station is described and findings from the use of this equipment are presented.

Hersey, D. R.↗
NASA NTRS1979

A catalog of jovian decameter-wave radio observations from 1957 - 1978

Data from over 200,000 hours of observation of Jupiter radio emission in the decameter-wavelength band, were collected from 13 observing sites and are available on magnetic tape. Observations were made at 14 fixed frequencies from 5 to 30 MHz. The characteristics of the tape recording technique and the data format are described. The combination of overlapping data from observing sites scattered world-wide lessens the effect of the earth's daily interruption of the ground-received signal. A power spectral analysis of the data shows no evidence of periodicities within the data other than the well-known influences of Jupiter, Io, and the earth. The dependence of the occurrence probability of emission on System 3 longitude and the phase of Io varies smoothly with frequency down to 15 MHz and then appears quite different at 10 MHz. The morphology of the radio sources is both complex and stable for periods of at least months and probably much longer.

Thieman, J. R.↗
NASA NTRS1978

Millimeter wavelength spectroscopy of trace atmospheric constituents from the Five College Radio Astronomy Observatory

The Five College Radio Astronomy Observatory system, located in western Massachusetts, is described. It is suggested that high sensitivity in the three-millimeter wavelength band facilitates detection and monitoring of a number of trace molecules in the earth's atmosphere as well as astonomical observation at radio wavelengths. Line formation and radiative transfer in the earth's atmosphere are discussed, and the receiver sensitivity is considered.

Huguenin, G. R.↗
NASA NTRS1978

Use of radio equipment for Space Shuttle navigation

Space Shuttle navigation is defined, in a narrow sense, as the task of maintaining adequate knowledge of vehicle position and velocity. The state of the Orbiter in terms of this goal is described by a vector of at least six elements, three for position and three for velocity, at a given time. These are referred to as the 'state vector' or simply as the state. Shuttle navigation will relay on a blend of ground-based and onboard systems. The onboard systems will be capable of state propagation at all times and will perform state determination during the latter part of the entry from orbit. The ground-based system will be capable of accurate state propagation for free-flight phases. Radio communication will be necessary in order for the ground and onboard capabilities to work as a coordinated system. The use of radio equipment for state determination is discussed for the ascent, orbit, rendezvous, descent, and abort phases of Shuttle missions.

Schiesser, E. R.↗
NASA NTRS1978

Low frequency spectra of type III solar radio bursts

Flux density spectra have been determined for 91 simple type III solar bursts observed by the Goddard Space Flight Center radio astronomy experiment on the IMP-6 spacecraft during 1971 and 1972. Spectral peaks were found to occur at frequencies ranging from 44 kHz up to 2500 kHz. Half of the bursts peaked between 250 kHz and 900 kHz, corresponding to emission at solar distances of about 0.3 to 0.1 AU. Maximum burst flux density sometimes exceeds 10 to the -14th W/sq m/Hz. The primary factor controlling the spectral peak frequency of these bursts appears to be a variation in intrinsic power radiated by the source as the exciter moves outward from the sun, rather than radio propagation effects between the source and IMP-6. Thus, a burst spectrum strongly reflects the evolution of the properties of the exciting electron beam, and according to current theory, beam deceleration could help account for the observations.

Weber, R. R.↗
NASA NTRS1979

Absorption models for low-frequency variability in compact radio sources

The consequences of the most plausible version of the absorption model for low-frequency variability in compact extragalactic radio sources are considered. The general restrictions placed on such a model are determined, and observational tests are suggested that can be used either to support the model or to discriminate among its various versions. It is shown that low-frequency variability in compact radio sources can be successfully explained by a class of models in which the flux is modulated by changes in free-free optical depth within an intervening ionized medium. Two versions of such a model are distinguished, one involving large changes in optical depth and the other, small changes. It is noted that while absorption effects are capable of causing rapid flux and structural variations at centimetric wavelengths, the models predict detailed behavior that is in direct conflict with observational data.

Marscher, A. P.↗