SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
An overview is presented of the development, verification, and recent implementation of the NASA-GSFC ionospheric model for satellite tracking data corrections. This model was incorporated into the Goddard Trajectory Determination System which is providing continuous trajectory computation support for the lunar orbiting Radio Astronomy Explorer-B launched on 10 June 1973.
A study of the circular polarization structure of solar active regions has been made from data obtained at 3.5 mm wavelength, using the 36-ft-diam radio telescope of the National Radio Astronomy Observatory at Kitt Peak, Arizona. The angular resolution of the telescope at this wavelength is 1.2 min. All important active regions observed at 3.5 mm are bipolar in nature; the degree of polarization ranges from 1 to about 2%. These oppositely polarized components correspond with the Mt. Wilson magnetic regions of opposite polarity; the line of zero polarization delineates the neutral line between the regions of opposite polarity on magnetograms. The longitudinal magnetic fields at the level of 3.5-mm emission computed from the degree of polarization are found to be several hundred gauss.
The empirical information on protostars is reviewed. 'Globules' are described, found to have the typical range of stellar masses and with gaseous compositions now well known thanks largely to radio astronomy. They also contain particulate matter identified as silicates, ice, and probably graphite and other carbon compounds. Current knowledge of the degree of stability of the planetary orbits over the past 4.5 b.y. is summarized. The statistics on the frequency and masses of asteroids and information on the Kirkwood gaps, both empirical and theoretical, are cited. An analogous discussion is made for the Rings of Saturn, including its extension observed in 1966 to the fourth Saturn satellite, Dione. The three main classes of meteorites - irons, stones, and carbonaceous chondrites - all appear to be of asteroidal origin and they yield the most direct evidence on the early thermal history of the solar system. The author sees in this evidence definite confirmation of the cold origin of the planetary system, followed by a hot phase due to the evolving sun that caused the dissolution of the solar nebula.
Before selecting the most suitable testing technique in a particular case, it has to be considered which of the two methods duplicates better the distribution of vibration responses to be expected during the actual launch phase. An investigation is conducted of the case of a large, low density spacecraft launched by a vehicle which produces significant acoustic noise and transmits relatively little vibration through the mechanical path provided by the vehicle structure in the area of the spacecraft interface. Criteria for vibration-acoustic equivalence are discussed along with tests conducted with the Synchronous Meteorological Satellite, the Radio Astronomy Explorer, and the Orbiting Geophysical Spacecraft. The investigation indicates that the vibration test is generally a poor substitute for an acoustic study.-
A survey of the galactic background radiation at 3.93 and 6.55 MHz is presented for the region between declinations of -60 and +60 deg. The observations were obtained with the 229-m traveling-wave V-antenna on the Radio Astronomy Explorer-1 satellite with an angular resolution of the order of one steradian. The results are consistent with the findings of high-resolution ground-based surveys at low frequencies and provide a first step in extending such observations over the whole sky.
The various subdisciplines of high-energy astrophysics are surveyed in a series of articles which attempt to give an overall view of the subject as a whole by emphasizing the basic physics common to all fields in which high-energy particles and quanta play a role. Successive chapters cover cosmic ray experimental observations, the abundances of nuclei in the cosmic radiation, cosmic electrons, solar modulation, solar particles (observation, relationship to the sun acceleration, interplanetary medium), radio astronomy, galactic X-ray sources, the cosmic X-ray background, and gamma ray astronomy. Individual items are announced in this issue.
The three-element interferometer of the National Radio Astronomy observatory and the two-element interferometer of the Hat Creek Observatory have been used to observe the fine structure of the sun at 11.1-, 3.7-, and 1.3-cm wavelengths. Solar active regions have been synthesized at 11.1- and 3.7-cm wavelengths with angular resolutions of 9 and 3 arc sec, respectively. Structural components on the scale of a few seconds of arc have also been detected in the quiet-sun and flare regions.
Recent technological developments have enabled application of the techniques of radio astronomy to problems of earth and ocean physics. To illustrate these applications, we review results from the 19.35 GHz Electrically Scanned Microwave Radiometer (ESMR) now in operation on Nimbus 5. A composite image of the earth made from ESMR observations taken between January 12 and January 16, 1973 illustrates the wide range of physical effects in single channel microwave observations. Multi-frequency observations made from aircraft have demonstrated an even greater potential for satellite radiometry when several frequencies and polarizations are used simultaneously. As an illustration of the considerations required in multi-channel radiometry, we discuss the choice of frequencies for the Scanning Multichannel Microwave Radiometer (SMMR) planned for the Nimbus G satellite.
Goddard activities are reported for 1973. An eight-year flight schedule for projected space missions is presented. Data acquired by spacecraft in the following disciplines are described: stellar ultraviolet, stellar X-rays, stellar gamma rays, solar radiation, radio astronomy, particles/fields, magnetosphere, aurora, and the upper atmosphere.
A mathematical procedure for analyzing the heat conductivity of the lunar surface is discussed. The solution is based on homogeneous and laminated moon models and considers the effects of radioactive elements conveyed to the lunar surface by melting. The various parameters which introduce uncertainties into the numerical analysis are identified. The application of data obtained from radio astronomy and from analyses of lunar samples returned by the Apollo flights is explained. Tables of data are included to show the types and amounts of radioactive materials which have been identified.
The requirements, conceptual design, tradeoffs, procedures, and techniques for orbital assembly of the support structure of the microwave power transmission system and the radio astronomy telescope are described. Thermal and stress analyses, packaging, alignment, and subsystems requirements are included along with manned vs. automated and transportation tradeoffs. Technical and operational concepts for the manned and automated maintenance of satellites were investigated and further developed results are presented.
Two dimensional source locations of individual terrestrial kilometric radiation (TKR) events were measured by the Radio Astronomy Explorer-2 (RAE-2) spacecraft in lunar orbit. Although the average source location is above the polar regions near the earth there are a significant number of events which occur at 7 RE from the earth. Furthermore, there is considerable evidence for multiple sources and source motion over the time scale of tens of minutes. Recent TKR mechanism theories which assume that the emission occurs at or near the local electron gyrofrequency would predict generation much closer to the earth's surface. It was suggested that alternative emission mechanisms (other than gyroemission) are required to explain all TKR events.
Microwave radiometer techniques were evaluated for use in atmospheric path length correction of Pacific Plate Motion Experiment interferometer measurements. It is shown that passive microwave radiometry allows precise measurement of the brightness temperature of the sky. It is also noted that the technological requirements of radiometers are very different from the requirements of radio astronomy. The technology was used in the construction of radiometers which are sufficient for use in the path length correction problem. A simulation study shows that, when combined with surface meteorology data, passive microwave radiometer data would allow a determination of the path length correction to better than 2 cm at the zenith. By a careful choice of frequencies, a dual frequency system would allow a measurement of the path length correction to better than 4 cm at zenith angles as great as 60 deg. Because of the wide range of weather conditions to be expected for the PPME sites (which include Alaska, Hawaii and Massachusetts), it will probably be necessary to use a separate correction algorithm for each site.
Ambient electron concentrations derived from observations with the Radio Astronomy Explorer 1 antenna capacitance probe have been compared with upper hybrid resonance measurements from the same spacecraft. From this comparison an empirical correction factor for the capacitance probe measurements has been derived. The differences between the two types of measurements is attributed to sheath effects.
Observations are presented of lunar occultations of the earth at 250 kHz obtained with the Radio-Astronomy-Explorer-2 satellite which were used to derive two dimensional maps of the location of the sources of terrestrial kilometric radiation (TKR). By examining the two dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere, the average three dimensional location of the emission regions can be estimated. Although TKR events at 250 kHz can often be observed at projected distances corresponding to the 250 kHz electron gyro or plasma level (approximately 2 earth radii), many events are observed much farther from the earth (between 5 and 15 earth radii). Dayside emission apparently in the region of the polar cusp and the magnetosheath and night emission associated with regions of the magnetotail are examined. The nightside emission is suggestive of a mechanism involving plasma sheet electron precipitation in the pre-midnight sector.
Continuing testing and refinement of the remote controlled, unattended automated pulsar observing station is noted, along with routine pulsar observations of 22 pulsars. Radar observations of geostationary satellite are discussed. Current status of the 400-kW X-band radar is reported along with routine automatic testing of the stability-reliability of the DSS 13 maser-receiver noise adding radiometer combination. A failure in the Faraday rotation receiving system is noted along with discussion in some detail of the activities of the high power transmitter maintenance facility. Continuation of receiver phase stability testing, specifically the effects of temperature on coaxial cables, is discussed and results reported. A demonstration at full power of the microwave power transmission facility is noted and routine support of the planetary radio astronomy experiment is discussed. Transmission of master clock synchronization signals to overseas DSN stations is also reported.
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.
The potential uses and techniques for the shuttle spacelab Millimeter Wave Large Aperture Antenna Experiment (MWLAE) are documented. Potential uses are identified: applications to radio astronomy, the sensing of atmospheric turbulence by its effect on water vapor line emissions, and the monitoring of oil spills by multifrequency radiometry. IF combining is preferable to RF combining with respect to signal to noise ratio for communications receiving antennas of the size proposed for MWLAE. A design approach using arrays of subapertures is proposed to reduce the number of phase shifters and mixers for uses which require a filled aperture. Correlation radiometry and a scheme utilizing synchronous Dicke switches and IF combining are proposed as potential solutions.