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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A very high frequency radio interferometer for investigating ionospheric disturbances using geostationary satellites. Determination of changes in exospheric electron content by a comparison of group delay and Faraday rotation

The theory and development of a VHF correlation radio interferometer for investigating ionospheric disturbances are discussed. The system was developed to receive signals from the geostationary Applications Technology Satellites. Amplitude and phase variations of the signal passing through the ionosphere can be detected by this instrument. The system consists of two superheterodyne receivers separated by a distance known as the baseline of the system. Since the system is a phase sensitive instrument, the local oscillators of the two receivers must be phase coherent. This is accomplished by using phase-locked loops for generating the local oscillators. The two signals from the separate receivers are cross-correlated by multiplying the two signals together and then time averaging the result. The sensitivity of the instrument is increased by off-setting one of the local oscillators by a small amount.

Terry, R.↗
NASA NTRS1973

Ogo 6 measurements of supercooled plasma in the equatorial exosphere.

Plasma measurements performed on Ogo 6 reveal electron and ion temperature values that on occasion appear to be well below the expected neutral gas temperature. The phenomenon is observed only at night above 500 km near the magnetic equator. It is suggested that the expansion cooling of the plasma is accomplished by downward motions of the F region plasma induced by winds or diffusion, by outward E x B drift, or more probably by the upward flow of plasma during interhemisphere transport along magnetic field lines. It is also suggested that preferential cooling of electrons because of their greater thermal conductivity should tend to give ion temperatures greater than electron temperatures during the postsunset cooling of the plasmasphere when photoelectrons are absent.

Hanson, W. B.↗
NASA NTRS1974

Exospheric temperature and composition from satellite beacon measurements

Routine measurements of the slab thickness of the ionosphere, from 1965 to 1971, are used to infer the changes in neutral temperature and ion composition at a mean latitude of 40 S. Values of neutral temperature at solar maximum are 5 to 10% above Northern Hemisphere backscatter results. The diurnal and seasonal changes agree closely with satellite drag and backscatter measurements, except that the maximum temperature occurs after sunset in winter. Winter night-time values of the O(+)/H(+) transition height were 500 km in 1965-1966, 800 km in 1968-1969, and 700 km in 1971. Changes in the transition height lag about six months behind the changes in solar flux. Diurnal variations have a minimum just before sunrise and a maximum 1 to 3 hr after noon. On winter nights the transition height descends to the level set by chemical equilibrium. On summer nights the transition height is always above this level, giving a continual production of H(+) which serves as an additional source for maintaining the night-time ionosphere in the winter hemisphere.

Titheridge, J. E.↗
NASA NTRS1975

Global exospheric temperatures and densities under active solar conditions

Temperatures measured by the OGO-6 satellite using the 6300 A airglow spectrum are compared with temperatures derived from total densities and N2 densities. It is shown that while the variation of the total densities with latitude and magnetic activity agree well with values used for CIRA (1972), the temperature behavior is very different. While the temperatures derived from the N2 density were in much better agreement there were several important differences which radically affect the pressure gradients. The variation of temperature with magnetic activity indicated a seasonal and local time effect and also a latitude and delay time variation different from previous density derived temperatures. A new magnetic index is proposed that is better correlated with the observed temperatures. The temperature variations at high latitudes were examined for three levels of magnetic activity for both solstices and equinox conditions. A temperature maximum in the pre-midnight sector and a minimum in the noon sector were noted and seasonal and geomagnetic time and latitude effects discussed. Neutral temperature, density, pressure and boundary oxygen variations for the great storm of March 8, 1970 are presented.

Wydra, B. J.↗
NASA NTRS1976

Exospheric density measurements from the drag-free satellite Triad

The Triad satellite is maintained within 1 mm of its proof mass (a small metal ball) in a purely gravitational orbit, using a drag-free control system, named Discos, as the disturbance compensation system. The Discos proof mass is surrounded by an outer shell which holds fuel tanks and cold gas jets. The shell shields the proof mass from such nongravitational forces as radiation pressure, atmospheric drag, and micrometeorite impact. Whenever these forces displace the outer shell relative to the proof mass, an error signal is generated by a capacitive bridge sensor, and the satellite is propelled by gas jets to remain centered on the proof mass when the error reaches 1 mm. Local atmospheric densities near 800 km were measured, using ball position data, and the observed accelerations were corrected for the effects of solar radiation pressure. The measured densities reveal a greater dependence on latitude than that indicated by balloon satellites, and also a dependence on longitude. Only a small dependence on Kp, however, was observed in the region where the measurements were made.

Moe, K.↗
NASA NTRS1977

Global exospheric temperatures and densities under active solar conditions

Temperatures measured by the OGO-6 satellite using the 6300 A airglow spectrum are compared with temperatures derived from total densities and N2 densities. It is shown that while the variation of the total densities with latitude and magnetic activity agree well with values used for CIRA (1972), the temperature behavior is very different. While the temperatures derived from the N2 density were in much better agreement there were several important differences which radically affect the pressure gradients. The variation of temperature with magnetic activity showed seasonal and local time variations. Neutral temperature, density, pressure and boundary oxygen variations for the storm of 8 March 1970 are presented.

Nisbet, J. S.↗
NASA NTRS1977

Mercury's helium exosphere after Mariner 10's third encounter

From Mariner 10 third encounter UV data, a value of .00045 was calculated as the fraction of the solar wind He++ flux intercepted and captured by Mercury's magnetosphere if the observed He atmosphere is maintained by the solar wind. If an internal source for He prevails, the corresponding upper bound for the global outgassing rate is estimated to be 4.5 x 10 to the 22nd power per sec. A surface temperature distribution was used which satisfies the heat equation over Mercury's entire surface using Mariner 10 determined mean surface thermal characteristics. The means stand off distance of Mercury's magnetopause averaged over Mercury's orbit was also used.

Curtis, S. A.↗
NASA NTRS1977

Interaction of the surfaces of the moon and Mercury with their exospheric atmospheres

A model of atmosphere-surface interactions on the moon and on Mercury is presented. This model rejects the traditional assumption that the atmospheric particle source is a 'saturated' absorbed surface layer of gas and instead assumes that interaction is with solid atoms bound in a lattice structure so that most collisions with the light atmospheric particles are free-free rather than free-bound. The energy accommodation per collision for He and H is dominated by first-order interaction terms and is generally less than 0.1 per collision. It follows that estimated thermal escape is drastically reduced for the light atoms on both bodies. Thus the model requires much reduced solar wind collection efficiencies for protons and alpha particles. Some peculiarities of the Mercury He and H atmospheres might possibly be explained by the nature of the gas-surface coupling.

Shemansky, D. E.↗
NASA NTRS1978

Non-thermal hydrogen in the Venus exosphere - The ionospheric source and the hydrogen budget

A nonthermal, or 'hot', Venus corona of H atoms has been observed by Mariners 5 and 10 and Venera 9. Of the sources investigated, reaction of H2 with ionospheric O(+) is still the strongest. It can explain the smaller densities but falls somewhat short of the largest (from Mariner 5). The subsequent recombination of OH(+), supplemented by solar-wind processes, may give an escape flux of 10 million atoms per sq cm/s. The low density of thermal H atoms on the day side has previously been attributed to either a large eddy diffusion coefficient or an escape flux tenfold greater than this. An alternative mechanism, suggested by Hartle and Mayr (1977) is supported: the hydrogen is swept to the night side by strong thermospheric winds. This process is analogous to the 'Johnson pump' for the terrestrial winter helium bulge. Large nightside bulges of H and H2 are predicted; the night/day density ratio is estimated to be as large as 100 for each.

Kumar, S.↗
NASA NTRS1979

Depletion of satellite atoms in a collisionless exosphere by radiation pressure

Perturbations of hydrogen atoms in Keplerian orbits are examined by analyzing the rates of change of the classical orbital elements. There are three main effects: high inclination orbits with eccentricities e at least 0.4 are forced toward the ecliptic plane within a few weeks, the perigees of direct orbits drift rapidly toward stable positions roughly westward of the planet, and satellite orbits in or near such a stable point rapidly lower their perigees and the satellite's life is ended by a collision in the atmosphere. Thus there are effects tending to diminish the number of highly eccentric orbits with distant apogees in six principal directions. The various lifetimes are compared for a sample of initial elements.

Chamberlain, J. W.↗
NASA NTRS1980

Exospheric perturbations by radiation pressure. 2: Solution for orbits in the ecliptic plane

The instantaneous rates of change for the orbital elements eccentricity, longitude of perigee from the Sun, and longitude from the Sun of the ascending node are integrated simultaneously for the case of the inclination i = 0. The results confirm the validity of using mean rates when the orbits are tightly bound to the planet and serve as examples to be reproduced by the complicated numerical solutions required for arbitrary inclination. Strongly bound hydrogen atoms escaping from Earth due to radiation pressure do not seem a likely cause of the geotail extending in the anti-sun direction. Instead, radiation pressure will cause those particles' orbits to deteriorate into the Earth's atmosphere.

Chamberlain, J. W.↗
NASA NTRS1980

Mass spectrometric measurements of the neutral gas composition of the thermosphere and exosphere of Venus

The neutral gas composition and density in the thermosphere of Venus is being measured with a quadrupole mass spectrometer on the Pioneer Venus orbiter. Data are obtained near periapsis once per day approximately 150-250 km above the surface. The principal gases in the thermosphere are CO2, CO, N2, O, N, and He. Atomic oxygen is the major constituent above 155 km on the dayside and also on the nightside up to 180 km when helium becomes the major constituent. The average values of CO2, CO, N2, O, and N remain nearly constant during day and night, but an abrupt change occurs across the terminator from a high dayside value to a low nightside value. The helium density varies in the opposite way, and a distinct bulge was observed at night near the morning terminator. The data have been used as the basis of an empirical model. Large orbit to orbit variations in densities were also observed on the nightside, suggesting perhaps strong turbulent motion in the atmosphere below. Kinetic temperatures inferred from scale heights are approximately 285 K on the dayside and 110 K at night. The average global temperature obtained from the model is 199 K.

Niemann, H. B.↗