Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “solar constant”

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.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

The Global Infrared Energy Budget of the Thermosphere from 1947 to 2016 and Implications for Solar Variability

We present an empirical model of the global infrared energy budget of the thermosphere over the past 70 years. The F(sub 10.7), Ap, and Dst indices are used in linear regression fits to the 14.5 year time series of radiative cooling by carbon dioxide and nitric oxide measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the TIMED satellite. Databases of these indices are used to develop the radiative cooling time series from 1947. No consistent relation between the occurrence of peak sunspot number and peak infrared cooling is found over the past six solar cycles. The total infrared energy radiated by the thermosphere, integrated over a solar cycle, is nearly constant over five complete solar cycles studied. This is a direct consequence of the geoeffective solar energy also being nearly constant over the same intervals. These results provide a new metric for assessing the terrestrial context of the long‐term record of solar‐related indices.

Mlynczak, Martin G.↗
NASA NTRS1988

Ionosphere-thermosphere momentum coupling at solar maximum and solar minimum from DE-2 and AE-C data

DE-2 and AE-C measurements of plasma and neutral densities were used to derive time constants for momentum transfer (MT) to neutrals from ions in the high-latitude thermosphere. The MT time constants for solar cycle maximum (DE-2) and for solar cycle minimum (AE-C) were averaged and binned according to geomagnetic latitude and LT to provide a quantitative measure for the tightness of ion-neutral momentum coupling (MC) in the 250-350-km altitude range. Comparisons with results obtained using the Chiu and MSIS-83 empirical models have provided an indication of the accuracy with which thermospheric general circulation models quantitatively reproduce the MC between ions and neutrals in the high-latitude F-region.

Ponthieu, J. J.↗
NASA NTRS2010

A New Way that Planets can Affect the Sun

As planets orbit the Sun, the Sun also has to move to keep the total momentum of the solar system constant. The Sun's small orbital motion plus its 25 day rotation about its axis combine to invigorate some solar instabilities. Occasional convection cells at the proper phase in their short life can be strengthened by factors of two or more. This local burst of extra kinetic energy eventually reaches the surface where it can increase the intensity of solar activity. It might explain some reports in the last century of how planetary positions correlate with solar activity. This is the first effect of planets that is large enough to cause a significant response on the Sun.

Wolff, Charles↗
NASA NTRS1978

Comparative radiation resistance calculation for graded- and constant-composition n Al/x/Ga/1-x/As-p Al/z/Ga/1-z/As solar cells

The performance and radiation resistance of a new double-graded-band-gap solar cell are theoretically determined. The performance of this device is similar to that of the single-graded-band-gap cell. The power-conversion efficiencies of both graded-band-gap structures are shown to be less sensitive to minority-carrier lifetime degradation than a similar constant-composition heteroface cell.

Hutchby, J. A.↗
NASA NTRS1980

Solar zenith angle dependence of ionospheric ion and electron temperatures and density on Venus

The measurements taken during the first year of the Pioneer Venus orbiter retarding potential analyzer indicate the changes of ion and electron temperatures with solar zenith angles. The ion density decreases by an order of magnitude from dayside to nightside; median ion temperatures above 300 km are constant with the solar zenith angle below 150 deg and reach 2300 K at the ionopause. The ion temperatures below 300 km are almost constant with solar zenith angles during the dayside, but increase with the angles on the nightside. The electron temperatures suggest a constant heat flux into the electron gas at the ionopause which may be supplied by dissipation of energy by the whistler mode plasma waves at the ionopause and/or conduction of heat from the ionosheath through the mantle.

Miller, K. L.↗
NASA NTRS1977

On the high correlation between long-term averages of solar wind speed and geomagnetic activity

Six-month and yearly averages of solar-wind speed from 1962 to 1975 are shown to be highly correlated with geomagnetic activity as measured by averages of the Ap index. On the same time scale the correlation between the southward component of the interplanetary magnetic field and geomagnetic activity is poor. Previous studies with hourly averages gave opposite results. The better correlation with the southward component on an hourly time scale is explained by its large variation compared with the relatively constant solar-wind speed. However, on a yearly time scale the magnitude of the variations in both parameters are about the same. This problem can be solved by invoking an energy transfer mechanism which is proportional to the first power of the southward component and a higher power of the solar-wind speed.

Crooker, N. U.↗
NASA NTRS1973

Constrained low-thrust guidance.

Constrained low thrust guidance algorithms for three axis and spin-stabilized, constant power, solar electric propelled spacecraft on fixed time rendezvous missions are developed. A 'bang-bang' type of minimum-propellant thrust program is used. Control constraints arise from the specification that the thrust vector must remain fixed relative to the solar panels. The guidance law is derived from deterministic linear perturbation theory and is controllable to first order on trajectories containing at least two thrust arcs. The number and timing of guidance updates and the effectiveness of the guidance law in compensating for state and control estimation biases and uncertainties are discussed. Numerical comparisons between the optimal control and the restricted control case are presented on a Encke comet rendezvous.

Ungs, M. J.↗
NASA NTRS1985

Viking radio science data analysis and synthesis

Viking radio data analysis and synthesis was used for the following: (1) Solar System Model and Data Set; (2) Rotation of Mars; and (3) Solar System Constants and Tests of Relativity.

Shapiro, I. I.↗
NASA NTRS1990

The AMPTE program's contribution to studies of the solar wind-magnetosphere-ionosphere interaction

The Active Magnetospheric Particle Tracer Explorers (AMPTE) program provided important information on the behavior of clouds of plasma artificially injected into the solar wind and the earth's magnetosphere. Now that the releases are over, data from the satellites are being analyzed to investigate the processes by which the ambient solar wind mass, momentum, and energy are transferred to the magnetosphere. Work in progress at APL indicates that the solar wind is much more inhomogeneous than previously believed, that the solar wind constantly buffets the magnetosphere, and that ground observers may remotely sense these interactions as geomagnetic pulsations.

Sibeck, David G.↗
NASA NTRS1981

Latitude dependence of solar wind velocity observed at not less than 1 AU

The large-scale solar wind velocity structure in the outer heliosphere has been systematically analyzed for Carrington rotations 1587-1541 (March 1972 to April 1976). Spacecraft data were taken from Imp 7/8 at earth, Pioneer 6, 8, and 9 near 1 AU, and Pioneer 10 and 11 between 1.6 and 5 AU. Using the constant radial velocity solar wind approximation to map all of the velocity data to its high coronal emission heliolongitude, the velocity structure observed at different spacecraft was examined for latitudinal dependence and compared with coronal structure in soft X-rays and H-alpha absorption features. The constant radial velocity approximation usually remains self-consistent in decreasing or constant velocity solar wind out to 5 AU, enabling us to separate radial from latitudinal propagation effects. Several examples of sharp nonmeridional stream boundaries in interplanetary space (about 5 deg latitude in width), often directly associated with features in coronal X-rays and H-alpha were found.

Mitchell, D. G.↗
NASA NTRS1995

Sensitivity of solar g-modes to varying G cosmologies

The sensitivity of the solar g-mode oscillation spectrum to variability in the universal gravitational constant G is described. Solar models in varying G cosmologies were constructed by evolving a zero-age main-sequence stellar model to the Sun's current age, while allowing the value of G to change according to the power law G(t) proportional to t(exp -beta), where Beta approximately equals delta G/GH and H is the Hubble constant. All solar models were constrained to the observed luminosity and radius at the current age of the Sun by adjusting the helium abundance and the mixing-length parameter of the models in the usual way for standard stellar models. Low-l g-mode oscillation periods were calculated for each of the models and compared to the claimed observation of the solar g-mode oscillation spectrum by Hill & Gu (1990). If one accepts Hill & Gu's claims, then within the uncertainties of the physics of the solar model calculation, our models rule out all but (delta G/GH) less than approximately 0.05. In other words, we conclude that G could not have varied by more than 2% over the past 4.5 Gyr, the lifetime of the present-day Sun. This result lends independent support to the validity of the standard solar model.

Guenther, D. B.↗
NASA NTRS1987

Latitudinal dependence of solar wind speed

The data of King (1979, 1983) and of Hoeksema et al. (1982, 1983) are used to investigate the solar-cycle evolution of solar wind bulk speed as a function of source magnetic field strength. The effects of solar transient events are removed. The data suggest that the latitudinal gradient in background solar wind speed is steepest at solar minimum and broadest at solar maximum. The lowest and highest background speeds are found to remain fairly constant throughout the solar cycle. A function developed for the background solar wind speed is inserted into the improved kinematic code of Hakamada and Akasofu (1982), and solar wind speed and IMF are simulated for two periods in the solar cycle. The observed parameters for specific coronal hole passage are well reproduced by the analysis.

Fry, C. D.↗
NASA NTRS2002

Science Prospects from the STEREO Mission

The solar magnetic field is constantly generated beneath the surface of the Sun by the solar dynamo. To balance this flux generation, there is constant dissipation of magnetic flux at and above the solar surface. The largest phenomenon associated with this dissipation is the Coronal Mass Ejection (CME). The Solar and Heliospheric Observatory (SOHO) has provided remarkable views of the corona and CMEs, and served to highlight how these large interplanetary disturbances can have terrestrial consequences. STEREO is the next logical step to study the physics of CME origin, propagation, and terrestrial effects. Two spacecraft with identical instrument complements will be launched on a single launch vehicle in November 2007. One spacecraft will drift ahead and the second behind the Earth at a separation rate of 22 degrees per year. Observation from these two vantage points will for the first time allow the observation of the three-dimensional structure of CMEs and the coronal structures where they originate. Each STEREO spacecraft carries a complement of 10 instruments, which include (for the first time) an extensive set of BOTH remote sensing and in-situ instruments. The remote sensing suite is capable of imaging CMEs from the solar surface out to beyond Earth's orbit (1 AU), and in-situ instruments are able to measure distribution functions for electrons, protons, and ions over a broad energy range, from the normal thermal solar in wind plasma to the most energetic solar particles. It is anticipated that these studies will ultimately lead to an increased understanding, of the CME process and eventually to the ability to predict CME occurrence and thereby 'forecast' the condition of the near-Earth environment.

Davila, Joseph M.↗
NASA NTRS2003

Solar Terrestrial Relations Observatory (STEREO)

The solar magnetic field is constantly generated beneath the surface of the Sun by the solar dynamo. To balance this flux generation, there is constant dissipation of magnetic flux at and above the solar surface. The largest phenomenon associated with this dissipation is the Coronal Mass Ejection (CME). The Solar and Heliospheric Observatory (SOHO) has provided remarkable views of the corona and CMEs, and served to highlight how these large interplanetary disturbances can have terrestrial consequences. STEREO is the next logical step to study the physics of CME origin, propagation, and terrestrial effects. Two spacecraft with identical instrument complements will be launched on a single launch vehicle in November 2007. One spacecraft will drift ahead and the second behind the Earth at a separation rate of 22 degrees per year. Observation from these two vantage points will for the first time allow the observation of the three-dimensional structure of CMEs and the coronal structures where they originate. Each STEREO spacecraft carries a complement of 10 instruments, which include (for the first time) an extensive set of both remote sensing and in-situ instruments. The remote sensing suite is capable of imaging CMEs from the solar surface out to beyond Earth's orbit (1 AU), and in-situ instruments are able to measure distribution functions for electrons, protons, and ions over a broad energy range, from the normal thermal solar wind plasma to the most energetic solar particles. It is anticipated that these studies will ultimately lead to an increased understanding of the CME process and provide unique observations of the flow of energy from the corona to the near-Earth environment. An international research program, the International Heliophysical Year (IHY) will provide a framework for interpreting STEREO data in the context of global processes in the Sun-Earth system.

Davila, Joseph M.↗
NASA NTRS1977

Exact Green's function method of solar force-free magnetic-field computations with constant alpha. I - Theory and basic test cases

Exact closed-form solutions to the solar force-free magnetic-field boundary-value problem are obtained for constant alpha in Cartesian geometry by a Green's function approach. The uniqueness of the physical problem is discussed. Application of the exact results to practical solar magnetic-field calculations is free of series truncation errors and is at least as economical as the approximate methods currently in use. Results of some test cases are presented.

Chiu, Y. T.↗
NASA NTRS2003

Places Only Sails Can Go

Solar sails are a near term, low thrust, propellantless propulsion technology suitable for orbital maneuvering, station keeping, and attitude control applications for small payloads. Furthermore, these functions can be highly integrated, reducing mass, cost and complexity. The solar sail concept is based on momentum exchange with solar flux reflected from a large, deployed thin membrane. Thrust performance increases as the square of the distance to the sun. In comparison to conventional chemical systems, there are missions where solar sails are vastly more and less economical. The less attractive applications involve large payloads, outer solar system transfers, and short trip times. However, for inclination changes and station keeping at locations requiring constant thrust, the solar sail is the only economical option for missions of more than a few weeks duration. We compare the location and energies required for these applications between solar sails, advanced electric propulsion, and conventional rockets. We address the effect on mass fraction to understand solar sail mission cost and capability. Finally, the benefit of potential applications to near term science missions is reported.

Montgomery, Edward E., IV↗