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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Sun-weather relationships

The possible processes in the lower atmosphere of the earth initiated or controlled by changes in the output of the sun are investigated. These changes can include solar variation in radiation (as in the constant, or in specific wavelength regions), in particles (as in physical properties of the solar wind, or in solar cosmic rays, or solar-modulated galactic cosmic rays), and in the extended magnetic field of the sun (as in circumstances of the passage of interplanetary sector boundaries). Changes of short term (in the weather) as well as long term (in regional or global climate) are considered.

Source record↗
NASA NTRS1977

A synoptic approach to sun-weather investigations

The influence of the sector structure on the fundamental quantities (densities, temperatures, pressure, composition, electric and magnetic fields, etc.) in the magnetosphere, ionosphere and atmosphere is discussed, and daily synoptic observations of these quantities are recommended for future sun-weather investigations. Extended Shuttle missions are proposed to carry out these observations. Continuous observations of the interplanetary quantities such as the solar wind velocity, density, temperature and composition, the vector interplanetary magnetic field, and energetic particle fluxes through a wide range of energies are also recommended for understanding the extraterrestrial causes of terrestrial effects. The Heliocentric Spacecraft of the International Sun-Earth Explorer Project which remains 0.01 astronomical units from the earth is found to be the best means of carrying out these interplanetary observations.

Wilcox, J. M.↗
NASA NTRS1977

Apollo-Soyuz pamphlet no. 3: Sun, stars, in between

The structure of the sun and its surface temperature and brightness are discussed as background for explaining the ASTP joint experiment to photograph the solar corona from Soyuz while the Apollo spacecraft created an artificial eclipse by blocking out the sun. Stellar spectra, stellar evolution, and the Milky Way galaxy are explored in relation to the MA-083 experiment to survey the sky for extreme ultraviolet sources and background radiation. Interstellar gas and the spectrum of helium are discussed in relation to the MA-088 experiment designed to detect interstellar helium entering the solar system and to measure its density and motion.

Page, L. W.↗
NASA NTRS1978

Possible measurement of the coefficient of the second zonal harmonic of the sun's gravitational field with a solar probe

The use of radio tracking of a solar probe to estimate accurately the coefficient of the second zonal harmonic of the sun's gravitational field was examined. Preliminary results indicate that the coefficient can be estimated with a standard error of 10 to the minus 8th power or less, provided that the probe is equipped with a suitable drag-free system to compensate for the effects of non-gravitational accelerations. For signal paths that pass near the sun, dual-band ranging to the probe can provide the tracking accuracy needed to insure that the standard of error is equal to or less than 10 to minus 8th power. The possibility of achieving such accuracy with a single-band radio uplink and a dual-band downlink is discussed.

Reasenberg, R. D.↗
NASA NTRS1978

Possible measurements of J sub 2 and the sun's angular momentum with the solar probe

The metric tensor is given for describing the dynamical effects of the sun on a solar probe and the gravitational redshift of a probe-based clock in a covariance analysis for the detectability of the solar quadrupole moment and the solar angular momentum. Unknown parameters were determined by least squares fit to the probe tracking data. A polar orbit was assumed with perihelion at 5 solar radii and with an earth-sun-probe angle of 135 deg at perihelion. Tracking was assumed to be Doppler only, with a basic uncertainity of .1 mm/sec in the radial velocity. A drag-free system which could reduce nongravitational forces below the level of 2 times 10 to the minus 12th power was found necessary to preserve this same level of accuracy. Both one way and two way Doppler were supposed in order to determine the gravitational redshift as well as the pure spacecraft dynamics.

Nordtvedt, K.↗
NASA NTRS1978

Effect of sun elevation upon remote sensing of ocean color over an acid waste dump site

Photographic flights were made over an ocean acid waste dump site while dumping was in progress. The flights resulted in wide angle, broadband, spectral radiance film exposure data between the wavelengths of 500 to 900 nanometers for sun elevation angles ranging from 26 to 42 degrees. It is shown from densitometer data that the spectral signature of acid waste discharged into ocean water can be observed photographically, the influence of sun elevation upon remotely sensed apparent color can be normalized by using a single spectral band ratioing technique, and photographic quantification and mapping of acid waste through its suspended iron precipitate appears possible.

Bressette, W. E.↗
NASA NTRS1979

Contingency study for the third international Sun-Earth Explorer (ISEE-3) satellite

The third satellite of the international Sun-Earth Explorer program was inserted into a periodic halo orbit about L sub 1, the collinear libration point between the Sun and the Earth-Moon barycenter. A plan is presented that was developed to enable insertion into the halo orbit in case there was a large underperformance of the Delta second or third stage during the maneuver to insert the spacecraft into the transfer trajectory. After one orbit of the Earth, a maneuver would be performed near perigee to increase the energy of the orbit. A relatively small second maneuver would put the spacecraft in a transfer trajectory to the halo orbit, into which it could be inserted for a total cost within the fuel budget. Overburns (hot transfer trajectory insertions) were also studied.

Dunham, D. W.↗
NASA NTRS1979

Gravitational time delay in orthogonally polarized radiation passing by the sun

Two parallel investigations into the degree, if any, to which orthogonally polarized rays are deflected differently on passing through the gravitational field of the sun were previously conducted. The first involved very long and intermediate length baseline radio interferometry. The second was initially based on observations of radiation transmitted by the Pioneer 6 spacecraft, on passing behind the sun in 1968. This work was extended by using Helios-A and Helios-B spacecraft. It was calculated that the differential deflection between orthogonally polarized components is less than one part in 10 to the 7th power of the total gravitational deflection, or less than about 10 to the -7th power arc sec, in total.

Harwit, M.↗
NASA NTRS1979

Interferometric observations of the quiet sun at 8 millimeter wavelength

Results are reported for observations of a quiet region at the center of the sun with an interferometer operating at a wavelength of 8.33 mm and with an east-west baseline giving a maximum angular resolution of 28 arcsec. It is found that strong fluctuations occur over time scales of approximately 10 to 30 min and dominate the data at large hour angles, that smaller and more rapid fluctuations in both amplitude and phase are detected at all hour angles, and that the strong fluctuations are consistent with those that may be produced by the natural time variation of the fringe pattern during observation of a fixed source distribution. The weaker and more rapid fluctuations are tentatively attributed to antenna-tracking variations and the observation of features in a greatly extended source. The results are compared directly with those of two other interferometric studies of the quiet sun at millimeter wavelengths.

Janssen, M. A.↗
NASA NTRS1978

Evaluation of radiation interference in the Voyager Sun Sensor's cadmium sulfide detector

The simulation of radiation interference effects and the results of a radiation interference test on two Voyager Sun Sensor prototype detector assemblies are reported. The derivation of test levels and requirements are discussed and show that cobalt 60 gamma radiation is an effective and practical simulator of the ionization dose rate effects induced by high-energy electron flux incident on the spacecraft at a rate of 3.7 x 10 to the 8th e/sq cm-sec (10 rad(Si)/s) during closest approach to Jupiter. The test results provide information that is used to confirm an analytic correlation, and to predict satisfactory performance of a spacecraft sun sensing device having stringent angular resolution requirements. The measured detector response shows that at dose rates incident on the detector elements of 2 rad(Si)/sec, which is four times that expected during Jupiter encounter, the radiation-induced angle error is almost an order of magnitude less than that allowed by the acceptance criteria.

Clarke, T. C.↗
NASA NTRS1979

Optimal control of sun tracking solar concentrators

Application of the modern control theory to derive an optimal sun tracking control for a point focusing solar concentrator is presented. A standard tracking problem converted to regulator problem using a sun rate input achieves an almost zero steady state tracking error with the optimal control formulation. However, these control techniques are costly because optimal type algorithms require large computing systems, thus they will be used mainly as comparison standards for other types of control algorithms and help in their development.

Hughes, R. O.↗
NASA NTRS1979

Gravitational lens of the sun - Its potential for observations and communications over interstellar distances

The gravitational field of the sun acts as a spherical lens to magnify the intensity of radiation from a distant source along a semi-infinite focal line. A spacecraft anywhere on that line in principle could observe, eavesdrop, and communicate over interstellar distances, using equipment comparable in size and power with what is now used for interplanetary distances. If one neglects coronal effects, the maximum magnification factor for coherent radiation is inversely proportional to the wavelength, being 100 million at 1 millimeter. The principal difficulties are that the nearest point on the focal half-line is about 550 times the sun-earth distance, separate spacecraft would be needed to work with each stellar system of interest, and the solar corona would severely limit the intensity of coherent radiation while also restricting operations to relatively short wavelengths.

Eshleman, V. R.↗
NASA NTRS1979

The impact of Sun-weather research on forecasting

The possible impact of Sun-weather research on forecasting is examined. The type of knowledge of the effect is evaluated to determine if it is in a form that can be used for forecasting purposes. It is concluded that the present understanding of the effect does not lend itself readily to applications for forecast purposes. The limits of present predictive skill are examined and it is found that skill is most lacking for prediction of the smallest scales of atmospheric motion. However, it is not expected that Sun-weather research will have any significant impact on forecasting the smaller scales since predictability at these scales is limited by the finite grid size resolution and the time scales of turbulent diffusion. The predictability limits for the largest scales are on the order of several weeks although presently only a one week forecast is achievable.

Larsen, M. F.↗
NASA NTRS1980

Doubly-periodic orbits in the Sun-Earth-Moon system

A series of periodic orbits in the Earth-Moon circular restricted problem of three bodies was found which is ideally suited for exploring the Earth's geomagnetic tail. The mean apsidal motion of the basic highly elliptical Earth orbit was maintained at about one degree per day by a sequence of lunar swingbys, keeping the apogees in the anti-Sun direction. The orbits were periodic in reference frames rotating at both lunar and solar rates. Apogee distances were alternately raised and lowered by the lunar swingby maneuvers. Several categories of these Sun-synchronous double lunar swingby orbits were identified. The strength and flexibility of this trajectory concept was demonstrated with real world simulations.

Farohar, R.↗
NASA NTRS1981

Low cost transfer into useful sun-synchronous orbits at Mars

Mars oblateness has been found to provide sun-synchronous orbits, including orbits with stationary apsides, similar to those used at earth. A low mass and low data rate complement of scientific instruments placed in such orbits can provide exciting planetary investigations such as the Mars Orbiter Water Mission described herein. Use of a modest Shuttle kickstage (PAM-A) and existing spacecraft hardware makes this mission low-cost. A preliminary mission and spacecraft design is described. The major emphasis of the paper is on the mechanics of heliocentric transfer for the 1986 and 1988 launch opportunities, Martian sun-synchronous orbit geometries, injectable mass capabilities, and methods of achieving these scientifically useful orbits.

Glickman, R. E.↗
NASA NTRS1981

The energy balance in coronal holes and average quiet-sun regions

Emission measure curves are presented for average coronal hole and quiet-sun spectra taken during the Skylab mission by Vernazza and Reeves (1978), and the curves are used to discuss the energy balance in each region. Close-coupling calculations are used for the Be sequence, assuming a 10 level ion; for B sequence ions mainly distorted wave calculations in an 11 level ion are used, but close-coupling cross sections are used for some ions; for C and Mg sequence ions, distorted wave calculations are used with 15 and 10 level ions, respectively, and close-coupling results are used for Li-like ions with two levels. Results are presented and include the following: the coronal hole spectrum shows a smaller slope in the emission measure distribution, consistent with the expected outflow effects. It is concluded that the simple constant pressure models of static coronal loops of constant cross section are basically able to match the observed emission measure distribution of the average quiet sun between 1,000,000 and 10,000,000 K. However, the cell center and network distributions are respectively steeper and shallower than predicted by the detailed cooling curve.

Raymond, J. C.↗
NASA NTRS1980

The ancient sun: Fossil record in the earth, moon and meteorites; Proceedings of the Conference, Boulder, CO, October 16-19, 1979

Papers are presented concerning theories of solar variability and their consequences for luminosity, particle emission and magnetic field changes within the past 4.5 billion years, and on the records of such solar behavior in lunar, meteoritic and terrestrial materials. Specific topics include the neutrino luminosity of the sun, the relation of sunspots to the terrestrial climate of the past 100 years, solar modulation of galactic cosmic rays, the historical record of solar activity, C-14 variations in terrestrial and marine reservoirs, and solar particle fluxes as indicated by track, thermoluminescence and solar wind measurements in lunar rocks. Attention is also given to the spin-down of the solar interior through circulation currents and fluid instabilities, grain surface exposure models in planetary regoliths, rare gases in the solar wind, nitrogen isotopic variations in the lunar regolith, the influence of solar UV radiation on climate, and the pre-main sequence evolution of the sun and evidence of the primordial solar wind in the electromagnetic induction heating of the asteroids and moon.

Pepin, R. O.↗
NASA NTRS1980

Rotational history of the sun: Spin-down of the interior by circulation currents and fluid instabilities

A number of astronomical observations show that solar-type stars begin the main-sequence stage with surface rotation rates which are much greater than that of the sun. The subsequent decrease in the surface rotation rate is due to the braking torque exerted by magnetically-coupled mass loss (the solar wind). The direct braking action of the solar wind should be confined to the convective envelope so the rotation of the radiative interior remains an open question. After reviewing the relevant astronomical data, we describe how angular momentum could be transported out of the radiative interior by fluid instabilities and estimate the time scales for such transport. This picture is used to construct an evolutionary model of the sun, which predicts the present rotation of the radiative interior. The results of such a model are interpreted in terms of the measured oblateness of the solar surface.

Endal, A. S.↗