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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Analytical tools and isolation of TOF events

Analytical tools are presented in two reports. The first is a probability analysis of the orbital distribution of events in relation to dust flux density observed in Pioneer 8 and 9 distributions. A distinction is drawn between asymmetries caused by random fluctuations and systematic variations, by calculating the probability of any particular asymmetry. The second article discusses particle trajectories for a repulsive force field. The force on a particle due to solar radiation pressure is directed along the particle's radius vector, from the sun, and is inversely proportional to its distance from the sun. Equations of motion which describe both solar radiation pressure and gravitational attraction are presented.

Wolf, H.↗
NASA NTRS1977

Perturbations of a close-earth satellite due to sunlight diffusely reflected from the earth. I - Uniform albedo

A semianalytic method has been developed to calculate the radiation-pressure perturbations of a close-earth satellite due to sunlight reflected from the earth. The assumptions made are that the satellite is spherically symmetric and that the solar radiation is reflected from the earth according to Lambert's Law with uniform albedo. By using expressions for the components of the radiation-pressure force due to Lochry, the expressions for the perturbations of the elements were developed into series in the true anomaly. The perturbations within a given revolution can be obtained analytically by integrating with respect to v while holding all slowly varying quantities constant. The long-range perturbations are then obtained by accumulating the net perturbations at the end of each revolution.

Lautman, D. A.↗
NASA NTRS1978

Mass loss and OH maser emission from Mira variables

The mass, radius, and luminosity of 26 Mira variables that are known OH sources of radio emission at 1612 MHz have been estimated. The time-independent solution of Salpeter's (1974) stellar-wind equation and a period-density relation are used to solve for basic stellar parameters, with the aid of the terminal expansion velocity of the OH maser cloud. Masses obtained from these calculations are consistent with other estimated values for masses of Mira variables. Good agreement is obtained when comparing the rate of mass loss as determined from Reimers's (1977) semiempirical relation with estimates of the mass-loss rate as deduced from theoretical models involving radiation pressure on grains. These calculations suggest a strong correlation between the mass-loss rate and the pulsation period. Arguments concerning the general properties of silicate grains from radiation-pressure-driven stellar-wind equations are discussed.

Michalitsianos, A. G.↗
NASA NTRS1988

The relationship between the Eddington limit, the observed upper luminosity limit for massive stars, and the luminous blue variables

The observed upper luminosity limits in the Galaxy and the LMC are compared with the Eddington limit as estimated for plane-parallel LTE model atmospheres which include the full effects of metal line opacities in the ultraviolet. It is shown that the Humphreys-Davidson (HD) limit corresponds to the locus of extremely low effective gravities. This result suggests that stars approaching the HD limit will suffer high mass-loss rates because of the reduction of the effective gravity due to radiation pressure. These high mass-loss rates ultimtely lead to the core mass fraction reaching its critical value and the reversal of the stellar evolution tracks. It is shown that radiation pressure, as an agent for producing enhanced mass loss near the HD limit, can in a natural way explain the kink in the HD limit near T(eff) roughly 10,000 K and the upper luminosity limit for yellow and red supergiants. The high mass-loss rates of the luminous blue variables, their location in the HR diagram, and their evolutionary stage are also discussed.

Lamers, Henny J. G. L. M.↗
NASA NTRS1993

Interaction of a jet with a radiation pressure-dominated atmosphere - The case of SS 433

A phenomenological model for the enigmatic object SS 433 is developed in which SS 433 is a neutron star (NS) surrounded by a dense accreted atmosphere. Jets are created close to the neutron star surface by the rapidly spinning NS, toward which matter flows at a super-Eddington rate. This supercritical accretion leads to a quasi-spherical atmosphere around the NS with very high pressure and density close to the surface. The interaction of the jet with the atmosphere as it propagates through it is discussed in detail. A boundary layer (BL) due to radiation viscosity forms between the jet and the surrounding medium. This BL can be visualized as a cocoon of low-density matter around the jet which prevents mass entrainment into the jet. A study of X-ray spectra shows how the radiation-viscous BL can explain the very small Delta v/v that is observed in the jets.

Arav, Nahum↗
NASA NTRS2018

The Formation and Early Evolution of Meteoroid Streams

Meteor showers occur when the Earth encounters a stream of particles liberated from the surface of a comet or, more rarely, an asteroid. Initially, meteoroids follow a trajectory that is similar to that of their parent comet but modified by both the outward flow of gas from the nucleus and radiation pressure. Sublimating gases impart an "ejection velocity" to solid particles in the coma; this ejection velocity is larger for smaller particles but cannot exceed the speed of the gas itself. Radiation pressure provides a repulsive force that, like gravity, follows an inverse square law, and thus effectively reduces the central potential experienced by small particles. Depending on the optical properties of the particle, the speed of the particle may exceed its effective escape velocity; such particles will be unbound and hence excluded from meteoroid streams and meteor showers. These processes also modify the heliocentric distance at which meteoroid orbits cross the ecliptic plane, and can thus move portions of the stream out of range of the Earth. This talk presents recent work on these components of the early evolution of meteoroid streams and their implications for the meteoroid environment seen at Earth.

Moorhead, Althea V.↗
NASA NTRS1984

Lageos orbit and the albedo problem

The objective was to obtain an analytic expression for the radiation pressure force on a satellite due to sunlight reflected from the Earth. The Lageos satellite undergoes unexplained along-track accelerations. These accelerations are believed to be due mainly to terrestrial radiation pressure. The effect of sunlight reflected off the surface of the Earth must thus be modeled to insure an accurate orbit for Lageos. An accurate orbit is necessary for carrying out Lageos' mission of measuring tectonic plate motion, polar motion, and Earth rotation. The present investigation focuses on a spherical harmonic approach to the problem. An equation for the force was obtained by assuming the Earth's surface reflects sunlight according to Lambert's law. The equation is an integral over the whole Earth's surface. Expressions occurring inside the integral are expressed in terms of spherical harmonics. The problem is thus reduced to integrating products of spherical harmonics.

Rubincam, D. P.↗
NASA NTRS1993

The nature of the hydrogen tori of Titan and Triton

The nature of the hydrogen tori of Titan and Triton is examined. Critical time scales of the two tori are discussed. For the Titan torus, where atom-atom collisions are not important, the time scale for solar radiation pressure to act on the system is shown to be comparable to the hydrogen lifetime due to ionization and charge exchange losses by solar, magnetospheric, and solar wind processes. The solar radiation pressure then provides a mechanism which destroys the initial azimuthal symmetry of the hydrogen atom orbits about the planet and causes atom orbits to move inward and to collide with the planet on its dusk side. For Triton, the atom-atom collision time scale dominates all other time scales in the system. The evolution of the torus is then an inherently nonlinear problem that depends upon the collisional redistribution of atom-orbit velocities in the presence of a planetary gravitational force field. This nonlinear process introduces an expansion mechanism into the torus problem which dramatically alters its structure.

Smyth, William H.↗
NASA NTRS1980

Feasibility studies for light scattering experiments to determine the velocity relaxation of small particles in a fluid

An approach for measuring the non-Markoffian component in the relaxation mechanism of a Brownian particle is proposed which combines desirable features of both the shock wave experiment and conventional light scattering experiments. It is suggested that the radiation pressure generated by a C.W. laser be used to guide an individual spherical particle to terminal velocity. At an appropriate time, the beam intensity is suddenly lowered to a value at which the radiation pressure is negligible, and the ensuing velocity relaxation is measured directly.

Acquista, C.↗
NASA NTRS2003

Laboratory Measurements of Optical Properties of Micron Size Individual Dust Grains

A laboratory program is being developed at NASA Marshall Space Flight Center for experimental determination of the optical and physical properties individual dust grains in simulated astrophysical environments. The experimental setup is based on an electrodynamic balance that permits levitation of single 0.1 - 10 micron radii dust grains in a cavity evacuated to pressures of approx. 10(exp -6) torr. The experimental apparatus is equipped with observational ports for measurements in the UV, visible, and infrared spectral regions. A cryogenic facility for cooling the particles to temperature of approx. 10-50K is being installed. The current and the planned measurements include: dust charging processes, photoelectric emissions and yields with UV irradiation, radiation pressure measurements, infrared absorption and scattering properties, and condensation processes, involving the analogs of cosmic dust grains. Selected results based on photoemissions, radiation pressure, and other laboratory measurements will be presented.

Abbas, M. M.↗
NASA NTRS1972

Radiation-driven efflux and circulation of dust in spiral galaxies.

Dust grains, which carry a net electric charge, may be driven out of the galactic disk along magnetic fields lines by radiation pressure of starlight. Large scale mixing or escape of the dust occurs along closed loops or open field lines, respectively. Mixing and escape also occur by means of instabilities of the galactic disk caused partially by radiation pressure on the grains. These processes could lead to the occurrence of a significant amount of intergalactic extinction.

Chiao, R. Y.↗
NASA NTRS1984

The dynamics and control of large flexible space structures, part 7

A preliminary Eulerian formulation of the in-plane dynamics of the proposed spacecraft control laboratory experiment configuration is undertaken when the mast is treated as a cantilever type beam and the reflector as a lumped mass at the end of the beam. Frequency and mode shapes are obtained for the open loop model of the beam system and the stability of closed loop control systems is analyzed by both frequency and time domain techniques. Environmental disturbances due to solar radiation pressure are incorporated into models of controlled large flexible orbiting platforms. Thermally induced deformations of simple beam and platform type structures are modelled and expressions developed for the disturbance torques resulting from the interaction of solar radiation pressure. Noise effects in the deterministic model of the hoop/column antenna system are found to cause a degradation in system performance. Appropriate changes in the ratio of plant noise to the measurement noise and/or changes in the control weighting matrix elements can improve transient and steady state performance.

Bainum, P. M.↗
NASA NTRS1986

Spacelab 3 drop dynamics experiments

Positioning techniques using the effects of acoustic-radiation pressure were used during the Spacelab 3 flight to carry out classical fluid dynamics experiments on liquid drops freely suspended in microgravity. Quantitative results dealing with the equilibrium shapes of acoustically rotated drops, with the response to the radiation pressure forces, and finally with the experimental measurement of surface tension have been obtained.

Trinh, E. H.↗
NASA NTRS1989

Mock gravity and the cosmic structure

The process of generating large-scale cosmic structure from the radiation-pressure or 'mock gravity' instability is studied with particular emphasis on the implications of the Berkeley-Nagoya rocket data for the submillimeter background. The linear theory of perturbations in an absorbing medium embedded in an expanding universe of radiation sources is presented. The instability sets up collapse velocities in linear perturbation theory which far exceed those from gravitational instability, so growth continues even after the instability switches off. Perturbation due to this effect is analyzed and related to the growth of large-scale cosmic structures at recent times; large-scale structure is shown to evolve very little from 1 + z about 5 to the present. Nonlinear small-scale effects of the instability are analyzed; it is shown that radiation pressure would compress gas into small, dense pressure-confined clouds with tau much greater than one.

Hogan, Craig J.↗
NASA NTRS1994

Observations of interplanetary Lyman-alpha with the Galileo Ultraviolet Spectrometer: Multiple scattering effects at solar maximum

The Galileo Ultravilet Spectrometer Experiment (UVS) obtained a partial celestial sphere map of interplanetary Lyman-alpha (IP L alpha) on 13-14 December 1990 during the first Earth encounter. The Galileo spacecraft was near the downwind axis of the local interstellar medium flow. These UVS measurements sampled the downwind, anti-sunward hemisphere. The data were modeled using a hot model of the interplanetary hydrogen density distribution with the goal of studying multiple scattering effects in the inner solar system. The derived ratio in the downwind direction of the observed brightness and a single scattering model brightness, both normalized to unity in the upwind direction, is 1.82 +/- 0.2. This brightness ratio requires a multiple scattering correction which is 36% larger than can be accounted for by theoretical calculations. The hot model may require: (1) a temperature perturbation of the interstellar wind velocity distribution or (2) an additional downstream source of interplanetary hydrogen. However, a more likely exlanation which affects the hot model is the latitude dependence of the radiation pressure. This dependence, based on the known solar L alpha flux latitude variation at solar maximum, causes a downwind brightness enhancement by preferential focusing of H-atoms with trajectory planes containing the solar poles. This result implies that radiation pressure near the solar poles is nearly independent of solar cycle and is insufficient to lead to a net repulsion of hydrogen atoms by the sun, as can occur near the ecliptic plane during the solar maximum. In addition, the UVS performed 13 observations of IP L alpha while in cruise between Venus and the Earth in 3 directions fixed in ecliptic coordinates.

Ajello, J. M.↗
NASA NTRS1973

Zonal gravity harmonics from long satellite arcs by a seminumeric method.

A zonal geopotential is presented to degree 21 from evaluation of mean elements for 21 satellites, including two of low (less than 20 deg) inclination. Each satellite is represented by an arc of at least one apsidal rotation. The lengths range from 50 to 660 days. Differential correction of the initial elements in all of the arcs, together with radiation pressure and atmospheric drag coefficients, is accomplished simultaneously with the correction for the zonal harmonics. The satellite orbits and their variations are generated by numerical integration of the Lagrange equations for mean elements. Disturbances due to precession and nutation, atmospheric drag, radiation pressure, and lunisolar gravity are added at 1- to 8-day intervals in the integrated orbits.

Wagner, C. A.↗
NASA NTRS1978

A hydrodynamic study of a slow nova outburst

The paper reports use of a Lagrangian implicit hydrodynamics computer code incorporating a full nuclear-reaction network to follow a thermonuclear runaway in the hydrogen-rich envelope of a 1.25 solar-mass white dwarf. In this evolutionary sequence the envelope was assumed to be of normal (solar) composition and the resulting outburst closely resembles that of the slow nova HR Del. In contrast, previous CNO-enhanced models resemble fast nova outbursts. The slow-nova model ejects material by radiation pressure when the high luminosity of the rekindled hydrogen shell source exceeds the local Eddington luminosity of the outer layers. This is in contrast to the fast nova outburst where ejection is caused by the decay of the beta(+)-unstable nuclei. Nevertheless, radiation pressure probably plays a major role in ejecting material from the fast nova remnants. Therefore, the sequence from slow to fast novae can be interpreted as a sequence of white dwarfs with increasing amounts of enhanced CNO nuclei in their hydrogen envelopes, although other parameters such as the white-dwarf mass and accretion rate probably contribute to the observed variation between novae.

Sparks, W. M.↗
NASA NTRS1984

Coma morphology and dust-emission pattern of periodic Comet Halley. II - Nucleus spin vector and modeling of major dust features in 1910

The continuous ejection of dust from discrete emission sources on the rotating nucleus of the Comet Halley is modelled in order to explain the evolution of spiral jets which unwind from the nucleus condensation into envelopes or halos in the comet head. The model is applied to digitally processed images of three features of the comet taken from Mount Wilson plates during the 1910 fly-by. The model permits a determination of the motion and spin vector for each emission source, its cometocentric coordinates, and a function relating particle ejection velocity to the solar radiation pressure exerted on the ejecta. It is found that the obliquity of the comet orbit's plane to its equatorial plane is 45 deg, the axis of rotation period of 17.3 days. The derived function of particle ejection velocity to the solar radiation pressure implied no contribution from grains larger than 10 microns in radius. High dust loading of gas flows from the June 1910 emission sources is indicated. It is estimated that because of the favorable approach geometry of the Gioto spacecraft during its 1986 flyby, the likelihood of encountering dense jets of dust is small.

Sekanina, Z.↗