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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 343 records · Page 19
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NASA NTRS1972

Backscatter of solar resonance radiation. I.

Calculation of the angular dependence of the intensity of solar Lyman alpha resonantly scattered from neutral interstellar hydrogen which has penetrated the solar system. A simple model which essentially neglects temperature effects, but which includes gravity, radiation pressure, photoionization and charge exchange is used for this calculation. The results are then compared with the observations. The resonant scattering of He I 584 A is also treated.

Johnson, H. E.↗
NASA NTRS1972

The determination of the satellite orbit of Mariner 9.

This paper presents a comprehensive analysis of the Mars orbital phase of the Mariner 9 trajectory as determined from Earth based radio data. Both the method and accuracy of the orbit determination process are reviewed. Analysis is presented to show the effects of Mars gravity model and node in the plane of the sky errors on the accuracy of orbit determination. In addition the long term evolution of the orbit from insertion to date is presented, and is decomposed into effects from the Mars gravity field, n-body perturbations, and solar radiation pressure. Since the orbit period is nearly commensurable with the Mars rotational period, the orbit experiences significant resonance perturbations. The primary perturbation is in-track with a maximum amplitude of 1000 km and a wavelength of 39 revolutions.

Born, G. H.↗
NASA NTRS1972

Comet Tails of Type 2

A summary is presented of a theory for the head and tail regions of Type 2 (dust) comets, wherein dust particles having a wide distribution of sizes are assumed to be released from the comet nucleus in an essentially continuous manner in time during the period of distinctive cometary phenomena. The dust particles are assumed to be accelerated radially outward from the nucleus as a result of a drag interaction with the expanding gas in the comet head. In the tail region the only significant forces assumed to act on the dust particles are solar gravity and the force of solar radiation pressure. It is shown how results describing the surface density in the tail are obtained and how by matching calculated distributions with measured ones it is possible to determine the dust and head-gas emission rates as a function of time, the distribution of dust particle sizes, and the emission velocity from the inner head region as a function of particle size and time. The results of matching calculated density distributions with light intensity measurements from Comet Arend-Roland 1956h are summarized.

Probstein, R. F.↗
NASA NTRS1973

A simulation of the San Andreas fault experiment

The San Andreas Fault Experiment, which employs two laser tracking systems for measuring the relative motion of two points on opposite sides of the fault, was simulated for an eight year observation period. The two tracking stations are located near San Diego on the western side of the fault and near Quincy on the eastern side; they are roughly 900 kilometers apart. Both will simultaneously track laser reflector equipped satellites as they pass near the stations. Tracking of the Beacon Explorer C Spacecraft was simulated for these two stations during August and September for eight consecutive years. An error analysis of the recovery of the relative location of Quincy from the data was made, allowing for model errors in the mass of the earth, the gravity field, solar radiation pressure, atmospheric drag, errors in the position of the San Diego site, and laser systems range biases and noise. The results of this simulation indicate that the distance of Quincy from San Diego will be determined each year with a precision of about 10 centimeters. This figure is based on the accuracy of earth models and other parameters available in 1972.

Agreen, R. W.↗
NASA NTRS1973

Techniques for the analysis of geodynamic effects using laser data

New orbit computation techniques have been developed to realize the full precision of laser ranging measurements from a single tracking station used to accurately determine the orbital inclination of a satellite. In order to evaluate earth and ocean tidal effects on the satellite and polar motion effects on the station latitude, improved computational techniques are described for perturbations significantly influencing the satellite's inclination, such as solar radiation pressure and geopotential resonance. By using the time independent value of maximum latitude reached by the satellite as the experimental variable, orbit tracking errors caused by imprecise modelling of the gravity field and atmospheric drag have been largely overcome and made possible long term analysis of osculating elements. With these techniques, quarter day spans of laser data have been employed to monitor the inclination of the satellite to the order 0.01 arcseconds precision over a period of seventeen months.

Dunn, P. J.↗
NASA NTRS1973

Effects of resonant tesseral gravity coefficients on Viking-type orbits.

A special perturbation technique has been developed for the long-period and secular motion of a Viking-type orbiter. The technique uses a method of singly averaging the perturbations over the mean anomaly to determine changes in orbital elements due to atmospheric drag, solar radiation pressure, solar gravity, and the asymmetrical Mars gravitational field. The technique has been specialized to treat resonant tesseral gravity effects resulting from the commensurability of the satellite orbit period with the rotational period of the primary. Results are presented which indicate that orbiter lifetimes can be significantly reduced by resonant tesserals for orbits near the critical inclination. Conversely, it is shown that lifetimes can be extended via capture in resonant orbits which are stable against small drag forces.

Compton, H. R.↗
NASA NTRS1973

Origin and evolution of recent Leonid meteor showers

The four most prominent returns of the Leonid shower in the past decade fall into two broad classes. The 1966 and 1969 showers were of short duration, had a high proportion of small particles, and occured with the longest apparent delay after the perihelion passage of the parent comet Temple-Tuttle. By contrast, the 1961 and 1965 returns were of long duration, and had more large particles. The 1961 return preceded the comet. There are three major influences on particle orbits: ejection velocity, radiation pressure, and close encounters with planets. The observations are explainable in a qualitative way on the basis of the first two. But some speculation concerning the results of planetary perturbations are invoked.

Mcintosh, B. A.↗
NASA NTRS1974

Rotational bursting of interplanetary dust particles

Solar radiation pressure is discussed as a cause of rotational bursting, and of eventual elimination of asymmetric dust particles from the solar system, by a windmill effect. The predicted life span with this process for metallic particles with radii of 0.00001 to 0.01 cm ranges from 10 to 10,000 years. The effects of magnetic spin damping were considered. This depletion mechanism works faster than the traditional Poynting-Robertson effect by approximately one order of magnitude for metallic particles and about two orders of magnitude for nonmetallic particles.

Paddack, S. J.↗
NASA NTRS1973

Accretion at a magnetic pole of a neutron star

As accreted material falls to the surface of a magnetized neutron star like Cen X-3 or Her X-1, it is arrested by radiation pressure in such a manner that a hot, dense mound of nearly stationary gas protrudes above each magnetic pole. Energy released above the mound diffuses out as moderately hard X rays; but that released within the mound emerges as soft X rays from the whole surface of the neutron star.

Davidson, K.↗
NASA NTRS1975

Broadband noise generated by turbulent inflow to rotor or stator blades in an annular duct

The Green's function relating the radiated pressure field to the fluctuating forces on rotor or stator blades is developed in the presence of dissipation due to turbulent velocity fluctuations and sound speed fluctuations. The resonances in the output power spectrum which would occur at the cut-off frequencies in the absence of dissipation should be removed and smeared out by the incorporation of dissipation. Wave number dependence is developed for an effective eddy viscosity due to the aforementioned fluctuations in the background medium. The space-time correlation function for blade-normal velocity fluctuations on a single or on two different blades is developed in terms of the velocity correlation tensor for the inflow under the assumptions of isotropy and (Taylor) frozen behavior. The correlation function is then simplified under certain approximations and the behavior of the blade-force correlation function is inferred.

Lnae, F.↗
NASA NTRS1975

Dynamic analysis of the long-term zonal earth energy budget experiment (LZEEBE) spacecraft

The motions of the flexible LZEEBE spacecraft after injection into a circular orbit were analyzed. The spacecraft consists of three spherical balloons connected to a central hub by three long flexible booms which lie in a plane such that the angle between any pair of booms is 120 degrees. The major torques acting on the spacecraft are gravity-gradient torques and torques due to solar radiation pressure acting on the balloons which have different reflective properties. A development of the equations of motion is presented. Computer simulations indicate that the spacecraft will have random motion, provided the injection into orbit does not create conditions favorable to gravity-gradient capture.

Meirovitch, L.↗
NASA NTRS1975

Analyses of the solid earth and ocean tidal perturbations on the orbits of the GEOS-1 and GEOS-2 satellites

The luni-solar tidal perturbations in the inclination of the GEOS-I and GEOS-II satellite orbits were analyzed for the solid Earth and ocean tide conditions. Precision reduced camera and TRANET Doppler observations spanning periods of over 600 days for each satellite were used to derive mean orbital elements. Perturbations due to the earth's gravity field, solar radiation pressure, and atmospheric drag were modelled, and the resulting inclination residuals were analyzed for tidal effects. The amplitudes of the observed total tidal effects were about 1.2 arc seconds (36 meters) in the inclination of GEOS-I and 4.5 arc seconds (135 meters) for GEOS-II. The solid earth tides were then modelled using earth tide measurements, earth rotation observations, and seismic data. The resulting inclination residuals were analyzed for ocean tide parameters. The derived parameters consist of one second degree coefficient and an accompanying phase angle in a spherical harmonic expansion of the ocean tidal potential for each tidal constituent. The results are presented.

Felsentreger, T. L.↗
NASA NTRS1974

A simulation of the San Andreas fault experiment

The San Andreas fault experiment (Safe), which employs two laser tracking systems for measuring the relative motion of two points on opposite sides of the fault, has been simulated for an 8-yr observation period. The two tracking stations are located near San Diego on the western side of the fault and near Quincy on the eastern side; they are roughly 900 km apart. Both will simultaneously track laser reflector equipped satellites as they pass near the stations. Tracking of the Beacon Explorer C spacecraft has been simulated for these two stations during August and September for 8 consecutive years. An error analysis of the recovery of the relative location of Quincy from the data has been made, allowing for model errors in the mass of the earth, the gravity field, solar radiation pressure, atmospheric drag, errors in the position of the San Diego site, and biases and noise in the laser systems. The results of this simulation indicate that the distance of Quincy from San Diego will be determined each year with a precision of about 10 cm. Projected improvements in these model parameters and in the laser systems over the next few years will bring the precision to about 1-2 cm by 1980.

Agreen, R. W.↗
NASA NTRS1974

On the nature of the anti-tail of Comet Kohoutek /1973f/. I - A working model

The model derived for the anti-tail of Comet Kohoutek describes it as a flat formation, confined essentially to the comet's orbit plane and composed of relatively heavy particles (mostly in the size range 0.1-1 mm) whose motions are controlled by solar gravity and solar radiation pressure. Almost all the material was produced by the comet before perihelion at a rate about an order of magnitude higher than for Comets Arend-Roland and Bennett. The latent heat of vaporization of the particle material is estimated at 40-45 kcal/mole or higher.

Sekanina, Z.↗
NASA NTRS1975

A source for hyperbolic cosmic dust particles

Earlier analyses of the Pioneer 8 and 9 experimental meteoroid data have shown that the detectors on these two spacecraft are intercepting meteoroids with hyperbolic orbital parameters. It is shown in this paper that these results are entirely consistent with and, indeed, to be expected from other observations of the interplanetary meteoroid complex. Collisional breakup of meteoroids and post-collision radiation pressure modification of their orbits is found to be a sufficient cause for the observed results. Details of the calculations as well as of the results are presented.

Zook, H. A.↗
NASA NTRS1975

Rotational bursting of interplanetary dust particles

Solar radiation pressure can cause rotational bursting and eventual elimination from the solar system of asymmetric dust particles by a windmill effect. The life span against this process for metallic particles with radii of 0.00001-0.01 cm ranges from 10 to 10,000 years. The effects of magnetic spin damping have been considered in this estimate. This depletion mechanism works faster than the traditional Poynting-Robertson effect by approximately one order of magnitude for metallic particles and about two-orders of magnitude for nonmetallic particles.

Paddack, S. J.↗
NASA NTRS1975

Solutions of the motion of synchronous satellites with arbitrary eccentricity and inclination

A first order, semianalytical theory for the long term motion of resonant satellites is presented. The theory is valid for all eccentricities and inclinations and for all commensurability ratios. The method allows the inclusion of all the zonal and tesseral harmonics as well as luni solar perturbations and radiation pressure. The method is applied to a synchronous satellite including only the J sub 2 and J sub 22 harmonics. Global, long term solutions for this problem, eccentricity, argument of perigee, and inclination are obtained.

Nacozy, P. E.↗
NASA NTRS1975

Satellite lifetime routine user's manual

A FORTRAN coded computer program which determines secular variations in mean orbital elements of earth satellites and the lifetime of the orbit is described. The dynamical model treats a point mass satellite subject to solar and lunar disturbing gravitational fields, second, third and fourth harmonics of the earth's oblate potential, earth's atmospheric drag, and solar radiation pressure. Each of these disturbing functions may be selectively simulated. Data preparation instructions, a sample problem, and definitions of output quantities are included.

Everett, H. U.↗