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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

SIRIO: One year of station keeping

The strategy followed in maintaining the station point and the results achieved are described. The method used for orbit determination is presented. Azimuth and elevation data from SHF antennas were used as input for the determination. An estimation of the uncertainty of the orbit was given and a comparison was made between determinations performed using the method here described and determinations performed using VHF ranging data. Also, the difference in using data from a single SHF station or two stations was shown. In the area of attitude determination, a study was carried out for predicting the spacecraft spin axis precession. The model used was explained and then the agreement between predicted and measured attitude outlined.

Palutan, F.↗
NASA NTRS1979

Magnetic suspension and pointing system

Apparatus for providing accurate pointing of instruments on a carrier vehicle and for providing isolation of the instruments from the vehicle's motion disturbances is presented. The apparatus includes two assemblies, with connecting interfaces, each assembly having a separate function. The first assembly is attached to the carrier vehicle and consists of an azimuth gimbal and an elevation gimbal which provide coarse pointing of the instruments by allowing two rotations of the instruments relative to the carrier vehicle. The second or vernier pointing assembly is made up of magnetic suspension and fine pointing actuators, roll motor segments, and an instrument mounting plate around which a continuous annular rim is attached which provides appropriate magnetic circuits for the actuators and the roll motor segments. The vernier pointing assembly provides six degree-of-freedom isolation from carrier motion disturbances.

Anderson, W. W.↗
NASA NTRS1978

On the nature and visibility of crater-associated streaks on Mars

The paper considers Mariner 9 and Viking data that contradict Kuzmin's (1975) hypothesis that all crater-associated wind streaks on Mars are depositional and consist of unresolved barchan-like dunes. According to Kuzmin's hypothesis, any streak can appear either bright or dark relative to its surroundings depending on the sun's position. The spacecraft images, however, show examples of dark and light streaks visible at the same azimuth angle of the sun. Evidence that bright and dark streaks differ both in morphology and in character is considered. It is suggested that the common ragged dark streaks are probably erosion scars while most bright streaks probably represent accumulations of bright dust-storm fallout.

Veverka, J.↗
NASA NTRS1978

Multiple-satellite studies of magnetospheric substorms - Plasma sheet recovery and the poleward leap of auroral zone activity

Particle observations from pairs of satellites (OGO 5 and Vela 4A and 5A) during 28 plasma sheet thickening events indicate that thickening of the nighttime plasma sheet during substorms occurs in two main stages. The early stage involves single or multiple expansions of the near-earth plasma sheet at the onset of substorm expansions (Pi 2 bursts) on the ground, while the later stage of plasma sheet recovery starts near the time of maximum auroral zone bay activity. This stage is characterized by a large-scale thickening toward higher latitudes that occurs over a broad azimuthal scale and at heights that range from the ionosphere to beyond the Vela orbit. A detailed analysis of two-satellite observations during eight plasma sheet recoveries is presented, and events that occurred within 5 min in widely separated locations at small distances from the tail's midplane as well as events that occurred concurrently in the Vela orbit and at high latitudes in the near-earth region are revealed.

Pytte, T.↗
NASA NTRS1978

The phase-integral method for radiative transfer problems with highly-peaked phase functions

Complete solutions to the radiative transfer equation, including both azimuth and depth dependence, are provided by the discrete-ordinate method of Chandrasekhar, but these solutions are often limited because of large computer requirements. This paper presents a 'phase-integral' method which greatly reduces the number of discrete ordinates needed in the solution for highly peaked phase functions. A composite quadrature method is shown to be effective in further reducing the number of discrete ordinates required for highly anisotropic phase functions. Examples are given to indicate convergence requirements and expected accuracy in the complete solution for Henyey-Greenstein and cloud-type phase functions.

Fricke, C. L.↗
NASA NTRS1978

Correlation studies of four submicron OH airglow bands during Spacelab simulation

The (7-2), (8-3), (5-1) and (6-2) bands of OH were observed from NASA's CV-990 aircraft during the Spacelab Simulation Mission. Both the average intensity and the fluctuations in intensity of each band were found to be strongly correlated to those of all other bands observed, suggesting that the excitation mechanisms for these bands are not independent processes. No significant correlation was observed between airglow intensity and latitude, azimuth, or local time for the ranges accessible during these flights. An additional ground-based experiment revealed a comparable correlation between the (6-0) and (8-3) bands.

Kieffaber, L. M.↗
NASA NTRS1979

Theory of prediction of solar eclipse as observed from a sounding rocket using rocket trajectory and eclipse ephemeris

The present paper deals with the problem of determining various solar eclipse variables as observed from a sounding rocket for various rocket trajectories. By applying the methods described to a set of trajectories, a set of boundary conditions, launch azimuth, quadrant elevation, and launch time may be selected to optimize any aspect of eclipse observation within the constraints imposed by rocket performance.

Mcgarvey, J. F.↗
NASA NTRS1979

Two-dimensional, time-dependent MHD description of interplanetary disturbances Simulation of high speed solar wind interactions

A two-dimensional, time-dependent nonlinear MHD model is used to simulate the general features of multiply-interacting, transient solar wind flows. The major advantage of the two-dimensional model over the one-dimensional one is the proper consideration of azimuthal gradients. In addition, the new model can provide contour maps for disturbed plasma properties in the equatorial plane, thereby enabling one to perform essential tests of the physical assumptions through direct comparison with space probe data.

Wu, S. T.↗
NASA NTRS1979

Numerical results for the thermal scattering functions

A recent formulation in radiative transfer defined the thermal scattering functions that characterize radiative transfer from a general plane-parallel finite medium driven solely by an internal distribution of thermal sources. Exiting diffuse intensities are expressed as space convolutions of the thermal scattering functions with any thermal source distribution. A parametric study is presented to obtain the basic structure of these scattering functions. The independent variables of these azimuthally independent functions are the direction cosine and source location, while the parameters are the single-scattering albedo, total optical depth, and the asymmetry factor in the Henyey-Greenstein phase function. The basic functional trends are discussed by using various parametric plots, and selected results are given to allow numerical checks. The computational method is invariant imbedding.

Cogley, A. C.↗
NASA NTRS1979

Quasi-periodic structure of a turbulent jet

The instantaneous near field pressure fluctuations of an axisymmetric subsonic jet were measured by using a longitudinal and an azimuthal microphone arrays in order to qualitatively determine the behaviors of the quasi-periodic structure within the flow. Statistical analysis is used to explain the characteristic of the pressure signals. In addition to the information obtained by forming the power spectral density, auto- and cross-correlation functions, two types of signals are extracted through a conditional probability analysis to represent the quasi-periodic and the random fine structures within the turbulent jet. The quasi-periodic structure first appears as a rolling up of the mixing layer flow within one nozzle diameter downstream of the exit, then becomes fully developed at approximately 3 nozzle diameters downstream with a preferred Strouhal number range 0.3-0.4, and finally disappears beyond the end of potential core. This behavior is also reflected in the variation of the convection velocity.

Maestrello, L.↗
NASA NTRS1979

The brightness distribution of IRC +10216 at 11 microns

The brightness distribution of IRC +10216 at a wavelength of 11 microns has been measured in detail by using spatial interferometer. This brightness distribution appears to have azimuthal symmetry; an upper limit of 1.1 may be set to the ellipticity at 11 microns if the object has a major axis oriented either along or perpendicular to the major axis of the optical image. The radial distribution shows both compact and extended emission. The extended component, which is due to thermal emission from circumstellar dust, contributes 91% of the total flux and has a 1/e diameter of 0.90 arcsec. The tapered shape of this component is consistent with a dust density dependence on the inverse square of radial distance. The compact component is unresolved (less than 0.2 arcsec in diameter) and represents emission from the central star seen through the circumstellar envelope.

Sutton, E. C.↗
NASA NTRS1979

Energetic protons in the Jovian magnetosphere

Time histories, angular distributions and energy spectra of energetic protons were observed over an energy range of 0.2 to 20 MeV for the four passes of Pioneers 10 and 11 through the Jovian magnetosphere. The energetic particle data from these four passes are remarkably different. Azimuthal anisotropies appear to dominate with time variations also contributing to the very complex topology. On the inbound P-10 pass the expected corotation anisotropy was not observed in the outer magnetosphere. The simplest explanation is that the particle reference frame (the magnetospheric plasma) is moving nearly radially, suggesting the existence of a planetary wind at that time.

Mcdonald, F. B.↗
NASA NTRS1979

Conductorlike behavior of a photoemitting dielectric surface

It has been suggested in the past that a uniformly illuminated photoemitting dielectric surface of finite extent acquires in the steady state a surface charge distribution as if the surface were conducting (i.e., the surface becomes equipotential). In this paper an analytical proof of this conductorlike behavior is given. The only restrictions are that the photoelectron emission from the surface has azimuthal symmetry and that the photosheath may be assumed to be collisionless. It is tacitly assumed that a steady state is attainable, which means that the photoelectron spectrum has a high-energy cutoff.

De, B. R.↗
NASA NTRS1979

Trajectories of charged particles in radial electric and uniform axial magnetic fields

Trajectories of charged particles were determined over a wide range of parameters characterizing motion in cylindrical low-pressure gas discharges and plasma heating devices which have steady radial electric fields perpendicular to uniform steady magnetic fields. Consideration was given to radial distributions characteristic of fields measured in a modified Penning discharge, in two NASA Lewis burnout-type plasma heating devices, and that estimated for the Ixion device. Numerical calculations of trajectories for such devices showed that differences between cyclotron frequency and qB/m and between azimuthal drift and a guiding center approximation are appreciable.

Englert, G. W.↗
NASA NTRS1979

Computation of subsonic and transonic flow about lifting rotor blades

An inviscid, nonconservative, three-dimensional potential flow code has been developed for computing the quasi-steady flow about an isolated lifting rotor blade. Calculations from the code were compared with chordwise pressure measurements obtained in a wind tunnel on a nonlifting rotor at transonic tip speeds at advance ratios from 0.40 to 0.55. The overall agreement between theoretical calculations and experiment was good. To illustrate the early capability of the program, the flow about a hypothetical lifting rotor blade having twist, airfoil thickness taper, and a 20 deg sweptback tip was analyzed at azimuthal positions of 60, 90, and 120 deg for an advance ratio of 0.342. A typical run on a CDC 7600 computer required about 5 min for one rotor position at transonic tip speeds.

Arieli, R.↗
NASA NTRS1979

International Planetary Patrol observations of Saturn's rings. I - Observations and data reduction

The paper describes the reduction procedure used for observations of Saturn's rings taken with the International Planetary Patrol Network in 1977. Corrections for atmospheric smearing are determined using an assumed ring model and performed by a two-dimensional Wiener filter developed at JPL's Image Processing Laboratory. These smearing corrections are shown to be consistent with the radial profile of the rings, not just on the major axis of the ring system, but over a range of azimuthal angle.

Lumme, K.↗