SEARCH · Engineering Papers
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.
High-lift wing concepts being considered for application to commercial STOL transports are discussed. The flow patterns which produce dynamic loads on these wings are indicated. Measurements of surface pressure and acceleration on a one-half-scale model of an externally blown double-slotted flap are reported. Root-mean-square values, power spectra, and scaling parameters are shown.
Hard X-ray bursts have been observed from two 1B flares located in the same sunspot region and separated in time by about 70 minutes on Dec. 8, 1970. The bursts are composed by many 'flashes' of 2 to 20 seconds duration. Power spectrum analysis reveals no strong periodicities although a significant peak appears at 7.5 sec. The characteristic times of 2 to 20 sec do not seem likely to be electron transit times since the flare size is so small. These times are evidently connected with the acceleration of the electrons. Fitting Takakura's model of the radio noise region to the observations, this region is found to be small, but the density of electrons above 100 keV is high, on the order of 10 million per cu cm.
A description is given of a model in which the Jupiter moon Io interacts with the Jovian magnetosphere through plasma sheaths in the vicinity of Io. Several recent results available from Pioneer 10 are used to revise a Io sheath model suggested by Gurnett (1972) and developed by Hubbard et al. (1974). The revised model is used to suggest an explanation for a number of observations. Attention is also given to other phenomena which might be detectable with the aid of future experiments.
The radioisotope thermoelectric generator (RTG) considered is to provide a continuous minimum power output of 0.5 watt at 6.0 to 8.5 volts for a minimum period of 15 years. The mechanical-electrical evaluation phase discussed involved the conduction of shock and vibration tests. The thermochemical-physical evaluation phase consisted of an analysis of the materials and the development of a thermal model. The thermoelectric evaluation phase included the accelerated testing of the thermoelectric modules.
The use of chemical and physical data as a supplement to linear regression models in the prediction of cell failure is discussed. Principal factors to be considered are the positive thickness and weight, and the negative thickness. A model for cell degradation and failure in accelerated life test cells is presented and predictions based on a teardown analysis are included.
Radio wave scattering data were collected at 3.6 and 13 cm wavelengths by means of the radio link between the Viking orbiters and the earth during the Nov. 25, 1976 solar conjunction of Mars, which occurred near the beginning of solar cycle 21; Mariner 10 solar activity observations during 1974 are also used. It is found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma, and the spectral index of electron density turbulence is obtained. The measurements of solar wind velocity and spectral index cover 78 days for Viking and 49 days for Mariner 10 and show the combined effects of changing heliocentric distance, solar latitude, and solar longitude as well as solar activity. It is concluded that the observational velocity profile differs significantly from the theoretical profiles in two ways: (1) the theoretical profile does not show the abrupt change in velocity at about 15 solar radii, and (2) the observational profile shows acceleration at larger radial distances than the model profiles. The observational profiles indicate velocities of less than about 150 km/sec out to 15 solar radii.
Analysis of 5.5 years of Lageos satellite range data reveal significant residual nodal signatures: an acceleration and annual and semiannual periods. These signatures primarily reflect variations in the zonal gravitational harmonic J2 coefficient and hence the polar moment of inertia. The implied decrease of J2 = -3 x 10 to the -11th/yr is consistent with both historical observations of the nontidal acceleration of the earth's rotation and models of viscous rebound of the solid earth from the decrease in load due to the last deglaciation.
A survey of solar wind ion velocity distributions and derived parameters (temperature, ion differential speed, heat flux, adiabatic invariants) is presented with emphasis on the heliocentric distance range between 0.3 and 1 AU traversed by the Helios solar probe. The radial evolution of nonthermal features are discussed which are observed to be most pronounced at perihelion. Within the framework of quasilinear plasma theory, wave particle interactions that may shape the ion distributions are considered. Some results of a self consistent model calculation are presented accounting for ion acceleration and heating by resonant momentum and energy exchange with ion cyclotron and magnetosonic waves propagating away from the Sun along the interplanetary magnetic field. Another tentative explanation for the occurrence of large perpendicular proton temperatures is offered in terms of heating by Landau damping of lower hybrid waves.
Recent experimental research on bow shock structure and theoretical studies of quasi-parallel shock structure and shock acceleration of energetic particles were reviewed, to point out the relationship between structure and particle acceleration. The phenomenological distinction between quasi-parallel and quasi-perpendicular shocks that has emerged from bow shock research; present efforts to extend this work to interplanetary shocks; theories of particle acceleration by shocks; and particle acceleration to shock structures using multiple fluid models were discussed.
The physics of the solar wind acceleration phenomena (e.g. effect of transient momentum deposition on the temporal and spatial variation of the temperature, density and flow speed of the solar wind, formation of shocks, etc.) and the resultant effects on observational signatures, particularly spectroscopic signature are studied. Phenomena under study include: (1) wave motions, particularly spectroscopic signatures are studied. Phenomena under study include:(1) wave motions, particularly Alfven and fast mode waves, (2) the formation of standing shocks in the inner heliosphere as a result of momentum and/or heat addition to the wind and (3) coronal transient phenomena where momentum and/or heat are deposited in the corona to produce transient plasma heating and/or mass ejections. Also included are the theoretical investigation of spectroscopic plasma diagnostics for the inner heliosphere and the analysis of existing Skylab and other relevant data.
According to the energetic particle model of solar flares particles are efficiently accelerated in the magnetic field loop of an active region (AR) by hydromagnetic turbulence. It is demonstrated that the isotopic overabundances observed in some flares are not a consequence of the flare itself but are characteristic of the plasma in the AR. Only when a flare releases the plasma into the interplanetary space it is possible to observe this anomalous composition at spacecraft locations.
Results of a measurement of high energy cosmic-ray electrons that was performed with a balloon-borne transition radiation/shower detector telescope are presented. The data cover the energy range from 5 to 300 GeV. The interstellar spectrum below 10 GeV, which is affected by solar modulation, is derived through analysis of the nonthermal galactic radio emission, and extended to lower energies (about 300 MeV). The interstellar differential spectrum is described by a power law dependence on E with an index of -1.4 below 2 GeV, but attaining a slope of -2.6 at 2-10 GeV, and steepening further to almost -3.6 at 30-300 GeV. The features of this spectrum are interpreted in the context of galactic propagation models, assuming that the spectrum at the acceleration site has the form of a single power law. It is concluded that: (1) regions outside the galactic disk contribute to the confinement volume of electrons, (2) the containment time of electrons is of the order 10 to the 7th years and is independent of energy, (3) the spectrum at the acceleration site has a power law exponent equal to -2.65, and (4) a specific mechanism is responsible for the apparent flattening of the electron spectrum below 2 GeV.
The detailed dynamics are presented of a model for AGNs and QSOs based on spherically symmetric accretion onto a black hole and dissipation of the accretion energy in a collisionless shock. The basic assumptions and equations relevant for the model are presented, and the relations between the physical parameters are given in terms of the shock parameters. The latter are calculated for varying Mach numbers, and the resulting scaling laws are discussed and compared to the data, in particular the recently discovered correlations between luminosity and mass. The model can naturally produce ultrarelativistic electrons with flat spectra, a feature which, when coupled with e(+)-e(-) pair production, can account for the observed continuum radiation from these objects over essentially the whole electromagnetic spectrum. The model also predicts the emission of high-energy neutrinos with a luminosity roughly equal to that of the photons.
Spherically symmetric plasmas with high expansion velocities have been produced by irradiating targets with eight beams from the Helios CO2 laser in the presence of gases at various pressures. Attention was given to the properties of the target-emitted ions in order to obtain information about the ion-acceleration mechanisms in plasma expansions. Photoionization of the ambient gases by the soft X-ray emission from the laser-irradiated targets produced background plasmas, permitting plasma counterstreaming experiments to be performed in spherical geometry. Successful laser-target coupling in the presence of back-ground gases is obtained; modification of the ion acceleration in accordance with isothermal-expansion models is observed; and an absence of collective coupling between collisionless counterstreaming plasmas is found.
The Thermal Control Working Group limited its evaluation to issues associated with Earth orbiting and planetary spacecraft with power levels up to 50 kW. It was concluded that the space station technology is a necessary precursor but does not meet S/C 2000 needs (life, high heat flux, long term cryogenics, and survivability). Additional basic and applied research are required (fluid/materials compatibility and two phase system modeling). Scaling, the key issue, must define accelerated life test criteria. The two phase systems require 0g to 1 g correlation. Additional ground test beds are required and combined space environment tests of materials.
High resolution spectra of the hot sdO star LSS 1362, a central star of a planetary nebula, are analyzed by means of model atmosphere techniques. Improved NLTE model atmospheres based on the newly developed 'accelerated lambda iteration' method are used. The very high effective temperature (100000 K) derived previously from the UV energy distribution is confirmed. The surface gravity (log g = 5.3) and a normal helium abundance are derived. A mass of 0.65 solar mass and a luminosity of 10 exp 3.9 solar luminosities result from a comparison with evolutionary tracks. The distance is 1.1 kpc and the nebula has a diameter of about 0.25 pc to 0.5 pc. Weak photospheric emission lines of He II, CIV, Nv, and O v are detected. These lines are slightly blue-shifted with respect to the absorption line spectrum which is regarded as evidence for an atmospheric velocity field. It is conjectured that the observed broadening of the metal lines (25 km/s) may be caused by the velocity field rather than by rotation.
A precision orbit determination technique for NASA's Earth Observing System (EOS) is discussed. The technique exploits the redundant geometric information from GPS carrier phase and P-code pseudorange measurements and minimizes the requirements for precision dynamical modeling. Performance estimates for the application of the technique to the orbit geometry planned for the EOS platforms show that decimeter accuracies of orbit position may be obtained. The sensitivity of the predicted orbit uncertainties to model errors for station locations, nongravitational platform accelerations, and earth gravity are presented.
Events observed in a fast plasma experiment, where the y-component of the plasma flow within the low latitude boundary layer and magnetopause current layer was oppositely directed to that in the adjacent magnetosheath, are examined. The observations are shown to be qualitatively and quantitatively consistent with previous observations of accelerated flows at the magnetopause and with models of magnetic reconnection, with reconnection occurring at low latitudes near the GSE XY plane, independently of the magnitude or the sign of the y-component ot the local magnetosheath magnetic field. Local magnetic shears at the magnetopause for these events (in 60-180 deg range) and the fact that these events occur at low latitudes do not support the antiparallel merging hypothesis. The observations of B(y)-dependent flow reversals demonstrate how the asymmetric polar cap convection and related phenomena, such as the Svalgaard-Mansurov effect, originate in magnetic reconnection at the dayside magnetopause.