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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Magnetically-conformed, Variable Area Discharge Chamber for Hall Thruster, and Method

The invention is a Hall thruster that incorporates a discharge chamber having a variable area channel including an ionization zone, a transition region, and an acceleration zone. The variable area channel is wider through the acceleration zone than through the ionization zone. An anode is located in a vicinity of the ionization zone and a cathode is located in a vicinity of the acceleration zone. The Hall thruster includes a magnetic circuit which is capable of forming a local magnetic field having a curvature within the transition region of the variable area channel whereby the transition region conforms to the curvature of the local magnetic field. The Hall thruster optimizes the ionization and acceleration efficiencies by the combined effects of the variable area channel and magnetic conformity.

Hofer, Richard R.↗
NASA NTRS2021

An Encounter with the Ion and Electron Diffusion Regions at a Flapping and Twisted Tail Current Sheet

We analyze data returned by the Magnetospheric Multiscale mission (MMS) constellation during a rapid (~1.5 s) traversal of a flapping and reconnecting current sheet (CS) in the near-Earth magnetotail (X ~ -20 RE). The CS was highly tilted, with its normal pointing strongly duskward. Its extreme thinness was confirmed by a curvature analysis of the magnetic field lines. The event was associated with a guide field of 8% of the reconnecting components. From the pitch angle distributions of low-energy electrons we infer that the crossing occurred earthward of the X-line. Traveling practically normal to the CS, MMS encountered an ion diffusion region (IDR) in which was embedded an electron diffusion region (EDR). IDR signatures included breaking of the ion frozen-in condition in the presence of Hall B and E fields. EDR signatures included a strong out of-plane current associated with a super-Alfvenic electron jet, evidence of positive energy transfer, and a temperature anisotropy (TeII > Te1) which disappeared at the field reversal. Derived scale sizes normal to the CS are: ~6.9 de (EDR) and ~0.4 di (IDR) (40 and 100 km). We estimate the average dimensionless reconnection rate as 0.077 + 0.050. The observations and inferences are supported by PIC numerical simulations. We find very good agreement in the reconnection rates. We also discuss the effects of asymmetries in the density, temperature and magnetic field strength on the Hall fields and length of the outflow jets. The event is associated with a substorm onset which began 7 min after the MMS observations.

C J Farrugia↗
NASA NTRS1977

Remote sensing operations (multispectral scanner and photographic) in the New York Bight, 22 September 1975

Ocean dumping of waste materials is a significant environmental concern in the New York Bight. One of these waste materials, sewage sludge, was monitored in an experiment conducted in the New York Bight on September 22, 1975. Remote sensing over controlled sewage sludge dumping included an 11-band multispectral scanner, fiver multispectral cameras and one mapping camera. Concurrent in situ water samples were taken and acoustical measurements were made of the sewage sludge plumes. Data were obtained for sewage sludge plumes resulting from line (moving barge) and spot (stationary barge) dumps. Multiple aircraft overpasses were made to evaluate temporal effects on the plume signature.

Johnson, R. W.↗
NASA NTRS1982

Earth Radiation Science Seminars

Earth radiation budget experiments, instrumentation, computational methods, and the effect of increased CO2 on climate were discussed.

Hall, J. B., Jr.↗
NASA NTRS1986

Effects of varying environmental parameters on trace contaminant concentrations in the NASA Space Station Reference Configuration

An evaluation is made of the NASA Space Station Reference Configuration trace contaminant production and depletion level effects of CO2, O2, humidity, temperature, and pressure variations, on the basis of a computer model of the Reference Configuration's chemical reactions and physical processes as functions of time. The effects of changes in the initial concentrations of such contaminants as nonmethane hydrocarbons and nitrogen oxides are also examined, and these are found to result in more significant changes in the concentration levels of trace contaminants than pressure and humidity variations. O2 and CO2 changes are found to have negligible effects on trace contaminant concentrations.

Brewer, Dana A.↗
NASA NTRS1996

Task 7: Endwall treatment inlet flow distortion analysis

The overall objective of this study was to develop a 3-D numerical analysis for compressor casing treatment flowfields, and to perform a series of detailed numerical predictions to assess the effectiveness of various endwall treatments for enhancing the efficiency and stall margin of modern high speed fan rotors. Particular attention was given to examining the effectiveness of endwall treatments to counter the undesirable effects of inflow distortion. Calculations were performed using three different gridding techniques based on the type of casing treatment being tested and the level of complexity desired in the analysis. In each case, the casing treatment itself is modeled as a discrete object in the overall analysis, and the flow through the casing treatment is determined as part of the solution. A series of calculations were performed for both treated and untreated modern fan rotors both with and without inflow distortion. The effectiveness of the various treatments were quantified, and several physical mechanisms by which the effectiveness of endwall treatments is achieved are discussed.

Hall, E. J.↗
NASA NTRS1987

Performance of laminar-flow leading-edge test articles in cloud encounters

An extensive data bank of concurrent measurements of laminar flow (LF), particle concentration, and aircraft charging state was gathered for the first time. From this data bank, 13 flights in the simulated airline service (SAS) portion were analyzed to date. A total of 6.86 hours of data at one-second resolution were analyzed. An extensive statistical analysis, for both leading-edge test articles, shows that there is a significant effect of cloud and haze particles on the extent of laminar flow obtained. Approximately 93 percent of data points simulating LFC flight were obtained in clear air conditions; approximately 7 percent were obtained in cloud and haze. These percentages are consistent with earlier USAF and NASA estimates and results. The Hall laminar flow loss criteria was verified qualitatively. Larger particles and higher particle concentrations have a more marked effect on LF than do small particles. A particle spectrometer of a charging patch are both acceptable as diagnostic indicators of the presence of particles detrimental to laminar flow.

Davis, Richard E.↗
NASA NTRS1978

Transient dynamics of a flexible rotor with squeeze film dampers

A series of simulated blade loss tests are reported on a test rotor designed to operate above its second bending critical speed. A series of analyses were performed which predicted the transient behavior of the test rig for each of the blade loss tests. The scope of the program included the investigation of transient rotor dynamics of a flexible rotor system, similar to modern flexible jet engine rotors, both with and without squeeze film dampers. The results substantiate the effectiveness of squeeze film dampers and document the ability of available analytical methods to predict their effectiveness and behavior.

Buono, D. F.↗
NASA NTRS1980

Silicon nitride passivation of IC's

Feasibility study looks at effectiveness of silicon nitride passivation coating against moisture and mobile ions. Coating was tested on CMOS microcircuits. Tests included temperature cycling, high-temperature electrical stress, and temperature and humidity exposure. Report concludes plastic-encapsulated circuits with protective coating exhibit high survival rates; it includes tables summarizing test results and figures that show effects of flexing.

Erickson, J. J.↗
NASA NTRS1985

Vacuum ultraviolet studies of electron impact of helium Excitation of He n1P0 Rydberg series and ionization-excitation of He(+) nl Rydberg series

The cross sections for the He I 1s2 1S-1snp 1P0 series have been measured using a relative flow method, with the absolute scale fixed by the H Ly-alpha dissociative excitation cross section standard. The results are compared with those obtained using a relative cross section data analysis by modified Born approximation, and good agreement is found. Cross sections for the ionization-excitation of the He II 121.51 nm and He II 164.04 nm transmissions have been measured, and the results strongly suggest that theoretical calculations of the reactions differ fundamentally from physical reality. The failure of the theory to describe experimental results stems from the neglect in the theory of electron correlation effects between the two orbital electrons.

Shemansky, D. E.↗
NASA NTRS1986

On the secondary instability of Taylor-Goertler vortices to Tollmien-Schlichting waves in fully-developed flows

There are many flows of practical importance where both Tollmien-Schlichting waves and Taylor-Goertler vortices are possible causes of transition to turbulence. The effect of fully nonlinear Taylor-Goertler vortices on the growth of small amplitude Tollmien-Schlichting waves is investigated. The basic state considered is the fully developed flow between concentric cylinders driven by an azimuthal pressure gradient. It is hoped that an investigation of this problem will shed light on the more complicated external boundary layer problem where again both modes of instability exist in the presence of concave curvature. The type of Tollmein-Schlichting waves considered have the asymptotic structure of lower branch modes of plane Poisseulle flow. Whilst instabilities at lower Reynolds number are possible, the latter modes are simpler to analyze and more relevant to the boundary layer problem. The effect of fully nonlinear Taylor-Goertler vortices on both two-dimensional and three-dimensional waves is determined. It is shown that, whilst the maximum growth as a function of frequency is not greatly affected, there is a large destabilizing effect over a large range of frequencies.

Bennett, James↗
NASA NTRS1988

On the secondary instability of Taylor-Goertler vortices to Tollmien-Schlichting waves in fully developed flows

There are many flows of practical importance where both Tollmien-Schlichting waves and Taylor-Goertler vortices are possible causes of transition to turbulence. The effect of fully nonlinear Taylor-Goertler vortices on the growth of small amplitude Tollmien-Schlichting waves is investigated. The basic state considered is the fully developed flow between concentric cylinders driven by an azimuthal pressure gradient. It is hoped that an investigation of this problem will shed light on the more complicated external boundary layer problem where again both modes of instability exist in the presence of concave curvature. The type of Tollmien-Schlichting waves considered have the asymptotic structure of lower branch modes of plane Poiseuille flow. Whilst instabilities at lower Reynolds number are possible, the latter modes are simpler to analyze and more relevant to the boundary layer problem. The effect of fully nonlinear Taylor-Goertler vortices on both two-dimensional and three-dimensional waves is determined. It is shown that, whilst the maximum growth as a function of frequency is not greatly affected, there is a large destabilizing effect over a large range of frequencies.

Bennett, James↗
NASA NTRS1988

Reflectances of glaciers as calculated using Landsat-5 Thematic Mapper data

Landsat-5 digital numbers have been used to compute the at-satellite planetary reflectance on spectrally similar zones on the Meares and Schwanda glaciers in Alaska and the Grossglockner glacier group in Austria. The patterns of TM-derived reflectances in the ablation areas of the Grossglockner glacier group and the Meares Glacier compare favorably with published reflectance curves measured on the surface of glacier ice, though the surface reflectance of snow-covered ice is higher than the Landsat-derived reflectance for the glaciers studied. The accuracy of the at-satellite planetary reflectances is shown to be affected by topographic and atmospheric effects and by the anisotropic nature of snow reflectance.

Hall, Dorothy K.↗
NASA NTRS1992

A three-dimensional radiative transfer method for optical remote sensing of vegetated land surfaces

A numerical method for solving the radiative transfer equation in three spatial dimensions is briefly discussed focusing on an efficient acceleration algorithm. The reliability of coding and accuracy of the algorithm are evaluated by benchmarking. Parameterization of the method and results of a simulation are presented to document the utility of the method for remote sensing applications. Attention is also given to a simple model of the hot spot effect and sample calculations.

Myneni, R. B.↗