SEARCH · Engineering Papers

Results for “EMPLOYMENT”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54

All sources NASA NTRS DOE OSTI

NASA NTRS1983

Short wavelength infrared hybrid focal plane arrays

The employment of area focal plane arrays (FPA) has made it possible to obtain second generation infrared imaging systems with high resolution and sensitivity. The Short Wavelength Infrared (SWIR) region (1-2.5 microns) is of importance for imaging objects at high temperature and under conditions of reflected sunlight. The present investigation is concerned with electrooptical characterization results for 32 x 32 SWIR detector arrays and FPAs which are suitable for use in a prototype imaging spectrometer. The employed detector material is Hg(1-x)Cd(x)Te grown by liquid phase epitaxy on a CdTe transparent substrate. Attention is given to details of processing, the design of the detector array, the multiplexer, the fabrication of the hybrid FPA, and aspects of performance.

Vural, K.↗

NASA NTRS1985

Analysis of some fully-discrete algorithms for the one-dimensional heat equation

The present investigation is concerned with a fully discrete accuracy and stability analysis of the one-dimensional heat equation, taking into account the evaluation of two-pass explicit schemes which simultaneously employ lumped and coupled capacity matrices. Schemes of the considered characteristics are not amenable to uncoupled semidiscrete and ordinary differential equation analyses. The obtained results illustrate that superior behavior may be achieved by schemes of the employed type when compared with the performance of the standard one-pass explicit schemes. The key idea in the considered approach is related to the utilization of a reduced-quadrature capacity matrix in the evaluation of the right-hand-side residual.

Hughes, T. J. R.↗

NASA NTRS1985

High-performance double-focusing mass spectrometer

Double focusing was first employed when mass spectrometers of a simpler design were not capable any longer to satisfy increasing demands in mass spectroscopy. One of the successful instruments of the 1930's was the mass spectrometer designed by Mattauch and Herzog (1934). The compactness of the Mattauch-Herzog geometry became particularly important in connection with studies involving the employment of rockets, satellites, or space probes. Another advantage of the considered spectrometer is related to the capability of measuring several masses of ions simultaneously. The instrument design was, therefore adopted for some rocket flights to the upper atmosphere, the investigation of the upper atmosphere of Mars, and for studying the upper atmosphere of Venus. Attention is given to laboratory applications involving the instrument in a somewhat enlarged version, and aspects of instrument operation and performance.

Nier, A. O.↗

NASA NTRS1985

A cost-effective component modes analysis for Shuttle payloads using a combination of frequency domain and time domain approaches

A combination of the time and frequency domains which employs the latter only where the former is inefficient or uncertain is used in Space Shuttle payloads' component mode analyses. Attention is given to the time histories at the launch vehicle/spacecraft interface. The frequency domain allows interface acceleration to be determined without recourse to a new, merged system eigenvalue solution and subsequent 'system modal' responses. The approach has been employed in Galileo spacecraft loads analyses.

Trubert, M.↗

NASA NTRS1984

Utilizing various test methods to study the stress corrosion behavior of Al-Li-Cu alloys

Recently, much attention has been given to aluminum-lithium alloys because of rather substantial specific-strength and specific-stiffness advantages offered over commercial 2000and 7000-series aluminum alloys. An obstacle to Al-Li alloy development has been inherent limited ductility. In order to obtain a more refined microstructure, powder metallurgy (P/M) has been employed in alloy development programs. As stress corrosion (SC) of high-strength aluminum alloys has been a major problem in the aircraft industry, the possibility of an employment of Al-Li alloys has been considered, taking into account a use of Al-Li-Cu alloys. Attention is given to a research program concerned with the evaluation of the relative SC resistance of two P/M processed Al-Li-Cu alloys. The behavior of the alloys, with and without an addition of magnesium, was studied with the aid of three test methods. The susceptibility to SC was found to depend on the microstructure of the alloys.

Pizzo, P. P.↗

NASA NTRS1985

A georeferenced Landsat digital database for forest insect-damage assessment

In 1869, the gypsy moth caterpillar was introduced in the U.S. in connection with the experiments of a French scientist. Throughout the insect's period of establishment, gypsy moth populations have periodically increased to epidemic proportions. For programs concerned with preventing the insect's spread, it would be highly desirable to be able to employ a survey technique which could provide timely, accurate, and standardized assessments at a reasonable cost. A project was, therefore, initiated with the aim to demonstrate the usefulness of satellite remotely sensed data for monitoring the insect defoliation of hardwood forests in Pennsylvania. A major effort within this project involved the development of a map-registered Landsat digital database. A complete description of the database developed is provided along with information regarding the employed data management system.

Williams, D. L.↗

NASA NTRS1984

Environmental control/life support

It is pointed out that the life support systems technology used on projects Mercury, Gemini, Apollo, and Space Shuttle required an employment of expendables. Skylab was the only manned space project which made use of regenerable life support technology, taking into account the employment of a silica gel/molecular sieve for carbon dioxide removal. A number of investigations indicate that significant launch weight and volume as well as recurring cost savings can be realized by using regenerative life support processes for a Space Station. A number of developed regenerative processes are believed to be applicable to a Space Station. Aspects of air revitalization are discussed, taking into account carbon dioxide reduction, oxygen generation, trace contaminant control, temperature and humidity control, instrumentation, and nitrogen supply. Attention is also given to water reclamation, solid waste treatment, and future development and testing programs.

Quattrone, P. D.↗

NASA NTRS1984

The utility of Thematic Mapper sensor characteristics for surface mine monitoring

The employment of Landsat Multispectral Scanner (MSS) data for surface coal mine inventory and inspection applications has been extensively investigated. However, in spite of encouraging research results, MSS data have not gained wide acceptance for surface mine monitoring operations. This situation is partly related to MSS spatial resolution (80 m), which is considered insufficient for detailed surface mine inspection. The Thematic Mapper (TM) employed on the Landsat-4 and 5 satellites provides an improved resolution (30 m) and other refinements which are expected to enhance the usefulness of TM data relative to MSS data. The present paper reports research which was conducted to assess the usefulness of actual TM data and to quantitatively evaluate the contribution of individual sensor characteristics to data utility for surface mine monitoring. The obtained results demonstrate that the TM spatial resolution can be of immediate benefit for certain applications such as surface mine monitoring.

Irons, J. R.↗

NASA NTRS1985

Aerothermodynamic environment for a Titan probe with deployable decelerator

It is pointed out that further exploration of Titan, Saturn's largest moon, is of current interest to the scientific community, particularly from the standpoint of the organic chemical evolution of its atmosphere. For a suitable study of this Saturnian satellite, a mission involving a Titan atmospheric entry probe is to be conducted. The probe is to employ a deployable decelerator with the aim to allow scientific measurements in the haze layer. The present investigation is concerned with an assessment of the aerothermodynamic environment for the considered probe during its hypervelocity, low-Reynolds-number entry. Attention is given to the employed computational method, the Titan probe configuration, the Titan probe trajectory, the viscous-layer regime of the aerothermodynamic environment, and the incipient merged-layer regime.

Green, M. J.↗

NASA NTRS1985

Automatic crack propagation tracking

A finite element based approach to fully automatic crack propagation tracking is presented. The procedure presented combines fully automatic mesh generation with linear fracture mechanics techniques in a geometrically based finite element code capable of automatically tracking cracks in two-dimensional domains. The automatic mesh generator employs the modified-quadtree technique. Crack propagation increment and direction are predicted using a modified maximum dilatational strain energy density criterion employing the numerical results obtained by meshes of quadratic displacement and singular crack tip finite elements. Example problems are included to demonstrate the procedure.

Shephard, M. S.↗

NASA NTRS1985

Spectrum and chemical composition of the remarkable planetary nebula NGC 6537

The planetary nebula NGC 6537 appears to be an irregular bipolar object. Conventional procedures have been employed to observe the spectrum of NGC 6537 with the image dissector scanner at the Lick 3-m telescope. Both red- and green-sensitive tubes were employed in order to cover the spectrum from the practical UV limit near lambda 3300 A to the near-infrared limit near lambda 8600 A. The instrumental response function was determined on the basis of the observation of suitable comparison stars. On Oct. 23, 1984, observations with the International Ultraviolet Explorer (IUE) were obtained. A table containing the optical region spectrum of NGC 6537 is presented along with a table providing the UV fluxes, a table listing the ionic concentrations, and a table with data describing the chemical composition of NGC 6537. Attention is given to theoretical models and the determination of the nebular chemical composition, and aspects of plasma diagnostics.

Feibelman, W.↗

NASA NTRS1985

Electrochemical concentration cell ozonesonde accuracy and precision

This paper is concerned with the results of a study designed to evaluate experimentally the accuracy and precision of electrochemical concentration cell (ECC) ozonesondes as prepared and flown by NASA, as a function of altitude. A combination of dual-instrument soundings and laboratory work using an environmental chamber was employed in the study. The ECC ozonesonde is a small, balloon-borne sensor developed for obtaining vertical profiles of atmospheric ozone. Attention is given to the design of the employed environmental chamber, ozone and temperature profiles used in simulated ozonesonde soundings, absolute and relative ECC ozonesonde precision estimates determined with the environmental chamber and from dual-instrument balloon soundings, and the ECC ozonesonde accuracy.

Barnes, R. A.↗

NASA NTRS1985

Electric Field Containerless Processing Technology

The objective of this task is to develop the science and technology base required to design and construct a high temperature electric field positioning module that could be used by materials scientists to conduct containerless science experiments in a low gravity environment. Containerless science modules that employ electric fields to position and manipulate samples offer several advantages over acoustic or electromagnetic systems. The electric field system will operate not only at atmospheric pressures but also in a vacuum, in contrast to the acoustic modules which can only operate in atmosphere where the acoustic forces are sufficient. The electric field technique puts minimum energy into the sample, whereas the electromagnetic system can deposit energy into the sample through eddy current heat as well as physical mixing in the sample. Two types of electric field modules have been constructed and tested to date. One employs a charged sample and uses electrostatic forces to position and control the sample. The second type of module induces electrical polarization of the sample and electric field gradients to position and control the sample.

Elleman, D. D.↗

NASA NTRS1985

Bounding solutions of geometrically nonlinear viscoelastic problems

Integral transform techniques, such as the Laplace transform, provide simple and direct methods for solving viscoelastic problems formulated within a context of linear material response and using linear measures for deformation. Application of the transform operator reduces the governing linear integro-differential equations to a set of algebraic relations between the transforms of the unknown functions, the viscoelastic operators, and the initial and boundary conditions. Inversion either directly or through the use of the appropriate convolution theorem, provides the time domain response once the unknown functions have been expressed in terms of sums, products or ratios of known transforms. When exact inversion is not possible approximate techniques may provide accurate results. The overall problem becomes substantially more complex when nonlinear effects must be included. Situations where a linear material constitutive law can still be productively employed but where the magnitude of the resulting time dependent deformations warrants the use of a nonlinear kinematic analysis are considered. The governing equations will be nonlinear integro-differential equations for this class of problems. Thus traditional as well as approximate techniques, such as cited above, cannot be employed since the transform of a nonlinear function is not explicitly expressible.

Stubstad, J. M.↗

NASA NTRS1985

Additional Results on the Radiating Properties of Ltsas and Cwsas

Results are presented on the theoretical experimental investigations of the radiating properties of Linearly Tapered Slot Antennas (LTSAs) and Constant Width Slot Antennas (CWSAs). The antenna is treated as a flared slot radiating in the presence of a conducting half plane. The aperture distribution in the flared slot is determined by approximating the tapered structure as a series of short sections of parallel slots. The slot field of a uniform slotline is determined by employing the spectral Galerkin's technique and a power conservation criterion is employed to match the fields at the step junction between two successive sections. Comparison is made between theory and experiment for several LTSAs and CWSAs etched on epsilon sub r = 2.22 and 2.55 substrates, and or flare angles 4 deg or = gamma or = 10 deg. It is shown that the theory adequately models the physics of the problem when the lateral dimension D of the antenna is large and when the propagation constant of a parallel slot line can be estimated very accurately. Newly observed effects of the lateral truncation on the radiation pattern of the antenna are discussed.

Source record↗

NASA NTRS1985

The effects of surface pretreatment and nitrogen tetroxide purification on the corrosion rate of Type 304L stainless steel

Corrosion rates of 304L stainless steel coupons in MON-1 oxidizer have been measured as a function of cleaning procedures employed, surface layer positions, propellant impurity levels, and short-term exposure durations (14 to 90 days). Of special interest was propellant contamination by buildup of soluble iron, which may cause flow decay. Surface treatments employed were combinations of cleaning, pickling, and passivation procedures. Propellants used were MIL-SPEC MON-1 and several types of purified NTO (i.e., low water, low chloride) which may, at a later time, be specified as spacecraft grade. Pretest coupon surface analysis by X-ray photoelectron spectroscopy (XPS-ESCA) has revealed important differences, for the different cleaning procedures, in the make-up of the surface layer, both in composition and state of chemical combination of the elements involved. Comparisons will be made of XPS/ESCA data, for different cleaning procedures, for specimens before and after propellant exposure.

Blue, G. D.↗

NASA NTRS1985

Close-in characteristics of LH2/LOX reactions

In deriving shock overpressures from space vehicles employing LH2 and LOX, separate methods of analyses and prediction are recommended, as a function of the distance. Three methods of treatment are recommended. For the Far Field - where the expected shock overpressure is less than 40 psi (lambda = 5) - use the classical PYRO approach to determine TNT yield, and employ classical ordnance (Kingery) curve to obtain the overall value. For the Close-In Range, a suggested limit is 3D, or a zone from a distance of three times the tank diameter to the tank wall. Rather than estimate a specific distance from the center of explosion to the target, it is only necessary to estimate whether this could be within one, two, or three diameters away from the wall; i.e., in the 1, 2, or 3D zone. Then assess whether mixing mode is by the PYRO CBGS (spill) mode or CBM (internal mixing) mode. From the zone and mixing mode, the probability of attaining various shock overpressures is determined from the plots provided herein. For the transition zone, between 40 psi and the 3D distance, it is tentatively recommended that both of the preceding methods be used, and to be conservative, the higher resulting value be used.

Riehl, W. A.↗

NASA NTRS1985

Memory metal actuator

A mechanical actuator can be constructed by employing a plurality of memory metal actuator elements in parallel to control the amount of actuating force. In order to facilitate direct control by digital control signals provided by a computer or the like, the actuating elements may vary in stiffness according to a binary relationship. The cooling or reset time of the actuator elements can be reduced by employing Peltier junction cooling assemblies in the actuator.

Ruoff, C. F.↗