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At least 721 records · Page 40

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NASA NTRS1972

Auroral helium precipitation.

Application of the metal foil sampling technique, which has been used to measure helium, neon, and argon fluxes in the solar wind, to the problem of measuring the fluxes of these gases in the auroral primary radiation. Aluminum and platinum foils have been flown into two bright auroras and have been recovered. The foils have been analyzed for helium and neon isotopes with a mass spectrometer; so far only He4 has been detected. In the first flight the precipitating flux of He4 with particle energies above about 1 keV was approximately 1,000,000 per sq cm per sec, and the backscattered flux was smaller by about a factor of 10. In the second flight the aurora was less bright, and the He4 fluxes were lower by a factor of about 2. A rough analysis suggests that the mean energy of the incident particles was greater than 3 keV.

Axford, W. I.↗

NASA NTRS1974

ASRDI oxygen technology survey, Volume 7: Characteristics of metals that influence system safety

A literature survey and analysis of the material and process factors affecting the safety of metals in oxygen systems is presented. In addition, the practices of those who specify, build, or use oxygen systems relative to the previous is summarized. Alloys based on iron, copper, nickel, and aluminum were investigated representing the bulk of metals found in oxygen systems. Safety-related characteristics of other miscellaneous metals are summarized. It was found that factors affecting the safety of metals in oxygen systems exit in all phases of the evolutionary process, from smelting and mill techniques through end-production fabrication. The safety of a given metal in an oxygen system was determined to be influenced by the particular service requirement. The metal characteristics should favorably influence fulfillment of these requirements. Thus, no singular metal or alloy could be classified as safest for all types of oxygen service.

Pelouch, J. J., Jr.↗

NASA NTRS1976

New thruster configurations for spacecraft attitude control systems

Design characteristics of thruster configurations for spacecraft attitude control systems investigated. A standard six engine approach is developed and used as the basis for comparison of different thruster configurations. These methods include cases of both skewed and non-skewed configurations. Simulation results are used as a basis for comparison, critical thruster design factors being given based on an analysis of the data.

Colburn, B. K.↗

NASA NTRS1977

Applications of advanced V/STOL aircraft concepts to civil utility missions, volume 1

The suitability of advanced V/STOL aircraft to civil utility applications was assessed for offshore oil support, forest fire support, transport, and humanitarian missions. The aircraft concepts considered were a lift fan aircraft, a tilt rotor aircraft, and an advanced helicopter. All the aircraft had a design payload of 2,268 kg. (5,000 lb.) with the maximum range varying from 2,224 km. (1,800 nm) for the lift fan STOL to 1,482 km (800 nm) for the advanced helicopter. The analysis of these missions considered such factors as aircraft performance, annual utilization, initial cost, and operating cost. It is concluded that all the advanced V/STOL aircraft concepts generally performed these missions better than contemporary aircraft. The lift fan aircraft and the tilt rotor aircraft were found to be effective for the offshore oil and the forest fire support missions. The lift fan aircraft in the VTOL mode was also found to be very attractive for the executive transport mission where the passenger time value was $30/hr. or more.

Source record↗

NASA NTRS1978

Phase 1 of the automated array assembly task of the low cost silicon solar array project

The results of a study of process variables and solar cell variables are presented. Interactions between variables and their effects upon control ranges of the variables are identified. The results of a cost analysis for manufacturing solar cells are discussed. The cost analysis includes a sensitivity analysis of a number of cost factors.

Pryor, R. A.↗

NASA NTRS1981

Factors controlling the occurrence of Pc 3 magnetic pulsations at synchronous orbit

The reported investigation has the purpose to extend the study of Pc 3 pulsations at synchronous orbit conducted by Arthur and McPherron (1977). A large data set is used with the goal of finding the factors related to the occurrence of Pc 3 pulsations at synchronous orbit. The results are compared with ground-based observations. The study demonstrates that the diurnal occurrence pattern has a maximum at a prenoon local time and shows a seasonal shift. Among the solar wind parameters, solar wind velocity and the direction of the IMF are found to be dominant factors. Attention is given to the analysis procedure, examples of 2-hour spectra, diurnal occurrence pattern, the correlation between solar wind parameters, and the solar wind stream structure and Pc 3 occurrence.

Takahashi, K.↗

NASA NTRS1981

InGaAsP/InP laser development for single-mode, high-data-rate communications

Materials studies as well as general and specific device development were carried out in the InGaAsP system. A comparison was made of three standard methods of evaluating substrate quality by means of dislocation studies. A cause of reduced yield of good wafers, the pullover of melt from one bin to the next, has been analyzed. Difficulties with reproducible zinc acceptor doping have been traced to segregation of zinc in the In/Zn alloy used for the doping source. Using EBIC measurments, the pn junction was shown to drift in location depending on factors not always under control. An analysis of contact structures by SIMS showed that the depth to which the sintered Au/Zn contact penetrates into the structure is typically 0.13 microns, or well within the cap layer and out of the p-type cladding and thus not deleterious to laser prformance. The problem of single-mode laser development was investigated and it was shown to be related to the growth habit over four different possible substrate configurations. The fabrication of constricted double heterojunctions, mesa stripe buried heterostructures, and buried heterostructures was discussed, and measurements were presented on the device properties of single-mode buried heterostructure lasers. Results include single spectral line emission at 3 mW and a threshold current of 60 mA.

Ladany, I.↗

NASA NTRS1981

Comparison of data inversion techniques for remotely sensed wide-angle observations of Earth emitted radiation

The shape factor, parameter estimation, and deconvolution data analysis techniques were applied to the same set of Earth emitted radiation measurements to determine the effects of different techniques on the estimated radiation field. All three techniques are defined and their assumptions, advantages, and disadvantages are discussed. Their results are compared globally, zonally, regionally, and on a spatial spectrum basis. The standard deviations of the regional differences in the derived radiant exitance varied from 7.4 W-m/2 to 13.5 W-m/2.

Green, R. N.↗

NASA NTRS1983

Stress intensity factors in two bonded elastic layers containing cracks perpendicular to and on the interface. I Analysis. II - Solution and results

The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled systems of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered. Previously announced in STAR as N80-18428 and N80-18429

Lu, M.-C.↗

NASA NTRS1985

Changes in classification accuracy due to varying Thematic Mapper and multispectral scanner spatial, spectral, and radiometric resolution

The present paper provides the results of a factorial experiment designed to study the classification differences resulting from varying TM and MSS sensor resolution. Eight simulated data sets of various TM and MSS spatial, spectral, and radiometric resolutions were generated on the basis of Daedalus aircraft scanner data. It is pointed out that the current study provides more precise results than previous work, because more exact methods of data simulation with regard to the three factors were emphasized. Two methods of analysis are considered in the paper. To improve on earlier studies, efforts were made to collect an extensive amount of ground reference data. The summaries of classification accuracies for the training sites in the factorial analysis are presented in a table.

Acevedo, W.↗

NASA NTRS1985

The case for a centralized repair depot for Space Shuttle

The first priority of the NSTS program is to make the Space Shuttle system fully operational and cost effective in providing routine access to space. In support of this priority an integrated logistics support system was planned, structured and is being implemented to support a launch-on-time goal of 95 percent. In achieving a 95 percent spares 'fill rate' in an environment of small fleet size, highly unique and high cost assets, significant spares cost can be incurred. A major portion of these costs are for the additional spares required when repair or acquisition times are lengthy. This paper provides a fundamental analysis of the costs and other factors involved in the spare and repair process and provides an optimized cost and process solution for the Space Shuttle program - a centralized repair depot located at KSC.

Enlow, R. D.↗

NASA NTRS1986

Comparison of modal identification techniques using a hybrid-data approach

Modal identification of seemingly simple structures, such as the generic truss is often surprisingly difficult in practice due to high modal density, nonlinearities, and other nonideal factors. Under these circumstances, different data analysis techniques can generate substantially different results. The initial application of a new hybrid-data method for studying the performance characteristics of various identification techniques with such data is summarized. This approach offers new pieces of information for the system identification researcher. First, it allows actual experimental data to be used in the studies, while maintaining the traditional advantage of using simulated data. That is, the identification technique under study is forced to cope with the complexities of real data, yet the performance can be measured unquestionably for the artificial modes because their true parameters are known. Secondly, the accuracy achieved for the true structural modes in the data can be estimated from the accuracy achieved for the artificial modes if the results show similar characteristics. This similarity occurred in the study, for example, for a weak structural mode near 56 Hz. It may even be possible--eventually--to use the error information from the artificial modes to improve the identification accuracy for the structural modes.

Pappa, Richard S.↗

NASA NTRS1986

Towards an optimised sputtered MoS2 lubricant film

It is shown that the tribological quality of MoS2 lubricant films formed by magnetron sputtering is determined by the choice of sputtering conditions. By selecting the appropriate conditions, films of extremely high lubricity and endurance (in vacuum), which are well suited to many space applications, are obtained. Such MoS2 films, when applied to precision ball hearings, give rise to the lowest torques (for the given test conditions) yet seen in our laboratory. While a remarkably good performance is obtained in vacuum, tests in air show a marked deterioration in lubricating qualities. It is demonstrated that this is attributable to the adsorption of water vapor on MoS2 surfaces and that the degree of deterioration is related to the partial pressure of water vapor present. Analysis of results indicates that the factors relevant to obtaining optimum films are deposition rate and film composition.

Roberts, E. W.↗

NASA NTRS1990

Intracavity Dye-Laser Absorption Spectroscopy (IDLAS) for application to planetary molecules

Time-resolved, quasi-continuous wave, intracavity dye-laser absorption spectroscopy is applied to the investigation of absolute absorption coefficients for vibrational-rotational overtone bands of water at visible wavelengths. Emphasis is placed on critical factors affecting detection sensitivity and data analysis. Typical generation-time dependent absorption spectra are given.

Lang, Todd M.↗

NASA NTRS1989

Abundances of the elements in the intergalactic medium

A summary of the X-ray and optical spectroscopic data on emission lines from elements in clusters of galaxies is presented. The best data exists for Fe. For the about 30 well-observed clusters, the mean Fe abundance is about 0.4 solar, but there appears to be a real variation of at least a factor of 2. X-ray emission lines from O, Mg, Si and S have been detected, and their abundances are within a factor of a few of solar. Analysis of optical emission lines from cooling gas due to O, N, and S also indicates abundances not too far from solar values. The implications of the presence of heavy elements in the intergalactic medium of clusters for the evolution of the chemical abundances of galaxies are discussed.

Mushotzky, Richard↗

NASA NTRS1990

Lunar orbiting microwave beam power system

A microwave-beam power system using lunar orbiting solar-powered satellite(s) and surface rectenna(s) is investigated as a possible energy source for the moon's surface. The concept has the potential of achieving reduced system mass by placing the power source in orbit. This can greatly reduce and/or eliminate the 14-d energy storage requirement of a lunar surface solar system. Also, propellants required to de-orbit to the surface are greatly reduced. To determine the practicality of the concept and the most important factors, a zeroth-order feasibility analysis is performed. Three different operation scenarios employing state of the art technology and forecasts for two different sets of advanced technologies are investigated. To reduce the complexity of the problem, satellite(s) are assumed to be in circular equatorial orbits around the moon, supplying continuous power to a single equatorial base through a fixed horizontal rectenna on the surface. State of the art technology yields specific masses greater than 2500 kg/kw, well above projections for surface systems. The specific masses are on the order of 100 kg/kW using advanced technologies, which is within the range of projections for surface nuclear (20 kg/kW) and solar systems (500 kg/kW). Further studies examining optimization of the scenarios, other technologies, such as laser transmitters and nuclear sources, and operational issues, such as logistics, maintenance, and support, are being carried out to support the Space Exploration Initiative (SEI) to the moon and Mars.

Fay, Edgar H.↗

NASA NTRS1991

Experimental investigation of the flow field in the head-end star slot section of a solid rocket motor

A test program has been developed to investigate the complex flowfield in the head-end, star grain section of a solid rocket motor. Documentation of the flowfield pattern is to be obtained using both flow visualization techniques and quantitative methods, including static pressure measurements, heat transfer coefficient measurements, and hot-wire anemometry. A cold-flow, one-tenth-scale model based on the geometry of the Space Shuttle SRM head-end section and its single-port igniter, along with two models of a four-port igniter, have been constructed. The scale factor is derived from a scaling analysis which matches Reynolds number between the model and the full-scale flowfield in the star grain section. The NASA Marshall Space Flight Center 14 x 14 inch trisonic wind tunnel will be utilized for the cold flow tests. Since the work is still in progress, no results are included.

Ciucci, A.↗

NASA NTRS1992

The Use of Subcarriers in Future DSN Missions

The performance of deep space telemetry signals that employ a residual carrier modulation technique is compared in the presence and absence of a subcarrier. When the subcarrier is present, the performance for the resulting pulse-coded modulation/phase-shift keyed/phase-modulated (PCM/PSK/PM) scheme is evaluated for both sine wave and square wave subcarriers and non-return-to zero (NRZ) data. When the subcarrier is absent, the performance for the resulting PCM/PM technique is evaluated for both the NRZ and the bi-phase data format. The comparison is based on telemetry performance as well as bandwidth efficiency. The first criterion is characterized in terms of the symbol error rate (SER) as a function of symbol SNR, loop bandwidth-to-data rate ratio, and modulation index. The bandwidth efficiency is characterized by the occupancy factor. The results of both the analysis and measurements show that when the interference-to-carrier ratio (ICR) is less than -15 dB, the performance degradation in the absence of a subcarrier is negligible. Various combinations of loop bandwidth-to-data rate ratios and modulation indices that achieve this performance are derived and listed. Bandwidth occupancy comparison indicates that PCM/PM/NRZ is the most efficient in this regard. Therefore, by eliminating the subcarrier and using the PCM/PM/NRZ scheme, many advantages can be realized without any sacrifice in performance.

Shihabi, M. M.↗