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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

An improved lamination technique for solar arrays

Encapsulating solar cells by lamination has been plagued with problems such as bubbles, cell shifting, ripples, and cracked cells. A low-cost laminating procedure has been developed using a double vacuum bagging technique and recently improved formulations of ethylene vinyl acetate, successfully minimizing these problems. The lamination fixturing used is described. The causes and cures of various problems are discussed and solutions to these problems presented. The apparent modulus of the face sheet seen by the module being laminated is believed to be the primary variable which must be optimized. Conditions at the module edge are also considered to be important for producing an acceptable product.

Garcia, A., III↗
NASA NTRS1981

The design of a microstrip antenna array for a UHF space telemetry link

An array of microstrip antenna panels was designed for use on a small instrumented satellite as part of a 400-MHz telemetry link between that satellite and NASA's shuttle spacecraft. A roughly omnidirectional phi-plane pattern was desired. The 1.4-wavelength diameter of the satellite and the various ports and structures on its surface presented strong constraints on the antenna array design. Eight antennas, each one a quarter-wavelength panel with one radiating and one shorted edge, were chosen. A phi-plane pattern ripple of 4.4 dB and a gain of at least 0.1 dB relative to a half-wavelength dipole were realized. The design technique used for the individual antenna panels included the study of feed-point location for impedance matching and the effect of losses in the dielectric. A superposition method was used to synthesize the radiation patterns for different numbers and different excitations of antennas on the satellite.

Post, R. E.↗
NASA NTRS1981

Venusian saltation

Numerical solutions are given for particle trajectory equations of motion for the surface of Venus. Particles in saltation obtain maximum heights of two or less centimeters, and have path lengths of less than a meter regardless of particle diameter. The saltation process and particle trajectories are found insensitive to surface pressure changes over the range of 70 to 100 bars, and temperature changes over the range of 600 to 900 K. Due to dense atmosphere, the net rate of surface material transport due to saltation is small for particles in diameters from 0.01 to 7 mm, as compared to earth which has 10 times more, and Mars which has 250 times more. Path length scales are also found to be very small, suggesting the presence of dunes on Venus; however, there is still a possibility that small ripples do exist, which cannot be detected by high-resolution radar images.

White, B. R.↗
NASA NTRS1981

Multisensor analysis of hydrologic features with emphasis on the Seasat SAR

Synthetic aperture radar (SAR) imagery of the Wind River Range area in Wyoming is compared with visible and near-infrared imagery of the same area. Data from the Seasat L-Band SAR and an aircraft X-Band SAR are compared with Landsat Return Beam Vidicon (RBV) visible data and near-infrared aerial photography and topographic maps of the same area. It is noted that visible and near-infrared data provide more information than the SAR data when conditions are the most favorable. The SAR penetrates clouds and snow, however, and data can be acquired day or night. Drainage density detail is good on SAR imagery because individual streams show up well owing to riparian vegetation; this causes higher radar reflections which result from the 'rough' surface which vegetation creates. In the winter image, the X-Band radar data show high returns because of cracks on the lake ice surfaces. High returns can also be seen in the L-Band SAR imagery of the lakes due to ripples on the surface induced by wind. It is concluded that the use of multispectral data would optimize analysis of hydrologic features.

Foster, J. L.↗
NASA NTRS1981

Flow and far field acoustic amplification properties of heated and unheated jets

The interaction of an acoustic pulse with the experimentally determined mean flow field of a spreading jet is simulated numerically. The simulation is obtained through solving the Euler equations linearized about the spreading jet. The model reveals a small, sustained oscillation long after the original pulse has passed. This remnant is considered a continual shedding of vortices from the nozzle lip, together with the generation of acoustic ripples. IT is shown that the jet also acts as an amplifier of sound. This amplification is traced to the jet's stability characteristics. It is demonstrated that some of the observed differences in the spectra of heated and unheated jets can be attributed to differences in the stability characteristics of the jets.

Maestrello, L.↗
NASA NTRS1982

Signal analysis of voltage noise in welding arcs

Gas tungsten arc welds were made on low alloy steel plates to which intentional defects (discontinuities) were imposed. Disruption of shielding gas, welding over surface films, and tack welds produce changes in what is otherwise a relatively uniform voltage signal. The arc voltage was 15 volts + or - 2 volts with 300 mV ripple noise from the power supply. Changes in this steady noise voltage varied from 50 mV to less than one millivolt depending on the severity and the type of change experienced. In some instances the changes were easily detected by analysis of the signal in real time, while in other cases the signal had to transformed to the frequency domain in order to detect the changes. Discontinuities as small as 1.5 mm in length were detected. The ultimate sensitivity and reproducibility of the technique is still being investigated.

Elis, E.↗
NASA NTRS1982

Summary of electric vehicle dc motor-controller tests

The differences in the performance of dc motors are evaluated when operating with chopper type controllers, and when operating on direct current. The interactions between the motor and the controller which cause these differences are investigated. Motor-controlled tests provided some of the data the quantified motor efficiency variations for both ripple free and chopper modes of operation.

Mcbrien, E. F.↗
NASA NTRS1982

Long cloud observations on Mars and implications for boundary layer characteristics over slopes

The times and locations of occurrence are measured, as are the wavelengths and, when possible, the apparent velocity of motion of these clouds. The wavelengths of the patches of ripple clouds that are often found with the long formations are tabulated. The long clouds are observed only in the early morning hours, suggesting that they are associated with drainage winds caused by a cold planetary boundary layer. Simple mathematical models are developed to examine various aspects of such boundary winds; these make it possible to construct a complete and self-consistent explanation of all the observed features of the cloud formations.

Kahn, R.↗
NASA NTRS1982

Quasi-liquid states observed on ion beam microtextured surfaces

Liquid-like properties have been observed on surface structures developed by means of ion beam microtexturing. The structures include cones, pyramids, or wavelike formations. The observed liquid-like effects are drips and ripples on the sides of cones, droplet formation, the apparent flow and coalescence of closely packed structures, wetting angle and other surface tension effects, and the bending of cones by additional heating. The bulk temperatures are in the range of 50-600 C. These effects are seen to some extent on Cu, Al, Au, Pb, and Ni substrates.

Rossnagel, S. M.↗
NASA NTRS1982

Simulation, flight performance and control of Dynamics Explorers-A and -B spacecraft

This paper presents the results obtained from a study conducted to evaluate the dynamic behavior of Dynamics Explorers-A and -B spacecraft. The effects of environmental torques on the spacecraft motion, momentum buildup due to these torques, and the long appendages on the main body motion are studied using numerical simulations. The numerical results are compared with flight data and are found to be in good agreement. A control philosophy for DE-B to minimize the pitch axis drift is developed. The performance of DE-B in inverted mode and during the inversion maneuver as well as in the normal mode are studied. The spin ripple effect on DE-A due to the long appendages is analyzed and the results are correlated with flight data.

Sellappan, R. G.↗
NASA NTRS1982

Off-line, built-in test techniques for VLSI circuits

It is shown that the use of redundant on-chip circuitry improves the testability of an entire VLSI circuit. In the study described here, five techniques applied to a two-bit ripple carry adder are compared. The techniques considered are self-oscillation, self-comparison, partition, scan path, and built-in logic block observer. It is noted that both classical stuck-at faults and nonclassical faults, such as bridging faults (shorts), stuck-on x faults where x may be 0, 1, or vary between the two, and parasitic flip-flop faults occur in IC structures. To simplify the analysis of the testing techniques, however, a stuck-at fault model is assumed.

Buehler, M. G.↗
NASA NTRS1982

Thematic mapper flight model preshipment review data package. Volume 4: Appendix. Part C: Power supply data

The acceptance test data package for the thematic mapper flight model power supply was reviewed and the data compared to the relevant specification. The power supply was found to be within specification. Final test data for outut voltage regulation and ripple, efficiency, over and undervoltage protection, telemetry, impedances, turn-on requirements, and input current limits are presented.

Source record↗
NASA NTRS1982

Evaluating software development by analysis of changes: The data from the software engineering laboratory

An effective data collection methodology for evaluating software development methodologies was applied to four different software development projects. Goals of the data collection included characterizing changes and errors, characterizing projects and programmers, identifying effective error detection and correction techniques, and investigating ripple effects. The data collected consisted of changes (including error corrections) made to the software after code was written and baselined, but before testing began. Data collection and validation were concurrent with software development. Changes reported were verified by interviews with programmers.

Source record↗
NASA NTRS1983

A study of the surface deterioration due to erosion

It is pointed out that materials exposed to particle impacts are eroded and subjected to deterioration of their surface quality. In the case of turbomachinery, this surface deterioration can lead to a significant decrease in engine performance. Tabakoff and Balan (1981) have conducted experiments on the erosion related performance changes in two-dimensional airfoil cascades. It was found that the increase in surface roughness associated with erosion is a major factor in the performance decrease of the cascades. Attention is given to experiments which were conducted on 6061 T6 flat plate aluminum specimens. A series of experiments were carried out in an erosion wind tunnel using a collimated beam of particles. In agreement with existing theories and experiments, erosion ripple generation was observed for the angles of attack up to 60 degrees.

Tabakoff, W.↗
NASA NTRS1984

A dc to dc converter

The object of the invention is to provide an improved converter for converting one direct current voltage to another. A plurality of phased square wave voltages are provided from a ring counter through amplifiers to a like plurality of output transformers. Each of these transformers has two windings, and S(1) winding and an S(2) winding. The S(1) windings are connected in series, then the S(2) windings are connected in series, and finally, the two sets of windings are connected in series. One of six SCRs is connected between each two series connected windings to a positive output terminal and one of diodes is connected between each set of two windings of a zero output terminal. By virtue of this configuration, a quite high average direct current voltage is obtained, which varies between full voltage and two-thirds full voltage rather than from full voltage to zero. Further, its variation, ripple frequency, is reduced to one-sixth of that present in a single phase system. Application to raising battery voltage for an ion propulsion system is mentioned.

Willis, A. E.↗
NASA NTRS1984

Radar-visible wind streaks in the Altiplano of Bolivia

Isolated knobs that are erosional remnants of central volcanoes or of folded rocks occur in several areas of the Altiplano are visible on both optical and images. The optically visible streaks occur in the immediate lee of the knobs, whereas the radar visible streaks occur in the zone downwind between the knobs. Aerial reconnaissance and field studies showed that the optically visible streaks consist of a series of small ( 100 m wide) barchan and barchanoid dunes, intradune sand sheets, and sand hummocks (large shrub coppice dunes) up to 15 m across and 5 m high. On LANDSAT images these features are poorly resolved but combine to form a bright streak. On the radar image, this area also appears brighter than the zone of the radar dark streak; evidently, the dunes and hummocks serve as radar reflectors. The radar dark streak consists of a relatively flat, smooth sand sheet which lacks organized aerolian bedforms, other than occasional ripples. Wind velocity profiles show a greater U value in the optically bright streak zone than in the radar dark streak.

Greeley, R.↗
NASA NTRS1984

An advanced pitch change mechanism incorporating a hybrid traction drive

A design of a propeller pitch control mechanism is described that meets the demanding requirements of a high-power, advanced turboprop. In this application, blade twisting moment torque can be comparable to that of the main reduction gearbox output: precise pitch control, reliability and compactness are all at a premium. A key element in the design is a compact, high-ratio hybrid traction drive which offers low torque ripple and high torsional stiffness. The traction drive couples a high speed electric motor/alternator unit to a ball screw that actuates the blade control links. The technical merits of this arrangement and the performance characteristics of the traction drive are discussed. Comparisons are made to the more conventional pitch control mechanisms.

Steinetz, B. M.↗
NASA NTRS1984

The 20 x 20 high speed microwave switches

Tests were conducted at NASA Lewis Research Center to characterize the proof-of-concept matrix switches built under NASA contract by Ford Aerospace and Aeronautics Corporation at Palo Alto, California, and the General Electric Company at Valley Forge, Pennsylvania. The contract requirements and goals are tabulated along with the results of the NASA tests. Characteristics examined are bandwidth, insertion loss, ripple, switching speed, isolation, standing wave ratio (input and output), deviation from linear phase, noise figure, reconfiguration rates, spurious responses, gain compression, and third order intermodulation distortion. A brief description of the testing method and a statistical analysis of the test results for each of the switches are provided.

Saunders, A.↗