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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 1,387 records · Page 77

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DOE OSTI2020

Four-phase interleaved TCM DC-DC buck converter with matrix inductor in battery charging application

In this paper, a 1-kW DC-DC buck converter with a four-phase interleaved matrix inductor is proposed for battery charging applications. It is well-known that the DC bias on the inductor will cause high core loss as it changes the B–H characteristic. Typically, the transient conduction mode employed in high voltage applications for zero-voltageswitching of devices would cause higher inductor current ripple. The conventional approach to reduce the effect of DC bias and inductor current ripple is employing multi-phases. However, the cost and size of the converter will increase significantly. This paper proposes the matrix inductor which has a small volume and reduces the effect of the DC bias by flux sharing and flux cancellation at the same time, results in low inductor core loss. With the interleaved operations the output current ripple can be lower which is suitable for battery charging application. Besides, the comparison of the synchronous and interleaved operation is presented. A 1-kW prototype is built and the experimental results show that the peak efficiency is 99.1% and 99.2% for synchronous and interleaved control, respectively. Additionally, the output current ripple of the interleaved operation is reduced by 85% in comparison with the synchronous operation.

14 SOLAR ENERGY↗

DOE OSTI2025

Tungsten control in long pulse operation: feedback from WEST to ITER

The full W environment that is now foreseen for ITER puts strong emphasis on experimental results obtained in present devices in similar conditions. In this context, the WEST tokamak is well equipped to bring key contributions to the preparation of ITER operation, thanks to its capability to perform long pulses in dominant electron heating, torque-free scheme based on RF systems, and its ITER-grade actively cooled divertor. Recent results of interest cover the understanding of tungsten contamination and the evaluation of conditioning methods, the feedback on the current ramp-up phase, and the ageing of the ITER divertor components in L-mode attached condition. Further, new directions are being explored, in particular low divertor temperature operation that should be the normal operating regime of ITER. We also report on tungsten peaking physics, and the role of light impurity content.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Kinetic Simulations of the Kruskal–Schwarzschild Instability in Accelerating Striped Outflows: Dynamics and Energy Dissipation

Astrophysical relativistic outflows are launched as Poynting-flux dominated, yet the mechanism governing efficient magnetic dissipation, which powers the observed emission, is still poorly understood. We study magnetic energy dissipation in relativistic "striped" jets, which host current sheets separating magnetically dominated regions with opposite field polarity. The effective gravity force g in the rest frame of accelerating jets drives the Kruskal–Schwarzschild instability (KSI), a magnetic analog of the Rayleigh–Taylor instability. By means of 2D and 3D particle-in-cell simulations, we study the linear and nonlinear evolution of the KSI. The linear stage is well described by linear stability analysis. The nonlinear stages of the KSI generate thin (skin-depth-thick) current layers, with length comparable to the dominant KSI wavelength. There, the relativistic drift-kink mode and the tearing mode drive efficient magnetic dissipation. The dissipation rate can be cast as an increase in the effective width Δ eff of the dissipative region, which follows dΔ eff /dt ≃ 0.05 $\sqrt{Δ_{eff} g}$. Our results have important implications for the location of the dissipation region in gamma-ray burst and active galactic nuclei jets.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

High noise immunity one shot

Multivibrator circuit, which includes constant current source, isolates line noise from timing circuitry and field effect transistor controls circuit's operational modes. Circuit has high immunity to supply line noise.

Schaffer, G. L.↗

NASA NTRS1975

Propagation predictions and studies using a ray tracing program combined with a theoretical ionospheric model

Radio wave propagation predictions are described in which modern comprehensive theoretical ionospheric models are coupled with ray-tracing programs. In the computer code described, a network of electron density and collision frequency parameters along a band about the great circle path is calculated by specifying the transmitter and receiver geographic coordinates, time, the day number, and the 2800-MHz solar flux. The ray paths are calculated on specifying the frequency, mode, range of elevation angles, and range of azimuth angles from the great circle direction. The current program uses a combination of the Penn State MKI E and F region models and the Mitra-Rowe D and E region model. Application of the technique to the prediction of satellite to ground propagation and calculation of oblique incidence propagation paths and absorption are described. The implications of the study to the development of the next generation of ionospheric models are discussed.

Lee, M. K.↗

NASA NTRS1977

Some geologic observations concerning lunar geophysical models

The distribution of lunar geologic units in space and time and their mode of origin were considered since they provided significant data which bear on a number of current problems in lunar geophysics. Observations and problems were discussed which deal with the characterization of the upper 25 km of the lunar crust, the tectonic style of the crust, the formation of mascons within major basins, analysis of lunar magnetic anomalies, and the history of the lunar crust.

Head, J. W.↗

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 NTRS1982

Results of chopper-controlled discharge life cycling studies on lead acid batteries

A group of 108 state of the art nominally 6 volt lead acid batteries were tested in a program of one charge/discharge cycle per day for over two years or to ultimate battery failure. The primary objective was to determine battery cycle life as a function of depth of discharge (25 to 75 percent), chopper frequency (100 to 1000 Hz), duty cycle (25 to 87.5 percent), and average discharge current (20 to 260 A). The secondary objective was to determine the types of battery failure modes, if any, were due to the above parameters. The four parameters above were incorporated in a statistically designed test program.

Ewashinka, J. G.↗

NASA NTRS1983

NASA redox storage system development project, calendar year 1982

Development was continued for iron-chromium battery operation at 65 C. Membranes that were adequate at 25 C were shown to be unacceptable at 65 C with regard to selectivity. This led to the elevated-temperature, mixed-reactant mode of operation, in which each reactant solution, when discharged, contains both ferrous and chromic chlorides. This operating mode allows the use of very low-resistivity membranes, resulting in high energy efficiencies at current densities. It also allows the use of very simple techniques to correct for solvent or reactant transfer through cell membranes. Screening of candidate catalysts for the chromium electrode led to the development of a bismuth-lead candidate having several attractive characteristics.

Source record↗

NASA NTRS1983

Electrical safety for high voltage arrays

A number of key electrical safety requirements for the high voltage arrays of central station photovoltaic power systems are explored. The suitability of representative industrial DC power switchgear for control and fault protection was evaluated. Included were AC/DC circuit breakers, electromechanical contactors and relays, load interruptors, cold disconnect devices, sectionalizing switches, and high voltage DC fuses. As appropriate, steady state and transient characteristics were analyzed. Failure modes impacting upon operation and maintenance safety were also identified, as were the voltage withstand and current interruption levels.

Marshall, N. A.↗

NASA NTRS1985

Approximation of Optimal Infinite Dimensional Compensators for Flexible Structures

The infinite dimensional compensator for a large class of flexible structures, modeled as distributed systems are discussed, as well as an approximation scheme for designing finite dimensional compensators to approximate the infinite dimensional compensator. The approximation scheme is applied to develop a compensator for a space antenna model based on wrap-rib antennas being built currently. While the present model has been simplified, it retains the salient features of rigid body modes and several distributed components of different characteristics. The control and estimator gains are represented by functional gains, which provide graphical representations of the control and estimator laws. These functional gains also indicate the convergence of the finite dimensional compensators and show which modes the optimal compensator ignores.

Gibson, J. S.↗

NASA NTRS1985

Orbital maneuvering vehicle guidance, navigation and control

This paper describes the Orbital Maneuvering Vehicle (OMV) concept and its intended role. It recaps the past activities leading up to the current concept and summarizes the present status and plans. The various types of missions and operating modes required by the OMV are described as the basis of the guidance, navigation and control (GN&C) requirements. The general GN&C problem is outlined with potential hardware solutions.

Huber, W. G.↗

NASA NTRS1986

Numerical simulation of flare energy build-up and release via Joule dissipation

A new numerical MHD model is developed to study the evolution of an active region due to photospheric converging motion, which leads to magnetic-energy buildup in the form of electric current. Because this new MHD model has incorporated finite conductivity, the energy conversion occurs from magnetic mode to thermal mode through Joule dissipation. In order to test the causality relationship between the occurrence of flare and photospheric motion, a multiple-pole configuration with neutral point is used. Using these results it is found that in addition to the converging motion, the initial magnetic-field configuration and the redistribution of the magnetic flux at photospheric level enhance the possibility for the development of a flare.

Wu, S. T.↗

NASA NTRS1988

Locking hinge

The space station configuration currently studied utilizes structures which require struts to be hinged in the middle in the stowed mode and locked into place in the deployed mode. Since there are hundreds of hinges involved, it is necessary that they have simple, positive locking features with a minimum of joint looseness or slack. This invention comprises two similar housings hinged together with a spring loaded locking member which assists in making as well as breaking the lock. This invention comprises a bracket hinge and bracket members with a spring biased and movable locking member. The locking or latch member has ear parts received in locking openings where wedging surfaces on the ear parts cooperate with complimentary surfaces on the bracket members for bringing the bracket members into a tight end-to-end alignment when the bracket members are in an extended position. When the locking member is moved to an unlocking position, pivoting of the hinge about a pivot pin automatically places the locking member to retain the locking member in an unlocked position. In pivoting the hinge from an extended position to a folded position, longitudinal spring members are placed under tension over annular rollers so that the spring tension in a folded position assists in return of the hinge from a folded to an extended position. Novelty lies in the creation of a locking hinge which allows compact storage and easy assembly of structural members having a minimal number of parts.

Wesselski, Clarence J.↗

NASA NTRS1990

Weather data dissemination to aircraft

Documentation exists that shows weather to be responsible for approximately 40 percent of all general aviation accidents with fatalities. Weather data products available on the ground are becoming more sophisticated and greater in number. Although many of these data are critical to aircraft safety, they currently must be transmitted verbally to the aircraft. This process is labor intensive and provides a low rate of information transfer. Consequently, the pilot is often forced to make life-critical decisions based on incomplete and outdated information. Automated transmission of weather data from the ground to the aircraft can provide the aircrew with accurate data in near-real time. The current National Airspace System Plan calls for such an uplink capability to be provided by the Mode S Beacon System data link. Although this system has a very advanced data link capability, it will not be capable of providing adequate weather data to all airspace users in its planned configuration. This paper delineates some of the important weather data uplink system requirements, and describes a system which is capable of meeting these requirements. The proposed system utilizes a run-length coding technique for image data compression and a hybrid phase and amplitude modulation technique for the transmission of both voice and weather data on existing aeronautical Very High Frequency (VHF) voice communication channels.

Mcfarland, Richard H.↗

NASA NTRS1991

Impact design methods for ceramic components in gas turbine engines

Methods currently under development to design ceramic turbine components with improved impact resistance are presented. Two different modes of impact damage are identified and characterized, i.e., structural damage and local damage. The entire computation is incorporated into the EPIC computer code. Model capability is demonstrated by simulating instrumented plate impact and particle impact tests.

Song, J.↗

NASA NTRS1992

Active galactic nuclei. IV - Supplying black hole clusters by tidal disruption and by tidal capture of stars

The extent to which individual holes in a cluster of black holes with a mass spectrum can liberate and accrete the resulting material by tidally disrupting stars they encounter, or by capturing stars as binary companions is studied. It is found that the smaller black holes in 'the halo' of such clusters can adequately supply themselves to the level M-dot sub h or greater than 0.0001(M-dot sub h) sub crit, and up to 0.05(M-dot sub h)sub crit for the smallest holes, by tidal disruption, as long as the cluster is embedded in a distribution of stars of relatively high density (not less than 0.1M sub cl/cu pc), and as long as the entire cluster of stars is not too compact (not less than 0.5 pc). Consideration is given to modifications this 'internal' mode of supply introduces in the spectrum emitted by such black hole clusters, and to the current status of their viability as models for AGN and QSOs in light of dynamical studies by Quinlan and Shapiro (1987, 1989).

Stoeger, W. R.↗

NASA NTRS1994

A long-baseline method for HST gyro drift rate bias calibration

The routine on-orbit calibration of the Hubble Space Telescope (HST) rate gyro assemblies (RGA's) has depended on several related algorithms for drift rate bias calibration. The gyros have exhibited time-varying biases, which must be regularly corrected to maintain pointing stability. Currently, gyro drift parameters are uplinked to the spacecraft every 1-2 days for low rate mode and every 7 days for high rate mode. In order to minimize the impact of frequent calibrations on the HST science schedule, we have refined the gyro calibration algorithms and data collection schemes to reduce the amounts of telemetry data and processing time required for accurate bias calibration. We present a review of the evolution of the gyro calibration algorithms, with particular attention to what we have called the long-baseline bias (LBBIAS) technique, and describe the relative success of these methods in maintaining spacecraft stability.

Boia, John J.↗