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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Acceleration processes in the quasi-steady magnetoplasmadynamic discharge

The flow field characteristics within the discharge chamber and exhaust of a quasi-steady magnetoplasmadynamic (MPD) arcjet were examined to clarify the nature of the plasma acceleration process. The observation of discharge characteristics unperturbed by insulator ablation and terminal voltage fluctuations, first requires the satisfaction of three criteria: the use of refractory insulator materials; a mass injection geometry tailored to provide propellant to both electrode regions of the discharge; and a cathode of sufficient surface area to permit nominal MPD arcjet operation for given combinations of arc current and total mass flow. The axial velocity profile and electromagnetic discharge structure were measured for an arcjet configuration which functions nominally at 15.3 kA and 6 g/sec argon mass flow. An empirical two-flow plasma acceleration model is advanced which delineates inner and outer flow regions and accounts for the observed velocity profile and calculated thrust of the accelerator.

Boyle, M. J.↗
NASA NTRS1977

Spectroscopic determination of electrical conductivity in an MHD duct from absolute intensity measurements

Measurements of the electrical conductivity in the NASA Lewis cesium seeded, H2-O2 MHD duct made by applying a voltage across the channel from one end electrode to the other, measuring the current, and using the inner electrodes as probes to monitor the voltage distribution along the channel were found to be in good agreement with theory except at low combustion pressures and/or high ratios of seed/oxygen mass flows. To corroborate these measurements and to analyze the possibility of nonuniform seed injection as a cause of the above deviations, a spectroscopic investigation of the plasma conductivity was undertaken. Radial profiles of emission coefficient were obtained from measured transverse profiles of the absolute integrated intensity by Abel inversion. Radial profiles of electrical conductivity were then obtained under two different assumptions. In the first the Cs seed fraction is assumed uniform and equal to the measured flow rate at the time when the temperature and conductivity were obtained. In the second method the local temperature and pressure are taken to be those given by a one-dimensional channel calculation including heat transfer and friction. The results of the two methods are compared to the previously measured conductivity.

Wang, S. Y.↗
NASA NTRS2011

Failure Modes in Capacitors When Tested Under a Time-Varying Stress

Power-on failure has been the prevalent failure mechanism for solid tantalum capacitors in decoupling applications. A surge step stress test (SSST) has been previously applied to identify the critical stress level of a capacitor batch to give some predictability to the power-on failure mechanism [1]. But SSST can also be viewed as an electrically destructive test under a time-varying stress (voltage). It consists of rapidly charging the capacitor with incremental voltage increases, through a low resistance in series, until the capacitor under test is electrically shorted. When the reliability of capacitors is evaluated, a highly accelerated life test (HALT) is usually adopted since it is a time-efficient method of determining the failure mechanism; however, a destructive test under a time-varying stress such as SSST is even more time efficient. It usually takes days or weeks to complete a HALT test, but it only takes minutes for a time-varying stress test to produce failures. The advantage of incorporating a specific time-varying stress profile into a statistical model is significant in providing an alternative life test method for quickly revealing the failure mechanism in capacitors. In this paper, a time-varying stress that mimics a typical SSST has been incorporated into the Weibull model to characterize the failure mechanism in different types of capacitors. The SSST circuit and transient conditions for correctly surge testing capacitors are discussed. Finally, the SSST was applied for testing Ta capacitors, polymer aluminum capacitors (PA capacitors), and multi-layer ceramic (MLC) capacitors with both precious metal electrodes (PME) and base metal electrodes (BME). The test results are found to be directly associated with the dielectric layer breakdown in Ta and PA capacitors and are independent of the capacitor values, the way the capacitors were built, and the capacitors manufacturers. The test results also show that MLC capacitors exhibit surge breakdown voltages much higher than the rated voltage and that the breakdown field is inversely proportional to the dielectric layer thickness. The SSST data can also be used to comparatively evaluate the voltage robustness of capacitors for decoupling applications.

Liu, David (Donhang)↗
NASA NTRS1999

Electrical and Thermal Characteristics of Lithium-Ion Cells

The 18,650 type lithium ion cells are characterized by a cell resistance of 130 mOmega, capacity of 1.27 Ah at 25 C, and a mid-discharge voltage of 3.6 V. The capacity loss in the 72-hour stand test was 3.39%. The heat dissipation properties were determined by a radiative calorimeter. During charge, initial endothermic cooling and subsequent exothermic cooling beyond 55% state- of-charge were observed. At C/2 rate of discharge (which is considered medium rate), the heat dissipated was 17 mW/cu cm. The heat dissipation profile during discharge is also unique in the presence of a minimum that is different from that observed for Ni-Cd, Ni-MH, and Ni-H2 cells.

Rao. Gopalskrishna M.↗
NASA NTRS1999

DS-2 Mars Microprobe Battery

In January of 1999 the NM DS-2 Mars microprobe will be launched to impact on Mars in December. The technical objectives of the missions are to demonstrate: key technologies, a passive atmospheric entry, highly integrated microelectronics which can withstand both low temperatures and high decelerations, and the capability to conduct in-situ, surface and subsurface science data acquisition. The scientific objectives are to determine if ice is present below the Martian surface, measure the local atmospheric pressure, characterize the thermal properties of the martian subsurface soil, and to estimate the vertical temperature gradient of the Martian soil. The battery requirements are 2-4 cell batteries, with voltage of 6-14 volts, capacity of 550 mAh at 80C, and 2Ah at 25C, shelf life of 2.5 years, an operating temperature of 60C and below, and the ability to withstand shock impact of 80,000 g's. The technical challenges and the approach is reviewed. The Li-SOCL2 system is reviewed, and graphs showing the current and voltage is displayed, along with the voltage over discharge time. The problems encountered during the testing were: (1) impact sensitivity, (2) cracking of the seals, and (3) delay in voltage. A new design resulted in no problems in the impact testing phase. The corrective actions for the seal problems involved: (1) pre weld fill tube, (2) an improved heat sink during case to cover weld and (3) change the seal dimensions to reduce stress. To correct the voltage delay problem the solutions involved: (1) drying the electrodes to reduce contamination by water, (2) assemblage of the cells within a week of electrode manufacture, (3) ensure electrolyte purity, and (4) provide second depassivation pulse after landing. The conclusions on further testing were that the battery can: (1) withstand anticipated shock of up to 80,000 g, (2) meet the discharge profile post shock at Mars temperatures, (3) meet the required self discharge rate and (4) meet environmental requirements.

Frank, H.↗
NASA NTRS1999

Electrical and Thermal Characteristics of Lithium-Ion Cells

The 18650 type lithium ion cells are characterized by a cell resistance of 130 m Omega, capacity of 1.27 Ah at 25C, and a mid-discharge voltage of 3.6 V. The capacity loss in the 72-hour stand test was 3.39 percent. The heat dissipation properties were determined by a radiative calorimeter. During charge, initial endothermic cooling and subsequent exothermic cooling beyond 55 percent state-of-charge were observed. At C/2 rate of discharge (which is considered medium rate), the heat dissipated was 17 mW/cc. The heat dissipation profile during discharge is also unique in the presence of a minimum that is different from that observed for Ni-Cd, Ni-MH, and Ni-H2 cells.

Vaidyanathan, Hari↗
NASA NTRSDate not supplied

Predicting Thermal Response in a Li-ion Cell on a UAV Fight Profile

As the energy storage devices continue to "pack" more energy in a small space, any damage, battery component failure, manufacturing defect, or electrically abusing the battery can lead to catastrophic thermal runaway events. A catastrophic thermal event in a cell leads to high temperature, in some instances spewing of battery materials due to gas development from side reactions initiated due to high internal temperatures. Also, a thermal runaway event can propagate from a single "failed" cell to the pack in a battery pack, leading to a more significant event. Mitigating a thermal runaway event is important in the commercial and automotive sectors. However, preventing such events in an electric aircraft (or air taxis) is paramount due to the lack of alternatives in the event of a failure. Battery prognostics algorithms allow the prediction of state-of-charge (SOC) and end-of-life (EOL) of a Li-ion battery in a UAV (unmanned air vehicle) [1]. For this presentation, we will extend this two-level battery predictive algorithm to predict SOC, EOL, and estimated maximum temperature during a simulated flight. The model is extended by integrating a lumped physics-driven thermal model for high current densities [2]. The parameters used to control SOC and EOL are maximum storable charge, time constant for Li-ion diffusivity in the carbon particles, and internal cell resistance. Cycling leads to an increase in the heat generated by an aged Li-ion cell with a LiyCoO2 (LCO) cathode and a LixC6 (MCMB) anode. The aging of a cell leads to increase in SEI layer thickness, the diffusion time for the lithium ions inside the electrodes, and the local reaction rates, in addition to the thermodynamic abuse caused by fixed cycling voltages controlled by a Battery Management System. As the battery ages, the cell resistance increases, while the onset temperature of the thermal runaway decreases (depends on the cell chemistry and cell abuse history). Any large deviation of the cell temperature from the estimated (expected) value can identify a faulty cell. Since SEI decomposition has the lowest onset temperature in the series of reactions leading to thermal runaway, the model considers the self-heating rate of the SEI decomposition as onset temperature (similar to Ref. [3]). The parameters in the Arrhenius equation for the SEI heating rate depend on the number of cycles, the cell's operating temperature, and the cell's abuse history [4,5]. Coupling the electrochemical, thermal, and aging model allow the prognostic algorithm to estimate a typical cell voltage and temperature as a function of age (cycling and calendar), whose departure from measured values from the BMS is used to identify a safety event. In addition, we will present the results from two simulated flight scenarios for a UAV: typical and extreme, since the power requirements vary significantly during take-off, landing, and changing altitudes, while the power requirements remain low during the cruise. For this presentation, the power requirement for a battery pack in a UAV is scaled to a single cell. This cell is cycled through a simulated profile, and the data is collected and used to predict a safety event.

Li-ion↗
NASA NTRS1988

An adaptive array antenna for mobile satellite communications

The adaptive array is linearly polarized and consists essentially of a driven lambda/4 monopole surrounded by an array of parasitic elements all mounted on a ground plane of finite size. The parasitic elements are all connected to ground via pin diodes. By applying suitable bias voltages, the desired parasitic elements can be activated and made highly reflective. The directivity and pointing of the antenna beam can be controlled in both the azimuth and elevation planes using high speed digital switching techniques. The antenna RF losses are neglible and the maximum gain is close to the theoretical value determined by the effective aperture size. The antenna is compact, has a low profile, is inexpensive to manufacture and can handle high transmitter power.

Milne, Robert↗
NASA NTRS1999

Control of Flowing Liquid Films by Electrostatic Fields in Space

The interaction of a spacially varying electric field and a flowing thin liquid film is investigated experimentally for the design of a proposed light weight space radiator. Electrodes are utilized to create a negative pressure at the bottom of a fluid film and suppress leaks if a micrometeorite punctures the radiator surface. Experimental pressure profiles under a vertical falling film, which passes under a finite electrode, show that fields of sufficient strength can be used safely in such a device. Leak stopping experiments demonstrate that leaks can be stopped with an electric field in earth gravity. A new type of electrohydrodynamic instability causes waves in the fluid film to develop into 3D cones and touch the electrode at a critical voltage. Methods previously used to calculate critical voltages for non moving films are shown to be inappropriate for this situation. The instability determines a maximum field which may be utilized in design, so the possible dependence of critical voltage on electrode length, height above the film, and fluid Reynolds number is discussed.

Griffing, E. M.↗
NASA NTRS1975

The 15 cm mercury ion thruster research 1975

Doubly charged ion current measurements in the beam of a SERT II thruster are shown to introduce corrections which bring its calculated thrust into close agreement with that measured during flight testing. A theoretical model of doubly charged ion production and loss in mercury electron bombardment thrusters is discussed and is shown to yield doubly-to-singly charged ion density ratios that agree with experimental measurements obtained on a 15 cm diameter thruster over a range of operating conditions. Single cusp magnetic field thruster operation is discussed and measured ion beam profiles, performance data, doubly charged ion densities, and discharge plasma characteristics are presented for a range of operating conditions and thruster geometries. Variations in the characteristics of this thruster are compared to those observed in the divergent field thruster and the cusped field thruster is shown to yield flatter ion beam profiles at about the same discharge power and propellant utilization operating point. An ion optics test program is described and the measured effects of grid system dimensions on ion beamlet half angle and diameter are examined. The effectiveness of hollow cathode startup using a thermionically emitting filament within the cathode is examined over a range of mercury flow rates and compared to results obtained with a high voltage tickler startup technique. Results of cathode plasma property measurement tests conducted within the cathode are presented.

Wilbur, P. J.↗
NASA NTRS2004

Mass flow sensor utilizing a resistance bridge

A mass flow sensor to be mounted within a duct and measures the mass flow of a fluid stream moving through the duct. The sensor is an elongated thin quartz substrate having a plurality of platinum strips extending in a parallel relationship on the strip, with certain of the strips being resistors connected to an excitation voltage. The resistors form the legs of a Wheatstone bridge. The resistors are spaced a sufficient distance inwardly from the leading and trailing edges of the substrate to lie within the velocity recovery region so that the measured flow is the same as the actual upstream flow. The resistor strips extend at least half-way through the fluid stream to include a substantial part of the velocity profile of the stream. Certain of the resistors detect a change in temperature as the fluid stream moves across the substrate to provide an output signal from the Wheatstone bridge which is representative of the fluid flow. A heater is located in the midst of the resistor array to heat the air as it passes over the array.

Fralick, Gustave C.↗
NASA NTRS1999

Low Energy Sputtering Experiments for Ion Engine Lifetime Assessment

The sputtering yield of molybdenum under xenon ion bombardment was measured using a Quartz Crystal Microbalance. The measurements were made for ion kinetic energies in the range 100-1keV on molybdenum films deposited by magnetron sputtering in conditions optimized to reproduce or approach bulk-like properties. SEM micrographs for different anode bias voltages during the deposition are compared, and four different methods were implemented to estimate the density of the molybdenum films. A careful discussion of the Quartz Crystal Microbalance is proposed and it is shown that this method can be used to measure mass changes that are distributed unevenly on the crystal electrode surface, if an analytical expression is known for the differential mass-sensitivity of the crystal and the erosion profile. Finally, results are presented that are in good agreement with previously published data, and it is concluded that this method holds the promise of enabling sputtering yield measurements at energies closer to the threshold energy in the very short term.

Duchemin Olivier B.↗
NASA NTRS2006

Performance of Solar Electric Powered Deep Space Missions Using Hall Thruster Propulsion

Power limited, low-thrust trajectories were assessed for missions to Jupiter, Saturn, and Neptune utilizing a single Venus Gravity Assist (VGA) and a primary propulsion system based on either a 3-kW high voltage Hall thruster, of the type being developed by the NASA In-Space Propulsion Technology Program, or an 8-kW variant of this thruster. These Hall thrusters operate with specific impulses below 3,000 seconds. A trade study was conducted to examine mission parameters that include: net delivered mass (NDM), beginning-of-life (BOL) solar array power, heliocentric transfer time, required launch vehicle, number of operating thrusters, and throttle profile. The top performing spacecraft configuration was defined to be the one that delivered the highest mass for a range of transfer times. In order to evaluate the potential future benefit of using next generation Hall thrusters as the primary propulsion system, comparisons were made with the advanced state-of-the-art (ASOA), 7-kW, 4,100 second NASA's Evolutionary Xenon Thruster (NEXT) for the same mission scenarios. For the BOL array powers considered in this study (less than 30 kW), the results show that the performance of the Hall thrusters, relative to NEXT, is largely dependant on the performance capability of the launch vehicle, and that at least a 10 percent performance gain, equating to at least an additional 200 kg dry mass at each target planet, is achieved over the higher specific impulse NEXT when launched on an Atlas 551.

Witzberger, Kevin E.↗
NASA NTRS1981

Evaluation of distributed gas cooling of pressurized PAFC for utility power generation

Two short stacks were pressure tested at 446 kPa (4.4 atm.) and the pressure gains were more than the theoretically predicted gains. Temperature profiles were observed to be independent of operating pressure. The pressure drop was found to be inversely proportional to operating pressure as expected. Continuous pressurized operation of a stack for 1000 hours verified the compatability of the fuel cell component design. A simple pressurization procedure was also developed. Six separate designs, covering two gas cooling schemes (DIGAS and separated) and two cooling channel geometries (straight through and treed), were analysed on the net voltage output basis. Separated cooling with 5 cells per cooler was recognized to be the best among the designs considered.

Farooque, M.↗
NASA NTRS1991

High reliability megawatt transformer/rectifier

The goal of the two phase program is to develop the technology and design and fabricate ultralightweight high reliability DC to DC converters for space power applications. The converters will operate from a 5000 V dc source and deliver 1 MW of power at 100 kV dc. The power weight density goal is 0.1 kg/kW. The cycle to cycle voltage stability goals was + or - 1 percent RMS. The converter is to operate at an ambient temperature of -40 C with 16 minute power pulses and one hour off time. The uniqueness of the design in Phase 1 resided in the dc switching array which operates the converter at 20 kHz using Hollotron plasma switches along with a specially designed low loss, low leakage inductance and a light weight high voltage transformer. This approach reduced considerably the number of components in the converter thereby increasing the system reliability. To achieve an optimum transformer for this application, the design uses four 25 kV secondary windings to produce the 100 kV dc output, thus reducing the transformer leakage inductance, and the ac voltage stresses. A specially designed insulation system improves the high voltage dielectric withstanding ability and reduces the insulation path thickness thereby reducing the component weight. Tradeoff studies and tests conducted on scaled-down model circuits and using representative coil insulation paths have verified the calculated transformer wave shape parameters and the insulation system safety. In Phase 1 of the program a converter design approach was developed and a preliminary transformer design was completed. A fault control circuit was designed and a thermal profile of the converter was also developed.

Zwass, Samuel↗
NASA NTRS2014

Development and Implementation of a Hardware In-the-Loop Test Bed for Unmanned Aerial Vehicle Control Algorithms

Successful prediction and management of battery life using prognostic algorithms through ground and flight tests is important for performance evaluation of electrical systems. This paper details the design of test beds suitable for replicating loading profiles that would be encountered in deployed electrical systems. The test bed data will be used to develop and validate prognostic algorithms for predicting battery discharge time and battery failure time. Online battery prognostic algorithms will enable health management strategies. The platform used for algorithm demonstration is the EDGE 540T electric unmanned aerial vehicle (UAV). The fully designed test beds developed and detailed in this paper can be used to conduct battery life tests by controlling current and recording voltage and temperature to develop a model that makes a prediction of end-of-charge and end-of-life of the system based on rapid state of health (SOH) assessment.

Battery Testbed↗
NASA NTRS1976

Performance characteristics of quasi-steady MPD discharges

The onset of voltage fluctuations in a multi-megawatt quasi-steady MPD accelerator, indicative of increased cathode ablation and a consequent degradation of performance, is found to be a function of cathode size. With longer cathodes, this onset shifts to substantially higher powers per unit mass flow and the plasma exhaust velocity can be increased to values previously thought inaccessible to accelerators of this class. Centerline velocities up to 30 km/sec have been measured in argon, which for the observed exhaust profiles translate into specific impulses up to 2400 sec and corresponding thrust efficiencies above 30%.

Rudolph, L. K.↗
NASA NTRS2001

SOHO Ultraviolet Coronagraph Spectrometer (UVCS) Mission Operations and Data Analysis

The scientific goal of UVCS is to obtain detailed empirical descriptions of the extended solar corona as it evolves over the solar cycle and to use these descriptions to identify and understand the physical processes responsible for coronal heating, solar wind acceleration, coronal mass ejections (CMEs), and the phenomena that establish the plasma properties of the solar wind as measured by "in situ" solar wind instruments. This report covers the period from 15 November 1998 to 14 March 2001. During that time, UVCS observations have consisted of three types: 1) standard synoptic observations comprising, primarily, the H I Lycc line profile and the O VI 103.2 and 103.7 nm intensity over a range of heights from 1.5 to about 3.0 solar radii and covering 360 degrees about the sun, 2) sit and stare watches for CMEs, and 3) special observations designed by the UVCS Lead Observer of the Week for a specific scientific purpose. The special observations are often coordinated with those of other space-based and ground based instruments and they often are part of SOHO joint observation programs and campaigns. Lead observers have included UVCS Co-Investigators, Guest Investigators, scientists from the solar physics community and several graduate and undergraduate level students. UVCS has continued to successfully meet its goal of using powerful spectroscopic diagnostic techniques to obtain a much more detailed description of coronal structures than existed before the SOHO mission. The new descriptions of coronal structures from UVCS have inspired a large number of theoretical studies aimed at identifying the physical processes responsible for solar wind acceleration in coronal holes and streamers. UVCS has proven to be a very stable instrument. Stellar observations have demonstrated its stability and the analysis of coordinated observations with Spartan 201 have verified the accuracy of the absolute calibration and spectral resolution at H I Ly (alpha) line profile. UVCS has required no flight software modifications and all mechanisms are operational. The UVCS O VI Channel with its redundant optical path for wavelengths near H I Ly (alpha) is capable of observing the entire UVCS wavelength range. Since December 1998, the O VI Channel has been used for all UVCS observations. Although the H I Ly (alpha) Channel and detector are still operational, increases in the dark count up to about 5x 10(exp-4) counts/sec/pixel and an increase in high voltage current to within a factor of two of the maximum used in the laboratory before flight led to the decision to not use that detector at the present time. There is no significant science impact since the O VI Channel can observe nearly the same wavelength range.

Kohl, John L.↗