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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Extending Ion Engine Technology to NEXT and Beyond

Extending ion engine technology beyond the current state-of-the art primary interplanetary electric propulsion system, the 2.3-kW NASA Solar Electric Propulsion Technology and Applications Readiness (NSTAR) system, will require thrusters with improved propellant throughput and total impulse capability. Many of the design choices that culminated in the NSTAR thrusters must be revisited, and their application to next generation ion engine technology must be evaluated. The concept of derating, which was successfully employed in NSTAR, has been applied to the 40 cm NASA Evolutionary Xenon Thruster (NEXT) currently under development at NASA Glenn Research Center (GRC). At 5-kW, NEXT operates with the same average beam current density as NSTAR, and at 10-kW, the peak beam current density is only ten percent greater than NSTAR. The result is that similar Ion optics technology is expected to yield comparable lifetime. Thick-accelerator- grid ion optics are also being tested to realize additional lifetime benefits. A 40-A discharge cathode is being developed for NEXT based on scaling the NSTAR design. Nevertheless, the experiences of the NSTAR ground tests and the thruster on the Deep Space One spacecraft indicate that the discharge cathode wear must be studied experimentally and theoretically to ensure that it meets the lifetime requirements. Although NEXT is in its infancy, investigations have already begun to examine possible modifications to engine design for even higher-power and higher-specific impulse engines. Ion optics using alternate materials such as titanium, graphite, or carbon-carbon composite are currently being investigated due to their low sputter yields at high voltage. To avoid the difficulties encountered using electrodes at high-currents, the use of a microwave-based ion thruster is under investigation for potential high-power ion thruster systems requiring long lifetimes. Additionally, alternative propellants are being considered for applications requiring high-specific impulse (>> 5000 s) and extremely long-life (>> 15,000 hr). Testing requirements make condensable propellants attractive for high-power engines. Although the NSTAR ion engine demonstrated the flight maturity of ion thruster technology, many challenges remain for the development of thrusters with improved propellant throughput and power handling capabilities.

Domonkos, Matthew T.↗
NASA NTRS1991

Small Business Innovations (MISER)

Lightwave Electronics Corporation, Mountain View, CA, developed the Series 120 and 122 non-planner diode pumped ring lasers based on a low noise ring laser with voltage tuning that they delivered to Jet Propulsion Laboratory under a Small Business Innovation Research (SBIR) contract. The voltage tuning feature allows "phase-locking" the lasers, making them "electronic," similar to radio and microwave electronic oscillators. The Series 120 and 122 can be applied to fiber sensing, coherent communications and laser radar.

Source record↗
NASA NTRS2005

Portable Airborne Laser System Measures Forest-Canopy Height

(PALS) is a combination of laser ranging, video imaging, positioning, and data-processing subsystems designed for measuring the heights of forest canopies along linear transects from tens to thousands of kilometers long. Unlike prior laser ranging systems designed to serve the same purpose, the PALS is not restricted to use aboard a single aircraft of a specific type: the PALS fits into two large suitcases that can be carried to any convenient location, and the PALS can be installed in almost any local aircraft for hire, thereby making it possible to sample remote forests at relatively low cost. The initial cost and the cost of repairing the PALS are also lower because the PALS hardware consists mostly of commercial off-the-shelf (COTS) units that can easily be replaced in the field. The COTS units include a laser ranging transceiver, a charge-coupled-device camera that images the laser-illuminated targets, a differential Global Positioning System (dGPS) receiver capable of operation within the Wide Area Augmentation System, a video titler, a video cassette recorder (VCR), and a laptop computer equipped with two serial ports. The VCR and computer are powered by batteries; the other units are powered at 12 VDC from the 28-VDC aircraft power system via a low-pass filter and a voltage converter. The dGPS receiver feeds location and time data, at an update rate of 0.5 Hz, to the video titler and the computer. The laser ranging transceiver, operating at a sampling rate of 2 kHz, feeds its serial range and amplitude data stream to the computer. The analog video signal from the CCD camera is fed into the video titler wherein the signal is annotated with position and time information. The titler then forwards the annotated signal to the VCR for recording on 8-mm tapes. The dGPS and laser range and amplitude serial data streams are processed by software that displays the laser trace and the dGPS information as they are fed into the computer, subsamples the laser range and amplitude data, interleaves the subsampled data with the dGPS information, and records the resulting interleaved data stream.

Nelson, Ross↗
DOE OSTI2024

Al‐Rich AlGaN Transistors with Regrown p‐AlGaN Gate Layers and Ohmic Contacts

Abstract Epitaxial regrowth processes are presented for achieving Al‐rich aluminum gallium nitride (AlGaN) high electron mobility transistor (HEMTs) with p‐type gates with large, positive threshold voltage for enhancement mode operation and low resistance Ohmic contacts. Utilizing a deep gate recess etch into the channel and an epitaxial regrown p‐AlGaN gate structure, an Al 0.85 Ga 0.15 N barrier/Al 0.50 Ga 0.50 N channel HEMT with a large positive threshold voltage (V TH = +3.5 V) and negligible gate leakage is demonstrated. Epitaxial regrowth of AlGaN avoids the use of gate insulators which can suffer from charge trapping effects observed in typical dielectric layers deposited on AlGaN. Low resistance Ohmic contacts (minimum specific contact resistance = 4 × 10 −6 Ω cm 2 , average = 1.8 × 10 −4 Ω cm 2 ) are demonstrated in an Al 0.85 Ga 0.15 N barrier/Al 0.68 Ga 0.32 N channel HEMT by employing epitaxial regrowth of a heavily doped, n‐type, reverse compositionally graded epitaxial structure. The combination of low‐leakage, large positive threshold p‐gates and low resistance Ohmic contacts by the described regrowth processes provide a pathway to realizing high‐current, enhancement‐mode, Al‐rich AlGaN‐based ultra‐wide bandgap transistors.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Programable Driver for Voltage-Controlled Oscillators

Electronically programable read-only memory (EPROM) and digital-to-analog converter provide customized time-varying voltage for frequency modulation. Voltage used to modulate IMPATT oscillator that serves as microwave pump for solid-state maser in low-noise amplifier. EPROM simple to tailor voltage waveform to suit characteristics of given maser. Digital information for waveform programed into EPROM chip; digital-to-analog converter reads information and produces corresponding analog wave. Principle readily adapted to other applications.

Fowler, L. E.↗
NASA NTRS2008

ISS Charging Hazards and Low Earth Orbit Space Weather Effects

Current collection by high voltage solar arrays on the International Space Station (ISS) drives the vehicle to negative floating potentials in the low Earth orbit daytime plasma environment. Pre-flight predictions of ISS floating potentials Phi greater than |-100 V| suggested a risk for degradation of dielectric thermal control coatings on surfaces in the U.S. sector due to arcing and an electrical shock hazard to astronauts during extravehicular activity (EVA). However, hazard studies conducted by the ISS program have demonstrated that the thermal control material degradation risk is effectively mitigated during the lifetime of the ISS vehicle by a sufficiently large ion collection area present on the vehicle to balance current collection by the solar arrays. To date, crew risk during EVA has been mitigated by operating one of two plasma contactors during EVA to control the vehicle potential within Phi less than or equal to |-40 V| with a backup process requiring reorientation of the solar arrays into a configuration which places the current collection surfaces into wake. This operation minimizes current collection by the solar arrays should the plasma contactors fail. This paper presents an analysis of F-region electron density and temperature variations at low and midlatitudes generated by space weather events to determine what range of conditions represent charging threats to ISS. We first use historical ionospheric plasma measurements from spacecraft operating at altitudes relevant to the 51.6 degree inclination ISS orbit to provide an extensive database of F-region plasma conditions over a variety of solar cycle conditions. Then, the statistical results from the historical data are compared to more recent in-situ measurements from the Floating Potential Measurement Unit (FPMU) operating on ISS in a campaign mode since its installation in August, 2006.

Minow, Joseph↗
DOE OSTI2021

Online Detection of Low-Quality Synchrophasor Data Considering Frequency Similarity

Here, this letter proposes a new approach for online detection of low-quality synchrophasor data under both normal and event conditions. The proposed approach utilizes the features of synchrophasor data in time and frequency domains to distinguish multiple regional PMU signals and detect low-quality synchrophasor data. It is more effective to detect low-quality data with apparently indistinguishable profiles. Case studies from recorded synchrophasor measurements verify the effectiveness of the proposed approach for detecting low-quality synchrophasor data in frequency, voltage magnitude and voltage angle.

42 ENGINEERING↗
DOE OSTI2026

Mechanism-Informed Breakdown: Understanding Degradation by Controlling Voltage-Hold Patterns in Proton Exchange Membrane Water Electrolyzers

Low catalyst loadings pose challenges to performance stability in proton exchange membrane (PEM) water electrolysis over extended operation. To study the impact of degradation mechanisms and voltage loss rates, different stress tests are applied to membrane electrode assemblies. Potential cycling conditions were observed to induce higher degrees of iridium (Ir) oxide crystallization, ionomer degradation, and catalyst layer (CL) thinning, which likely contributed to higher kinetic loss rates. On the other hand, while Ir migrating into the PEM (Ir band) generally impairs performance, the interconnected and more uniform Ir band formed under a constant 2 V hold may allow for Ir at the catalyst/membrane interface to remain electronically connected and kinetically accessible, as well as indicate greater Ir site access during the applied stressor. The 2 V hold also demonstrates improved kinetic durability through a lower Tafel slope, faster polarization kinetics, and reduced charge transfer resistance. In contrast, potential cycling caused the migration of disconnected Ir agglomerates into the membrane bulk and created a steady increase in charge transfer resistance, a more dramatic decrease in capacitance (46.7% loss), and significant damage to the surrounding ionomer, indicating a decline in both the quality and quantity of active sites in the anode CL. This work underscores the distinct degradation pathways associated with load holds versus cycling, highlighting the role of catalyst-ionomer interactions in kinetic performance and long-term stability. These insights can inform operational strategies for PEM electrolyzers powered by intermittent energy sources, aiming to minimize efficiency losses over extended operation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Carbon Corrosion in CO2 Electrolysis Systems

Driven by concerns over climate change, interest in CO2 conversion technologies has dramatically increased in recent years. By viewing CO2 as a readily available feedstock, many pathways for the production of carbon-neutral fuels and chemicals become available. In converting CO2, low carbon emitting energy sources must be used to ensure a low carbon footprint of the fuel and chemical products. The low-temperature electrochemical conversion of CO2 is a promising technology and allows for direct integration with renewable electricity sources. The development of low-temperature CO2 electrolysis technologies is informed by both PEM fuel cells and water electrolyzers, both of which are at a higher stage of development. However, CO2 electrolysis operates at a much higher cell voltage (-3V) than other low-temperature electrochemical processes, which can have implications for materials compatibility in the electrolyzer device. Carbon corrosion is of particular concern for the anode of CO2 electrolyzers, as a large driving force for corrosion exists due to the high required cell potentials. In this presentation, recent observations will be shared on carbon corrosion of the anode gas diffusion electrode (GDE) in low-temperature alkaline exchange membrane CO2 electrolysis. Results from ex-situ tests designed to isolate the carbon corrosion process for anode GDEs will be shared. These results will provide guidance on materials selection for CO2 utilization MEAs, which need to have a lifetime of several years to ensure industrial viability.

BIOMASS FUELS↗
DOE OSTI2024

High-current, high-voltage AlN Schottky barrier diodes

AlN Schottky barrier diodes with low ideality factor (<1.2), low differential ON-resistance (<0.6 mΩ cm 2 ), high current density (>5 kA cm −2 ), and high breakdown voltage (680 V) are reported. The device structure consisted of a two-layer, quasi-vertical design with a lightly doped AlN drift layer and a highly doped Al 0.75 Ga 0.25 N ohmic contact layer grown on AlN substrates. A combination of simulation, current–voltage measurements, and impedance spectroscopy analysis revealed that the AlN/AlGaN interface introduces a parasitic electron barrier due to the conduction band offset between the two materials. This barrier was found to limit the forward current in fabricated diodes. Further, we show that introducing a compositionally-graded layer between the AlN and the AlGaN reduces the interfacial barrier and increases the forward current density of fabricated diodes by a factor of 10 4 .

Quiñones, C. E. (ORCID:0000000192703747)↗
NASA NTRS1991

PASP, a high voltage array/plasma interaction experiment

The author discusses the photovoltaic array space power (PASP) experiment, which is designed to obtain data on the interaction between high-voltage photovoltaic arrays and the polar, low-earth plasma environment. Up to six small test arrays (three each of planar and concentrator designs) can be voltage biased over a range of +/- 500 V. During the bias voltage sequence, the array current leakage is measured and array arc events are monitored. If any arcing occurs the arc characteristics will be measured by a transient pulse monitor. An emitter is included to allow voltage bias to be applied to a plasma-charged or uncharged spacecraft. Similarly, the frames of the concentrator arrays can be left floating or can be tied to the negative array terminal. An environmental data scan is made before each bias voltage sequence. This scan collects information on the plasma, array-current-versus-voltage curves, and neutral particle partial pressure. The requirement for high voltages created problems which were met by circuit isolation and logical fault protection.

Burger, Dale R.↗
DOE OSTI2021

Feed-Forward Compensation for Model Predictive Control in Tri-port Current-Source Medium-Voltage String Inverters for PV-Plus-Storage Farms

The novel tri-port current-source medium-voltage string inverter (TCS-MVSI) is a promising candidate for large-scale PV-plus-storage (PVS) farms owing to its galvanic isolation, easy storage integration, soft-switching capability across entire load range, controlled low dv/dt and EMI, benign fault tolerance, etc. Due to its low inertia feature, traditional PI-based control cannot manage large transients effectively. Instead, a model-based predictive control (MPC) is proposed to achieve robust and stable operation. As is well known, the control performance of MPC is compromised by the sampling and computational delay during implementation significantly, if not well addressed. This paper analyzed and quantified these delays and then proposes feed-forward compensation (FFC) for the MPC method to compensate the delays and the large parameter variations due to the low-inertia nature. In addition, this method also compensates for the high dc-link ripple within each switching cycle, a unique issue for low-inertia converters. Here, the proposed method requires low computational effort, allowing it to be extended for multiple ports. The effectiveness of the proposed method has been validated in experiments. In 10 kW test, the proposed method decreases the average dc-link current by 17%, leading to ~20% conduction losses and ~0.5% increase in converter efficiency. In addition, the peak dc-link current also decreases by 15%, resulting in reduced transformer size. As a result, an increased power density can be achieved with the proposed method. Similar improvements have been observed across the power range from 2 kW to 10 kW.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS1987

Test results of a 60 volt bipolar nickel-hydrogen battery

In July, l986, a high-voltage nickel-hydrogen battery was assembled at the NASA Lewis Research Center. This battery incorporated bipolar construction techniques to build a 50-cell stack with approximately 1.0 A-hr capacity (C) and an open-circuit voltage of 65 V. The battery was characterized at both low and high current rates prior to pulsed and nonpulsed discharges. Pulse discharges at 5 and 10 C were performed before placing the battery on over 1400, 40% depth-of-discharge, low-earth-orbit cycles. The successful demonstration of a high-voltage bipolar battery in one containment vessel has advanced the technology to where nickel-hydrogen high-voltage systems can be constructed of several modules instead of hundreds of individual cells.

Cataldo, Russell L.↗
NASA NTRS1987

Test results of a 60 volt bipolar nickel-hydrogen battery

In July 1986, a high-voltage nickel-hydrogen battery was assembled at the NASA Lewis Research Center. This battery incorporated bipolar construction techniques to build a 50-cell stack with approximately 1.0 A-hr capacity (C) and an open-circuit voltage of 65 V. The battery was characterized at both low and high current rates prior to pulsed and nonpulsed discharges. Pulse discharges at 5 and 10 C were performed before placing the battery on over 1400, 40-percent depth-of-discharge, low-earth-orbit cycles. The successful demonstration of a high-voltage bipolar battery in one containment vessel has advanced the technology to where nickel-hydrogen high-voltage systems can be constructed of several modules instead of hundreds of individual cells.

Cataldo, Robert L.↗
DOE OSTI2020

DC Link Voltage Balancing of the Active Front-End for the Extreme Fast Charging Stations

One of the most important challenges of the extreme fast charging (XFC) stations is to balance the DC link voltages of the active front-end (AFE). The multilevel cascaded H-bridge (CHB) converter is a great topology for the AFE applications due to the high power density, low total harmonic distortion (THD), and a low number of active and passive components. In this paper, a technique is proposed for balancing DC-link capacitor voltages of a three-phase CHB converter, when a phase shiftPWM modulation technique is used on all cells of the converter. To reach this goal, the redundant states of the CHB converters are used for generating different AC voltage levels by sorting the voltages of the converters. The proposed voltage balancing technique uses the principles that are employed for the DC link voltage balancing of the low-frequency modulation techniques to balance the DC link voltages of the CHB converter. As shown in this paper, the DC link voltages of the CHB converter can accurately be balanced very fast without using PI controllers, which are used in the conventional DC link voltage balancing techniques. A controller also is proposed which will be used to control the dq currents of the CHB converter. To verify the advantages of the proposed technique, the simulation results of the proposed technique will be carried out in a three-phase 7-cell CHB AFE.

Grid-tied converters, cascaded H-bridge, DC link v↗
DOE OSTI2023

Low-damage electron beam lithography for nanostructures on Bi 2 Te 3 -class topological insulator thin films

Nanostructured topological insulators (TIs) have the potential to impact a wide array of condensed matter physics topics, ranging from Majorana physics to spintronics. However, the most common TI materials, the Bi 2 Se 3 family, are easily damaged during nanofabrication of devices. In this paper, we show that electron beam lithography performed with a 30 or 50 kV accelerating voltage—common for nanopatterning in academic facilities—damages both nonmagnetic TIs and their magnetically doped counterparts at unacceptable levels. We additionally demonstrate that electron beam lithography with a 10 kV accelerating voltage produces minimal damage detectable through low-temperature electronic transport. In conclusion, although reduced accelerating voltages present challenges in creating fine features, we show that with careful choice of processing parameters, particularly the resist, 100 nm features are reliably achievable.

42 ENGINEERING↗