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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 109 records · Page 6

All sources NASA NTRS DOE OSTI

NASA NTRS1987

High-Frequency ac Power-Distribution System

Loads managed automatically under cycle-by-cycle control. 440-V rms, 20-kHz ac power system developed. System flexible, versatile, and "transparent" to user equipment, while maintaining high efficiency and low weight. Electrical source, from dc to 2,200-Hz ac converted to 440-V rms, 20-kHz, single-phase ac. Power distributed through low-inductance cables. Output power either dc or variable ac. Energy transferred per cycle reduced by factor of 50. Number of parts reduced by factor of about 5 and power loss reduced by two-thirds. Factors result in increased reliability and reduced costs. Used in any power-distribution system requiring high efficiency, high reliability, low weight, and flexibility to handle variety of sources and loads.

Hansen, Irving G.↗

NASA NTRS1987

Radiation from large space structures in low earth orbit with induced ac currents

Large conducting space structures in low earth orbit will have a nonnegligible motionally induced potential across their structures. The induced current flow through the body and the ionosphere causes the radiation of Alfven and lower hybrid waves. This current flow is taken to be ac and the radiated power is studied as a function of the ac frequency. The current may be ac due either to inductive coupling from the power system on the structure or by active modulation. A Space Station-like structure and tether are studied. For the Space Station structure the radiation impedance is particularly high for frequencies in the tens of kilohertz range which suggests that the Space Station may be efficient source of lower hybrid waves. The tether is also shown to be a generator of VLF waves up to source ac frequencies in the megahertz range. The implications for these two structures are discussed.

Hastings, D. E.↗

NASA NTRS1992

Electromechanical systems with transient high power response operating from a resonant AC link

The combination of an inherently robust asynchronous (induction) electrical machine with the rapid control of energy provided by a high frequency resonant AC link enables the efficient management of higher power levels with greater versatility. This could have a variety of applications from launch vehicles to all-electric automobiles. These types of systems utilize a machine which is operated by independent control of both the voltage and frequency. This is made possible by using an indirect field-oriented control method which allows instantaneous torque control in all four operating quadrants. Incorporating the AC link allows the converter in these systems to switch at the zero crossing of every half cycle of the AC waveform. This zero loss switching of the link allows rapid energy variations to be achieved without the usual frequency proportional switching loss. Several field-oriented control systems were developed by LeRC and General Dynamics Space Systems Division under contract to NASA. A description of a single motor, electromechanical actuation system is presented. Then, focus is on a conceptual design for an AC electric vehicle. This design incorporates an induction motor/generator together with a flywheel for peak energy storage. System operation and implications along with the associated circuitry are addressed. Such a system would greatly improve all-electric vehicle ranges over the Federal Urban Driving Cycle (FUD).

Burrows, Linda M.↗

NASA NTRS1991

Development of software to improve AC power quality on large spacecraft

To insure the reliability of a 20 kHz, alternating current (AC) power system on spacecraft, it is essential to analyze its behavior under many adverse operating conditions. Some of these conditions include overloads, short circuits, switching surges, and harmonic distortions. Harmonic distortions can become a serious problem. It can cause malfunctions in equipment that the power system is supplying, and, during distortions such as voltage resonance, it can cause equipment and insulation failures due to the extreme peak voltages. To address the harmonic distortion issue, work was begun under the 1990 NASA-ASEE Summer Faculty Fellowship Program. Software, originally developed by EPRI, called HARMFLO, a power flow program capable of analyzing harmonic conditions on three phase, balanced, 60 Hz AC power systems, was modified to analyze single phase, 20 kHz, AC power systems. Since almost all of the equipment used on spacecraft power systems is electrically different from equipment used on terrestrial power systems, it was also necessary to develop mathematical models for the equipment to be used on the spacecraft. The modelling was also started under the same fellowship work period. Details of the modifications and models completed during the 1990 NASA-ASEE Summer Faculty Fellowship Program can be found in a project report. As a continuation of the work to develop a complete package necessary for the full analysis of spacecraft AC power system behavior, deployment work has continued through NASA Grant NAG3-1254. This report details the work covered by the above mentioned grant.

Kraft, L. Alan↗

NASA NTRS1993

The AC-120: The advanced commercial transport

The main objective of this design was to fulfill a need for a new airplane to replace the aging 100 to 150 passenger, 1500 nautical mile range aircraft such as the Douglas DC9 and Boeing 737-100 airplanes. After researching the future aircraft market, conducting extensive trade studies, and analysis on different configurations, the AC-120 Advanced Commercial Transport final design was achieved. The AC-120's main design features include the incorporation of a three lifting surface configuration which is powered by two turboprop engines. The AC-120 is an economically sensitive aircraft which meets the new FM Stage Three noise requirements, and has lower NO(x) emissions than current turbofan powered airplanes. The AC-120 also improves on its contemporaries in passenger comfort, manufacturing, and operating cost.

Duran, David↗

NASA NTRS1998

Optical Metrology for the Filter Set for the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)

The Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) will employ a wide variety of spectral filtration components including narrow band, medium band, wide band, and far ultraviolet (FUV) long pass filters, spatially- variable filters (ramp filters), VIS/IR polarizers, NUV polarizers, FUV prisms, and a grism. These components are spread across ACS's Wide Field, High Resolution, and Solar Blind channels which provide diffraction-limited imaging of astronomical targets using aberration-correcting optics which remove most aberrations from HST's Optical Telescope Assembly (OTA). In order for ACS to be truly advanced, these filters must push the state-of-the-art in performance in a number of key areas at the same time. Important requirements which these filters must meet include outstanding transmitted wavefront, high transmittance, uniform transmittance across each filter, spectrally structure-free bandpasses, exceptionally high out of band rejection, and a high degree of parfocality. These constitute a very stringent set of requirements indeed, especially for filters which are up to 90 mm in diameter. The development of optical metrology stations used to demonstrate that each ACS filter will meet its design specifications is discussed. Of particular note are specially-designed spectral transmissometers and interferometers.

Leviton, Douglas B.↗

NASA NTRS1998

Broadband Interferometer for Measuring Transmitted Wavefronts of Optical Bandpass Filters for HST (ACS)

The transmitted wavefronts of optical filters for the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) are characterized using the Wildly and Openly Modified Broadband Achromatic Twyman Green (WOMBAT) Interferometer developed in the NASA/GSFC Optics Branch's Diffraction Grating Evaluation Facility (DGEF). Because only four of thirty-three of ACS's optical bandpass filters transmit the 633 nm light of most commercial interferometers, a broadband interferometer is required to verify specified transmitted wavefront of ACS filters. WOMBAT's design is a hybrid of the BAT interferometer developed by JPL used for HST Wide Field and Planetary Camera 2 (WFPC-2) filters and a WYKO 400 phase shifting interferometer. It includes a broadband light source, monochromator, off-axis, parabolic collimating and camera mirrors, an aluminum-coated fused silica beam splitter, flat retroreflecting mirrors for the test and reference arms, and a LTV-sensitive CCD camera. An outboarded, piezo-electric phase shifter holds the flat mirror in the interferometer's reference arm. The interferometer is calibrated through interaction between the WYKO system's software and WONMAT hardware for the test wavelength of light entering the beam splitter. Phase-shifted interferograms of the filter mounted in the test arm are analyzed using WYKO's Vision' software. Filters as large as 90 mm in diameter have been measured over a wavelength range from 200 to 1100 nm with a sensitivity of lambda/200 rms at lambda = 633 nm. Results of transmitted wavefront measurements are shown for ACS fixed band pass and spatially-variable bandpass filters for a variety of wavelengths.

Boucarut, R. A.↗

NASA NTRS1998

Development and Testing of Automatically Generated ACS Flight Software for the MAP Spacecraft

By integrating the attitude determination and control system (ACS) analysis and design, flight software development, and flight software testing processes, it is possible to improve the overall spacecraft development cycle, as well as allow for more thorough software testing. One of the ways to achieve this integration is to use code-generation tools to automatically generate components of the ACS flight software directly from a high-fidelity (HiFi) simulation. In the development of the Microwave Anisotropy Probe (MAP) spacecraft, currently underway at the NASA Goddard Space Flight Center, approximately 1/3 of the ACS flight software was automatically generated. In this paper, we will examine each phase of the ACS subsystem and flight software design life cycle: analysis, design, and testing. In the analysis phase, we scoped how much software we would automatically generate and created the initial interface. The design phase included parallel development of the HiFi simulation and the hand-coded flight software components. Everything came together in the test phase, in which the flight software was tested, using results from the HiFi simulation as one of the bases of comparison for testing. Because parts of the spacecraft HiFi simulation were converted into flight software, more care needed to be put into its development and configuration control to support both the HiFi simulation and flight software. The components of the HiFi simulation from which code was generated needed to be designed based on the fact that they would become flight software. This process involved such considerations as protecting against mathematical exceptions, using acceptable module and parameter naming conventions, and using an input/output interface compatible with the rest of the flight software. Maintaining good configuration control was an issue for the HiFi simulation and the flight software, and a way to track the two systems was devised. Finally, an integrated test approach was devised to support flight software testing at both the unit- and build-test levels using the HiFi simulation to generate data for performance verification. Another benefit of the simulation and code-generation application used on the MAP project is that it supported bringing flight software and test data into the HiFi simulation environment. It was possible to integrate parts of the hand-coded flight software into the HiFi simulation, and also possible to import flight software test data for comparison and performance verification. This capability was used to incorporate the flight software Kalman filter into the HiFi simulation. This enabled us to greatly increase the amount of testing that could be done on the filter, because we could exert a greater degree of control over the software-only simulation than over the flight software test environment. Also, since the simulation could be used to run the Kalman filter faster than real time, our testing efficiency was greatly increased. We will conclude our discussion with a summary of the lessons learned thus far using automatically- generated code for the MAP project, and the spacecraft status as we work towards our scheduled launch in the year 2000.

ODonnell, James R., Jr.↗

NASA NTRS2001

Reduced Toxicity Fuel Satellite Propulsion System Including Axial Thruster and ACS Thruster Combination

A reduced toxicity fuel satellite propulsion system including a reduced toxicity propellant supply for consumption in an axial class thruster and an ACS class thruster. The system includes suitable valves and conduits for supplying the reduced toxicity propellant to the ACS decomposing element of an ACS thruster. The ACS decomposing element is operative to decompose the reduced toxicity propellant into hot propulsive gases. In addition the system includes suitable valves and conduits for supplying the reduced toxicity propellant to an axial decomposing element of the axial thruster. The axial decomposing element is operative to decompose the reduced toxicity propellant into hot gases. The system further includes suitable valves and conduits for supplying a second propellant to a combustion chamber of the axial thruster, whereby the hot gases and the second propellant auto-ignite and begin the combustion process for producing thrust.

Steven J Schneider↗

NASA NTRS1998

Charging in the ac Conductance of a Double Barrier Resonant Tunneling Structure

There have been many studies of the linear response ac conductance of a double barrier resonant tunneling structure (DBRTS), both at zero and finite dc biases. While these studies are important, they fail to self consistently include the effect of the time dependent charge density in the well. In this paper, we calculate the ac conductance at both zero and finite do biases by including the effect of the time dependent charge density in the well in a self consistent manner. The charge density in the well contributes to both the flow of displacement currents in the contacts and the time dependent potential in the well. We find that including these effects can make a significant difference to the ac conductance and the total ac current is not equal to the simple average of the non-selfconsistently calculated conduction currents in the two contacts. This is illustrated by comparing the results obtained with and without the effect of the time dependent charge density included correctly. Some possible experimental scenarios to observe these effects are suggested.

Anantram, M. P.↗

NASA NTRS2003

Final Report for the Advanced Camera for Surveys (ACS) from Ball Aerospace and Technologies Corporation

The Advanced Camera for Surveys ACS was launched aboard the Space Shuttle Columbia just before dawn on March 1, 2002. After successfully docking with the Hubble Space Telescope (HST), several components were replaced. One of the components was the Advanced Camera for Surveys built by Ball Aerospace & Technologies Corp. (BATC) in Boulder, Colorado. Over the life of the HST contract at BATC hundreds of employees had the pleasure of working on the concept, design, fabrication, assembly and test of ACS. Those employees thank NASA - Goddard Space Flight Center and the science team at Johns Hopkins University (JHU) for the opportunity to participate in building a great science instrument for HST. After installation in HST a mini-functional test was performed and later a complete functional test. ACS performed well and has continued performing well since then. One of the greatest rewards for the BATC employees is a satisfied science team. Following is an excerpt from the JHU final report, "The foremost promise of ACS was to increase Hubble's capability for surveys in the near infrared by a factor of 10. That promise was kept. "

Volmer, Paul↗

NASA NTRSDate not supplied

Thermal Modeling of a Novel Air-Cooled Temperature Swing Adsorption Compressor (AC-TSAC)

Contaminant removal technology, such as the Carbon Dioxide Removal Assembly (CDRA) on the International Space Station (ISS), is critical to Environmental Close-Loop Life Support Systems (ECLSS), which enable humans to live and work in outer space. The CDRA includes an adsorbent bed, which absorbs CO2 and releases it to a Sabatier reactor for water production when thermally cycled. An effective system would heat and cool the adsorbent quickly and uniformly to maximize the amount of CO2 removed from the cabin. Air-Cooled Temperature Swing Adsorption Compressors (AC-TSAC) are promising because they are a simple alternative to more mechanically-complex compressors currently used on the ISS. The current investigation addresses the thermal modeling of potential AC-TSAC designs. Design trades include bed geometry (rectangular vs. cylindrical), bed structural material, and configuration of heat pipes within the bed. Also investigated is AC-TSAC performance sensitivity to the thermal conductivity of the adsorbent material and the heat pipes, the input power for heating, and various heat loss mechanisms. The results from these studies will inform the design of the next generation of the AC-TSAC, and the thermal modeling results will be validated through testing.

Hannah Alpert↗

NASA NTRSDate not supplied

Thermal Modeling of a Novel Air-Cooled Temperature Swing Adsorption Compressor (AC-TSAC)

Contaminant removal technology, such as the Carbon Dioxide Removal Assembly (CDRA) on the International Space Station (ISS), is critical to Environmental Control and Life Support Systems (ECLSS), which enable humans to live and work in outer space. The CDRA includes an adsorbent bed, which absorbs CO 2 from the cabin air and releases it to a Sabatier reactor for water production when thermally cycled. An effective system would heat and cool the adsorbent quickly and uniformly to maximize the amount of CO 2 removed from the cabin and delivered to the Sabatier reactor. Air-Cooled Temperature Swing Adsorption Compressors (AC-TSAC) are promising for use downstream of the CDRA because they are a simple alternative to more mechanically-complex compressors, which are currently in use on the ISS. The current investigation addresses the thermal modeling of potential AC-TSAC designs. An initial thermal model was created and validated by comparing the model outputs to experimental data for the heating phase. Several design trades were conducted, including bed geometry (rectangular vs. cylindrical), bed structural material (i.e., the material that makes up the walls and shelves), and configuration of heat spreading elements within the bed. Also investigated is AC-TSAC performance sensitivity to the thermal conductivity of the adsorbent material and the heat pipes as well as the input power for heating. The results from these studies will inform the design of the next generation of the AC-TSAC, and the thermal modeling results will be further validated through testing.

Hannah S. Alpert↗

DOE OSTI2021

Soft-switching, high performance single-phase AC-DC converter

A soft-switching, high-performance single-phase alternating current (AC)-direct current (DC) converter is provided. The AC-DC converter described herein provides a new circuit topology for single-stage, single-phase or multi-phase AC-DC power conversion with power factor correction (PFC) and galvanic isolation using a high-frequency isolation transformer. The AC-DC converter improves power conversion efficiency and power density—two of the most important metrics for a power converter. It achieves soft switching for high frequency switches in the circuit, leading to higher efficiency and lower electromagnetic interference (EMI).

Ayyanar, Rajapandian↗

DOE OSTI2022

OPF-Learn: An Open-Source Framework for Creating Representative AC Optimal Power Flow Datasets: Preprint

Increasing levels of renewable generation motivate a growing interest in data-driven approaches for AC optimal power flow (AC OPF) to manage uncertainty. However, a lack of disciplined dataset creation and benchmarking prohibits useful comparison between approaches in the literature. To instigate confidence, models must be able to reliably predict solutions across a wide range of operating conditions. This paper develops the OPF-Learn package for Julia and Python which uses a computationally efficient approach to create representative datasets that span a wide spectrum of the AC OPF feasible region. Load profiles are uniformly sampled from a convex set that contains the AC OPF feasible set. For each infeasible point found, the convex set is reduced using infeasibility certificates, found by utilizing properties of a relaxed formulation. The framework is shown to generate datasets which are more representative of the entire feasible space versus traditional techniques seen in the literature, improving machine learning model performance.

dataset↗

DOE OSTI2020

Stochastic AC optimal power flow: A data-driven approach

There is an emerging need for efficient solutions to stochastic AC Optimal Power Flow (AC-OPF) to ensure optimal and reliable grid operations in the presence of increasing demand and generation uncertainty. Herein this paper presents a highly scalable data-driven algorithm for stochastic AC-OPF that has extremely low sample requirement. The novelty behind the algorithm’s performance involves an iterative scenario design approach that merges information regarding constraint violations in the system with data-driven sparse regression. Compared to conventional methods with random scenario sampling, our approach is able to provide feasible operating points for realistic systems with much lower sample requirements. Furthermore, multiple sub-tasks in our approach can be easily paralleled and based on historical data to enhance its performance and application. We demonstrate the computational improvements of our approach through simulations on different test cases in the IEEE PES PGLib-OPF benchmark library.

42 ENGINEERING↗

DOE OSTI2021

A learning-augmented approach for AC optimal power flow

Because of the high nonlinearity of AC optimal power flow (OPF), numerous efforts have been made in recent decades to find efficient methods. Machine learning (ML) has proven to significantly reduce the computational costs in many real-world problems. Thus, this paper develops a learning-augmented method for solving AC OPF, which integrates both power network equations and ML to yield near-optimal solutions. More specifically, ML models are developed to first predict bus voltage magnitudes and angles. Then, physics-based network equations are employed to calculate the power injection at different buses. Three ML algorithms, i.e., random forest, multi-target decision tree, and extreme learning machine, are explored and compared. To evaluate the efficiency of the proposed learning-augmented AC OPF solver, the MATPOWER Interior Point Solver is adopted as a baseline. Case studies on both 500-bus and 4918-bus test networks show that the proposed learning-augmented method has reduced the computational time by 15–100 times depending on the network size with a minimal loss in optimality.

42 ENGINEERING↗

DOE OSTI2022

Investigation of signal characteristics and charge sharing in AC-LGADs with laser and test beam measurements

AC-LGADs, also referred to as resistive silicon detectors, are a recent development of low-gain avalanche detectors (LGADs), based on a sensor design where the multiplication layer and n + contact are continuous, and only the metal layer is patterned. In AC-LGADs, the signal is capacitively coupled from the continuous, resistive n + layer over a dielectric to the metal electrodes. Therefore, the spatial resolution is not only influenced by the electrode pitch, but also the relative size of the metal electrodes. Signal propagation between the metallized areas and charge sharing between electrodes plays a larger role in these detectors than in conventional silicon sensors read out in DC mode. AC-LGADs from two manufacturers were studied in beam tests and with infrared laser scans. The impact of n + layer resistivity and metal electrode pitch on the charge sharing and achievable position resolution is shown. For strips with 100 μm pitch, a resolution of ¡ 5 μm can be reached. Additionally, the charge sharing between neighboring strips is investigated in more detail, indicating the induction of signal charge and subsequent re-sharing over the n + layer. Furthermore, an approach to identify signal sharing over large distances is presented.

47 OTHER INSTRUMENTATION↗