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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Simulation of the Microwave Emission of Multi-layered Snowpacks Using the Dense Media Radiative Transfer Theory: the DMRT-ML Model

DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1-200 GHz similar to those acquired routinely by spacebased microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT) theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT) to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large icesheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada) and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python.

snowpacks↗
NASA NTRS1978

Quiet, Clean, Short-Haul, Experimental Engine (QCSEE) Under-The-Wing (UTW) engine acoustic design

The acoustic considerations involved in the low source noise basic engine design and the design procedures followed in the development of the under-the-wing (UTW) engine boilerplate and composite nacelle acoustic treatment designs are presented. Laboratory experiments, component tests, and scale model and engine tests supporting the UTW engine acoustic design are referenced. Acoustic design features include a near-sonic inlet, low fan and core pressure ratios, low fan tip speed, high and low frequency stacked core treatment, multiple thickness treatment, and fan frame and stator vane treatment.

Sowers, H. D.↗
NASA NTRS1978

Quiet, Clean, Short-Haul Experimental Engine (QCSEE) Over-The-Wing (OTW) engine acoustic design

The acoustic considerations involved in the low source noise basic engine design and the design procedures followed in the development of the over-the-wing (OTW) nacelle acoustic treatment design are presented. Laboratory experiments, component tests, and scale model and engine tests supporting the OTW engine acoustic design are referenced. Acoustic design features include a near-sonic inlet, low fan and core pressure ratios, low fan tip speed, high and low frequency stacked core treatment, multiple thickness treatment, and fan frame and stator vane treatment.

Sowers, H. D.↗
NASA NTRS2001

A Low Cost, Self Acting, Liquid Hydrogen Boil-Off Recovery System

The purpose of this research was to develop a prototype liquid hydrogen boll-off recovery system. Perform analyses to finalize recovery system cycle, design detail components, fabricate hardware, and conduct sub-component, component, and system level tests leading to the delivery of a prototype system. The design point and off-design analyses identified cycle improvements to increase the robustness of the system by adding a by-pass heat exchanger. Based on the design, analysis, and testing conducted, the recovery system will liquefy 31% of the gaseous boil off from a liquid hydrogen storage tank. All components, including a high speed, miniature turbocompressor, were designed and manufacturing drawings were created. All hardware was fabricated and tests were conducted in air, helium, and hydrogen. Testing validated the design, except for the turbocompressor. A rotor-to-stator clearance issue was discovered as a result of a concentricity tolerance stack-up.

Pelfrey, Joy W.↗
NASA NTRS2004

Bearingless Switched-Reluctance Motor Improved

The Morrison rotor, named after its inventor, is a hybrid rotor for use in a switched reluctance electric motor. The motor is characterized as bearingless in the sense that it does not rely on conventional mechanical bearings: instead, it functions as both a magnetic bearing and a motor. Bearingless switched-reluctance motors are attractive for use in situations in which large variations in temperatures and/or other extreme conditions preclude the use of conventional electric motors and mechanical bearings. In the Morrison motor, as in prior bearingless switched-reluctance motors, a multipole rotor is simultaneously levitated and rotated. In the prior motors, simultaneous levitation and rotation are achieved by means of two kinds of stator windings: (1) main motor windings and (2) windings that exert levitating forces on a multipole rotor. The multipole geometry is suboptimum for levitation because it presents a discontinuous surface to the stator pole faces, thereby degrading the vibration suppression capability of the magnetic bearing. The Morrison rotor simplifies the stator design in that it contains only one type of winding. The rotor is a hybrid that includes both (1) a circular lamination stack for levitation and (2) a multipole lamination stack for rotation. Simultaneous levitation and rotation at 6000 rpm were achieved with a prototype that included six rotor poles and eight stator poles. During normal operation, two of the four pairs of opposing stator poles (each pair at right angles to the other pair) levitate the rotor. The remaining two pairs of stator poles exert torque on the six-pole rotor lamination stack to produce rotation. The relative length of the circular and multipole lamination stacks on the rotor can be chosen to tailor the performance of the motor for a specific application. For a given overall length, increasing the length of the multipole stack relative to the circular stack results in an increase in torque relative to the levitation load capacity and vice versa.

Morrison, Carlos R.↗
NASA NTRS2005

Multi-Band and Broad-Band Infrared Detectors Based on III-V Materials for Spectral Imaging Instruments

Quantum well infrared photodetector technology has shown remarkable success by realizing large-format focal plane arrays in both broad-bands and in multi-bands. The spectral response of these detectors based on the III-V material system are tailorable within the mid and long wavelength IR bands (similar to 3-25 mu m) and possibly beyond. Multi-band and broad-band detector arrays have been developed by vertically integrating stacks of multi quantum wells tailored for response in different wavelengths bands. Each detector stack absorbs photons within the specified wavelength band while allowing the transmission other photons, thus efficiently permitting multiband detection. Flexibility in many design parameters of these detectors allows for tuning and tailoring the spectral shape according to application requirements, specifically for spectral imaging instruments.

quantum well devices↗
NASA NTRS2011

Design, Development and Test Challenges: Separation Mechanisms for the Orion Pad Abort-1 Flight Test

On May 6, 2010, NASA launched the first successful integrated flight test, Pad Abort-1, of the Orion Project from the White Sands Missile Range in Las Cruces, New Mexico. This test demonstrated the ability to perform an emergency pad abort of a full-scale 4.8 m diameter, 8200 kg crew capsule. During development of the critical separation mechanisms for this flight test, various challenges were overcome related to environments definition, installation complications, separation joint retraction speed, thruster ordnance development issues, load path validation and significant design loads increases. The Launch Abort System retention and release (LAS R&R) mechanism consisted of 6 discrete structural connections between the LAS and the crew module (CM) simulator, each of which had a preloaded tension tie, Superbolt torque-nut and frangible nut. During the flight test, the frangible nuts were pyrotechnically split, permitting the CM to separate from the LAS. The LAS separation event was the driving case in the shock environment for many co-located hardware items. During development testing, it was necessary to measure the source shock during the separation event so the predicted shock environment could be validated and used for certification testing of multiple hardware items. The Lockheed Martin test team measured the source separation shock due to the LAS R&R function, which dramatically decreased the predicted environment by 90% at 100 Hz. During development testing a hydraulic tensioner was used to preload the joint; however, the joint relaxation with the tensioner proved unsatisfactory so the design was modified to include a Superbolt torque-nut. The observed preload creep during lab testing was 4% after 30 days, with 2.5% occurring in the first 24 hours. The conversion of strain energy (preload) to kinetic energy (retraction) was measured to be 50-75%. Design features and careful monitoring of multiple strain gauges on each tension tie allowed a pure tensile load to be applied after stacking at the launch pad. Following installation, preload in each joint was monitored for 24 hours. Due to unforeseen complications and the influence of temperature on the portable data acquisition system, the team encountered difficulty in tracking the joint relaxation. In some cases, bond-line failure of the strain gauges occurred.

Dinsel, Alison↗
NASA NTRS2019

Software and System Health Management with R2U2

R2U2 (Realizable, Responsive, Unobtrusive Unit) is a hardware-supported tool and framework for the real-time system and software health management of cyber-physical systems. R2U2 continuously monitors properties about safety, performance, and security of the vehicle and can perform diagnostic reasoning. Efficient observers for past-time and future-time Metric Temporal Logic, reasoners for Bayesian Networks, and model-based prognostics algorithms are major components of R2U2. Their combination makes it possible to design powerful models for system runtime monitoring, diagnostics, software health management, prognostics, and security monitoring. The R2U2 monitoring engine is designed for minimal runtime overhead and is available as Simulink block or as a software component for integration into the flight software stack, and enables R2U2 to monitor complex cyber-physical systems without any instrumentation of the flight software. In this presentation, we give an overview of R2U2 architecture and reasoning algorithms, present its features, and give a life demo of the tool.

Schumann, Johann↗
NASA NTRSDate not supplied

Status of the Advanced Oxygen Generation Assembly Design

Future Exploration missions will require an Oxygen Generation Assembly (OGA) to electrolyze water to supply oxygen for crew metabolic consumption. The system design will be based on the international Space Station (ISS) OGA but with added improvements based on lessons learned during ISS operations and technological advances since the original OGA was designed and built. The goal of these improvements will be to reduce system mass, crew maintenance time and spares mass while increasing reliability. The design team has performed trade studies, tests and analyses to inform the redesign. Upgrades being considered include: redesign of the electrolysis cell stack, redesign of the hydrogen dome, replacement of the hydrogen sensors, redesign of the recirculation loop deionizing bed and redesign of the cell stack Power Supply Module. The ISS OGA will be upgraded to an Advanced OGA (AOGA) configuration and its operation demonstrated in a flight environment.

ECLSS↗
NASA NTRS2021

Effect of Reactant Pressure on Proton Exchange Membrane Fuel Cell Performance

It is an objective of the National Aeronautics and Space Administration (NASA) to return to the moon and to create sustained lunar operations. Since many applicable lander and upper stage vehicles utilize cryogenic hydrogen and oxygen propellants, it is appealing to incorporate fuel cells into potential mission concepts. A fuel cell could generate electricity, heat, and water from the residual hydrogen and oxygen propellants. Such a concept depends on the capability of the fuel cell to utilize dry, propellant-grade reactants at reduced pressures compared to typical fuel cell operating conditions. This report describes a NASA evaluation of two passive water removal, non-flow-through proton exchange membrane (PEM) fuel cells: a twelve-cell 50 sq. cm active area stack and a seven-cell 150 sq. cm active area stack. Both stacks operated on research grade hydrogen and oxygen reactants supplied at pressures ranging from 20 psia up to the 45-48 psia design operating point, reliably supporting current densities of at least 450 mA/sq. cm at reduced pressures. Polarization curves, fitted with a semi-empirical equation for overpotential, show an increase in effective ohmic resistance and decrease in reversible cell potential, hydrogen crossover current, and Tafel slope when operating at lower pressures, resulting in a reduction in cell voltage at all current densities. Fitted parameters are compared to published values and rationalized with first principles explanations.

fuel cells↗
NASA NTRS2004

Electrical Transfer Function and Poling Mechanisms for Nonlinear Optical Polymer Modulators

Electro-Optic Polymers hold great promise in increased electro-optic coefficients as compared to their inorganic corollaries. Many researchers have focused on quantum chemistry to describe how the dipoles respond to temperature and electric fields. Much work has also been done for single layer films to confirm these results. For optical applications, waveguide structures are utilized to guide the optical waves in 3 layer stacks. Electrode poling is the only practical poling method for these structures. This research takes an electrical engineering approach to develop poling models and electrical and optical transfer functions of the waveguide structure. The key aspect of the poling model is the large boundary charge density deposited during the poling process. The boundary charge density also has a large effect on the electrical transfer function which is used to explain the transient response of the system. These models are experimentally verified. Exploratory experiment design is used to study poling parameters including time, temperature, and voltage. These studies verify the poling conditions for CLDX/APC and CLDZ/APEC guest host electro optic polymer films in waveguide stacks predicted by the theoretical developments.

Watson, Michael Dale↗
NASA NTRS2012

Theory of a Traveling Wave Feed for a Planar Slot Array Antenna

Planar arrays of waveguide-fed slots have been employed in many radar and remote sensing applications. Such arrays are designed in the standing wave configuration because of high efficiency. Traveling wave arrays can produce greater bandwidth at the expense of efficiency due to power loss in the load or loads. Traveling wave planar slot arrays may be designed with a long feed waveguide consisting of centered-inclined coupling slots. The feed waveguide is terminated in a matched load, and the element spacing in the feed waveguide is chosen to produce a beam squinted from the broadside. The traveling wave planar slot array consists of a long feed waveguide containing resonant-centered inclined coupling slots in the broad wall, coupling power into an array of stacked radiating waveguides orthogonal to it. The radiating waveguides consist of longitudinal offset radiating slots in a standing wave configuration. For the traveling wave feed of a planar slot array, one has to design the tilt angle and length of each coupling slot such that the amplitude and phase of excitation of each radiating waveguide are close to the desired values. The coupling slot spacing is chosen for an appropriate beam squint. Scattering matrix parameters of resonant coupling slots are used in the design process to produce appropriate excitations of radiating waveguides with constraints placed only on amplitudes. Since the radiating slots in each radiating waveguide are designed to produce a certain total admittance, the scattering (S) matrix of each coupling slot is reduced to a 2x2 matrix. Elements of each 2x2 S-matrix and the amount of coupling into the corresponding radiating waveguide are expressed in terms of the element S11. S matrices are converted into transmission (T) matrices, and the T matrices are multiplied to cascade the coupling slots and waveguide sections, starting from the load end and proceeding towards the source. While the use of non-resonant coupling slots may provide an additional degree of freedom in the design, resonant coupling slots simplify the design process. The amplitude of the wave going to the load is set at unity. The S11 parameter, r of the coupling slot closest to the load, is assigned an arbitrary value. A larger value of r will reduce the power dissipated in the load while increasing the reflection coefficient at the input port. It is now possible to obtain the excitation of the radiating waveguide closest to the load and the coefficients of the wave incident and reflected at the input port of this coupling slot. The next coupling slot parameter, r , is chosen to realize the excitation of that radiating waveguide. One continues this process moving towards the source, until all the coupling slot parameters r and hence the S11 parameter of the 4-port coupler, r, are known for each coupling slot. The goal is to produce the desired array aperture distribution in the feed direction. From an interpolation of the computed moment method data for the slot parameters, all the coupling slot tilt angles and lengths are obtained. From the excitations of the radiating waveguides computed from the coupling values, radiating slot parameters may be obtained so as to attain the desired total normalized slot admittances. This process yields the radiating slot parameters, offsets, and lengths. The design is repeated by choosing different values of r for the last coupling slot until the percentage of power dissipated in the load and the input reflection coefficient values are satisfactory. Numerical results computed for the radiation pattern, the tilt angles and lengths of coupling slots, and excitation phases of the radiating waveguides, are presented for an array with uniform amplitude excitation. The design process has been validated using computer simulations. This design procedure is valid for non-uniform amplitude excitations as well.

Rengarajan, Sembiam↗
NASA NTRS1986

Fracture of thick laminated composites

The fracture of thick laminated graphite/epoxy composites has been the subject of an extensive research program. The program was divided into three major areas of investigation which included laminate thickness, laminate stacking sequence, and part-through surface flaws. The results from this program are reviewed with emphasis placed on their applicability to the design of thick laminated composite structures.

Harris, C. E.↗
NASA NTRS1986

Application of wedge and strip image readout systems to detectors for astronomy

Microchannel plate (MCP) detector systems that use wedge and strip anodes for imaging radiation in the range 50 A to 8000 A are described. Test data, obtained from the calibration of the Extreme Ultraviolet Explorer Satellite detectors and the ARIA EUV aeronomy sensor is presented. The long-term performance characteristics of Z-stack microchannel plates are investigated and it is shown that stable operation is achieved after an initial settling period. Conventional and new anode designs and their potential for increasing the position resolution are discussed. Position resolution of better than 80 microns FWHM has been attained for 50 mm devices, and this is shown to be essentially independent of event location. Image nonlinearity of less than 0.3 percent has been achieved with stability to better than 0.1 percent. Differential nonlinearity of less than 1 percent and stability to better than 1 percent have been obtained. Measurements of the quantum efficiency of a CsI photocathode on an MCP are presented, demonstrating efficiencies as high as 47 percent.

Siegmund, O. H. W.↗
NASA NTRS1996

Status of multijunction solar cells

This paper describes Applied Solar's present activity on Multijunction (MJ) space cells. We have worked on a variety of MJ cells, both monolithic and mechanically stacked. In recent years, most effort has been directed to GaInP2/GaAs monolithic cells, grown on Ge substrates, and the status of this cell design will be reviewed here. MJ cells are in demand to provide satellite power because of the acceptance of the overwhelming importance of high efficiency to reduce the area, weight and cost of space PV power systems. The need for high efficiencies has already accelerated the production of GaAs/Ge cells, with efficiencies 18.5-19%. When users realized that MJ cells could provide higher efficiencies (from 22% to 26%) with only fractional increase in costs, the demand for production MJ cells increased rapidly. The main purpose of the work described is to transfer the MOCVD growth technology of MJ high efficiency cells to a production environment, providing all the space requirements of users.

Yeh, Y. C. M.↗
NASA NTRS1997

A Novel Silicon Micromachined Integrated MCM Thermal Management System

"Micromachining" is a chemical means of etching three-dimensional structures, typically in single- crystalline silicon. These techniques are leading toward what is coming to be referred to as MEMS (Micro Electro Mechanical Systems), where in addition to the ordinary two-dimensional (planar) microelectronics, it is possible to build three-dimensional n-ticromotors, electrically- actuated raicrovalves, hydraulic systems and much more on the same microchip. These techniques become possible because of differential etching rates of various crystallographic planes and materials used for semiconductor n-ticrofabfication. The University of Cincinnati group in collaboration with Karl Baker at NASA Lewis were the first to form micro heat pipes in silicon by the above techniques. Current work now in progress using MEMS technology is now directed towards the development of the next generation in MCM (Multi Chip Module) packaging. Here we propose to develop a complete electronic thermal management system which will allow densifica6on in chip stacking by perhaps two orders of magnitude. Furthermore the proposed technique will allow ordinary conu-nercial integrated chips to be utilized. Basically, the new technique involves etching square holes into a silicon substrate and then inserting and bonding commercially available integrated chips into these holes. For example, over a 100 1/4 in. by 1 /4 in. integrated chips can be placed on a 4 in. by 4 in. silicon substrate to form a Multi-Chip Module (MCM). Placing these MCM's in-line within an integrated rack then allows for three-diniensional stacking. Increased miniaturization of microelectronic circuits will lead to very high local heat fluxes. A high performance thermal management system will be specifically designed to remove the generated energy. More specifically, a compact heat exchanger with milli / microchannels will be developed and tested to remove the heat through the back side of this MCM assembly for moderate and high heat flux applications, respectively. The high heat load application of particular interest in mind is the motor controller developed by Martin Marietta for Nasa to control the thruster's directional actuators on space vechicles. Work is also proposed to develop highly advanced and improved porous wick structures for use in advanced heat loops. The porous wick will be micromachined from silicon using MEMS technology, thus permitting far superior control of pore size and pore distribution (over wicks made from sintered n-ietals), which in turn is expected to led to significantly improved heat loop performance.

Kazmierczak, M. J.↗
NASA NTRS2010

Evaluation of 3D Plus Packaging Test Structures for NASA Goddard Space Flight Center

Environmental tests were performed on packaging test structures designed and manufactured for ESA and CNES by 3D PLus ELectronics. The design provided circuit elements that acted as thermal, mechanical and moisture sensors. Other design features showed the compatibility of the packaging with chip passives, bare electronic dice and plastic encapsulated microcircuits packaged together in an innovative, stacked multichip module. The NASA GSFC testing augmented long duration testing on the same units carried out by ESA and CNES. The NASA portion demonstrated packaging stability over temperature, in moisture, with voltage stress, in shock and in vibration environments.

Plante, Jeannette↗
NASA NTRS2003

Improved Bearingless Switched-Reluctance Motor

The Morrison rotor, named after its inventor, is a hybrid rotor for use in a bearingless switched-reluctance electric motor. The motor is characterized as bearingless in the sense that it does not rely on conventional mechanical bearings: instead, it functions as both a magnetic bearing and a motor. Bearingless switched-reluctance motors are attractive for use in situations in which large variations in temperatures and/or other extreme conditions preclude the use of conventional electric motors and mechanical bearings. In the Morrison motor, as in a prior bearingless switched-reluctance motor, a multipole rotor is simultaneously levitated and rotated. In the prior motor, simultaneous levitation and rotation are achieved by means of two kinds of stator windings: (1) main motor windings and (2) windings that exert levitating forces on a multipole rotor. The multipole geometry is suboptimum for levitation in that it presents a discontinuous surface to the stator pole faces, thereby degrading the vibration-suppression capability of the magnetic bearing. The Morrison rotor simplifies the stator design in that the stator contains only one type of winding. The rotor is a hybrid that includes both (1) a circular lamination stack for levitation and (2) a multipole lamination stack for rotation. A prototype includes six rotor poles and eight stator poles (see figure). During normal operation, two of the four pairs of opposing stator poles (each pair at right angles to the other pair) levitate the rotor. The remaining two pairs of stator poles exert torque on the six-pole rotor lamination stack to produce rotation. The relative lengths of the circular and multipole lamination stacks on the rotor can be chosen to tailor the performance of the motor for a specific application. For a given overall length, increasing the length of the multipole stack relative to the circular stack results in an increase in torque relative to levitation load capacity and stiffness, and vice versa.

Morrison, Carlos R.↗