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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 NTRS2002

Instrumentation and Methodology Development for Mars Mission

The Mars environment comprises a dry, cold and low air pressure atmosphere with low gravity (0.38g) and high resistivity soil. The global dust storms that cover a large portion of Mars were observed often from Earth. This environment provides an idea condition for triboelectric charging. The extremely dry conditions on the Martian surface have raised concerns that electrostatic charge buildup will not be dissipated easily. If triboelectrically generated charge cannot be dissipated or avoided, then dust will accumulate on charged surfaces and electrostatic discharge may cause hazards for future exploration missions. The low surface temperature on Mars helps to prolong the charge decay on the dust particles and soil. To better understand the physics of Martian charged dust particles is essential to future Mars missions. We research and design two sensors, velocity/charge sensor and PZT momentum sensors, to detect the velocity distribution, charge distribution and mass distribution of Martian charged dust particles. These sensors are fabricated at NASA Kenney Space Center, Electromagnetic Physics Testbed. The sensors will be tested and calibrated for simulated Mars atmosphere condition with JSC MARS-1 Martian Regolith simulant in this NASA laboratory.

Chen, Yuan-Liang Albert↗
NASA NTRS2008

New Materials for the Repair of Polyimide Electrical Wire Insulation

Two viable polyimide backbone materials have been identified that will allow the repair of polyimide electrical wire insulation found on the Space Shuttle and other aging aircraft. This identification is the outcome of ongoing efforts to assess the viability of using such polyimides and polyimide precursors (polyamic acids [PAAs]) as repair materials for aging polyimide electrical wire insulation. These repair materials were selected because they match the chemical makeup of the underlying wire insulation as closely as possible. This similarity allows for maximum compatibility, coupled with the outstanding physical properties of polyimides. The two polyimide backbone materials allow the polymer to be extremely flexible and to melt at low temperatures. A polymer chain end capping group that allows the polymer to crosslink into a nonflowable repair upon curing at around 200 C was also identified.

Source record↗
NASA NTRSDate not supplied

Computational and Physics-Based Modeling for the Development of in-Space Welding Technology

Welding will be an enabling technology for in-space assembly and manufacturing (ISAM) and in-space repair operations in support of the growing Space Economy. Prospective use cases of welding include metal repair on long-duration lunar surface missions and assembly of large structures that exceed dimensions of the currently available launch vehicle envelopes such as space arrays, tall lunar transmission towers, or even large transit vehicles powered by nuclear propulsion. There is a brief history of beam welding for in-space use. Soviet and NASA astronauts performed electron beam welds (EBW) in space in the late-1960s through mid-1980s and several parabolic flights of laser beam welding (LBW) were undertaken in the USA and Canada in the early-1990s. Work has since stagnated until the recent boom of the in-space economy has demonstrated need for continued development of EBW and LBW processes, which are desirable for their compactness, low mass, low power consumption, and high wall plug efficiency. No space-based manufacturing laboratory capable of demonstrating, developing, and applying welding processes exists, and costs are high to develop and fly individual space-based trials. This drives the current approach to develop welding technology with computational and physics-based models in tandem with earth-based experiments. Several approaches are taken to complement and drive the selection of instrumentation for planned parabolic and suborbital flights. First, a thermal model of Skylab EBW experiments is established and compared to empirical data. Next, the model is used to show variation between Earth-based and in-space weld structure and properties through exploration of key variables that define the Low earth orbit and lunar surface space environments, namely temperature (40 – 400 K), pressure (10-10 to 104 Pa), and gravity (10-6 g to 1 g). Finally, physical processes associated with heat and mass transport during welding are evaluated through several case studies across the above variable ranges demonstrating need for further research.

in-space welding↗
NASA NTRS1993

X-Band Ultra-Low Noise Maser Amplifier Performance

Noise temperature measurements of an 8440 MHz ultra-low noise maser amplifier (ULNA) have been performed at sub-atmospheric, liquid helium temperatures. The traveling wave maser operated while immersed in a liquid helium bath. The lowest input noise temperature measured was 1.23 plus or minus 0.16 K at a physical temperature of 1.60 kelvin. At this physical temperature the observed gain per unit length of ruby was 4.6 dB/cm, and the amplifier had a 3 dB-bandwidth of 76 MHz.

ultra-low noise maser amplifier X-band maser syste↗
NASA NTRS1987

New insights from a global view of X-ray bursts

It is shown here that the behavior of nuclear burning on accreting neutron stars depends on the mass accretion rate per unit area sigma-dot, the temperature T, and the column density of accreted matter sigma, and is thus intrinsically a three-dimensional problem. The concepts of a nuclear fuel surface and an ignition surface in (sigma-dot, T, sigma) space is introduced. It is shown that certain cuts taken through the ignition surface correspond to particular physical situations. It is found that at high temperatures a succession of hydrogen flashes leads eventually to a pure helium flash. At low temperatures, compressional heating completely determines the burst behavior. Burst sources are expected to show highly erratic behavior if they lie near the boundaries of the H and He ignition surfaces, resolving a major discrepancy between the thermonuclear flash model and observations.

Fushiki, Ikko↗
NASA NTRS2000

The Preparation Conditions of Chromium Doped ZnSe and Their Effect on The Infrared Luminescence Properties

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the Physical Vapor Transport method. Room temperature lifetime values between 6 and 8 microseconds were measured for samples with Cr (2+) concentrations from low 10 (exp 17) to high 10 (exp 18) per cubic centimeter range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10 (exp 19) per cubic centimeter.

Burger, A.↗
NASA NTRS2001

The Effect of the Wall Contact and Post-Growth C001-Down on Defects in CdTe Crystals Grown by Contactless PVT

In crystal growth, the quality of the final material may depend, among other factors, on its interaction with the walls of the ampoule during and after the growth, and on the rate of the crystal cool-down at the end of ate the process. To investigate the above phenomena, a series of CdTe crystal growth processes was carried out, The crystals were grown by physical vapor transport without contact with the side walls of the silica glass ampoules, applying the Low Supersaturation Nucleation technique. The source temperature was 930 C, the undercooling was a few degrees. The crystals, having the diameter of 25 mm, grew at the rate of a few mm per day. The post-growth cool-down to the room temperature was conducted at different rates, and lasted from a few minutes to four days. The crystals were characterized using chemical etching low temperature luminescence, and Synchrotron White Beam X-ray Topography techniques. The dislocation (etch pit) density was measured and its distribution was analyzed by comparison with Poisson curves and with the Normalized Radial Distribution Correlation Function. It was found that the contact of the crystal with silica leads to a strain field and high (in the 105 sq cm range) dislocation (etch pit) density. Similar defect concentrations were found in crystals subjected to fast post-growth cool-down. Typical EPD values for lower cool-down rates and in regions not affected by wall interactions are in the lower 10(exp 4) sq cm range. In some areas the actual dislocation density was about 10(exp 3) sq cm or even less. No apparent effect of the cool-down rate on polygonization was observed. A fine structure could be discerned in low-temperature PL spectra of crystals with low dislocation density.

Palosz, W.↗
NASA NTRS2002

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows. ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, were grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals were characterized extensively to correlate the grown crystal properties with the growth conditions. The following are the research progress in the past two years. In-situ monitoring of partial pressure by optical absorption technique and visual observation of the growing crystal were performed during vapor growth of ZnSe. Low-temperature photoluminescence (PL) spectra and glow discharge mass spectroscopy (GDMS) were measured on ZnSe starting materials provided by various vendors and on bulk crystals grown from these starting materials by physical vapor transport (PVT) to study the effects of purification and contamination during crystal growth process. Optical characterization was performed on wafers sliced from the grown crystals of ZnSe, ZnTe and ZnSe(1-x),Te(x), (0<x<0.4). Energy band gaps at room temperature were determined from optical transmission measurements and a best fit curve to the band gap vs. composition, x, data gives a bowing parameter of 1.45. Low-temperature photoluminescence (PL) spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for the ZnSe(1-x),Te(x), samples, 0.09<x<0.39. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the exciton bound to Te clusters because of the high Te content in these samples. To validate numerical codes, in-situ monitoring during the PVT of HgI2 was designed. Optical absorption spectra of the vapor phase over HgI2 were measured for wavelengths between 200 and 600nm at sample temperatures between 349 and 610K. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were determined. From these constants the vapor pressure of HgI2 was established as a function of temperature for the liquid and the solid Beta-phases To characterize the growth conditions during the PVT growth of In-doped ZnSe the optical absorbance of the vapor phase over the In-Se system were measured and were used to obtain the partial pressures of Se2(g) and In2Se(g).

Su, Ching-Hua↗
NASA NTRS2004

Low-Temperature Plasma Functionalization of Carbon Nanotubes

A low-temperature plasma process has been devised for attaching specified molecular groups to carbon nanotubes in order to impart desired chemical and/or physical properties to the nanotubes for specific applications. Unlike carbon-nanotube- functionalization processes reported heretofore, this process does not involve the use of wet chemicals, does not involve exposure of the nanotubes to high temperatures, and generates very little chemical residue. In addition, this process can be carried out in a relatively simple apparatus and can readily be scaled up to mass production.

Khare, Bishun↗
NASA NTRS2022

Solid-State Ultracapacitor Polymer Composite

An ultracapacitor made from a polymer loaded with ceramic powder would have several advantages over current ultracapacitors and batteries. First is the possibility of it being printable, which would allow for printing the energy storage device along with the circuit instead of having to find a way to add one later without damaging the rest of the components. When not printed in a specific design for use on a printed wiring board, this type of ultracapacitor could still be cured via a mold to a shape suitable to specific applications. Many polymers maintain some flexibility even after curing, such as the silicone used in this study. The manufacturing process would also be far simpler than that of conventional ultracapacitors.In this work, solid-state ultracapacitors were made by adding the dielectric powder to a two-part polymer (resin and hardener) at the same time. The mixture was then cured in the desired shape at a low temperature until completely set. The addition of the powder to the polymer increased its dielectric properties while leaving most of its physical properties unaltered. At higher powder loading percentages, there were some physical changes as the maximum loading point was approached. To determine the efficiency of these solid-state ultracapacitors, their capacitances were tested, and their dielectric constants (DCs) were measured and compared.

energy storage↗
NASA NTRS1987

Coatings for high-temperature bearings and seals

Criteria are discussed for predicting the probable lubricating ability of candidate solid materials from a consideration of their basic chemical and physical properties. The properties considered to be important in the model are thermochemical potential, adhesion, low hardness, plasticity, yield strength in shear, and brittle-to-ductile transition characteristics. A review of the selection and tribological testing of materials, which were selected for use in self-lubricating composite coatings by employing this model, is given. Two series of plasma-sprayed coatings with good tribological properties over a wide temperature spectrum are described. The PS 100 series of coatings contain oxidatively stable solid lubricants in a nichrome matrix. The PS 200 series contains the same solid lubricants in a very wear resistant metal-bonded chromium carbide matrix. Examples are given of applications of these coatings in high speed shaft seals, sliding contact bearings, and Stirling engine cylinder liners.

Sliney, Harold E.↗
NASA NTRS1992

Energetics and structural properties of twist grain boundaries in Cu

Structural and energetics properties of atoms near a grain boundary are of great importance from theoretical and experimental standpoints. From various experimental work it is concluded that diffusion at low temperatures at polycrystalline materials take place near grain boundary. Experimental and theoretical results also indicate changes of up to 70 percent in physical properties near a grain boundary. The Embedded Atom Method (EAM) calculations on structural properties of Au twist grain boundaries are in quite good agreement with their experimental counterparts. The EAM is believed to predict reliable values for the single vacancy formation energy as well as migration energy. However, it is not clear whether the EAM functions which are fitted to the bulk properties of a perfect crystalline solid can produce reliable results on grain boundaries. One of the objectives of this work is to construct the EAM functions for Cu and use them in conjunction with the molecular static simulation to study structures and energetics of atoms near twist grain boundaries in Cu. This provides tests of the EAM functions near a grain boundary. In particular, we determine structure, single vacancy formation energy, migration energy, single vacancy activation energy, and interlayer spacing as a function of distance from grain boundary. Our results are compared with the available experimental and theoretical results from grain boundaries and bulk.

Karimi, Majid↗
NASA NTRS1999

Young Impact Craters as Potential Sites for the Exploration of the Martian Subsurface

Orbiter and lander data indicate that a global, oxidizing regolith may blanket the surface of Mars. New sub-km crater counts by Hartmann indicate that an impact-gardened regolith may exist to a depth of at least 15 m (assuming a mean surface age of 2 Gyr), although the original meter-scale geology may still persist at certain locations such as the outflow channel of the Pathfinder landing site. The pervasive regolith appears to have an aeolian-mobilized component which may frustrate attempts to find key minerals such as carbonates or nitrates. It may also stymie searches for physical and chemical signs of past or present life. Various mechanical (penetrators, drills) means of obtaining access to the subsurface have been proposed: Here I propose to let Nature do the work by using a young impact crater. Both the nearby ejecta blanket and the crater rim may provide freshly exposed subsurface material. The crater must be large enough to penetrate the regolith but still young enough that chemical and physical weathering of exposed material is minor. A high latitude site may be preferable since organics may oxidize much more slowly at low temperatures. The tradeoffs in crater and site selection are presented, and possible crater exploration strategies are suggested.

Gaidos, E. J.↗
NASA NTRS1999

Composting on Mars or the Moon: I. Comparative evaluation of process design alternatives

As a candidate technology for treating solid wastes and recovering resources in bioregenerative Advanced Life Support, composting potentially offers such advantages as compactness, low mass, near ambient reactor temperatures and pressures, reliability, flexibility, simplicity, and forgiveness of operational error or neglect. Importantly, the interactions among the physical, chemical, and biological factors that govern composting system behavior are well understood. This article comparatively evaluates five Generic Systems that describe the basic alternatives to composting facility design and control. These are: 1) passive aeration; 2) passive aeration abetted by mechanical agitation; 3) forced aeration--O2 feedback control; 4) forced aeration--temperature feedback control; 5) forced aeration--integrated O2 and temperature feedback control. Each of the five has a distinctive pattern of behavior and process performance characteristics. Only Systems 4 and 5 are judged to be viable candidates for ALS on alien worlds, though which is better suited in this application is yet to be determined.

Review↗
NASA NTRS2017

Ice Nucleation in the Tropical Tropopause Layer: Implications for Cirrus Occurrence, Cirrus Microphysical Properties, and Dehydration of Air Entering the Stratosphere

Recent laboratory experiments have advanced our understanding of the physical properties and ice nucleating abilities of aerosol particles atlow temperatures. In particular, aerosols containing organics will transition to a glassy state at low temperatures, and these glassy aerosols are moderately effective as ice nuclei. These results have implications for ice nucleation in the cold Tropical Tropopause Layer (TTL; 13-19 km). We have developed a detailed cloud microphysical model that includes heterogeneous nucleation on a variety of aerosol types and homogeneous freezing of aqueous aerosols. This model has been incorporated into one-dimensional simulations of cirrus and water vapor driven by meteorological analysis temperature and wind fields. The model includes scavenging of ice nuclei by sedimenting ice crystals. The model is evaluated by comparing the simulated cloud properties and water vapor concentrations with aircraft and satellite measurements. In this presentation, I will discuss the relative importance of homogeneous and heterogeneous ice nucleation, the impact of ice nuclei scavenging as air slowly ascends through the TTL, and the implications for the final dehydration of air parcels crossing the tropical cold-point tropopause and entering the tropical stratosphere.

tropopause↗
NASA NTRS1996

Mullite fiber reinforced reaction bonded Si3N4 composites

Fracture toughnesses of brittle ceramic materials have been improved by introducing reinforcements and carefully tailored interface layers. Silicon carbide and Si3N4 have been emphasized as matrices of structural composites intended for high temperature service because they combine excellent mechanical, chemical, thermal and physical properties. Both matrices have been successfully toughened with SiC fibers, whiskers and particles for ceramic matrix composite (CMC) parts made by sintering, hot pressing or reaction forming processes. These SiC reinforced CMCs have exhibited significantly improved toughnesses at low and intermediate temperature levels, as well as retention of properties at high temperatures for selected exposures; however, they are vulnerable to attack from elevated temperature dry and wet oxidizing atmospheres after the matrix has cracked. Property degradation results from oxidation of interface layers and/or reinforcements. The problem is particularly acute for small diameter (-20 tim) polymer derived SiC fibers used for weavable toes. This research explored opportunities for reinforcing Si3N4 matrices with fibers having improved environmental stability; the findings should also be applicable to SiC matrix CMCs.

Saleh, T.↗
NASA NTRS2021

Coexisting Quantum Gases in Earth’s Orbit

Summary: Ultracold atomic gases provide a unique tool for exploring the quantum nature of matter and for probing the foundations of modern physics. Researchers with NASA’s Cold Atom Lab (CAL) have now simultaneously produced gases of two atomic species (rubidium and potassium) in a uniquely quantum (wave-like) phase of matter called a Bose-Einstein condensate (BEC) for the first time in space. CAL scientists are using the unique micro gravity environment onboard the International Space Station to study interactions, molecule formation, and the emergence of structure and complexity in these coexisting dual-species gases at unprecedented low temperatures, for long times in free fall, and specifically in the absence of the perturbing force of gravity.

quantum gases↗
NASA NTRS1981

Atmospheric noise temperature measurements

Radiometric microwave noise temperature measurements were used to estimate atmospheric transmission loss. The following lumped element model expression is used for the noise temperature contribution, T double prime = T sub p (1 - 1/L). This relationship is used to estimate the transmission loss L in terms of T double prime and the atmosphere effective physical temperature T sub p. This report evaluates T sub p in terms of assumed distributed loss and temperature models. Simplified expressions are presented for low loss applications. For these applications L was determined directly and accurately without integration or iteration.

Stelzried, C.↗