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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Flammability of Epoxy Resins Containing Phosphorus

As part of a program to develop fire-resistant exterior composite structures for future subsonic commercial and general aviation aircraft, flame-retardant epoxy resins are under investigation. Epoxies and their curing agents (aromatic diamines) containing phosphorus were synthesized and used to prepare epoxy formulations. Phosphorus was incorporated within the backbone of the epoxy resin and not used as an additive. The resulting cured neat epoxy formulations were characterized by thermogravimetric analysis, propane torch test, elemental analysis, microscale combustion calorimetry, and fire calorimetry. Several formulations showed excellent flame retardation with phosphorous contents as low as 1.5% by weight. The fracture toughness and compressive strength of several cured formulations showed no detrimental effect due to phosphorus content. The chemistry and properties of these new epoxy formulations are discussed.

Flammability studies↗
NASA NTRS2006

Opposed Jet Burner Approach for Characterizing Flameholding Potentials of Hydrocarbon Scramjet Fuels

Opposed Jet Burner (OJB) tools have been used extensively by the authors to measure Flame Strength (FS) extinction limits of laminar H2/N2 air and (recently) hydrocarbon (HC) air Counterflow Diffusion Flames (CFDFs) at one atm. This paper details normalization of FSs of N2- diluted H2 and HC systems to account for effects of fuel composition, temperature, pressure, jet diameter, inflow Reynolds number, and inflow velocity profile (plug, contoured nozzle; and parabolic, straight tube). Normalized results exemplify a sensitive accurate means of validating, globally, reduced chemical kinetic models at approx. 1 atm and the relatively low temperatures approximating the loss of non-premixed idealized flameholding, e.g., in scramjet combustors. Laminar FS is defined locally as maximum air input velocity, U(sub air), that sustains combustion of a counter-jet of g-fuel at extinction. It uniquely characterizes a fuel. And global axial strain rate at extinction (U(sub air) normalized by nozzle or tube diameter, D(sub n or (sub t)) can be compared directly with computed extinction limits, determined using either a 1-D Navier Stokes stream-function solution, using detailed transport and finite rate chemistry, or (better yet) a detailed 2-D Navier Stokes numerical simulation. The experimental results define an idealized flameholding reactivity scale that shows wide ranging (50 x) normalized FS s for various vaporized-liquid and gaseous HCs, including, in ascending order: JP-10, methane, JP-7, n-heptane, n-butane, propane, ethane, and ethylene. Results from H2 air produce a unique and exceptionally strong flame that agree within approx. 1% of a recent 2-D numerically simulated FS for a 3 mm tube-OJB. Thus we suggest that experimental FS s and/or FS ratios, for various neat and blended HCs w/ and w/o additives, offer accurate global tests of chemical kinetic models at the Ts and Ps of extinction. In conclusion, we argue the FS approach is more direct and fundamental, for assessing, e.g., idealized scramjet flameholding potentials, than measurements of laminar burning velocity or blowout in a Perfectly Stirred Reactor, because the latter characterize premixed combustion in the absence of aerodynamic strain. And FS directly measures a chemical kinetic characteristic of non-premixed combustion at typical flameholding temperatures. It mimics conditions where gfuels are typically injected into a subsonic flameholding recirculation zone that captures air, where the effects of aerodynamic strain and associated multi-component diffusion become important.

Pellett, Gerald L.↗
NASA NTRS1997

Portable Long-Wavelength Infrared Camera for Civilian Application

In this paper, we discuss the performance of this portable long-wavelength infrared camera in quantum efficiency, NEAT, minimum resolvable temperature differnce (MRTD), uniformity, etc. and its application in science, medicine and defense.

infrared wavelength portable↗
NASA NTRS2005

The development of a Kalman filter clock predictor

A Kalman filter based clock predictor is developed, and its performance evaluated using both simulated and real data. The clock predictor is shown to possess a neat to optimal Prediction Error Variance (PEV) when the underlying noise consists of one of the power law noise processes commonly encountered in time and frequency measurements. The predictor's performance is the presence of multiple noise processes is also examined. The relationship between the PEV obtained in the presence of multiple noise processes and those obtained for the individual component noise processes is examined. Comparisons are made with a simple linear clock predictor. The clock predictor is used to predict future values of the time offset between pairs of NPL's active hydrogen masers.

clock predictor↗
NASA NTRS2005

Multi-Color Megapixel QWIP focal plane arrays for remote sensing

In this paper, we will discuss the performance in terms of quantum efficiency, NEAT, uniformity, operability, and modulation transfer functions of the 1024x1024 pixel arrays and the progress of dualband QWIP focal plane array development work.

infixed imaging↗
NASA NTRS2003

Development of a safe ground to space laser propagation system for the optical communications telescope laboratory

Furthering pursuits in high bandwidth communications to future NASA deep space and neat-Earth probes, the Jet Propulsion Laboratory (JPL) is building the Optical communications Telescope Laboratory (OCTL) atop Table Mountain in Southern California. This R&D optical antenna will be used to develop optical communication strategies for future optical ground stations. Initial experiments to be conducted include propagating high-powered, Q-switched laser beams to retro-reflecting satellites. Yet laser beam propagation from the ground to space is under the cognizance of various government agencies, namely: the Occupational Safety and Health Administration (ISHA) that is responsible for protecting workforce personnel; the Federal Aviation Administration (FAA) responsible for protecting pilots and aircraft; and the Laser Clearinghouse of Space Command responsible for protecting space assets. To ensure that laser beam propagation from the OCTL and future autonomously operated ground stations comply with the guidelines of these organizations, JPL is developing a multi-tiered safety system that will meet the coordination, monitoring, and reporting functions required by the agencies. At Tier 0, laser operators will meet OSHA safety standards for protection and access to the high power lasers area will be restricted and interlocked. Tier 1, the area defined from the telescope dome out to a range of 3.4-km, will utilize long wave infrared camera sensors to alert operators of at risk aircraft in the FAA controlled airspace. Tier 2, defined to extend from 3.4-km out to the aircraft service ceiling in FAA airspace, will detect at risk aircraft by radar. Lastly, beam propagation into space, defined as Tier 3, will require coordination with the Laser Clearinghouse. A detailed description of the four tiers is presented along with the design of the integrated monitoring and beam transmission control system.

laser safety↗
NASA NTRS2006

Dielectric relaxation behavior of poly(acrylonitri1e-co-methacrylonitrile) microcapsules dispersed in a silicone matrix

The dielectric relaxation behavior of poly(acry1onitrile-co-methacrylonitrile) dispersed in a cured polydimethyl siloxane (PDMS) matrix as microcapsules was investigated over multiple thermal cycles and at varying concentrations. The copolymer microcapsules contained an isopentane core. In the PDMS matrix this copolymer displayed a pronounced relaxation signal at temperatures above the glass transition of the copolymers due to Maxwell-Wagner-Sillars (MWS) relaxation. The mechanism of MWS relaxation interpreted by the Havriliak-Negami and Kohlrausch-Williams-Watts relaxation functions was found to be very similar to previous studies of neat polyacrylonitrile and its copolymer. The activation energy of the relaxation decreased over successive thermal cycling coincident with a decreasing strength of the relaxation. These observations were attributed to the decreasing concentration of nitrile groups due to intramolecular cyclizations.

Park, Taigyoo↗
NASA NTRS2006

Dielectric Relaxation Behavior of Poly(acrylonitrile-co-methacrylonitrile) Microcapsules Dispersed in a Silicone Matrix

The dielectric relaxation behavior of poly(acrylonitrile-co-methacrylonitrile) dispersed in a cured polydimethyl siloxane (PDMS) matrix as microcapsules was investigated over multiple thermal cycles and at varying concentrations. The copolymer microcapsules contained an isopentane core. In the PDMS matrix this copolymer displayed a pronounced relaxation signal at temperatures above the glass transition of the copolymers due to Maxwell-Wagner-Sillars (MWS) relaxation. The mechanism of MWS relaxation interpreted by the Havriliak-Negami and Kohlrausch-Williams-Watts relaxation functions was found to be very similar to previous studies of neat polyacrylonitrile and its copolymer. The activation energy of the relaxation decreased over successive thermal cycling coincident with a decreasing strength of the relaxation. These observations were attributed to the decreasing concentration of nitrile groups due to intramolecular cyclizations.

Park, Taigyoo↗
NASA NTRS2007

Application of Carbon Based Nano-Materials to Aeronautics and Space Lubrication

The tribology program at NASA Glenn Research Center in Cleveland, Ohio, is investigating carbon based nano-particles for their potential in advanced concept lubrication products. Service conditions range from high temperature atmospheric to low temperature vacuum. Some of the lubricants and surface coatings of tribological significance that we have evaluated include neat nano-particles, both grown in-situ and as bulk material deposited on the substrate, and nano-particles dispersed in oils which are all highly substrate interactive. We discuss results of testing these systems in a spiral orbit tribometer (SOT) and a unidirectional pin-on-disc (PoD) tribometer. A nano-onions/Krytox mixture evaluated as a lubricant for angular contact bearings in air caused a marked lowering of the coefficient of friction (CoF) (0.04 to 0.05) for the mixture with an eight-fold improvement in lifetime over that of the Krytox alone. In vacuum, no effect was observed from the nano-onions. Multi-walled nanotubes (MWNT) and graphitized MWNT were tested under sliding friction in both air and vacuum. The MWNT which were grown in-situ oriented normal to the sliding surface exhibited low CoF (0.04) and long wear lives. Bulk MWNT also generate low CoF (0.01 to 0.04, vacuum; and 0.06, air) and long wear life (>1 million orbits, vacuum; and >3.5 million, air). Dispersed graphitized MWNT were superior to MWNT and both were superior to aligned MWNT indicating that orientation is not an issue for solid lubrication. Single-walled nanotubes (SWNT) were modified by cutting into shorter segments and by fluorination. All SWNTs exhibited low CoF in air, with good wear lives. The SWNT with slight fluorination yielded an ultra-low CoF of 0.002 although the best wear life was attributed to the nascent SWNT.

Street, Kenneth W., Jr.↗
NASA NTRS2007

Improved Thermal Design of a Compression Mold

An analysis of the heat transfer in a tool for producing neat resin disks was conducted to determine how to bring about a better agreement between the tool temperature and the applied temperature profile. Using the commercial code FLUENT to investigate the relative effects of heat conduction into the tool and heat loss from the tool by convection, it was shown that convective heat transfer appears more important than conduction in controlling the tool performance. Decreasing the height of the tool was predicted to decrease the heat losses by convection. Redesign of the tool based on this analysis resulted in the tool experiencing the applied temperature profile.

Kuczmarski, Maria A.↗
NASA NTRS2008

Surface Analysis of 4-Aminothiophenol Adsorption at Polycrystalline Platinum Electrodes

Formation of self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been studied by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), Raman spectroscopy, reflection absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) experiments give an idea about the packing quality of the monolayer. RAIR and Raman spectra for 4-ATP modified platinum electrodes showed the characteristic adsorption bands for neat 4-ATP indicating the adsorption of 4-ATP molecules on platinum surface. The adsorption on platinum was also evidenced by the presence of sulfur and nitrogen peaks by XPS survey spectra of the modified platinum electrodes. High resolution XPS studies and RAIR spectrum for platinum electrodes modified with 4-ATP indicate that molecules are sulfur-bonded to the platinum surface. The formation of S-Pt bond suggests that ATP adsorption gives up an amino terminated SAM. Thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses. Derivatization of 4-ATP SAM was performed using 16-Br hexadecanoic acid.

Rosario-Castro, Belinda I.↗
NASA NTRS2006

Thermal Conductivity of Ultem(TradeMark)/Carbon Nanofiller Blends

In an effort to improve polymer thermal conductivity (TC), Ultem(TradeMark) 1000 was compounded with nano-fillers of carbon allotropes. Ultem(TradeMark) 1000 was selected since it is both solution and melt processable. As-received and modified multiwalled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. MWCNTs were modified by functionalizing the surface through oxidization with concentrated acids, mixing with an alkyl bromide, and addition of alkyl and phosphorus compounds after initial treatment with n-butyl lithium. Functionalization was performed to improve the TC compatibility between the resin and MWCNTs. It was postulated that this may provide an improved interface between the MWCNT and the polymer which would result in enhanced TC. The nano-fillers were mixed with Ultem(TradeMark) 1000 in the melt and in solution at concentrations ranging from 5 to 40 wt%. Ribbons were extruded from the blends to form samples where the nano-fillers were aligned to some degree in the extrusion direction. Samples were also fabricated by compression molding resulting in random orientation of the nano-fillers. Thermal properties of the samples were evaluated by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analyzer (TGA). Tensile properties of aligned samples were determined at room temperature. The specimens were cut from the ribbons in the extrusion direction; hence the nano-fillers are somewhat aligned in the direction of stress. Typically it was observed that melt mixed samples exhibited superior mechanical properties compared to solution mixed samples. As expected, increased filler loading led to increased modulus and decreased elongation with respect to the neat polymer. The degree of dispersion and alignment of the nano-fillers was determined by high-resolution scanning electron microscopy (HRSEM). HRSEM of the ribbons revealed that the MWCNTs and CNFs were predominantly aligned in the flow direction. The TC of the samples was measured using a Nanoflash(TradeMark) instrument. Since the MWCNTs and CNF are anisotropic, the TC was expected to be different in the longitudinal (parallel to the nanotube and fiber axis) and transverse (perpendicular to the nanotube and fiber axis) directions. The extruded ribbons provided samples for transverse TC measurements. However, to determine the TC in the longitudinal direction, the ribbons needed to be stacked and molded under 1.7 MPa and 270 C. Samples were then obtained by cutting the molded block with a diamond saw. The largest TC improvement was achieved for aligned samples when the measurement was performed in the direction of MWCNT and CNF alignment (i.e. longitudinal axis). Unaligned samples also showed a significant improvement in TC and may be potentially useful in applications when it is not possible to align the nano-filler. The results of this study will be presented.

Ghose, S.↗
NASA NTRS2008

Improved Silica Aerogel Composite Materials

A family of aerogel-matrix composite materials having thermal-stability and mechanical- integrity properties better than those of neat aerogels has been developed. Aerogels are known to be excellent thermal- and acoustic-insulation materials because of their molecular-scale porosity, but heretofore, the use of aerogels has been inhibited by two factors: (1) Their brittleness makes processing and handling difficult. (2) They shrink during production and shrink more when heated to high temperatures during use. The shrinkage and the consequent cracking make it difficult to use them to encapsulate objects in thermal-insulation materials. The underlying concept of aerogel-matrix composites is not new; the novelty of the present family of materials lies in formulations and processes that result in superior properties, which include (1) much less shrinkage during a supercritical-drying process employed in producing a typical aerogel, (2) much less shrinkage during exposure to high temperatures, and (3) as a result of the reduction in shrinkage, much less or even no cracking.

Paik, Jong-Ah↗
NASA NTRS2008

"Built-In" Action/Issues Tracking and Post-Ops Analysis Tool for Realtime Console Operations

Marshall Space Flight Center's (MSFC) Payload Operations Integration Center (POIC) for the International Space Station (ISS) uses a number of formal databases to manage and track flight plan changes, onboard and ground equipment anomalies, and other events. However, individual console positions encounter many action items and/or occurrences that don't fit neatly into the databases, and while console logs are comprehensive, manual or automated searches do not always yield consistent results. The Payload Communications Manager (PAYCOM) team, whose members speak directly with the ISS onboard crew with respect to NASA payload operations, has found a creative way to reformat a mandatory Daily Report to organize action items, standing reminders, significant events, and other comments. While the report keeps others appraised of PAYCOMs activities and issues of the moment, the format makes it easy to capture very brief summaries of the items in a "Roll Off Matrix", including start and stop dates, resolution, and possible applicability to future ops. The matrix provides accountability for all action items, gives direct insight into the issues surrounding various payloads and methods of dealing with them, yields indirect information on PAYCOM priorities and processes, and provides a roadmap that makes it easier to get back to extensive details if needed. This paper describes how the ISS PAYCOM Daily Report and Roll Off Matrix are organized, used, and inter-related to each other and the PAYCOM operations log. While the application is for a manned vehicle, the concepts could apply in a wide spectrum of operational settings.

Scott, David W.↗
NASA NTRS2009

Production of Lightning NO(x) and its Vertical Distribution Calculated from 3-D Cloud-scale Chemical Transport Model Simulations

A 3-D cloud scale chemical transport model that includes a parameterized source of lightning NO(x), based on observed flash rates has been used to simulate six midlatitude and subtropical thunderstorms observed during four field projects. Production per intracloud (P(sub IC) and cloud-to-ground (P(sub CG)) flash is estimated by assuming various values of P(sub IC) and P(sub CG) for each storm and determining which production scenario yields NO(x) mixing ratios that compare most favorably with in-cloud aircraft observations. We obtain a mean P(sub CG) value of 500 moles NO (7 kg N) per flash. The results of this analysis also suggest that on average, P(sub IC) may be nearly equal to P(sub CG), which is contrary to the common assumption that intracloud flashes are significantly less productive of NO than are cloud-to-ground flashes. This study also presents vertical profiles of the mass of lightning NO(x), after convection based on 3-D cloud-scale model simulations. The results suggest that following convection, a large percentage of lightning NO(x), remains in the middle and upper troposphere where it originated, while only a small percentage is found near the surface. The results of this work differ from profiles calculated from 2-D cloud-scale model simulations with a simpler lightning parameterization that were peaked near the surface and in the upper troposphere (referred to as a "C-shaped" profile). The new model results (a backward C-shaped profile) suggest that chemical transport models that assume a C-shaped vertical profile of lightning NO(x) mass may place too much mass neat the surface and too little in the middle troposphere.

Ott, Lesley↗
NASA NTRS2008

Photochemically Synthesized Polyimides

An alternative to the conventional approach to synthesis of polyimides involves the use of single monomers that are amenable to photopolymerization. Heretofore, the synthesis of polyimides has involved multiple-monomer formulations and heating to temperatures that often exceed 250 C. The present alternative approach enables synthesis under relatively mild conditions that can include room temperature. The main disadvantages of the conventional approach are the following: Elevated production temperatures can lead to high production costs and can impart thermal stresses to the final products. If the proportions of the multiple monomeric ingredients in a given batch are not exactly correct, the molecular weight and other physical properties of the final material could be reduced from their optimum or desired values. To be useful in the alternative approach, a monomer must have a molecular structure tailored to exploit Diels-Alder trapping of a photochemically generated ortho-quinodimethane. (In a Diels-Alder reaction, a diene combines with a dienophile to form molecules that contain six-membered rings.) In particular, a suitable monomer (see figure) contains ortho-methylbenzophenone connected to a dienophile (in this case, a maleimide) through a generic spacer group. Irradiation with ultraviolet light gives rise to a photochemical intermediate the aforementioned ortho-quinodimethane from the ortho-methylbenzophenone. This group may react with the dienophile on another such monomer molecule to produce an oligomer that, in turn may react in a stepgrowth manner to produce a polyimide. This approach offers several advantages in addition to those mentioned above: The monomer can be stored for a long time because it remains unreactive until exposed to light. Because the monomer is the only active starting ingredient, there is no need for mixing, no concern for ensuring correct proportions of monomers, and the purity of the final product material is inherently high. The use of solvents is optional: The synthesis can be performed using the neat monomer or the monomer mixed with one or more solvent(s) in dilute or concentrated solution. The solubility of the monomer and the physical and chemical properties of the final polymer can be tailored through selection of the spacer group.

Meador, Michael A.↗
NASA NTRS2009

Polyimide-Foam/Aerogel Composites for Thermal Insulation

Composites of specific types of polymer foams and aerogel particles or blankets have been proposed to obtain thermal insulation performance superior to those of the neat polyimide foams. These composites have potential to also provide enhanced properties for vibration dampening or acoustic attenuation. The specific type of polymer foam is denoted "TEEK-H", signifying a series, denoted H, within a family of polyimide foams that were developed at NASA s Langley Research Center and are collectively denoted TEEK (an acronym of the inventors names). The specific types of aerogels include Nanogel aerogel particles from Cabot Corporation in Billerica, MA. and of Spaceloft aerogel blanket from Aspen Aerogels in Northborough, MA. The composites are inherently flame-retardant and exceptionally thermally stable. There are numerous potential uses for these composites, at temperatures from cryogenic to high temperatures, in diverse applications that include aerospace vehicles, aircraft, ocean vessels, buildings, and industrial process equipment. Some low-temperature applications, for example, include cryogenic storage and transfer or the transport of foods, medicines, and chemicals. Because of thermal cycling, aging, and weathering most polymer foams do not perform well at cryogenic temperatures and will undergo further cracking over time. The TEEK polyimides are among the few exceptions to this pattern, and the proposed composites are intended to have all the desirable properties of TEEK-H foams, plus improved thermal performance along with enhanced vibration or acoustic-attenuation performance. A composite panel as proposed would be fabricated by adding an appropriate amount of TEEK friable balloons into a mold to form a bottom layer. A piece of flexible aerogel blanket material, cut to the desired size and shape, would then be placed on the bottom TEEK layer and sandwiched between another top layer of polyimide friable balloons so that the aerogel blanket would become completely encased in an outer layer of TEEK friable balloons. Optionally, the process could be further repeated to produce multiple aerogel-blanket layers interspersed with and encased by TEEK friable balloons.

Williams, Martha↗