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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 sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Prospects for Geostationary Doppler Weather Radar

A novel mission concept, namely NEXRAD in Space (NIS), was developed for detailed monitoring of hurricanes, cyclones, and severe storms from a geostationary orbit. This mission concept requires a space deployable 35-m diameter reflector that operates at 35-GHz with a surface figure accuracy requirement of 0.21 mm RMS. This reflector is well beyond the current state-of-the-art. To implement this mission concept, several potential technologies associated with large, lightweight, spaceborne reflectors have been investigated by this study. These spaceborne reflector technologies include mesh reflector technology, inflatable membrane reflector technology and Shape Memory Polymer reflector technology.

Precipitation Radar↗
NASA NTRS1981

Two-dimensiosnal electron beam charging model for polymer films

A two dimensional model was developed to describe the charging of thin polymer films exposed to a uniform mon-energetic electron beam. The study was motivated by observed anomalous behavior of geosynchronous satellites which was attributed to electrical discharges associated with the differential charging of satellite surfaces of magnetospheric electrons. Electric fields both internal and external to the irradiated specimen were calculated at steady state in order to identify regions of high electrical stress. Particular emphasis was placed on evaluating the charging characteristics near the material's edge. The model was used to identify and quantify the effects of some of the experimental parameters notably: beam energy; beam angle of incidence; beam current density; material thickness; and material width. Simulations of the following situations were also conducted: positive or negative precharging over part of the surface; a central gap in the material; and a discontinuity in the material's thickness.

Reeves, R. D.↗
NASA NTRS1997

Automated Fabrication of High Performance Composites: An Overview of Research at the Langley Research Center

Automated heated placement of consolidated fiber reinforced polymer ribbon/tape is a rapid, cost effective technique for net shape fabrication of high performance composites. Several research efforts in the United States are developing the heated head robotic hardware and associated software needed to bring this technology into widespread use for building aircraft parts. These efforts emphasize the use of pre-consolidated thermoplastic ribbon or tape which is thermally welded on-the-fly . The approach provides in-situ consolidation and obviates the need for autoclave processing and massive debulking, thereby reducing costs. Addressed in this paper are some key issues being pursued at NASA Langley related to this technology. These include: (a) preparation of high quality intermediate materials forms such as thermoplastic powders, powder-coated towpreg and consolidated ribbon/tape and (b) achievement of precise control of the following: robot head positioning on the tool; material placement; heat delivery to the lay-down zone; and cut/add, start/stop capability. Heated head development has dealt with the use of hot gases alone and in combination with focused infrared radiation as heat sources.

Johnston, N. J.↗
NASA NTRS2011

Failure Modes in Capacitors When Tested Under a Time-Varying Stress

Power-on failure has been the prevalent failure mechanism for solid tantalum capacitors in decoupling applications. A surge step stress test (SSST) has been previously applied to identify the critical stress level of a capacitor batch to give some predictability to the power-on failure mechanism [1]. But SSST can also be viewed as an electrically destructive test under a time-varying stress (voltage). It consists of rapidly charging the capacitor with incremental voltage increases, through a low resistance in series, until the capacitor under test is electrically shorted. When the reliability of capacitors is evaluated, a highly accelerated life test (HALT) is usually adopted since it is a time-efficient method of determining the failure mechanism; however, a destructive test under a time-varying stress such as SSST is even more time efficient. It usually takes days or weeks to complete a HALT test, but it only takes minutes for a time-varying stress test to produce failures. The advantage of incorporating a specific time-varying stress profile into a statistical model is significant in providing an alternative life test method for quickly revealing the failure mechanism in capacitors. In this paper, a time-varying stress that mimics a typical SSST has been incorporated into the Weibull model to characterize the failure mechanism in different types of capacitors. The SSST circuit and transient conditions for correctly surge testing capacitors are discussed. Finally, the SSST was applied for testing Ta capacitors, polymer aluminum capacitors (PA capacitors), and multi-layer ceramic (MLC) capacitors with both precious metal electrodes (PME) and base metal electrodes (BME). The test results are found to be directly associated with the dielectric layer breakdown in Ta and PA capacitors and are independent of the capacitor values, the way the capacitors were built, and the capacitors manufacturers. The test results also show that MLC capacitors exhibit surge breakdown voltages much higher than the rated voltage and that the breakdown field is inversely proportional to the dielectric layer thickness. The SSST data can also be used to comparatively evaluate the voltage robustness of capacitors for decoupling applications.

Liu, David (Donhang)↗
NASA NTRS2012

The Enantiomeric Ratios of Meteoritic Organic Compounds: Their Possible Roles in the Origin of Life

This talk will give an overview of the enantiomer (mirror-image) ratios of organic compounds in meteorites and also describe the results of the present work in my lab. The primary focus will be on sugar derivatives (sugar acids) of carbonaceous meteorites. Our work begins to address questions associated with chirality, i.e., the origins of homochirality. On Earth, biological monomers (amino acids, sugars, etc.) are usually found with one of the enantiomers more abundant than the other. However, biological polymers (proteins, nucleic acids, etc.) are only composed of one enantiomer i.e., they are homochiral. There are hints in meteorites that some organic molecules may also exist in homochiral forms. The talk will address questions such as: did extraterrestrial sources aid in the beginning of this homochirality? Do the increasing size and apparent enantiomer excesses of some meteoritic compounds also extend to larger meteoritic compounds and polymers?

Cooper, George↗
NASA NTRS1990

Spatial light modulators and applications III; Proceedings of the Meeting, San Diego, CA, Aug. 7, 8, 1989

Recent advances in the technology and applications of spatial light modulators (SLMs) are discussed in review essays by leading experts. Topics addressed include materials for SLMs, SLM devices and device technology, applications to optical data processing, and applications to artificial neural networks. Particular attention is given to nonlinear optical polymers, liquid crystals, magnetooptic SLMs, multiple-quantum-well SLMs, deformable-mirror SLMs, three-dimensional optical memories, applications of photorefractive devices to optical computing, photonic neurocomputers and learning machines, holographic associative memories, SLMs as parallel memories for optoelectronic neural networks, and coherent-optics implementations of neural-network models.

Efron, Uzi↗
NASA NTRS2000

Chemical Fabrication Used to Produce Thin-Film Materials for High Power-to- Weight-Ratio Space Photovoltaic Arrays

The key to achieving high specific power (watts per kilogram) space solar arrays is the development of a high-efficiency, thin-film solar cell that can be fabricated directly on a flexible, lightweight, space-qualified durable substrate such as Kapton (DuPont) or other polyimide or suitable polymer film. Cell efficiencies approaching 20 percent at AM0 (air mass zero) are required. Current thin-film cell fabrication approaches are limited by either (1) the ultimate efficiency that can be achieved with the device material and structure or (2) the requirement for high-temperature deposition processes that are incompatible with all presently known flexible polyimide or other polymer substrate materials. Cell fabrication processes must be developed that will produce high-efficiency cells at temperatures below 400 degrees Celsius, and preferably below 300 degress Celsius to minimize the problems associated with the difference between the coefficients of thermal expansion of the substrate and thin-film solar cell and/or the decomposition of the substrate.

Hepp, Aloysius F.↗
NASA NTRS2011

Failure Modes in Capacitors When Tested Under a Time-Varying Stress

Steady step surge testing (SSST) is widely applied to screen out potential power-on failures in solid tantalum capacitors. The test simulates the power supply's on and off characteristics. Power-on failure has been the prevalent failure mechanism for solid tantalum capacitors for decoupling applications. On the other hand, the SSST can also be reviewed as an electrically destructive test under a time-varying stress. It consists of rapidly charging the capacitor with incremental voltage increases, through a low resistance in series, until the capacitor under test is electrically shorted. Highly accelerated life testing (HALT) is usually a time-efficient method for determining the failure mechanism in capacitors; however, a destructive test under a time-varying stress like SSST is even more effective. It normally takes days to complete a HALT test, but it only takes minutes for a time-varying stress test to produce failures. The advantage of incorporating specific time-varying stress into a statistical model is significant in providing an alternative life test method for quickly revealing the failure modes in capacitors. In this paper, a time-varying stress has been incorporated into the Weibull model to characterize the failure modes. The SSST circuit and transient conditions to correctly test the capacitors is discussed. Finally, the SSST was applied for testing polymer aluminum capacitors (PA capacitors), Ta capacitors, and multi-layer ceramic capacitors with both precious metal electrode (PME) and base-metal-electrodes (BME). It appears that testing results are directly associated to the dielectric layer breakdown in PA and Ta capacitors and are independent on the capacitor values, the way the capacitors being built, and the manufactures. The testing results also reveal that ceramic capacitors exhibit breakdown voltages more than 20 times the rated voltage, and the breakdown voltages are inverse proportional to the dielectric layer thickness. The possibility of ceramic capacitors in front-end decoupling applications to block the surge noise from a power supply is also discussed.

Liu, David (Donhang)↗
NASA NTRS1991

LaRC dry powder towpreg process

The dry powder towpreg process overcomes many of the difficulties associated with melt, solution and slurry prepregging of advanced composite materials. In the process, fluidized powder is deposited on spread tow bundles and melted on the fibers by radiant heating to adhere the polymer to the fiber. Bench scale design and operating data have been correlated for use in process scale up to commercial operation. Powdered towpreg has been woven and molded into preform material of good quality. Cost estimates suggest that processing costs are comparable to those of conventional hot melt prepreg. In the future, from a part fabrication point of view, powder coated prepreg tape, woven broad goods and woven and braided preforms may be considered as options to similar materials made by other methods.

Marchello, Joseph M.↗
NASA NTRS2019

Reexamination of the Edge Crack Torsion Test for Determining the Mode III Delamination Toughness of Laminated Composites

The edge crack torsion (ECT) test is reexamined to address two primary concerns with this method. The first of these relates to inconsistencies in the data reduction procedure that was originally proposed and is most commonly used to compute the mode III interlaminar fracture toughness, G(sub IIIc), from the experimental data. The second relates to the observation that plies neighboring the preimplanted insert in the standard ECT layup are unable to contain initiation and growth of intralaminar cracks, and that growth of these cracks contributes to errors in the apparent values of G(sub IIIc). To address these issues, an alternative data reduction technique, which uses a polynomial expression to represent the ECT specimen’s compliance versus crack length relation, is proposed. The accuracy and potential drawbacks of this expression are investigated using FE simulations. Next, seven groups of ECT specimens are fabricated and tested. Each of these groups contains specimens with preimplanted inserts that are bounded by plies at different +q and -q orientations. The seven groups consist of values of q that vary from 0° to 90° in 15° increments. Tests on these specimens show that intralaminar cracking occurs in specimens from all batches except those for which q equals 15° or 30°. However, values of G(sub IIIc) measured using specimens with these two ply orientations were not equal and, for q = 30°, the values of G(sub IIIc) that were obtained were not completely independent of initial starter crack length. Potential issues accounting for these observations and other challenges associated with measuring G(sub IIIc) using the ECT test are discussed.

Polymer matrix composites↗
NASA NTRS1992

LDEF results for polymer matrix composite experiment AO 180

This report represents a summary of the results obtained to-date on a polymer matrix composite experiment (AO 180) located at station D-12, about 82 deg off the 'ram' direction. Different material systems comprised of graphite, boron, and aramid (Kevlar) fiber reinforcements were studied. Although previous results were presented on in-situ thermal-vacuum cycling effects, particularly dimensional changes associated with outgassing, additional comparative data will be shown from ground-based tests on control and flight samples. The system employed was fully automated for thermal-vacuum cycling using a laser interferometer for monitoring displacements. Erosion of all three classes of materials due to atomic oxygen (AO) will also be discussed, including angle of incidence effects. Data from this experiment will be compared to published results for similar materials in other LDEF experiments. Composite materials' erosion yields will be presented on an AO design nomogram useful for estimating total material loss for given exposure conditions in low Earth orbit (LEO). Optical properties of these materials will also be compared with control samples. A survey of the damage caused by micrometeoroids/debris impacts will be addressed as they relate to polymer matrix composites. Correlations between hole size and damage pattern will be given. Reference to a new nomogram for estimating the number distribution of micrometeoroid/debris impacts for a given space structure as a function of time in LEO will be addressed based on LDEF data.

Tennyson, R. C.↗
NASA NTRS1994

Dewatering of contaminated river sediments

Dewatering of slurries has been successfully accomplished by the proper use of polymers in flocculating the fine particulate matter suspended in mineral processing streams. The U.S. Bureau of Mines (USBM) entered into a cooperative research effort with the U.S. Army Corps of Engineers (Corps) for the purpose of testing and demonstrating the applicability of mining flocculation technology to dredging activities associated with the removal of sediments from navigable waterways. The Corps has the responsibility for maintaining the navigable waterways in the United States. Current technology relies primarily on dredging operations which excavate the material from the bottom of waterways. The Corps is testing new dredging technology which may reduce resuspension of sediments by the dredging operation. Pilot plant dredging equipment was tested by the Corps which generated larger quantities of water when compared to conventional equipment, such as the clam shell. The transportation of this 'excess' water adds to the cost of sediment removal. The process developed by the USBM consists of feed material from the barge being pumped through a 4-in line by a centrifugal pump and exiting through a 4-in PVC delivery system. A 1,000-gal fiberglass tank was used to mix the polymer concentrate. The polymer was pumped through a 1-in line using a variable speed progressive cavity pump and introduced to the 4-in feed line prior to passing through a 6-in by 2-ft static mixer. The polymer/feed slurry travels to the clarifying tank where the flocculated material settled to the bottom and allowed 'clean' water to exit the overflow. A pilot scale flocculation unit was operated on-site at the Corps' 'Confined Disposal Facility' in Buffalo, NY.

Church, Ronald H.↗
NASA NTRS1979

Inexpensive cross-linked polymeric separators made from water soluble polymers

Polyvinyl alcohol (PVA) crosslinked chemically with aldehyde reagents produces membranes which demonstrate oxidation resistance, dimensional stability, low ionic resistivity, low zincate diffusivity, and low zinc dendrite penetration rate which make them suitable for use as alkaline battery separators. They are intrinsically low in cost and environmental health and safety problems associated with commercial production appear minimal. Preparation, property measurements, and cell test results in Ni/Zn and Ag/Zn cells are described and discussed.

Hsu, L. C.↗
NASA NTRSDate not supplied

Polymeric Materials Application and Testing for Space Missions

The EM41 Non-metallics polymers team performs polymeric materials screening, characterization, development, qualification, verification and validation testing for flight hardware and in-space applications. They perform insight, testing and application of polymeric materials for launch vehicles and space environments. Personnel have a deep understanding of the technologies associated with cryogenic insulation, high temperature thermal protection materials, paints, primers, coatings, and adhesive materials. Numerous TPS material characterization tests can also be performed by the Lab. The team has both internal and partner test capabilities to subject polymeric materials to Aerospace and Space environments Material properties, response and performance are tested within environments from the launch pad, through the launch environment and into space. A primary role of the team is to select materials and organize test regimen then analyze test results. Test regiment are established to confirm the materials meet the performance requirements levied by customers within the environments that are expected for the mission.

Thermal↗
NASA NTRS1974

Low-temperature relaxations in amorphous polyolefins

The dynamic mechanical relaxation behavior of two series of amorphous polyolefins, was investigated from 4.2 K to the glass transition. Most of the polymers show a damping maximum or plateau in the 40 to 50 K region. Various mechanisms which have been suggested for cryogenic relaxations in amorphous polymers are considered as they might relate to the polyolefins. Two secondary relaxation processes above 80 K are distinguished. A relaxation at about 160 K (beta) in the second and third member of each series is associated with restricted blackbone motion. This process requires a certain degree of chain flexibility since it is not observed in the first member of each series. A lower temperature process (gamma) is observed in each member of the second series and is attributed to motion of the ethyl side group.

Hiltner, A.↗
NASA NTRS1993

Projections on structures and material strength in the computational context

The ideas associated with the subsequent viewgraphs are summarized. The primary motivation behind this presentation is to observe that certain macroscopic, microscopic, and submicroscopic phenomena are being understood that have basic influence on understanding the durability and high temperature sensitivity of polymers and polymer-based composites. This understanding covers important issues of long term stability with respect to residual stresses and deformations which can have very deleterious effects on structures used for long periods of time as a result of the heat-involving manufacturing process. Beyond this, important progress is being made in understanding the nonlinear material response of polymers in the fracture context, because the nonlinear mechanics of the material at the tip of a crack, either propagating or ready to do so, is being understood with increasing precision.

Knauss, Wolfgang G.↗
NASA NTRS1986

Origin of life and iron-rich clays

The premise that life began with self-replicating iron-rich clays is explored. In association with these clays and UV light, polar organic molecules, such as oxalic acid, were synthesized. The carbonaceous chondrites have both iron-rich clays and organic molecules. It is convenient to classify meteoritic organic matter into 3 categories: insoluble polymer, hydrocarbons and polar organics (soluble in water). Recent work on the delta D, delta N-15 and delta C-13 has made it clear that these three fractions have been made by three different mechanisms. A significant fraction of the insoluble polymer has a delta-D which suggests that it was made in an interstellar medium. The hydrocarbons seem to have been made on a parent body by a Fischer-Tropsch mechanism. The polar organics were probably synthesized in a mixture of carbonate (NH4)2CO3, Fe(++) ion and liquid water by radiolysis. In a set of experiments the radiolysis of (NH4)2CO3 in the presence and absence of Fe(++) ion has been examined. The synthesis of glycine in the presence of Fe(++) ion is 3-4 times that in the absence of ferrous ion. The effects of the addition of hydrocarbons to this mixture are explored. Iron-rich clays at low temperature and pressure are synthesized. So far the results are not sufficiently crystalline to look for replication. It should be noted that organic chelating agents such as oxalic acid do increase the crystallinity of the clays but not sufficiently. The hydrothermal synthesis of iron-rich clays is being examined.

Hartman, H. H.↗