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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

High Temperature Polymers for use in Fuel Cells

NASA Glenn Research Center (GRC) is currently working on polymers for fuel cell and lithium battery applications. The desire for more efficient, higher power density, and a lower environmental impact power sources has led to interest in proton exchanges membrane fuels cells (PEMFC) and lithium batteries. A PEMFC has many advantages as a power source. The fuel cell uses oxygen and hydrogen as reactants. The resulting products are electricity, heat, and water. The PEMFC consists of electrodes with a catalyst, and an electrolyte. The electrolyte is an ion-conducting polymer that transports protons from the anode to the cathode. Typically, a PEMFC is operated at a temperature of about 80 C. There is intense interest in developing a fuel cell membrane that can operate at higher temperatures in the range of 80 C- 120 C. Operating the he1 cell at higher temperatures increases the kinetics of the fuel cell reaction as well as decreasing the susceptibility of the catalyst to be poisoned by impurities. Currently, Nafion made by Dupont is the most widely used polymer membrane in PEMFC. Nafion does not function well above 80 C due to a significant decrease in the conductivity of the membrane from a loss of hydration. In addition to the loss of conductivity at high temperatures, the long term stability and relatively high cost of Nafion have stimulated many researches to find a substitute for Nafion. Lithium ion batteries are popular for use in portable electronic devices, such as laptop computers and mobile phones. The high power density of lithium batteries makes them ideal for the high power demand of today s advanced electronics. NASA is developing a solid polymer electrolyte that can be used for lithium batteries. Solid polymer electrolytes have many advantages over the current gel or liquid based systems that are used currently. Among these advantages are the potential for increased power density and design flexibility. Automobiles, computers, and cell phones require highly efficient power density for lowering emissions and meeting increasing consumer demands. Many of the solutions can be provided by proton exchange membrane fuel cells and lithium batteries. NASA Glenn Research Center has recognized this need, and is presently engaged in a solution. The goals for the summer include mastering synthesis techniques, understanding the reactions occurring during the synthesis, and characterizing the resulting polymer membranes using NMR, DSC, and TGA for the PEMFC and lithium batteries.

Peplowski, Katherine M.↗
NASA NTRS1983

The mobile Sousy-Doppler radar: Technical design and first results

A mobile VHF Doppler system was developed. The electronic part is installed in a 20 ft container and tested using a special log periodic aerial to illuminate the 300 m dish. The system was extended by designing a mobile phased antenna array with finally 576 Yagi elements. The grouping of the single Yagis, the system of transmission lines, the phase shifters, the power splitters and the T/R switch are described. Results from the first two campaigns and a survey of future programs demonstrating the flexibility of this mobile system are summarized.

Czechowsky, P.↗
NASA NTRS2000

Effect of Negative Ions on the Conductivity of the Titan Atmosphere

In an earlier paper, Borucki et al (1987) calculated the electrical conductivity and electrical charge on aerosols in Titan's atmosphere due to the ionization by galactic cosmic rays and electron precipitation from Saturn's magnetosphere. The lower atmosphere was predicted to be substantially more conducting than the atmospheres of Earth and Venus because of the high concentration of free electrons. The prediction of a high conductivity is based on the lack of electrophillic species which form negative ions with low mobility and which reduce the number of free electrons. At that time, no molecular species capable of forming negative ions in concentrations sufficient to perturb the atmospheric conductivity were identified. Recently, E. Bakes and her colleagues have been investigating the formation of nitrogenous macromolecules using quantum mechanical methods. Their calculations indicate that the molecules will be highly electrophillic and are likely to be present in the atmosphere at mixing ratios of order 10(exp -7). This mixing ratio is sufficiently large that a substantial reduction in the conductivity is expected at altitudes below 100 km. Revision of the atmospheric model to accommodate the presence of negative ions and to increase the fidelity of the modeling will be described.

Borucki, W. J.↗
NASA NTRS1992

Deposition temperature dependence of the deep defect density for a-Si:H films grown by electron cyclotron resonance microwave plasma

The dependence on deposition temperature of the mobility gap density of states has been determined for hydrogenated amorphous silicon (a-Si:H) films grown by electron cyclotron resonance (ECR) microwave plasma CVD. A minimum in the integrated deep defect density of 1 x 10 exp 16/cu cm was found to occur at a temperature of approximately 250 C, while an Urbach slope minimum of 52 meV was observed at 175 C under our deposition conditions. Based on these measurements the ECR-grown films were found to be of excellent device quality and comparable to a-Si:H films grown by RF plasma-enhanced CVD.

Essick, J. M.↗
NASA NTRS1996

A proof of concept investigation: A unique mobility spectrometer for In Situ diagnostics of positive and negative ion distributions in the mesosphere and lower ionosphere

We have carried out a proof-of-concept development and test effort that not only promises the reduction of parasitic effects of surface contamination (therefore increasing the integrity of 'in situ' measurements in the 60-130 km regime), but promises a uniquely expanded measurement set that includes electron densities, plasma conductivities, charged-particle mobilities, and mass discrimination of positive and negative ion distributions throughout the continuum to free-molecular-flow regimes. Three different sensor configurations were designed, built and tested, along with specialized driving voltage, electrometer and channeltron control electronics. The individual systems were tested in a variety of simulated space environments ranging from pressures near the continuum limit of 100 mTorr to the collisionless regime at 10(exp -6) Torr. Swept modes were initially employed to better understand ion optics and ion 'beam' losses to end walls and to control electrodes. This swept mode also helped better understand and mitigate the influences of secondary electrons on the overall performance of the PIMS design concept. Final results demonstrated the utility of the concept in dominant single-ion plasma environments. Accumulated information, including theoretical concepts and laboratory data, suggest that multi-ion diagnostics are fully within the instrument capabilities and that cold plasma tests with minimized pre-aperture sheath acceleration are the key ingredients to multi-ion success.

Szuszczewicz, Edward P.↗
NASA NTRS1992

ACTS aeronautical experiments

A description of the two aeronautical mobile satellite experiments utilizing NASA's Advanced Communications Technology Satellite (ACTS) is presented. The low bit rate experiment is principally a Ka-band technology demonstration of a prototype 4.8 Kbps aeronautic mobile terminal employing three experimental active electronically steered arrays. The high bit rate experiment can demonstrate a 64 Kbps to 384 Kbps satellite link between a ground terminal and an aircraft.

Nguyen, Tien M.↗
NASA NTRS1996

Skutterudite Compounds For Power Semiconductor Devices

New semiconducting materials with p-type carrier mobility values much higher than state-of-art semiconductors discovered. Nine compounds, antimonides CoSb(sub3), RhSb(sub3), IrSb(sub3), arsenides CoAs(sub3), RhAs(sub3), IrAs(sub3), and phosphides CoP(sub3), RhP(sub3) and IrP(sub3), exhibit same skutterudite crystallographic structure and form solid solutions of general composition Co(1-x-y)RH(x)Ir(y)P(1-w-z)As(w)Sb(z). Materials exhibit high hole mobilities, high doping levels, and high electronic figures of merit. Some compositions show great potential for application to thermoelectric devices.

Fleurial, Jean-Pierre↗
NASA NTRS2014

Innovation in Deep Space Habitat Interior Design: Lessons Learned From Small Space Design in Terrestrial Architecture

Increased public awareness of carbon footprints, crowding in urban areas, and rising housing costs have spawned a 'small house movement' in the housing industry. Members of this movement desire small, yet highly functional residences which are both affordable and sensitive to consumer comfort standards. In order to create comfortable, minimum-volume interiors, recent advances have been made in furniture design and approaches to interior layout that improve both space utilization and encourage multi-functional design for small homes, apartments, naval, and recreational vehicles. Design efforts in this evolving niche of terrestrial architecture can provide useful insights leading to innovation and efficiency in the design of space habitats for future human space exploration missions. This paper highlights many of the cross-cutting architectural solutions used in small space design which are applicable to the spacecraft interior design problem. Specific solutions discussed include reconfigurable, multi-purpose spaces; collapsible or transformable furniture; multi-purpose accommodations; efficient, space saving appliances; stowable and mobile workstations; and the miniaturization of electronics and computing hardware. For each of these design features, descriptions of how they save interior volume or mitigate other small space issues such as confinement stress or crowding are discussed. Finally, recommendations are provided to provide guidance for future designs and identify potential collaborations with the small spaces design community.

Simon, Matthew A.↗
NASA NTRS2017

The Lighter Side of Things: The Inevitable Convergence of the Internet of Things and Cybersecurity

By the year 2020 it is estimated that there will be more than 50 billion devices connected to the Internet. These devices not only include traditional electronics such as smartphones and other mobile compute devices, but also eEnabled technologies such as cars, airplanes and smartgrids. The IoT brings with it the promise of efficiency, greater remote management of industrial processes and further opens the doors to world of vehicle autonomy. However, IoT enabled technology will have to operate and contend in the contested domain of cyberspace. This discussion will touch on the impact that cybersecurity has on IoT and the people, processes and technology required to mitigate cyber risks.

Internet of Things↗
NASA NTRS1995

Two Carrier Analysis of Persistent Photoconductivity in Modulation-Doped Structures

A simultaneous fit of Hall and conductivity data gives quantitative results on the carrier concentration and mobility in both the quantum well and the parallel conduction channel. In this study this method was applied to reveal several new findings on the effect of persistent photoconductivity (PPC) on free-carrier concentrations and mobilities. The increase in the two-dimensional electron-gas (2DEG) concentration is significantly smaller than the apparent one derived from single carrier analysis of the Hall coefficient. In the two types of structures investigated, delta doped and continuously doped barrier, the apparent concentration almost doubles following illumination, while analysis reveals an increase of about 20% in the 2DEG. The effect of PPC on mobility depends on the structure. For the sample with a continuously doped barrier the mobility in the quantum well more than doubles. This increase is attributed to the effective screening of the ionized donors by the large electron concentration in the barrier. In the delta doped barrier sample the mobility is reduced by almost a factor of 2. This decrease is probably caused by strong coupling between the two wells, as is demonstrated by self-consistent analysis.

Schacham, S. E.↗
NASA NTRS2017

High Mobility Transport Layer Structures for Rhombohedral Si/Ge/SiGe Devices

An electronic device includes a trigonal crystal substrate defining a (0001) C-plane. The substrate may comprise Sapphire or other suitable material. A plurality of rhombohedrally aligned SiGe (111)-oriented crystals are disposed on the (0001) C-plane of the crystal substrate. A first region of material is disposed on the rhombohedrally aligned SiGe layer. The first region comprises an intrinsic or doped Si, Ge, or SiGe layer. The first region can be layered between two secondary regions comprising n+doped SiGe or n+doped Ge, whereby the first region collects electrons from the two secondary regions.

Choi, Sang Hyouk↗
NASA NTRS2001

The Athena SDM rover: A testbed for Mars rover mobility

In this paper we describe the software aspects of the overall Athena SDM rover mobility system in three parts: the control electronics, the software architecture and development environment, and surface navigation software. The Athena SDM architecture has been shown to be capable of meeting mission navigation requirements by being able to safely drive 100 meters using allowable resources within three hours.

design↗
NASA NTRS2007

Radiation Test Results for a MEMS Microshutter Operating at 60 K

The James Webb Space Telescope (JWST), the successor to the Hubble Space Telescope, is due to be launched in 2013 with the goal of searching the very distant Universe for stars that formed shortly after the Big Bang. Because this occurred so far back in time, the available light is strongly red-shifted, requiring the use of detectors sensitive to the infrared portion of the electromagnetic spectrum. HgCdTe infrared focal plane arrays, cooled to below 30 K to minimize noise, will be used to detect the faint signals. One of the instruments on JWST is the Near Infrared Spectrometer (NIRSPEC) designed to measure the infrared spectra of up to 100 separate galaxies simultaneously. A key component in NIRSPEC is a Micro-Electromechanical System (MEMS), a two-dimensional micro-shutter array (MSA) developed by NASA/GSFC. The MSA is inserted in front of the detector to allow only the light from the galaxies of interest to reach the detector and to block the light from all other sources. The MSA will have to operate at 30 K to minimize the amount of thermal radiation emitted by the optical components from reaching the detector array. It will also have to operate in the space radiation environment that is dominated by the MSA will be exposed to a large total ionizing dose of approximately 200 krad(Si). Following exposure to ionizing radiation, a variety of MEMS have exhibited performance degradation. MEMS contain moving parts that are either controlled or sensed by changes in electric fields. Radiation degradation can be expected for those devices where there is an electric field applied across an insulating layer that is part of the sensing or controlling structure. Ionizing radiation will liberate charge (electrons and holes) in the insulating layers, some of which may be trapped within the insulating layer. Trapped charge will partially cancel the externally applied electric field and lead to changes in the operation of the MEMS. This appears to be a general principle for MEMS. Knowledge of the above principle has raised the concern at NASA that the MSA might also exhibit degraded performance because, i) each shutter flap is a multilayer structure consisting of metallic and insulating layers and ii) the movement of the shutter flaps is partially controlled by the application of an electric field between the shutter flap and the substrate (vertical support grid). The whole mission would be compromised if radiation exposure were to prevent the shutters from opening and closing properly. energetic ionizing particles. Because it is located A unique feature of the MSA is that, as outside the spacecraft and has very little shielding, previously mentioned, it will have to operate at temperatures near 30 K. To date, there are no published reports on how very low temperatures (- 30K) affect the response of MEMS devices to total ionizing dose. Experiments on SiO2 structures at low temperatures (80 K) indicate that the electrons generated by the ionizing radiation are mobile and will move rapidly under the application of an external electric field. Holes, on the other hand, that would normally move in the opposite direction through the SiO2 via a "thermal hopping" process, are effectively immobile at low electric fields as they are trapped close to their generation sites. However, for sufficiently large electric fields (greater than 3 MV/cm) holes are able to move through the SiO2. The larger the field, the more rapidly the holes move. The separation of the electrons and holes leads to a reduced electric field within the insulating layer. To overcome this reduction in electric field, a greater external voltage will have to be applied that alters the normal operation of the device. This report presents the results of radiation testing of the MSA at 60 K. The temperature was higher than the targeted temperature because of a faulty electrical interconnect on the test board. Specifically, our goal was to determine whether the MSA would function propey after a TID of 200 krad(Si).

Rapchun, David A.↗
NASA NTRS1990

AlSb/InAs/AlSb quantum wells

Researchers studied the InAs/AlSb system recently, obtaining 12nm wide quantum wells with room temperature mobilities up to 28,000 cm(exp 2)/V center dot S and low-temperature mobilities up to 325,000 cm(exp 2)/V center dot S, both at high electron sheet concentrations in the 10(exp 12)/cm(exp 2) range (corresponding to volume concentrations in the 10(exp 18)/cm(exp 2) range). These wells were not intentionally doped; the combination of high carrier concentrations and high mobilities suggest that the electrons are due to not-intentional modulation doping by an unknown donor in the AlSb barriers, presumably a stoichiometric defect, like an antisite donor. Inasmuch as not intentionally doped bulk AlSb is semi-insulating, the donor must be a deep one, being ionized only by draining into the even deeper InAs quantum well. The excellent transport properties are confirmed by other observations, like excellent quantum Hall effect data, and the successful use of the quantum wells as superconductive weak links between Nb electrodes, with unprecendentedly high critical current densities. The system is promising for future field effect transistors (FETs), but many processing problems must first be solved. Although the researchers have achieved FETs, the results so far have not been competitive with GaAs FETs.

Kroemer, Herbert↗
NASA NTRS1987

Improving the method of calculating electronic properties of narrow bandgap semiconductors

A previously developed code for calculating the mobility of charge carriers in narrow bandgap semiconductors does not predict the correct temperature dependence in all cases. It is thought that this is due to the way the electronic screening of the carriers is treated in the model. The objective of this research is to improve the handling of the screening by going beyond the current first Born approximation. Much of this work is directly related to the alloy semiconductor Hg sub 1-xCd sub xTe which is important for infrared detectors and is a good candidate for microgravity crystal growth. The principal conclusion, so far, is that the major difficulty is probably the treatment of short range screening at higher temperatures.

Patterson, James D.↗