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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Diamagnetic studies on as-processed carbon fibers

The Faraday method has been used to measure the diamagnetic susceptibilities of small bundles of aligned carbon fibers of different types at room temperature. It was found that the tensor trace susceptibility of the fibers varies systematically over the range 0.8-20 (in units of -10 to the -6th emu/g) as a function of precursor type and processing history. The susceptibility increases, in general, with increasing nominal treatment temperature and hot stretching, and with increasing tensile elastic modulus. The anisotropy ratio of fibers increases approximately linearly with tensile elastic modulus for all fibers from about 1 for a modulus of about 70 GN/sq m to about 22 for a modulus of 700 GN/sq m in air, and is quantitatively consistent with the layer-plane orientation textures determined by X-ray diffraction when appropriate values of the crystallite principal susceptibilities are used.

Scott, C. B.↗
NASA NTRS1986

Upwelling O(+) ion source characteristics

The characteristics of an upwelling ion source are discussed. A typical upwelling event is analyzed using Dynamic Explorer 1 satellite retarding ion mass spectrometer (RIMS) observations of the low-energy plasma, and energetic ion and local electromagnetic field observations. The RIMS spectrograms of the O(+) ion species, radial and axial head data for O(+), and spin plan O(+) distribution functions are examined. The features of the upwelling observed include: (1) transverse ion heating to temperature of 100,000 K, (2) large outward flows of O(+), (3) enhanced flow of H(+) and He (+), (4) moderately strong field-aligned current sheets, (5) an associated intense eastward convection channel, and (6) strong wave emissions in the range near and below the proton gyrofrequency. The association between the upwelling O(+) signature and auroral current is investigated. Plasma wave and electric field environments are studied and plasma flows and densities are derived. It is noted that the mechanism for ion heating which defines the source region for these polar ion outflows is related to field-aligned currents and an associated auroral convection channel or jet.

Moore, T. E.↗
NASA NTRS1985

Some strategies for quantitative scanning Auger electron microscopy

The general applicability of power law forms of the background in electron spectra is pointed out and exploited for background removal from under Auger peaks. This form of B(E) is found to be extremely sensitive to instrumental alignment and to fault-free construction - an observation which can be used to set up analyser configurations in an accurate way. Also, differences between N(E) and B(E) can be used to derive a spectrometer transmission function T(E). The questions of information density in an energy-analysing spatially-resolving instrument are addressed after reliable instrumental characterization has been established. Strategies involving ratio histograms, showing the population distribution of the ratio of a pair of Auger peak heights, composition scatter diagrams and windowed imaging are discussed and illustrated.

Browning, R.↗
NASA NTRS2000

Cloning and characterization of ftsZ and pyrF from the archaeon Thermoplasma acidophilum

To characterize cytoskeletal components of archaea, the ftsZ gene from Thermoplasma acidophilum was cloned and sequenced. In T. acidophilum ftsZ, which is involved in cell division, was found to be in an operon with the pyrF gene, which encodes orotidine-5'-monophosphate decarboxylase (ODC), an essential enzyme in pyrimidine biosynthesis. Both ftsZ and pyrF from T. acidophilum were expressed in Escherichia coli and formed functional proteins. FtsZ expression in wild-type E. coli resulted in the filamentous phenotype characteristic of ftsZ mutants. T. acidophilum pyrF expression in an E. coli mutant lacking pyrF complemented the mutation and rescued the strain. Sequence alignments of ODCs from archaea, bacteria, and eukarya reveal five conserved regions, two of which have homology to 3-hexulose-6-phosphate synthase (HPS), suggesting a common substrate recognition and binding motif. Copyright 2000 Academic Press.

Bacterial Proteins/chemistry/genetics/metabolism↗
NASA NTRS2022

Surface Corrected Lunar MTF Measurements in MODIS and VIIRS Using the SP Model

Lunar observations have been used for sensor performance assessments for a number of Earth-observing instruments, including the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra and Aqua and the Visible Infrared Imaging Radiometer Suite (VIIRS) on board Suomi-NPP (SNPP) and NOAA-20 (N20). While the primary purpose of lunar observations in MODIS and VIIRS is radiometric calibration, these observations have been leveraged for other sensor performance assessments such as spatial registration and deriving the modulation transfer function (MTF). In this work, we will derive the lunar MTF using a knife edge approach similar to previous work. However, to further isolate the edge of the lunar disk when deriving the edge spread function (ESF), we will apply a lunar surface variation correction using a model based on data obtained by the Spectral Profiler (SP) on board the SELENE spacecraft. This model was provided to us by AIST in Japan. To align the measured and modeled data, we developed techniques for projecting the measured lunar surface pixels onto the radiance maps produced by the SP model. We correct the lunar surface variation while preserving the signal of the lunar disk edge in the ESF, and then calculate the MTF results using standard techniques. These results are in good agreement with previously published results from both Moon-based observations in MODIS and VIIRS and from the spectroradiometric calibration assembly (SRCA) on MODIS. With the exception of MODIS bands 1 and 2, the MTF is stable on orbit for the reflective bands in both instruments.

MODIS↗
NASA NTRS1994

Electron collection by a highly positive satellite in the ionosphere: Test aprticle simulation

Collection of electrons by a satellite at a relatively high potential in low Earth orbit, including the effects of the satellite's orbital motion, remains a poorly understood phenomenon. Using a test particle simulation in which charged particle motion is tracked in prescribed electric fields, we calculate here the current collection and the nature of the energy distribution function of the electrons collected by the satellite, including the effects of the satellite orbital motion. Calculations of the collected current without the orbital motion show an excellent agreement with the current from the Parker-Murphy model, but with the orbital motion of the satellite the current collection is enhanced, the degree of enhancement depending on the size of the satellite sheath extending along the magnetic field line. In the latter case, the flow of electrons around the satellite shows some interesting behaviors including azimuthal E x B drift around the satellite, axial trapping along the magnetic field, and formation of field-aligned flow of electrons in the wake region. The total energy of the collected electrons is approximately equal e phi(sub 0), where phi(sub 0) is the satellite potential, but the partition of the energy into components parallel (W(sub parallel)) and perpendicular (W(sub perpendicular)) to the magnetic field shows interesting features. For the magnetic field along the polar axis Z, the energy distributions near the poles are perfectly field aligned, that is, the parallel energy (W(sub parallel) = e phi(sub 0). The perpendicular component (W(sub perpendicular)) progressively increases toward the 'equator' of the spherical satellite. For a sufficiently large bias potential phi(sub 0), the equatorial energy distributions f(W(sub parallel)) and f(W(sub perpendicular)) show fine structures having multiple peaks. These features of the distribution functions result from the chaotic motion of electrons and the associated coupling between the electron motions parallel and perpendicular to the magnetic field in strongly nonuniform electric fields near the satellite.

Singh, Nagendra↗
NASA NTRS1977

Particle acceleration in axisymmetric, magnetized neutron stars

The potential drop in the polar cap region of a rotating, magnetized neutron star is found assuming that the magnetic field is dipolar, with the field aligned (or anti-aligned) with the rotation axis. The curvature of the field lines is of critical importance. Charge flow is assumed to be along magnetic field lines. The electric field has a maximum at radius 1.5 R and the magnitude and functional form of the current is determined.

Baker, K. B.↗
NASA NTRS1985

Theoretical analysis of Wolter/LSM X-ray telescope systems

A ray tracing analysis has been performed for the spectral slicing zoom X-ray telescope for configurations in which a convex layered synthetic microstructure (LSM) optic is placed in front of the prime focus or a concave LSM optic is placed behind the prime focus. The analysis has considered the geometrical shape of the LSM optic to be either a hyperboloid, sphere, ellipsoid or constant optical path aspheric element for two configurations of the glancing incidence X-ray telescope: the ATM Experimental S-056 Wolter I system and the Stanford/MSFC Wolter-Schwarzchild nested system. For the different systems the RMS blur circle radii, the point spread function (PSF), the full width half maximum (FWHM) of the PSF have been evaluated as a function of field angle and magnification of the secondary to determine resolution of the system. The effects of decentration and tilt of the selected LSM element on the performance of the system have been studied to determine mounting and alignment tolerances.

Shealy, D. L.↗
NASA NTRS1986

The cyclic stress-strain behavior of PWA 1480 at 650 deg C

The monotonic plastic flow behavior of several single crystal nickel-base, superalloys has been shown to vary significantly with crystallographic orientation. In the present study, the cyclic plastic flow response of one such alloy, PWA 1480, was examined at 650 deg C in air. Single crystal specimens aligned near several crystallographic directions were tested in fully reversed, total-strain-controlled low cycle fatigue tests at a frequency of 0.1 Hz. The cyclic stress-strain response and general cyclic hardening behavior was analyzed as a function of crystallographic orientation and inelastic strain range.

Gabb, T. P.↗
NASA NTRS1990

Ellipsometric study of YBa2Cu3O(7-x) laser ablated and co-evaporated films

High temperature superconducting films of YBa2Cu3O(7-x) (YBCO were grown on SrTiO3, LaA1O3, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R=O)=90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaported films was much lower than the value reported for single crystals, and was sample dependent.

Alterovitz, S. A.↗
NASA NTRS1990

Ellipsometric study of YBa2Cu3O(7-x) laser ablated and co-evaporated films

High temperature superconducting films of YBa2Cu3O(7-x) (YBCO) were grown on SrTiO3, LaAl03, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R = 0) = 90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaporated films was much lower than the value reported for single crystals, and was sample dependent.

Alterovitz, S. A.↗
NASA NTRS1992

Progress on ten-meter optical receiver telescope

A ten-meter hexagonally segmented Cassegrain optical telescope is being considered at the Jet Propulsion Laboratory for use as a research and development facility for optical communications technology. The goal of the study is to demonstrate technology which can eventually be used to develop a network of such telescopes to continuously track and communicate with the spacecraft. Hence, the technology has to be economical enough to allow replication for a ground or space based network. As we need to collect signal photons only, the telescope cost can be substantially reduced by accepting lower image quality. An important design consideration for the telescope is its ability to look very close to the sun. The telescope for optical communications must function during the daytime. Indeed, for some planetary missions it may be necessary that the system be capable of looking within a few degrees of the sun. To enable this, a unique sunshade consisting of hexagonal tubes in precise alignment with the mirror segments has been proposed which will also serve as the support for the secondary. Recent progress on the design and analysis of such an optical reception station is discussed here.

Shaik, Kamran↗
NASA NTRS2001

A Quasi-Static Method for Determining the Characteristics of a Motion Capture Camera System in a "Split-Volume" Configuration

To confidently report any data collected from a video-based motion capture system, its functional characteristics must be determined, namely accuracy, repeatability and resolution. Many researchers have examined these characteristics with motion capture systems, but they used only two cameras, positioned 90 degrees to each other. Everaert used 4 cameras, but all were aligned along major axes (two in x, one in y and z). Richards compared the characteristics of different commercially available systems set-up in practical configurations, but all cameras viewed a single calibration volume. The purpose of this study was to determine the accuracy, repeatability and resolution of a 6-camera Motion Analysis system in a split-volume configuration using a quasistatic methodology.

Miller, Chris↗
NASA NTRS2011

Mercury-Cadmium-Telluride Focal Plane Array Performance Under Non-Standard Operating Conditions

This paper highlights a new technique that allows the Teledyne Scientific & Imaging LLC TCM6604A Mercury-Cadmium-Telluride (MCT) Focal Plane Array (FPA) to operate at room temperature. The Teledyne MCT FPA has been a standard in Imaging Spectroscopy since its creation in the 1980's. This FPA has been used in applications ranging from space instruments such as CRISM, M3 and ARTEMIS to airborne instruments such as MaRS and the Next Generation AVIRIS Instruments1. Precise focal plane alignment is always a challenge for such instruments. The current FPA alignment process results in multiple cold cycles requiring week-long durations, thereby increasing the risk and cost of a project. These alignment cycles are necessary because optimal alignment is approached incrementally and can only be measured with the FPA and Optics at standard operating conditions, requiring a cold instrument. Instruments using this FPA are normally cooled to temperatures below 150K for the MCT FPA to properly function. When the FPA is run at higher temperatures the dark current increases saturating the output. This paper covers the prospect of warm MCT FPA operation from a theoretical and experimental perspective. We discuss the empirical models and physical laws that govern MCT material properties and predict the optimal settings that will result in the best MCT PA performance at 300K. Theoretical results are then calculated for the proposed settings. We finally present the images and data obtained using the actual system with the warm MCT FPA settings. The paper concludes by emphasizing the strong positive correlation between the measured values and the theoretical results.

Focal Plane Array (FPA)↗
NASA NTRS2013

Multi-Scale CNT-Based Reinforcing Polymer Matrix Composites for Lightweight Structures

Reinforcing critical areas in carbon polymer matrix composites (PMCs), also known as fiber reinforced composites (FRCs), is advantageous for structural durability. Since carbon nanotubes (CNTs) have extremely high tensile strength, they can be used as a functional additive to enhance the mechanical properties of FRCs. However, CNTs are not readily dispersible in the polymer matrix, which leads to lower than theoretically predicted improvement in mechanical, thermal, and electrical properties of CNT composites. The inability to align CNTs in a polymer matrix is also a known issue. The feasibility of incorporating aligned CNTs into an FRC was demonstrated using a novel, yet commercially viable nanofiber approach, termed NRMs (nanofiber-reinforcing mats). The NRM concept of reinforcement allows for a convenient and safe means of incorporating CNTs into FRC structural components specifically where they are needed during the fabrication process. NRMs, fabricated through a novel and scalable process, were incorporated into FRC test panels using layup and vacuum bagging techniques, where alternating layers of the NRM and carbon prepreg were used to form the reinforced FRC structure. Control FRC test panel coupons were also fabricated in the same manner, but comprised of only carbon prepreg. The FRC coupons were machined to size and tested for flexural, tensile, and compression properties. This effort demonstrated that FRC structures can be fabricated using the NRM concept, with an increased average load at break during flexural testing versus that of the control. The NASA applications for the developed technologies are for lightweight structures for in-space and launch vehicles. In addition, the developed technologies would find use in NASA aerospace applications such as rockets, aircraft, aircraft/spacecraft propulsion systems, and supporting facilities. The reinforcing aspect of the technology will allow for more efficient joining of fiber composite parts, thus offering additional weight savings. More robust structures capable of withstanding micrometeoroid and space debris impacts will be possible with the enhanced mechanical properties imparted by the aligned CNTs incorporated into the fiber composite structure, as well as the potential for improved electrical and thermal properties. The materials fabrication approach developed in the present effort is a platform for customer applications where additional reinforcement is required or would be beneficial, especially in FRC structures and component parts. Depending upon the specific customer application, the NRM could be tailored to the specific matrix resin and desired property enhancement.

Eberly, Daniel↗
NASA NTRS2015

An Alternative Humans to Mars Approach: Reducing Mission Mass with Multiple Mars Flyby Trajectories and Minimal Capability Investments

Mars flyby trajectories and Earth return trajectories have the potential to enable lower- cost and sustainable human exploration of Mars. Flyby and return trajectories are true minimum energy paths with low to zero post-Earth departure maneuvers. By emplacing the large crew vehicles required for human transit on these paths, the total fuel cost can be reduced. The traditional full-up repeating Earth-Mars-Earth cycler concept requires significant infrastructure, but a Mars only flyby approach minimizes mission mass and maximizes opportunities to build-up missions in a stepwise manner. In this paper multiple strategies for sending a crew of 4 to Mars orbit and back are examined. With pre-emplaced assets in Mars orbit, a transit habitat and a minimally functional Mars taxi, a complete Mars mission can be accomplished in 3 SLS launches and 2 Mars Flyby's, including Orion. While some years are better than others, ample opportunities exist within a given 15-year Earth-Mars alignment cycle. Building up a mission cadence over time, this approach can translate to Mars surface access. Risk reduction, which is always a concern for human missions, is mitigated by the use of flybys with Earth return (some of which are true free returns) capability.

Whitley, Ryan J.↗
NASA NTRS2004

Improved Phase-Mask Fabrication of Fiber Bragg Gratings

An improved method of fabrication of Bragg gratings in optical fibers combines the best features of two prior methods: one that involves the use of a phase mask and one that involves interference between the two coherent laser beams. The improved method affords flexibility for tailoring Bragg wavelengths and bandwidths over wide ranges. A Bragg grating in an optical fiber is a periodic longitudinal variation in the index of refraction of the fiber core. The spatial period (Bragg wavelength) is chosen to obtain enhanced reflection of light of a given wavelength that would otherwise propagate relatively unimpeded along the core. Optionally, the spatial period of the index modulation can be made to vary gradually along the grating (such a grating is said to be chirped ) in order to obtain enhanced reflection across a wavelength band, the width of which is determined by the difference between the maximum and minimum Bragg wavelengths. In the present method as in both prior methods, a Bragg grating is formed by exposing an optical fiber to an ultraviolet-light interference field. The Bragg grating coincides with the pattern of exposure of the fiber core to ultraviolet light; in other words, the Bragg grating coincides with the interference fringes. Hence, the problem of tailoring the Bragg wavelength and bandwidth is largely one of tailoring the interference pattern and the placement of the fiber in the interference pattern. In the prior two-beam interferometric method, a single laser beam is split into two beams, which are subsequently recombined to produce an interference pattern at the location of an optical fiber. In the prior phase-mask method, a phase mask is used to diffract a laser beam mainly into two first orders, the interference between which creates the pattern to which an optical fiber is exposed. The prior two-beam interferometric method offers the advantage that the period of the interference pattern can be adjusted to produce gratings over a wide range of Bragg wavelengths, but offers the disadvantage that success depends on precise alignment and high mechanical stability. The prior phase-mask method affords the advantages of compactness of equipment and relative insensitivity to both misalignment and vibration, but does not afford adjustability of the Bragg wavelength. The present method affords both the flexibility of the prior two-beam interferometric method and the compactness and stability of the prior phase-mask method. In this method (see figure), a laser beam propagating along the x axis is normally incident on a phase mask that lies in the (y,z) plane. The phase of light propagating through the mask is modulated with a spatial periodicity, p, along the y axis chosen to diffract the laser light primarily to first order at the angle . (The zero-order laser light propagating along the x axis can be used for alignment and thereafter suppressed during exposure of the fiber.) The diffracted light passes through a concave cylindrical lens, which converts the flat diffracted wave fronts to cylindrical ones, as though the light emanated from a line source. Then two parallel flat mirrors recombine the diffracted beams to form an interference field equivalent to that of two coherent line sources at positions A and B (virtual sources). The interference pattern is a known function of the parameters of the apparatus and of position (x,y) in the interference field. Hence, the tilt, wavelength, and chirp of the Bragg grating can be chosen through suitable adjustments of the apparatus and/or of the position and orientation of the optical fiber. In particular, the Bragg wavelength can be adjusted by moving the fiber along the x axis, and the bandwidth can be modified over a wide range by changing the fiber tilt angle or by moving the phase mask and/or the fiber. Alignment is easy because the zero-order beam defines the x axis. The interference is relatively stable and insensitive to the mechanical vibration because of the gh symmetry and compactness of the apparatus, the fixed positions of the mirrors and lens, and the consequent fixed positions of the two virtual line sources, which are independent of the translations of the phase mask and the laser relative to the lens.

Grant, Joseph↗
NASA NTRS2016

Performance of NICER Flight X-Ray Concentrator

Neutron star Interior Composition ExploreR (NICER) is a NASA instrument to be onboard International Space Station, which is equipped with 56 pairs of an X-ray concentrator (XRC) and a silicon drift detector for high timing observations. The XRC is based on an epoxy replicated thin aluminum foil X-ray mirror, similar to those of Suzaku and ASTRO-H (Hitomi), but only a single stage parabolic grazing incidence optic. Each has a focal length of 1.085 m and a diameter of 105 mm, with 24 confocally aligned parabolic shells. Grazing incident angles to individual shells range from 0.4 to 1.4 deg. The flight 56 XRCs have been completed and successfully delivered to the payload integration. All the XRC was characterized at the NASA/GSFC 100-m X-ray beamline using 1.5 keV X-rays (some of them are also at 4.5 keV). The XRC performance, effective area and point spread function, was measured by a CCD camera and a proportional counter. The average effective area is about 44 sq cm at 1.5 keV and about 18 sq cm at 4.5 keV, which is consistent with a micro-roughness of 0.5 nm from individual shell reflectivity measurements. The XRC focuses about 91% of X-rays into a 2mm aperture at the focal plane, which is the NICER detector window size. Each XRC weighs only 325 g. These performance met the project requirement. In this paper, we will present summary of the flight XRC performance as well as co-alignment results of the 56 XRCs on the flight payload as it is important to estimate the total effective for astronomical observations.

X-ray concentrator↗