Instrument for rapid measurement of surface deformations of a 210ft radio telescope.
Instrument designed for rapid measurement of surface deformations of 210-ft radio telescope at Parkes, Australia
RADIO TELESCOPE↗
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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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Investigation of two bifurcated-duct inlet systems from Mach 0 to 2.0 over a wide range of angles of attack
A 15.354 percent/scale lightweight fighter type inlet/forebody was tested over a Mach number range of 0 to 2.0. Model configurations consisted of side mounted normal shock and fixed overhead ramp type inlets. Each configuration consisted of two inlets ducted (bifurcated) to supply a single engine face. The normal shock inlet variables included a boundary layer splitter bleed system, alternate boundary layer splitter plates, alternate upper and lower cowl lip shapes, and a blow-in-door (auxiliary inlet) in one lower lip. The only variable of the fixed overhead ramp inlet was the boundary layer bleed flow. Reynolds numbers ranged from 7.6 x 1 million to 19.5 x 1 million/m. Angle of attack ranged from -10 to 35 deg and angle of sideslip from -8 to 8 deg. Test measurements included engine face total pressure recovery, steady state distortion, dynamic distortion, and surface static pressures on the forebody and inlet surfaces.
Latham, E. A.↗
How successful were the lunar sampling tools: Implications for sampling Mars
Like the Mars Sample Return endeavor, the Apollo lunar-sample program began with definition of strategy for sample collection and of scientific requirements for sampling hardware design. Several lessons can be illustrated by specific tools. The evolution of drive tubes from narrow 2 cm diameter, thick-walled tubes (used on Apollo 11, 12 and 14) to 4 cm diameter, thin-walled tubes used on Apollo 15, 16, and 17) as an example of the improvements made possible during multiple missions. The original Apollo 11 drive tube was designed to work in fluffy soil; thus, only 50 percent of the relatively dense lunar soil was recovered, and the core was distorted. The final configuration resulted in nearly 100 pct recovery with little distortion. The surface samplers (Contact Soil Sampling Devices) were designed to collect the upper 100 micrometer or the upper 1 mm of soil. It was over 2 years after the mission before these particularly specific samplers were opened because interest in them waned. Both core tubes and surface samplers were difficult to open in the laboratory. The Apollo Lunar Sample Return Containers (ALSRCs) were constructed with one indium and 2 Viton seals. They were closed on the lunar surface. Interior container pressures measured upon return to the laboratory indicate that these seals were not reliable in the lunar environment. Also, choice of indium as a sealing material interfered with siderophile analyses of samples.
Allton, J. H.↗
Combining Thermal And Structural Analyses
Computer code makes programs compatible so stresses and deformations calculated. Paper describes computer code combining thermal analysis with structural analysis. Called SNIP (for SINDA-NASTRAN Interfacing Program), code provides interface between finite-difference thermal model of system and finite-element structural model when no node-to-element correlation between models. Eliminates much manual work in converting temperature results of SINDA (Systems Improved Numerical Differencing Analyzer) program into thermal loads for NASTRAN (NASA Structural Analysis) program. Used to analyze concentrating reflectors for solar generation of electric power. Large thermal and structural models needed to predict distortion of surface shapes, and SNIP saves considerable time and effort in combining models.
Winegar, Steven R.↗
Microwave backscattering and emission model for grass canopies
A two-layer model is developed that treats the grass canopy as a collection of randomly oriented elliptical dielectric discs over a layer of thatch with underlying soil surface. The distorted Born approximation in conjunction with the Peake formulation is used to calculate the backscattering coefficient and the emissivity from the canopy. Two particular features of this model which are unique for grass canopies are the variation of the canopy structure and the presence of the thatch layer. The basic parameters in the model such as the size and orientation of grass blades, dielectric constant of soil and vegetation, and thickness and water content of the thatch layer have been obtained from ground truth data. To interpret the available experimental observations of grasslands, numerical results from both passive and active models at L-band (1.4 GHz) are generated and various scattering and emission properties of the grass canopies are discussed.
Saatchi, Sasan S.↗
Gas distribution and starbursts in shell galaxies
Detailed maps of most elliptical galaxies reveal that, whereas the greatest part of their luminous mass originates from a smooth distribution with a surface brightness approximated by a de Vaucouleurs law, a small percentage of their light is contributed by low surface brightness distortions termed 'fine structures'. The sharp-edged features called 'shells' are successfully reproduced by merger and infall models involving accretion from less massive companions. In this context, dwarf spheroidal and compact disk galaxies are likely progenitors of these stellar phenomena. However, it is probable that the sources of shell-forming material also contain significant amounts of gas. This component may play an important role in constraining the formation and evolution of shell galaxies. To investigate the effects of the gaseous component, numerical simulations were performed to study the tidal disruption of dwarf galaxies containing both gas and stars by more massive primaries, and the evolution of the ensuing debris. The calculations were performed with a hybrid N-body/hydrodynamics code. Collisionless matter is evolved using a conventional N-body technique and gas is treated using smoothed particle hydrodynamics in which self-gravitating fluid elements are represented as particles evolving according to Lagrangian hydrodynamic equations. An isothermal equation of state is employed so the gas remains at a temperature 104 K. Owing to the large mass ratio between the primary and companion, the primary is modeled as a rigid potential and the self-gravity of both galaxies is neglected.
Weil, Melinda L.↗
NASA'S Great Observatories
Why are space observatories important? The answer concerns twinkling stars in the night sky. To reach telescopes on Earth, light from distant objects has to penetrate Earth's atmosphere. Although the sky may look clear, the gases that make up our atmosphere cause problems for astronomers. These gases absorb the majority of radiation emanating from celestial bodies so that it never reaches the astronomer's telescope. Radiation that does make it to the surface is distorted by pockets of warm and cool air, causing the twinkling effect. In spite of advanced computer enhancement, the images finally seen by astronomers are incomplete. NASA, in conjunction with other countries' space agencies, commercial companies, and the international community, has built observatories such as the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-ray Observatory to find the answers to numerous questions about the universe. With the capabilities the Space Shuttle provides, scientist now have the means for deploying these observatories from the Shuttle's cargo bay directly into orbit.
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Sulfuric Acid on Europa's Surface and the Radiolytic Sulfur Cycle
Galileo infrared spectra of Europa's surface show distorted water bands that have been attributed to hydrated evaporite salts (McCord et al., J. Geophys. Res. 104, 11827, 1999) or to the scattering properties of ice (Dalton and Clark, Bull. Am. Astron. Soc. 30, 1081, 1998).
Jupiter satellites composition infrared↗
Behavior of Three Metallic Alloys under Combined Axial-Shear Stresses at Elevated Temperature
Type 316 stainless steel, Haynes 188, and Inconel 718 samples were subjected to an axial-shear strain controlled loading history while the specimen temperature was held at 650 C to quantify the evolution of material state under a complex biaxial load path when the material is in the viscoplastic domain. Yield surfaces were constructed in the axial-shear stress plane using a sensitive, 30 x 10(exp -6)m/m, equivalent offset strain definition for the yield strain. Subsequent yield surfaces were constructed at various points along the strain path to define the material evolution. These subsequent yield surface translated, expanded, and distorted relative to the initial yield surface. Each of these very different materials exhibited components of isotropic, kinematic and distortional hardening. Furthermore, subsequent yield surfaces for each material have a very well defined front face and a poorly defined, flattened, back side.
Colaiuta, J. F.↗
Deformable Composite/Honeycomb Telescope Mirror
Piezoelectric transducers bonded to rear face sheet of honeycomb panel support spherical reflecting surface. Voltages applied to transducers compensate for distortions of reflecting surface.
Kuo, Chin-Po↗
Deformable subreflector computed by geometric optics
Using a Cassegrainian geometry, the 64-meter antenna with its distorted paraboloidal reflecting surface is forced to produce a uniform phase wavefront by a pathlength-compensating subreflector. First, the computed distortion vectors at the joints or nodes of the main reflector structure supporting the surface panels are best fitted to a paraboloid. Second, the resulting residual distortion errors are used to determine a compensating subreflector surface by ray tracing using geometric optics principles. Third, the totally corrected subreflector surface is defined by the normal directions and distances to the surface of the original symmetric hyperboloid for the purpose of evaluation. Finally, contour maps of distortions of the paraboloid reflector and the compensating subreflector are presented. A field-measured check of the subreflector in focused position as computed by the described methodology is also presented for the antenna position at horizon look with the geometry at 45 degrees elevation.
Katow, M. S.↗
Further evaluation of the constrained least squares electromagnetic compensation method
Technologies exist for construction of antennas with adaptive surfaces that can compensate for many of the larger distortions caused by thermal and gravitational forces. However, as the frequency and size of reflectors increase, the subtle surface errors become significant and degrade the overall electromagnetic performance. Electromagnetic (EM) compensation through an adaptive feed array offers means for mitigation of surface distortion effects. Implementation of EM compensation is investigated with the measured surface errors of the NASA 15 meter hoop/column reflector antenna. Computer simulations are presented for: (1) a hybrid EM compensation technique, and (2) evaluating the performance of a given EM compensation method when implemented with discretized weights.
Smith, William T.↗
Local Structural Distortions and Failure of the Surface-Stress "Core-Shell" Model in Brookite Titania Nanorods
Abstract not provided
Krayzman, Victor↗
Strain Engineering: Reduction of Microstrain at the Perovskite Surface via Alkali Metal Chloride Treatment Enhances Stability
Degradation of halide perovskites under a humid atmosphere is the major challenge preventing widespread commercial deployment of this material class. Here it is shown that strain engineering via alkali metal chloride treatment at the FAPbI 3 /SnO 2 interface effectively improves moisture-related stability. CsCl and KCl treatments reduce microstrain at the perovskite surface and slow the α- to δ-phase transformation. Alkali metal treatments with LiCl, NaCl, and RbCl led to an increase in microstrain and faster degradation. The compressive strain at the perovskite surface was the smallest for CsCl and was linked to improved stability. First-principles density functional theory calculations confirm the preferential formation of alkali defects at interstitial positions at the perovskite surface. Particularly CsCl and KCl treatments lead to a release of compressive strain at the perovskite surface and local structural distortions that may favor passivation of surface defects. In contrast, the room-temperature dynamics of Li interstitials result in an overall expansion of lattice volume, which may be linked to more facile lattice degradation.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Evaluation of Optical Distortion Measurement Techniques for Curved Optical Surfaces
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Mark Nurge↗
Fabrication of the Advanced X-ray Astrophysics Facility (AXAF) Optics: A Deterministic, Precision Engineering Approach to Optical Fabrication
The mirror assembly of the AXAF observatory consists of four concentric, confocal, Wolter type 1 telescopes. Each telescope includes two conical grazing incidence mirrors, a paraboloid followed by a hyperboloid. Fabrication of these state-or-the-art optics is now complete, with predicted performance that surpasses the goals of the program. The fabrication of these optics, whose size and requirements exceed those of any previous x-ray mirrors, presented a challenging task requiring the use of precision engineering in many different forms. Virtually all of the equipment used for this effort required precision engineering. Accurate metrology required deterministic support of the mirrors in order to model the gravity distortions which will not be present on orbit. The primary axial instrument, known as the Precision Metrology Station (PMS), was a unique scanning Fizeau interferometer. After metrology was complete, the optics were placed in specially designed Glass Support Fixtures (GSF's) for installation on the Automated Cylindrical Grinder/Polishers (ACG/P's). The GSF's were custom molded for each mirror element to match the shape of the outer surface to minimize distortions of the inner surface. The final performance of the telescope is expected to far exceed the original goals and expectations of the program.
Gordon, T. E.↗
Deployable reflector antenna performance optimization using automated surface correction and array-feed compensation
Methods for increasing the electromagnetic (EM) performance of reflectors with rough surfaces were tested and evaluated. First, one quadrant of the 15-meter hoop-column antenna was retrofitted with computer-driven and controlled motors to allow automated adjustment of the reflector surface. The surface errors, measured with metric photogrammetry, were used in a previously verified computer code to calculate control motor adjustments. With this system, a rough antenna surface (rms of approximately 0.180 inch) was corrected in two iterations to approximately the structural surface smoothness limit of 0.060 inch rms. The antenna pattern and gain improved significantly as a result of these surface adjustments. The EM performance was evaluated with a computer program for distorted reflector antennas which had been previously verified with experimental data. Next, the effects of the surface distortions were compensated for in computer simulations by superimposing excitation from an array feed to maximize antenna performance relative to an undistorted reflector. Results showed that a 61-element array could produce EM performance improvements equal to surface adjustments. When both mechanical surface adjustment and feed compensation techniques were applied, the equivalent operating frequency increased from approximately 6 to 18 GHz.
Schroeder, Lyle C.↗
Measurements of print-through in graphite fiber epoxy composites
High-reflectance accurate-contour mirrors are needed for solar dynamic space power systems. Graphite fiber epoxy composites are attractive candidates for such applications owing to their high modulus, near-zero coefficient of thermal expansion, and low mass. However, mirrors prepared from graphite fiber epoxy composite substrates often exhibit print-through, a distortion of the surface, which causes a loss in solar specular reflectance. Efforts to develop mirror substrates without print-through distortion require a means of quantifying print-through. Methods have been developed to quantify the degree of print-through in graphite fiber epoxy composite specimens using surface profilometry.
Jaworske, Donald A.↗