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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1949

Flight Investigations at High-Subsonic, Transonic, and Supersonic Speeds to Determine Zero-Lift Drag of Fin-Stabilized Bodies of Revolution having Fineness Ratios of 12.5, 8.91, and 6.04 and Varying Positions of Maximum Diameter

Rocket-powered models were flown at high-subsonic, transonic, and supersonic speeds to determine the zero-lift drag of fin-stabilized parabolic bodies of revolution differing in fineness ratio and in position of maximum diameter. The present paper presents the results for fineness ratio 12.5, 8.91 and 6.04 bodies having maximum diameters located at stations of 20, 40, 60, and 80 percent of body length. All configurations had cut-off sterns and all had equal base, frontal, and exposed fin areas. For most of the supersonic-speed range models having their maximum diameters at the 60-percent station gave the lowest values of drag coefficient. At supersonic speeds, increasing the fineness ratio generally reduced the drag coefficient for a given position of maximum diameter.

Hart, Roger G.↗
NASA NTRS1940

The Lateral Stability of Equal-flanged Aluminum-alloy I-beams Subjected to Pure Bending

Equal-flange beams of a special extruded I-section of 27ST aluminum alloy were tested in pure bending. Complete end fixity was not attained. Loading was continued until a definite maximum value had been reached. Tensile tests were made on specimens cut from the flanges and the web of each beam. Compressive stress-strain characteristics were determined by pack compression tests on specimens cut from the flanges. Values computed from an equation previously suggested by one of the authors for the critical stress at which such beams become unstable were found to be in good agreement with values computed from experimentally determined critically bending moments.

Dumont, C↗
NASA NTRS2004

Spatial Statistics of Large Astronomical Databases: An Algorithmic Approach

In this AISRP, the we have demonstrated that the correlation function i) can be calculated for MAP in minutes (about 45 minutes for Planck) on a modest 500Mhz workstation ii) the corresponding method, although theoretically suboptimal, produces nearly optimal results for realistic noise and cut sky. This trillion fold improvement in speed over the standard maximum likelihood technique opens up tremendous new possibilities, which will be persued in the follow up.

Szapudi, Istvan↗
NASA NTRS1985

Coal-Sizing Auger

Aft end of auger, like forward, face-piercing end, equipped with hard cutting bits such as diamonds. As auger breaks face, pulls broken coal lumps into jaws and forces them into hardened throat section. There, cutting bits chew up lumps: Clearance between throat and auger shaft sets maximum size for coal particles that pass through. Auger motion pushes coal particles into mixing chamber, where paddles combine them with water.

Lewis, E. V.↗
NASA NTRS2001

Supersonic Wind Tunnel Tests of a Half-axisymmetric 12 Deg-spike Inlet to a Rocket-based Combined-cycle Propulsion System

Results of an isolated inlet test for NASA's GTX air-breathing launch vehicle concept are presented. The GTX is a Vertical Take-off/ Horizontal Landing reusable single-stage-to-orbit system powered by a rocket-based combined-cycle propulsion system. Tests were conducted in the NASA Glenn 1- by 1-Foot Supersonic Wind Tunnel during two entries in October 1998 and February 1999. Tests were run from Mach 2.8 to 6. Integrated performance parameters and static pressure distributions are reported. The maximum contraction ratios achieved in the tests were lower than predicted by axisymmetric Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD). At Mach 6, the maximum contraction ratio was roughly one-half of the CFD value of 16. The addition of either boundary-layer trip strips or vortex generators had a negligible effect on the maximum contraction ratio. A shock boundary-layer interaction was also evident on the end-walls that terminate the annular flowpath cross section. Cut-back end-walls, designed to reduce the boundary-layer growth upstream of the shock and minimize the interaction, also had negligible effect on the maximum contraction ratio. Both the excessive turning of low-momentum comer flows and local over-contraction due to asymmetric end-walls were identified as possible reasons for the discrepancy between the CFD predictions and the experiment. It is recommended that the centerbody spike and throat angles be reduced in order to lessen the induced pressure rise. The addition of a step on the cowl surface, and planar end-walls more closely approximating a plane of symmetry are also recommended. Provisions for end-wall boundary-layer bleed should be incorporated.

DeBonis, J. R.↗
NASA NTRS1988

Optoelectronic gain control of a microwave single stage GaAs MESFET amplifier

Gain control of a single stage GaAs MESFET amplifier is demonstrated by the use of optical illumination of photon energy greater than the GaAs bandgap. The optical illumination is supplied by a semiconductor laser diode and is coupled to the Schottky gate of the MESFET by an optical fiber. The increase in gain is observed to be as much as 5.15 dB when the MESFET is biased close to pinchoff, that is, V(sub gs) equals -1.5 V and with optical illumination of 1.5 mW. The computed maximum available gain (MAG) and current gain (bar h sub 21 bar) from the de-embedded s-parameters show that MAG is unaffected by optical illumination, however, bar h(sub 21)bar increases by more than 2 dB under optical illumination of 1.5 mW. The maximum frequency of oscillation (F sub max) and the unity current gain cut-off frequency (F sub t) obtained by extrapolating the MAG and bar h(sub 21)bar curves, respectively, show that the F(sub max) is insensitive to optical illumination but F(sub t) increases by 5 GHz.

Simons, Rainee N.↗
NASA NTRS2012

Inductively Coupled Plasma Etching for Delineation of InAs/GaSb Pixels

We developed 320x256 Complimentary Barrier Infrared (CBIRD) focal plane array (FPA) for long wave infrared (LWIR) imaging application. The FPA layers grown by molecular beam epitaxy (MBE) had 300 periods 1.9 micro m thick absorber. The CBIRD arrays showed the mean dark current density of 2.2 x 10(exp -4) A/cm2, when 128 mV bias voltage was applied. The long wave cut off was observed at 8.8 micrometers at the 50% peak and the maximum quantum efficiency was 54% at 5.6 micrometers. The arrays had 81% fill factor with 97% operability with noise equivalent difference temperature (NE(delta)T) of 18.6 mK and a mean detectivity of D*=1.3 x 10(exp 11) Hz(exp 1/2)/W.

InAs/GaSb↗
NASA NTRS1994

Amazon Rain Forest Classification Using J-ERS-1 SAR Data

The Amazon rain forest is a region of the earth that is undergoing rapid change. Man-made disturbance, such as clear cutting for agriculture or mining, is altering the rain forest ecosystem. For many parts of the rain forest, seasonal changes from the wet to the dry season are also significant. Changes in the seasonal cycle of flooding and draining can cause significant alterations in the forest ecosystem.Because much of the Amazon basin is regularly covered by thick clouds, optical and infrared coverage from the LANDSAT and SPOT satellites is sporadic. Imaging radar offers a much better potential for regular monitoring of changes in this region. In particular, the J-ERS-1 satellite carries an L-band HH SAR system, which via an on-board tape recorder, can collect data from almost anywhere on the globe at any time of year.In this paper, we show how J-ERS-1 radar images can be used to accurately classify different forest types (i.e., forest, hill forest, flooded forest), disturbed areas such as clear cuts and urban areas, and river courses in the Amazon basin. J-ERS-1 data has also shown significant differences between the dry and wet season, indicating a strong potential for monitoring seasonal change. The algorithm used to classify J-ERS-1 data is a standard maximum-likelihood classifier, using the radar image local mean and standard deviation of texture as input. Rivers and clear cuts are detected using edge detection and region-growing algorithms. Since this classifier is intended to operate successfully on data taken over the entire Amazon, several options are available to enable the user to modify the algorithm to suit a particular image.

J-ERS-1↗
NASA NTRS1986

Dc and microwave characteristics of a high current double interface GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistor

Extremely large current double interface GaAs/In(0.15)Ga(0.85)As/Al(0.15)Ga(0.85)As pseudomorphic modulation-doped field-effect transistors (MODFET's) grown by molecular beam epitaxy were achieved. The 1-micron gate devices studied have peak current levels (430 mA/mm at 300 K and 483mA/mm at 77 K) roughly one and a half to two times that found in single interface pseudomorphic MODFET's. These devices also retain high transconductances over a broad range of gate voltage, peaking at 312 mS/mm at 300 K and 362 mS/mm at 77 K. Excellent microwave performance is also obtained with a maximum frequency of oscillation (f-max) of 37 GHz and a current gain cut-off frequency of as high as 23 GHz at 300 K. An output power level of 14 dBm (1 dB gain compression) was obtained at 6 GHz for a 290-micron gate width. This double interface single quantum well MODFET may be of great importance in millimeter wave power amplifiers.

Henderson, T.↗
NASA NTRS1972

Research plans for solar power in space.

The developments in space solar power technology are reviewed, with the emphasis on solar power output improvement as the goal of further efforts. It is contended that the biggest pay-off should be expected not from cost cutting in solar cell fabrication but from versatile improvement of solar cell designs to a feasible maximum.

Cohn, E. M.↗
NASA NTRS2013

Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing

Two flash lidars, integrated from a number of cutting-edge components from industry and NASA, are lab characterized and flight tested for determination of maximum operational range under the Autonomous Landing and Hazard Avoidance Technology (ALHAT) project (in its fourth development and field test cycle) which is seeking to develop a guidance, navigation, and control (GN&C) and sensing system based on lidar technology capable of enabling safe, precise crewed or robotic landings in challenging terrain on planetary bodies under any ambient lighting conditions. The flash lidars incorporate pioneering 3-D imaging cameras based on Indium-Gallium-Arsenide Avalanche Photo Diode (InGaAs APD) and novel micro-electronic technology for a 128 x 128 pixel array operating at 30 Hz, high pulse-energy 1.06 micrometer Nd:YAG lasers, and high performance transmitter and receiver fixed and zoom optics. The two flash lidars are characterized on the NASA-Langley Research Center (LaRC) Sensor Test Range, integrated with other portions of the ALHAT GN&C system from partner organizations into an instrument pod at NASA-JPL, integrated onto an Erickson Aircrane Helicopter at NASA-Dryden, and flight tested at the Edwards AFB Rogers dry lakebed over a field of human-made geometric hazards during the summer of 2010. Results show that the maximum operational range goal of 1 km is met and exceeded up to a value of 1.2 km. In addition, calibrated 3-D images of several hazards are acquired in real-time for later reconstruction into Digital Elevation Maps (DEM's).

Roback, Vincent↗
NASA NTRS1977

Effects of simulated flight on fan noise suppression

Attenuation properties of three treated fan inlets were evaluated in the NASA-Lewis Anechoic Wind Tunnel using a subsonic tip speed, 50.8 cm-diameter fan. Tunnel flow simulated the inflow clean-up effect on source noise observed in flight and allowed observation of the blade passage frequency tone cut-off phenomenon. Acoustic data consisted of isolated inlet noise measured in the far field at two positions and with traverses at four frequencies. Averaged attenuation properties showed relative agreement of the inlets with their design intent; however, tunnel flow significantly affected the attenuation spectra. With no tunnel flow the strong blade passage tone was more highly attenuated than the adjacent broadband noise. With tunnel flow, when cut-off was observed, the attenuation at the tone frequency was comparable to that for broadband noise. Tunnel flow increased by several dB the maximum attenuation occurring at midfrequencies of the attenuation spectra. The combined effect of tunnel flow on attenuation and source noise resulted in suppressed fan noise levels throughout the spectra. Tunnel flow caused some substantial directivity variations that are interpreted as acoustic mode changes, with tunnel flow generally reducing the proportion of modes near cut-off.

Heidmann, M. F.↗
NASA NTRS1973

Analytic and experimental performance of two isentropic mixed compression axisymmetric inlets at Mach numbers 0.8 to 2.65

A mixed compression axisymmetric inlet model with a capture diameter of 50 cm was tested at Mach numbers ranging from 0.8 to 2.65 at 0 deg angle of attack and a constant total pressure of approximately 1 atm. Analytical methods accounting for the effects of both viscous and inviscid flows and incorporating empirical bleed discharge coefficients were used in the procedure for designing the inlet contours and the bleed system. Experimental results are compared with analytic predictions and are also compared with results from earlier tests of an inlet with the same internal contours but with a bleed system developed by cut and try methods in the wind tunnel. With the bleed configuration predicted by the design procedure, maximum total pressure recovery at the engine face at the design Mach number of 2.65 was 93 percent, with a total pressure distortion less than 10 percent. Corresponding bleed mass flow was approximately 7.5 percent, which was about 1.3 percent less than predicted. At lower supersonic Mach numbers, pressure recovery and bleed were generally lower and distortion generally higher.

Smeltzer, D. B.↗
NASA NTRS1981

Incorporating spatial context into statistical classification of multidimensional image data

Compound decision theory is employed to develop a general statistical model for classifying image data using spatial context. The classification algorithm developed from this model exploits the tendency of certain ground-cover classes to occur more frequently in some spatial contexts than in others. A key input to this contextural classifier is a quantitative characterization of this tendency: the context function. Several methods for estimating the context function are explored, and two complementary methods are recommended. The contextural classifier is shown to produce substantial improvements in classification accuracy compared to the accuracy produced by a non-contextural uniform-priors maximum likelihood classifier when these methods of estimating the context function are used. An approximate algorithm, which cuts computational requirements by over one-half, is presented. The search for an optimal implementation is furthered by an exploration of the relative merits of using spectral classes or information classes for classification and/or context function estimation.

Bauer, M. E.↗
NASA NTRS2000

Near-Net-Shape Processing of Sintered Fibrous Ceramics Achieved

A variety of sintered fibrous ceramic (SFC) materials have been developed over the last 50 years as thermal barrier materials for reentry applications. SFC materials typically exhibit very low thermal conductivities combined with low densities and good thermal stability up to 2500 F. These materials have flown successfully on the space shuttle orbiters since the 1960's. More recently, the McDonnell Douglas Corporation successfully used SFC tiles as a heat shield on the underside of its DC X test vehicle. For both of these applications, tiles are machined from blocks of a specific type of SFC called an alumina-enhanced thermal barrier (AETB). The sizes of these blocks have been limited by the manufacturing process. In addition, as much as 80 to 90 percent of the material can be lost during the machining of tiles with significant amounts of curvature. To address these problems, the NASA Glenn Research Center at Lewis Field entered a cooperative contract with the Boeing Company to develop a vacuum-assisted forming process that can produce large (approximately 4 square feet), severely contoured panels of AETB while saving costs in comparison to the conventional cast-and-machine billet process. For shuttle use, AETB is slurry cast, drained, and fired to form square billets conforming to the shape of the filtration box. The billets are then cut into tiles of the appropriate size for thermally protecting the space shuttle. Processing techniques have limited the maximum size of AETB billets to 21.5 square inches by 6.5-in. thick, but the space shuttles use discrete heat shield tiles no more than 8 to 12 square inches. However, in other applications, large, complex shapes are needed, and the tiling approach is undesirable. For such applications, vacuum-assisted forming can produce large parts with complex shapes while reducing machining waste and eliminating cemented joints between bonded billets. Because it allows contoured shapes to be formed, material utilization is inherently high. Initial estimates show that the amount of material lost during machining can be reduced by 50 percent or more. In addition, a fiber alignment favorable for minimum heat transfer is maintained for all panel shapes since the fibers are aligned parallel to the contoured surface of the forming tool or mold. The vacuum-assisted forming process can complete the entire forming operation in a matter of minutes and can produce multiple parts whose size is limited only by the size of the forming tool. To date, panels as large as 2 square feet have been demonstrated The vacuum-assisted forming process starts with the fabrication of a permeable forming tool, or mold, with the proper part contour. This reusable tool is mounted over an internal rib support structure, as depicted in the diagram, such that a vacuum can be pulled on the bottom portion of the tool. AETB slurry is then poured over and around the tool, liquid is drawn from the slurry, and the part forms over the tool surface. The part is then dried, fired, and finished machined. Future plans include an evaluation of the need for additional coatings and surface-toughness treatments to extend the durability and performance of this material.

Angel, Paul W.↗
NASA NTRS1985

Diurnal variations of cosmic ray geomagnetic cut-off threshold rigidities

The spectrographic global survey method was used to investigate the rigidity variations Rc of geomagnetic cut-off as a function of local time and the level of geomagnetic disturbance for a number of stations of the world wide network. It is shown that geomagnetic cut-off threshold rigidities undergo diurnal variations. The diurnal wave amplitude decreases with increasing threshold rigidity Rc, and the wave maximum occurs at 2 to 4 hr LT. The amplitude of diurnal variations increases with increasing geomagnetic activity. The results agree with those from trajectory calculations made for an asymmetric model of the magnetosphere during different geomagnetic disturbance conditions.

Dvornikov, V. M.↗
NASA NTRS1992

The Edge supersonic transport

As intercontinental business and tourism volumes continue their rapid expansion, the need to reduce travel times becomes increasingly acute. The Edge Supersonic Transport Aircraft is designed to meet this demand by the year 2015. With a maximum range of 5750 nm, a payload of 294 passengers and a cruising speed of M = 2.4, The Edge will cut current international flight durations in half, while maintaining competitive first class, business class, and economy class comfort levels. Moreover, this transport will render a minimal impact upon the environment, and will meet all Federal Aviation Administration Part 36, Stage III noise requirements. The cornerstone of The Edge's superior flight performance is its aerodynamically efficient, dual-configuration design incorporating variable-geometry wingtips. This arrangement combines the benefits of a high aspect ratio wing at takeoff and low cruising speeds with the high performance of an arrow-wing in supersonic cruise. And while the structural weight concerns relating to swinging wingtips are substantial, The Edge looks to ever-advancing material technologies to further increase its viability. Heeding well the lessons of the past, The Edge design holds economic feasibility as its primary focus. Therefore, in addition to its inherently superior aerodynamic performance, The Edge uses a lightweight, largely windowless configuration, relying on a synthetic vision system for outside viewing by both pilot and passengers. Additionally, a fly-by-light flight control system is incorporated to address aircraft supersonic cruise instability. The Edge will be produced at an estimated volume of 400 aircraft and will be offered to airlines in 2015 at $167 million per transport (1992 dollars).

Agosta, Roxana↗
NASA NTRS2007

Optically Transparent Split-Ring Antennas for 1 to 10 GHz

Split-ring antennas made from optically transparent, electrically conductive films have been invented for applications in which there are requirements for compact antennas capable of operation over much or all of the frequency band from 1 to 10 GHz. Primary examples of such applications include wireless local-area networks and industrial, scientific, and medical (ISM) applications. These antennas can be conveniently located on such surfaces as those of automobile windows and display screens of diverse hand-held electronic units. They are fabricated by conventional printed-circuit techniques and can easily be integrated with solid-state amplifier circuits to enhance gain. The structure of an antenna of this type includes an antenna/feed layer supported on the top or outer face of a dielectric (e.g., glass) and, optionally, a ground layer on the bottom or inner face of the substrate. The ring can be in the form of either a conductive strip or a slot in the antenna/feed layer. The ring can be of rectangular, square, circular, elliptical, or other suitable shape and can be excited by means of a microstrip, slot line, or coplanar waveguide. For example, the antenna shown in the figure features a square conductive-strip split ring with a microstrip feed. In general, an antenna fed at its external boundary in the manner of this invention presents very high impedance, thereby creating an impedance-matching problem. Splitting the ring . that is, cutting a notch through the ring . offers a solution to the problem in that the notch fixes the location of maximum electric field, which location is directly related to the impedance. Thus, an excellent impedance match can be achieved through proper choice of the location of the notch. In geometric layout, such a ring antenna structure is typically between 1.4 and 1.3 the size of a patch antenna capable of operating in the same frequency range. This miniaturization of the antenna is desirable, not only because it contributes to overall miniaturization of equipment, but also because minimization of the extent of the optically transparent, electrically conductive film helps to minimize the electrical loss associated with the surface resistance ( 5 ohms per square) of the transparent, electrically conductive film material. Incidentally, even at 5 ohms per square, this surface resistance is significantly less than that of indium tin oxide film (typically > 25 ohms per square), which, heretofore has been the transparent, electrically conductive film material of choice. At the time of writing this article, information on the composition of the lower-resistance film used in the antennas of this invention was not available.

Lee, Richard Q.↗