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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

An experimental investigation of control surface effectiveness and real-gas simulation for biconics

Aerodynamic coefficients, pressure distributions, and oil-flow patterns measured on spherically blunted, 13 degrees/7 degrees on-axis and bent biconics at Mach 6 and 10 in air are compared. Angle of attack, referenced to the axis of the aft cone, was varied from zero to 40 degrees. The effect of deflection of base-mounted flaps on aerodynamic characteristics was examined at Mach 10. Real-gas effects on aerodynamic coefficients, pressure distributions and shock detachment distance were simulated by testing the biconic models in Mach 6 air and Mach 6 CF4 flows. (Density ratio equal to 5.3 for air and 12 for CF4.) The on-axis biconic is stable but cannot be trimmed at angles of attack above zero with the assumed center of gravity and flap configuration. Flaps on the bent biconic produced a stable and trim configuration for angles of attack from zero to 23 degrees. A significant effect of density ratio on aerodynamic coefficients, pressure distribution, and shock detachment distance was observed.

Miller, C. G.↗
NASA NTRS1983

Focusing the parabolic antenna

The focused parabolic antenna has far field pattern characteristics in the radiating near field region. Therefore, it can provide fine resolutions in the across range dimensions. The technique of focusing the parabolic antenna is discussed and applied to a 2-1/2 foot parabolic antenna at X-band. The results of the pattern measurements at various ranges from 2.8 m to 5 m are provided.

Wu, L. K.↗
NASA NTRS1986

High-gain backup antenna design for Pioneer Venus Orbiter spacecraft

The development and performance is described of a high-gain antenna designed to serve on the Pioneer Venus Orbiter spacecraft as a backup to the principal high-gain antenna unit in the unlikely event the mechanically despun antenna mechanism malfunctioned. The final design, a center-fed standing wave array of six sleeve dipoles enclosed in a fiber glass radome, performed successfully, as did all the antennas, on the Pioneer Orbiter spacecraft which was launched on May 20, 1978, as part of the Pioneer Venus mission. Photographs of experimental models giving details of design and construction are included, as well as graphs showing measured pattern and impedance matching characteristics of the subject antenna.

Glaser, J. I.↗
NASA NTRS1986

Large space reflector technology on the Space Station

This paper discusses the role of the Space Station in the evolutionary development of large space reflector technology and the accommodation of mission systems which will apply large space reflectors during the late 1990s and the early part of the next century. Reflectors which range from 10 to 100 meters in size and which span the electromagnetic spectrum for applications that include earth communications, earth observations, astrophysics and solar physics, and deep space communications are discussed. The role of the Space Station in large space reflector technology development and system performance demonstration is found to be critical; that role involves the accommodation of a wide variety of technology demonstrations and operational activities on the Station, including reflector deployment and/or assembly, mechanical performance verification and configuration refinement, systematic diagnostics of reflector surfaces, structural dynamics and controls research, overall system performance characterization and modification (including both radio frequency field pattern measurements and required end-to-end system demonstrations), and reflector-to-spacecraft integration and staging. A unique facility for Space Station-based, large space reflector research and development is proposed. A preliminary concept for such a Space Station-based Large Space Reflector Facility (LSRF) is described.

Mankins, J. C.↗
NASA NTRS1987

Hollowness of the observed auroral kilometric radiation pattern

Presumably also generated by electron cyclotron emission, the earth's auroral kilometric radiation would be expected to exhibit a hollow pattern in the direction of the source magnetic field, similar to that reported for the comparable emissions from Jupiter. Although previously overlooked, such hollowness is clearly present in the new pattern measurements of Green and Gallagher (1985) at 56 kHz, occupying source-centered latitudes of 30 to 45 deg and hence occurring exactly where it was predicted and previously observed. Being distributed in longitude and spanning the entire evening sector, presumably reflecting a similar longitudinal distribution of auroral zone sources, this hollowness is attributed to sources beamed preferentially in the poleward magnetic meridian.

Calvert, W.↗
NASA NTRS1987

Bow-tie antennas on a dielectric half-space - Theory and experiment

A new formulation is discussed for the rigous calculation of the radiation pattern of a bow-tie antenna of finite length and infinitesimal thickness, placed on a lossless dielectric substrate. The analysis is based on a representation of the current density on the metal surface of the antenna as a sum of an imposed (quasistatic) term and a set of current modes with unknown amplitudes. Free-space fields that are expressed in terms of continuous spectra of symmetrized plane waves are matched to the current modes using the method of moments. The resulting set of equations are solved for the unknown current amplitudes. The calculations show that for increasing bow length the antenna impedance spirals rapidly to a value predicted by transmission line theory. The theory also shows that the E-plane pattern of a two-wavelength, 60-deg bow-tie antenna is dominated by low-loss current modes propagating at the dielectric wavenumber. As the bow tie narrows, the loss of the modes increases, and the dominant wavenumber tends to the quasi-static value. Pattern measurements made at 94 GHz are shown to agree well with theoretical predictions. Measurements for a long-wire antenna, a linear array of bow-tie elements, and a log-periodic antenna are also presented.

Compton, Richard C.↗
NASA NTRS1989

A surface distortion analysis applied to the hoop/column deployable mesh reflector antenna

A practical approach is demonstrated for the deterministic analysis of surface distortions in reflector antennas, based on a first-order approximation to the aperture field phase. Measured pattern results from a 15-m-diameter hoop/column deployable mesh reflector antenna are used to demonstrate the accuracy which can be obtained with this surface distortion analysis. The only practical limitation of the first-order approximation is determined by the slope derivations of the distorted surface from the best-fit paraboloid.

Lee, Teh-Hong↗
NASA NTRS1988

Vehicle antenna for the mobile satellite experiment

A low profile, low cost, printed circuit, electronically steered, right hand circularly polarized phase array antenna system has been developed for the Mobile Satellite Experiment (MSAT-X) Program. The success of this antenna is based upon the development of a crossed-slot element array and detailed trade-off analyses for both the phased array and pointing system design. The optimized system provides higher gain at low elevation angles (20 degrees above the horizon) and broader frequency coverage (approximately 8 1/2 percent bandwidth) than is possible with a patch array. Detailed analysis showed that optimum performance could be achieved with a 19 element array of a triangular lattice geometry of 3.9 inch element spacing. This configuration has the effect of minimizing grating lobes at large scan angles plus it improves the intersatellite isolation. The array has an aperture 20 inches in diameter and is 0.75 inch thick overall, exclusive of the RF and power connector. The pointing system employs a hybrid approach that operates with both an external rate sensor and an internal error signal as a means of fine tuning the beam acquisition and track. Steering the beam is done electronically via 18, 3-bit diode phase shifters. A nineteenth phase shifter is not required as the center element serves as a reference only. Measured patterns and gain show that the array meets the stipulated performance specifications everywhere except at some low elevation angles.

Peng, Sheng Y.↗
NASA NTRS1991

Integrated 222-GHz corner-reflector antennas

A high-gain monolithic millimeter-wave antenna has been designed, fabricated, and tested at 222 GHz. The structure consists of a traveling-wave antenna integrated on a 1.2-micron dielectric membrane and suspended in a longitudinal cavity etched in a silicon wafer. A new traveling-wave antenna design yields a wideband input impedance and a low cross-polarization component in the E- and quasi-H-plane patterns. A directivity of 17.7 dB and a main-beam efficiency of 88.5 percent are calculated from the 222-GHz pattern measurements. The integrated corner-reflector antenna is well suited for millimeter- and submillimeter-wave imaging applications in large f-number systems.

Gearhart, Steven S.↗
NASA NTRS1990

Experimental and analytical study of close-coupled ventral nozzles for ASTOVL aircraft

Flow in a generic ventral nozzle system was studied experimentally and analytically with a block version of the PARC3D computational fluid dynamics program (a full Navier-Stokes equation solver) in order to evaluate the program's ability to predict system performance and internal flow patterns. Measurements showed about 5.5-percent flow-turning loss, reasonable nozzle performance coefficients, and a significant aftward axial component of thrust due to flow turning more than 90 deg. Flow behavior into and through the ventral duct is discussed and illustrated with paint streak flow visualization photographs. PARC3D flow visualization images are shown for comparison with the paint streak photographs. Modeling and computational issues encountered in the analytical work are discussed.

Mcardle, Jack G.↗
NASA NTRS1992

A novel antenna for ultra-wide-band applications

An ultrawideband antenna based on a slotline feed structure, a bowtie horn, and a rolled edge termination was developed, analyzed, and measured. Empirical data showed that its beamwidths and bandwidth are dependent on its physical dimensions which are easily controllable by an antenna designer. Measured patterns of models with various radiation properties are shown to substantiate these design rules. A flat plateau-like main beam, low voltage standing-wave ratio (VSWR), the ability to produce both wide (60 deg) and narrow (30 deg) half-power beamwidths, low sidelobes and backlobe (40-50 dB down), low cross-polarized levels (20-25 dB down), and independent control of E- and H-plane beamwidths over an ultrawide bandwidth, say 2-18 GHz, are some of the strong points of this antenna type.

Lai, Albert K. Y.↗
NASA NTRS1992

A 32-GHz phased array transmit feed for spacecraft telecommunications

A 21-element phased array transmit feed was demonstrated as part of an effort to develop and evaluate state-of-the-art transmitter and receiver components at 32 and 34 GHz for future deep-space missions. Antenna pattern measurements demonstrating electronic beam steering of the two-dimensional array are reported and compared with predictions based on measured performance of MMIC-based phase shifter and amplifier modules and Vivaldi slotline radiating elements.

Lee, K. A.↗
NASA NTRS1992

94 GHz integrated horn monopulse antennas

A monolithic azimuthal monopulse antenna for 94 GHz applications has been developed. The structure consists of a single dipole suspended in one plane of an integrated horn cavity to obtain the sum pattern, and an antiparallel pair of dipoles suspended in a different plane of the same horn cavity to achieve the difference pattern. Pattern measurements of microwave models and on the millimeter-wave antennas show good agreement with theory and exhibit symmetry with a sharp -30 dB null at broadside for the difference antenna. Microwave model measurements show input impedances close to 50 Ohms, with greater than -25 dB isolation between sum and difference antennas across a 10 percent bandwidth.

Ling, Curtis C.↗
NASA NTRS1991

High quality flame deposited diamond films for infrared optical windows

The IR absorption in polycrystalline diamond films deposited in oxygen-acetylene flames is characterized using FTIR. The one-phonon absorption coefficient in the region from 7 to 12 microns that is related to extrinsic defects in the diamond films shows a strong dependence on the flame conditions as well as the substrate temperature. A high degree of diamond crystalline perfection, as judged from the undetectable one-phonon absorption, is achieved under the optimized deposition conditions for our flame setup. This is further supported by the sharp Raman peak at 1332/cm as well as the high purity in crystal orientation according to the X-ray diffraction pattern measured for the high quality diamond films.

Tzeng, Y.↗
NASA NTRS1993

The Upper Atmosphere Research Satellite (UARS)

The Upper Atmosphere Research Satellite (UARS) was launched by the Space Shuttle on September 12, 1991 into a near circular orbit at 585 km altitude inclined 57 degrees to the Equator. Measurements were initiated a few days later, including solar energy inputs to the atmosphere and vertical profiles of temperature, important minor gas species, and wind fields. The orbital parameters, combined with the sensor measurements characteristics, yield a measurement pattern that produces near global coverage with a duty cycle that periodically favors the Northern or the Southern Hemispheres. A few spacecraft and instrument anomalies have impacted the total amount of data obtained to date, but the overall performance of the mission has been very good.

Reber, Carl A.↗
NASA NTRS1995

A new planar feed for slot spiral antennas

This report presents a new planar, wideband feed network for a slot spiral antenna, and the subsequent design and performance of a VHF antenna utilizing this feed design. Both input impedance and radiation pattern measurements are presented to demonstrate the performance and usefulness of this feed. Almost all previous designs have utilized wire spirals, requiring bulky, non-planar feeds with separate baluns, and large absorbing cavities. The presented slot spiral antenna feed integrates the balun into the structure of the slot spiral antenna, making the antenna and feed planar. This greatly simplifies the design and construction of the antenna, in addition to providing repeatable accuracy. It also allows the use of a very shallow reflecting cavity for conformal applications. Finally, this feeding approach now makes many of the known miniaturization techniques viable options.

Nurnberger, M. W.↗
NASA NTRS1997

Physical Vapor Transport of Mercurous Chloride Crystals: Design of a Microgravity Experiment

Flow field characteristics predicted from a computational model show that the dynamical state of the flow, for practical crystal growth conditions of mercurous chloride, can range from steady to unsteady. Evidence that the flow field can be strongly dominated by convection for ground-based conditions is provided by the prediction of asymmetric velocity profiles bv the model which show reasonable agreement with laser Doppler velocimetry experiments in both magnitude and planform. Unsteady flow is shown to be correlated with a degradation of crystal quality as quantified by light scattering pattern measurements, A microgravity experiment is designed to show that an experiment performed with parameters which yield an unsteady flow becomes steady (diffusive-advective) in a microgravity environment of 10(exp -3) g(sub 0) as predicted by the model, and hence yields crystals with optimal quality.

Duval, W, M. B.↗
NASA NTRS2001

Reconfigurable Array Antenna Using Microelectromechanical Systems (MEMS) Actuators

The paper demonstrates a patch antenna integrated with a novel microelectromechanical systems (MEMS) actuator for reconfiguring the operating frequency. Experimental results demonstrate that the center frequency can be reconfigured by as much as 1.6 percent of the nominal operating frequency at K-Band In addition, a novel on-wafer antenna pattern measurement technique is demonstrated.

Simons, Rainee N.↗