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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Flow Analysis of Space Shuttle Feed Line 17-inch Disconnect Valve

A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle External Tank/Orbiter propellant feed line disconnect flapper valves with upstream elbows. The full Navier-Stokes code, INS3D, is modified to handle interior obstacles. Grids are generated by SVTGD3D code. Two dimensional initial grids in the flow cross section with and without the flappers are improved by elliptic smoothing to provide better orthogonality, clustering and smoothness to the three dimensional grid. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 x 10(exp 6). The results will serve as a guide to improved design and enhanced testing of the disconnect.

Kandula, Max↗
NASA NTRS1989

Feasibility study of a synthesis procedure for array feeds to improve radiation performance of large distorted reflector antennas

Surface errors on parabolic reflector antennas degrade the overall performance of the antenna. The errors are in the form of roughness on the surface, distortions in the shape, or structural design details. They cause amplitude and phase errors in the aperture field which lower the gain, raise the sidelobes, and fill in the nulls. These are major problems in large space reflector antennas. Planned mobile satellite communications systems having limited signal margin need high gain from the space reflectors. Future multiple beam antenna systems requiring spatial isolation to allow frequency reuse could be rendered useless if high sidelobes are present. High sidelobes are also responsible for noise. Ways of compensating for surface errors by pattern synthesis using an array of feed antennas are examined. Pattern corrections are directed specifically toward portions of the pattern requiring improvements. The pattern synthesis does not require knowledge of the surface errors. Both the amplitude and phase of the high side lobes caused by the distortion are required.

Stutzman, W. L.↗
NASA NTRS1988

Reflector antenna distortion compensation by array feeds - An experimental verification

Reflector antennas are subject to surface distortions which may result from thermal or gravitational effects. Surface distortions degrade antenna performance by reducing gain and introducing high sidelobe levels. In the letter, results of an experimental study are presented to demonstrate how effectively a properly excited array feed in the focal plane of the reflector antenna can compensate for the undesirable effects of slowly varying surface distortions. The application of the array compensation concept could prove to be very useful for future large space or ground antennas.

Rahmat-Samii, Y.↗
NASA NTRS1990

Array Feed To Compensate For Distortion In Antenna

System partly restores desired far-field radiation pattern. Adaptive array feed for paraboloidal-reflector antenna helps compensate for effects of slow changes in shape of reflecting surface. Counteracts distortion by illuminating reflector with wave fronts that have "opposite" distortion.

Rahmat-Samii, Y.↗
NASA NTRS1991

Megawatt Square Microwave Feed Horn

Prototype multiflare square horn antenna designed to combine phased 8.51-GHz outputs of four 250-kW amplifiers into single 1-MW continuous-wave beam. Main lobe and side lobes reasonably below main lobe obtained by choosing tapers of multiflare horn to couple power from TE(Sub10) mode into three other modes. Intended to illuminate subreflector of 70-m-diameter radar antenna. Nearly duplicates radiation pattern of corrugated round feed horn.

Hoppe, Daniel J.↗
NASA NTRS1991

Digital Signal Combiner For Receiving-Antenna Feed Array

Proposed digital system combines digitized baseband samples of signals received by array of feeds in large Cassegrainian paraboloidal-dish antenna. Signals received by subantennas in focal-plane array of large dish antenna combined by system compensating in real time for distortions of wave fronts caused by mechanical distortions of antenna. Signal-combining system combines baseband output signals of receiver front ends according to complex weighting parameters estimated from signals themselves. Intended to compensate in real time for degradation of signal-to-noise ratio by vibrational, gravitational, and wind-induced deformations of antenna structure.

Vilnrotter, Victor A.↗
NASA NTRS1991

Diamond-Coated Wire-Feeding Nozzle

Hard vacuum-deposited film improves nozzle properties. Tip and bore surfaces of proposed nozzle for feeding wire for gas/tungsten arc welding coated with film of synthetic diamond. Film gives nozzle following advantages: lower friction, thermal conductivity, less wear, electrical isolation of wire from nozzle, and high resistance to corrosion.

Gilbert, Jeffrey L.↗
NASA NTRS1989

Computational fluid dynamics analysis of space shuttle main propulsion feed line 17-inch disconnect valves

A steady incompressible three-dimensional (3-D) viscous flow analysis was conducted for the Space Shuttle Main Propulsion External Tank (ET)/Orbiter (ORB) propellant feed line quick separable 17-inch disconnect flapper valves for liquid oxygen (LO2) and liquid hydrogen (LH2). The main objectives of the analysis were to predict and correlate the hydrodynamic stability of the flappers and pressure drop with available water test data. Computational Fluid Dynamics (CFD) computer codes were procured at no cost from the public domain, and were modified and extended to carry out the disconnect flow analysis. The grid generator codes SVTGD3D and INGRID were obtained. NASA Ames Research Center supplied the flow solution code INS3D, and the color graphics code PLOT3D. A driver routine was developed to automate the grid generation process. Components such as pipes, elbows, and flappers can be generated with simple commands, and flapper angles can be varied easily. The flow solver INS3D code was modified to treat interior flappers, and other interfacing routines were developed, which include a turbulence model, a force/moment routine, a time-step routine, and initial and boundary conditions. In particular, an under-relaxation scheme was implemented to enhance the solution stability. Major physical assumptions and simplifications made in the analysis include the neglect of linkages, slightly reduced flapper diameter, and smooth solid surfaces. A grid size of 54 x 21 x 25 was employed for both the LO2 and LH2 units. Mixing length theory applied to turbulent shear flow in pipes formed the basis for the simple turbulence model. Results of the analysis are presented for LO2 and LH2 disconnects.

Kandula, Max↗
NASA NTRS1991

Channel assignments and array gain bounds for the Ka-band array feed compensation system

The performance of a real-time digital combining system for use with array feeds was considered previously. The purpose of the combining operation is to recover signal to noise ratio (SNR) losses due to antenna deformations and atmospheric effects. Previously, arbitrary signal powers and noise variances were assumed, but no attempt was made to match the receiver channels to the available signal powers. It is shown that for any signal power and noise variance distribution, a best channel assignment exists that maximizes the combined SNR in the limit of vanishingly small combining losses. This limit can be approached in practice by observing sufficiently many samples. Specific signal power and noise variance distributions are considered, and it is shown that even relatively noisy channels can be used effectively to recover SNR losses resulting from signals diverted out of a high-quality channel by antenna deformations.

Vilnrotter, V. A.↗
NASA NTRS1991

Low loss waveguide four-port crossover circuit and its application for cross-slot antenna feed

A four-way crossover circuit using a cylindrical cavity with four rectangular input/output ports has been designed to feed a cross-slot antenna to achieve dual polarization. Because all the input and output circuits are waveguides, the network is especially useful for high power systems and millimeter wave applications. The crossover circuit exhibits a very low insertion loss and good isolation.

Chang, K.↗
NASA NTRS1991

Feasibility study of a synthesis procedure for array feeds to improve radiation performance of large distorted reflector antennas

Virginia Tech is involved in a number of activities with NASA Langley related to large aperture radiometric antenna systems. These efforts are summarized and the focus of this report is on the feasibility study of a synthesis procedure for array feeds to improve radiation performance of large distorted reflector antennas; however, some results for all activities are reported.

Stutzman, W. L.↗
NASA NTRS1991

The L-/C-band feed design for the DSS 14 70-meter antenna (Phobos mission)

A dual-frequency (1.668 and 5.01 GHz) feed was designed for the Deep Space Station (DSS) 14 70-m antenna to support the Soviet Phobos Mission. This antenna system was capable of supporting telemetry, two-way Doppler, and very long baseline interferometry (VLBI). VLBI and two-way Doppler information on the Phobos spacecraft was acquired with this antenna in 1989.

Stanton, P. H.↗
NASA NTRS1992

A pattern synthesis technique for array feeds to improve radiation performance of large distorted reflector antennas

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 the reflectors increase, the subtle surface errors become significant and degrade the overall electromagnetic performance. Electronic compensation through an adaptive feed array offers a means for mitigation of surface distortion effects. A pattern synthesis approach for electromagnetic compensation of surface error is presented. The pattern synthesis approach uses a localized algorithm in which pattern corrections are directed toward specific portions of the pattern requiring improvement. The pattern synthesis technique uses radiation pattern data to perform the compensation.

Smith, William T.↗
NASA NTRS1992

Analysis and testing of propellant feed system priming process

This paper presents the analytical and the experimental results pertaining to the priming process of the propellant feed system with initial line pressures starting from 0 psia and greater. The analytical methods employ the method of characteristics to solve for the one-dimensional liquid transients in the liquid-full segments and the lumped inertia technique to model the dynamics of the partially filled segments or the two-phase segments. The advantages of these methods are (1) fluid compressibility and piping flexibility are accounted for in the solution; and (2) the characteristics method can be used in the solution of a complex system. The analytical results were compared with test results. Excellent correlation was obtained between predictions and test results verifying the essential aspects of the analytical modeling techniques and providing the foundation for analyzing a complicated network system.

Lin, T. Y.↗
NASA NTRS1992

Phased array feed design technology for Large Aperture Microwave Radiometer (LAMR) Earth observations

An assessment of the potential and limitations of phased array antennas in space-based geophysical precision radiometry is described. Mathematical models exhibiting the dependence of system and scene temperatures and system sensitivity on phased array antenna parameters and components such as phase shifters and low noise amplifiers (LNA) are developed. Emphasis is given to minimum noise temperature designs wherein the LNA's are located at the array level, one per element or subarray. Two types of combiners are considered: array lenses (space feeds) and corporate networks. The result of a survey of suitable components and devices is described. The data obtained from that survey are used in conjunction with the mathematical models to yield an assessment of effective array antenna noise temperature for representative geostationary and low Earth orbit systems. Practical methods of calibrating a space-based, phased array radiometer are briefly addressed as well.

Schuman, H. K.↗
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.↗