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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Television monitor field shifter and an opto-electronic method for obtaining a stereo image of optimal depth resolution and reduced depth distortion on a single screen

A method and apparatus for obtaining a stereo image with reduced depth distortion and optimum depth resolution. Static and dynamic depth distortion and depth resolution trade-off is provided. Cameras obtaining the images for a stereo view are converged at a convergence point behind the object to be presented in the image, and (a) the collection-surface-to-object distance, (b) the camera separation distance, and (c) the focal lengths of zoom lenses for the camera are all increased. Doubling the distances cuts the static depth distortion in half while maintaining image size and depth resolution. Dynamic depth distortion is minimized by panning a stereo view-collecting camera system about a circle which passes through the convergence point and the cameras' first nodal points. Horizontal field shifting of the television fields on a television monitor brings both the monitor and the stereo views within the viewer's limit of binocular fusion.

Daniel B Diner↗
NASA NTRS1990

Effects of amplitude distortions and IF equalization on satellite communication system bit-error rate performance

Satellite communications links are subject to distortions which result in an amplitude versus frequency response which deviates from the ideal flat response. Such distortions result from propagation effects such as multipath fading and scintillation and from transponder and ground terminal hardware imperfections. Bit-error rate (BER) degradation resulting from several types of amplitude response distortions were measured. Additional tests measured the amount of BER improvement obtained by flattening the amplitude response of a distorted laboratory simulated satellite channel. The results of these experiments are presented.

Kerczewski, Robert J.↗
NASA NTRS1990

Microwave background distortions from domain walls

Domain walls arising in a cosmic phase transition after decoupling were recently proposed as seeds for the formation of large scale structure. The distortion induced in the microwave background radiation is calculated in dependence of the wall thickness, surface density, scalar field potential, cosmic redshift and the velocity of the wall. It was found that the maximal redshift distortion for both spherical and planar walls is of the order pi G sigma H(sup -1)(sub 0), where sigma is the surface energy density and H(sup -1)(sub 0) the Hubble parameter. It was also found that, for a wall thickness smaller than the horizon, walls can be treated as infinitely thin, i.e., the redshift distortion is independent of the wall thickness and the specific form of the scalar potential. For planar walls moving with a Lorentz-factor gamma the redshift distortion is enhanced by gamma cubed.

Goetz, Guenter↗
NASA NTRS1990

Effects of amplitude distortions and IF equalization on satellite communication system bit-error rate performance

Satellite communications links are subject to distortions which result in an amplitude versus frequency response which deviates from the ideal flat response. Such distortions result from propagation effects such as multipath fading and scintillation and from transponder and ground terminal hardware imperfections. Laboratory experiments performed at NASA Lewis measured the bit-error-rate (BER) degradation resulting from several types of amplitude response distortions. Additional tests measured the amount of BER improvement obtained by flattening the amplitude response of a distorted laboratory-simulated satellite channel. This paper presents the results of these experiments.

Kerczewski, Robert J.↗
NASA NTRS1990

Mapping and distortions of auroral structures in the quiet magnetosphere

The closed quiet magnetosphere model of Beard (1979) and Beard et al. (1982) is used to identify those features of commonly observed dayside auroras that can be explained by either of two processes: mapping distortions or distortions caused by nearby Birkeland currents. It is shown that single and multiple linear and hooked auroral forms can be easily explained in terms of mapping distortions in a quiet magnetosphere. On the other hand, the shapes of bright twisted or folded auroral forms can be more easily explained as distortions produced by localized Birkeland currents.

Kaufmann, Richard L.↗
NASA NTRS1990

Array feeds for reflector surface distortion compensation - Concepts and implementation

The development of a compensation algorithm based on the use of array feeds and a focal-plane conjugate field approach is discussed. Results of numerical simuations performed to verify the accuracy of the computer programs are examined, and an experimental study is described. Both the numerical and experimental results show that the array will compensate for the slowly varying surface distortion. In particular, for some typical, slowly varying thermal or gravitational surface distortions, a 19-element array feed can improve the reflector performance considerably. Additionally, it is demonstrated that it will be possible to compensate for the surface distortion without actual knowledge of the distortion itself.

Rahmat-Samii, Yahya↗
NASA NTRS1990

Finite element analysis of thermal distortion effects on optical performance of solar dynamic concentrator for Space Station Freedom

An analysis was performed to predict the thermal distortion of the solar dynamic concentrator for Space Station Freedom in low earth orbit and to evaluate the effects of that thermal distortion on concentrator on-orbit performance. The analysis required substructural finite element modeling of critical concentrator structural subsystems, structural finite element modeling of the concentrator, mapping of thermal loading onto the structural finite element model, and the creation of specialized postprocessors to assist in interpreting results. Concentrator temperature distributions and thermally induced displacements and slope errors and the resulting receiver flux distribution profiles are discussed. Results determined for a typical orbit indicate that concentrator facet rotations are less than 0.2 mrad and that the change in facet radius due to thermal flattening is less than 5 percent. The predicted power loss due to thermal distortion effects is less than 0.3 percent. As a consequence the thermal distortions of the solar dynamic concentrator in low earth orbit will have a negligible effect on the flux distribution profiles within the receiver.

Doherty, Michael P.↗
NASA NTRS1991

Novel array-feed distortion compensation techniques for reflector antennas

Degradation of antenna performance by reflector surface distortion, which lowers gain and increases sidelobe levels, is addressed. Distortion compensation concepts based on the applications of properly matched array feeds are presented. Results of conceptual developments, numerical simulations, and measurement verifications are presented in support of this approach, with particular attention to the measurement technique. It is shown that the concept is most useful for overcoming the deterioration effects of slowly varying surface distortions, which would make the method very useful for future large space and ground antennas. It is further shown that for a typical, slowly varying thermal or gravitational surface distortion, a 19-element array feed can improve the reflector performance considerably.

Rahmat-Samii, Yahya↗
NASA NTRS1993

System overview on electromagnetic compensation for reflector antenna surface distortion

The system requirements and hardware implementation for electromagnetic compensation of antenna performance degradations due to thermal effects was investigated. Future commercial space communication antenna systems will utilize the 20/30 GHz frequency spectrum and support very narrow multiple beams (0.3 deg) over wide angle field of view (15-20 beamwidth). On the ground, portable and inexpensive very small aperture terminals (VSAT) for transmitting and receiving video, facsimile and data will be employed. These types of communication system puts a very stringent requirement on spacecraft antenna beam pointing stability (less than .01 deg), high gain (greater than 50 dB) and very lowside lobes (less than -25 dB). Thermal analysis performed on the advanced communication technology satellite (ACTS) has shown that the reflector surfaces, the mechanical supporting structures and metallic surfaces on the spacecraft body will distort due thermal effects from a varying solar flux. The antenna performance characteristics (e.g., pointing stability, gain, side lobe, etc.) will degrade due to thermal distortion in the reflector surface and supporting structures. Specifically, antenna RF radiation analysis has shown that pointing error is the most sensitive antenna performance parameter to thermal distortions. Other antenna parameters like peak gain, cross polarization level (beam isolation), and side lobe level will also degrade with thermal distortions. In order to restore pointing stability and in general antenna performance several compensation methods were proposed. In general these compensation methods can be classified as being either of mechanical or electromagnetic type. This paper will address only the later one. In this approach an adaptive phased array antenna feed is used to compensate for the antenna performance degradation. Extensive work has been devoted to demonstrate the feasibility of adaptive feed compensation on space communication antenna systems. This paper addresses the system requirements for such a system and identify candidate technologies (analog and digital) for possible hardware implementation.

Acosta, R. J.↗
NASA NTRS1993

Temperature induced distortions in space telescope mirrors

In this paper, it is illustrated how measured instantaneous coefficients of thermal expansion (CTE) can be accurately taken into account when modeling the structural behavior of space based optical systems. In particular, the importance of including CTE spatial variations in the analysis of optical elements is emphasized. A comparison is made between the CTE's of three optical materials commonly used in the construction of space mirrors (ULE, Zerodur, and beryllium). The overall impact that selection of any one of these materials has on thermal distortions is briefly discussed. As an example of how temperature dependent spatial variations in thermal strain can be accurately incorporated in the thermo-structural analysis of a precision optical system, a finite element model is developed, which is used to estimate the thermally induced distortions in the Hubble Space Telescope's (HST) primary mirror. In addition to the structural analysis, the optical aberrations due to thermally induced distortions are also examined. These calculations indicate that thermal distortions in HST's primary mirror contribute mainly to defocus error with a relatively small contribution to spherical aberration.

Nied, H. F.↗
NASA NTRS1993

Compensation for 6.5 K cryogenic distortion of a fused quartz mirror by refiguring

A 46 cm diameter, lightweight, Amersil TO8E, fused-natural-quartz mirror with a single-arch cross section was tested at the NASA-Ames Research Center Cryogenic Optical Test Facility to measure its cryogenic distortion at 6.5 K. Then the mirror was refigured with the inverse of the measured cryogenic distortion to compensate for this figure defect. The mirror was retested at 6.5 K and found to have a significantly improved figure. The compensation for cryogenic distortion was not complete, but preliminary analysis indicates that the compensation was better than 0.25 waves P-V if edge effects are ignored. The feasibility of compensating for cryogenic distortion by refiguring has thus been verified.

Augason, Gordon C.↗
NASA NTRS1993

Experimental study of three exit pressure distortions on turbine performance

A cold flow air test of the Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) turbine was conducted with a circumferential pressure distortion at the turbine exit. The effects of three circumferential exit pressure distortions on turbine efficiency and pressure ratio, are presented. Circumferential and radial total pressure, total temperature, static pressure, and flow angle distributions at the turbine exit are also presented. Efficiency and total-to-total pressure ratio are shown to have a circumferential variation as high as 13.7 percent (or points of efficiency) and 7.1 percent, respectively. A slight pressure distortion was measured downstream of the first stage nozzle and the distortion increased across subsequent blade rows to a maximum downstream of the second stage rotor for all three plates. A brief discussion of the test facility, model, instrumentation, and test plan is given for completeness.

Gaddis, Stephen W.↗
NASA NTRS1994

Redshift distortions of galaxy correlation functions

To examine how peculiar velocities can affect the two-, three-, and four-point redshift correlation functions, we evaluate volume-average correlations for configurations that emphasize and minimize redshift distortions for four different volume-limited samples from each of the CfA, SSRS, and IRAS redshift catalogs. We present the results as the correlation length r(sub 0) and power index gamma of the two-point correlations, bar-xi(sub 0) = (r(sub 0)/r)(exp gamma), and as the hierarchical amplitudes of the three- and four-point functions, S(sub 3) = bar-xi(sub 3)/bar-xi(exp 2)(sub 2) and S(sub 4) = bar-xi(sub 4)/bar-xi(exp 3)(sub 2). We find a characteristic distortion for bar-xi(sub 2), the slope gamma is flatter and the correlation length is larger in redshift space than in real space; that is, redshift distortions 'move' correlations from small to large scales. At the largest scales (up to 12 Mpc), the extra power in the redshift distribution is compatible with Omega(exp 4/7)/b approximately equal to 1. We estimate Omega(exp 4/7)/b to be 0.53 +/- 0.15, 1.10 +/- 0.16, and 0.84 +/- 0.45 for the CfA, SSRS, and IRAS catalogs. Higher order correlations bar-xi(sub 3) and bar-xi(sub 4) suffer similar redshift distortions but in such a way that, within the accuracy of our ananlysis, the normalized amplitudes S(sub 3) and S(sub 4) are insensitive to this effect. The hierarchical amplitudes S(sub 3) and S(sub 4) are constant as a function of scale between 1 and 12 Mpc and have similar values in all samples and catalogs, S(sub 3) approximately equal to 2 and S(sub 4) approximately equal to 6, despite the fact that bar-xi(sub 2), bar-xi(sub 3), and bar-xi(sub 4) differ from one sample to another by large factors (up to a factor of 4 in bar-xi(sub 2), 8 for bar-xi(sub 3), and 12 for bar-xi(sub 4)). The agreement between the independent estimations of S(sub 3) and S(sub 4) is remarkable given the different criteria in the selection of galaxies and also the difference in the resulting range of densities, luminosities, and locations between samples.

Fry, J. N.↗
NASA NTRS1959

Investigation on the use of a Freely Rotating Rotor at the Cowl Face of a Supersonic Conical Inlet to Reduce Inlet Flow Distortion

An investigation has been made on the use of a freely rotating rotor at the cowl face of a supersonic conical diffuser to determine its effectiveness in reducing inlet flow distortion and the penalty in terms of total-pressure loss imposed by such a device when distortions are negligible. Tests were made with a rotor having an inlet tip diameter of 2.18 inches and a ratio of hub radius to tip radius of 0.52, in conjunction with a conical inlet having a 25 deg semi-vertex cone angle, at a Mach number of 2.1 over an angle-of-attack range of 0 deg to 8 deg. A simplified analysis showing that a supersonic, freely rotating rotor with maximum solidity for noninterference between blades will operate in an undistorted flow with a total-pressure defect of 1 percent or less was experimentally verified. Overall total-pressure distortions of 0.1 to 0.4 and Mach number distortions of 0.4 to 1.4, obtained at 4 deg to 8 deg angle of attack, were reduced about 30 percent and 23 percent, respectively, because of the presence of the rotor, with no measurable total-pressure loss. The rotor increased the peak total-pressure recovery at the simulated combustion chamber 1 1/2 and 3 1/2 percent at 6 deg and 8 deg angles of attack, respectively. This increase is attributed to lower diffusion duct losses as a consequence of a more uniform flow created by the rotor.

Goldberg, Theodore J.↗
NASA NTRS2002

Control of Inflow Distortion in a Scarf Inlet

The scarf inlet has the potential to reduce aircraft inlet noise radiation to the ground by reflecting it into the space above the engine. Without forward motion of the engine, the non-symmetry of the inlet causes inflow distortion which generates noise that is greater than the noise reduction of the scarf. However, acoustic evaluations of aircraft engines are often done on static test stands. A method to reduce inflow distortion by boundary layer suction is proposed and evaluated using a model of a high bypass ratio engine located in an anechoic chamber. The design goal of the flow control system is to make the inflow to the inlet circumferentially uniform and to eliminate reversed flow. This minimizes the inflow distortion and allows for acoustic evaluation of the scarf inlet on a static test stand. The inlet boundary layer suction effectiveness is evaluated both by aerodynamic and by acoustic measurements. Although the design goal is not met, the control system is found to have a beneficial effect on the engine operation, reducing blade stall and speed variation. This is quantified by two acoustic benefits, reduction both of the variability of tone noise and of the low frequency wideband noise due to the inflow distortion. It is felt that a compromise in the manufacture of the control hardware contributes to the inability of the control system to perform as expected from the analysis. The control system with sufficient authority is felt to have the potential to permit reliable acoustic testing in a static configuration of engines with non-symmetric inlets. Because the control system can improve operation of the engine, it may also have the potential to reduce noise and vibration and enhance engine longevity during low speed ground operations in the terminal area.

Gerhold, Carl H.↗
NASA NTRS2010

An Overview of Thermal Distortion Modeling, Analysis, and Model Validation for the JWST ISIM Structure

This paper describes thermal distortion modeling, analysis, and model validation activities completed in support of the design and qualification of the JWST ISIM Structure. An overview of the building blocks approach utilized to develop the structural design and modeling capabilities to meet thermal distortion performance requirements will be provided. This effort culminated in a cryogenic (35 K) distortion test of the flight ISIM Structure hardware, the Cryoset Test that both verified the thermal distortion performance and provided data for validation of the structural models. An overview of the modeling, analysis, and model validation development effort will be discussed, and the results of the Cryoset Test and the subsequent model validation will be described.

Johnston, John↗
NASA NTRS2011

Tone Noise Predictions for a Spacecraft Cabin Ventilation Fan Ingesting Distorted Inflow and the Challenges of Validation

A fan tone noise prediction code has been developed at NASA Glenn Research Center that is capable of estimating duct mode sound power levels for a fan ingesting distorted inflow. This code was used to predict the circumferential and radial mode sound power levels in the inlet and exhaust duct of an axial spacecraft cabin ventilation fan. Noise predictions at fan design rotational speed were generated. Three fan inflow conditions were studied: an undistorted inflow, a circumferentially symmetric inflow distortion pattern (cylindrical rods inserted radially into the flowpath at 15deg, 135deg, and 255deg), and a circumferentially asymmetric inflow distortion pattern (rods located at 15deg, 52deg and 173deg). Noise predictions indicate that tones are produced for the distorted inflow cases that are not present when the fan operates with an undistorted inflow. Experimental data are needed to validate these acoustic predictions, as well as the aerodynamic performance predictions. Given the aerodynamic design of the spacecraft cabin ventilation fan, a mechanical and electrical conceptual design study was conducted. Design features of a fan suitable for obtaining detailed acoustic and aerodynamic measurements needed to validate predictions are discussed.

Koch, L. Danielle↗
NASA NTRS2012

Systems and methods for mirror mounting with minimized distortion

A method for mounting a mirror for use in a telescope includes attaching the mirror to a plurality of adjustable mounts; determining a distortion in the mirror caused by the plurality adjustable mounts, and, if the distortion is determined to be above a predetermined level: adjusting one or more of the adjustable mounts; and determining the distortion in the mirror caused by the adjustable mounts; and in the event the determined distortion is determined to be at or below the predetermined level, rigidizing the adjustable mounts.

Antonille, Scott R.↗