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Results for “reflector accuracy”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Electromagnetic analysis for large reflector antennas

A comparison is made between the measured E and H plane patterns of the 35 GHz offset paraboloidal reflector and the calculated patterns for the same reflector using the 200 points to describe the surface. The accuracy of the computer prediction is quite good considering that the only description of the surface was the coordinates of a finite number of points on the reflector. The results indicate the possibility of acceptable accuracy in the prediction of electromagnetic performance for arbitrarily distorted reflectors using the coordinates of a practical number of measured points. An optimization of the number and distribution of points, and experimental verification for a distorted reflector are planned.

Bailey, M. C.↗
NASA NTRS2011

The Effect of Boundary Support and Reflector Dimensions on Inflatable Parabolic Antenna Performance

For parabolic antennas with sufficient surface accuracy, more power can be radiated with a larger aperture size. This paper explores the performance of antennas of various size and reflector depth. The particular focus is on a large inflatable elastic antenna reflector that is supported about its perimeter by a set of elastic tendons and is subjected to a constant hydrostatic pressure. The surface accuracy of the antenna is measured by an RMS calculation, while the reflector phase error component of the efficiency is determined by computing the power density at boresight. In the analysis, the calculation of antenna efficiency is not based on the Ruze Equation. Hence, no assumption regarding the distribution of the reflector surface distortions is presumed. The reflector surface is modeled as an isotropic elastic membrane using a linear stress-strain constitutive relation. Three types of antenna reflector construction are considered: one molded to an ideal parabolic form and two different flat panel design patterns. The flat panel surfaces are constructed by seaming together panels in a manner that the desired parabolic shape is approximately attained after pressurization. Numerical solutions of the model problem are calculated under a variety of conditions in order to estimate the accuracy and efficiency of these antenna systems. In the case of the flat panel constructions, several different cutting patterns are analyzed in order to determine an optimal cutting strategy.

Coleman, Michael J.↗
NASA NTRS1979

Study of advanced sunflower precision deployable antenna

The maximum deployed diameter stowable in shuttle was determined for the original concept and for new more efficient concepts. Estimates of weight, surface accuracy and cost were made for the various configurations. Five critical technologies were identified which would be required to manufacture large solid deployable reflectors. These technologies are concerned with surface accuracy improvement and verification.

Giebler, M. M.↗
NASA NTRS1987

Experimental evaluation of the performance of pulsed two-color laser-ranging systems

Two-color laser-ranging systems can be used to estimate the atmospheric delay by measuring the difference in propagation times between two optical pulses transmitted at different wavelengths. This paper describes horizontal-path ranging experiments that were conducted using flat diffuse targets and cube-corner reflector arrays. Measurements of the timing accuracy of the cross-correlation estimator, atmospheric delay, received pulse shapes, and signal power spectra are presented. The results are in general agreement with theory and indicate that target speckle can be the dominant noise source when the target is small and is located far from the ranging system or when the target consists of a small number of cube-corner reflectors.

Im, Kwaifong E.↗
NASA NTRS1991

A fiber-coupled heterodyne interferometric displacement sensor

Space-based interferometers and large segmented reflectors will require precision metrology with nanometer accuracy for active control systems. This paper summarizes an experimental study of an optical heterodyne interferometer with resolution of about 3 nm. Optical signals are carried to and from the interferometer by optical fibers to avoid thermally loading the reflector panels. Heterodyne detection provides far greater precision than does traditional interferometry.

Nerheim, Noble↗
NASA NTRS1980

Preliminary design of large reflectors with flat facets

A concept for approximating curved antenna surfaces using flat facets is discussed. A preliminary design technique for determining the size of the reflector surface facets necessary to meet antenna surface accuracy requirements is presented. A proposed large Microwave Radiometer Satellite is selected as an application, and the far field electromagnetic response of a faceted reflector surface is compared with that from a spherical reflector surface.

Agrawal, P. K.↗
NASA NTRS1980

FY-79 - LSST antenna technology development

The development of technology needed to design, fabricate, transport, and deploy large antenna systems is reported. Accomplishments include: (1) development of scenarios for near term missions in communications, microwave radiometry, and radio astronomy; (2) conceptual designs for critical components of a hoop/column reflector; (3) development of a surface accuracy measurement system; and (4) development of electromagnetic analysis methods for large aperture antennas.

Campbell, T. G.↗
NASA NTRS1981

Preliminary design of large reflectors with flat facets

A concept for approximating curved antenna surfaces using flat facets is discussed. A preliminary design technique for determining the size of the reflector surface facets necessary to meet antenna surface accuracy requirements is presented. A proposed large microwave radiometer satellite (MRS) is selected as an application, and the far-field electromagnetic response of a faceted reflector surface is compared with that from a spherical reflector surface.

Agrawal, P. K.↗
NASA NTRS1990

A new fabrication method for precision antenna reflectors for space flight and ground test

The use of higher frequencies on communications satellites has led to the requirement for increasingly precise antenna reflectors for use in space. Typical industry fabrication methods for space antenna reflectors employ successive molding techniques for reflector face sheets and a final fit-up to a master mold in order to achieve the required accuracies. However, new missions at much higher frequencies will require greater accuracies than may be achievable using these present methods. A new approach for the fabrication of ground-test antenna reflectors is to machine the reflective surface into a stainless steel and fiberglass composite structure. A 2.7-m diameter ground-test antenna reflector fabricated using this method has an accuracy of better than 0.013 mm (0.0005 in.) rms. A similar design concept for a solid surface reflector for use on spacecraft would involve fabrication in a similar manner but using space-qualified materials. This report describes the design, analysis, and fabrication of the 2.7-m-diameter precision antenna reflector for antenna ground test and the extension of this technology to precision space antenna reflectors.

Sharp, G. Richard↗
NASA NTRS1981

Techniques for prediction of large nonanalytic reflector antenna performance

Projected spacecraft missions for communications, radio astronomy and earth observations indicate a need for very large (on the order of 100 meters) space deployable or erectable antennas. This paper discusses a numerical method of analyzing reflector characteristics which is applicable to large reflector antennas whose surfaces are subject to mechanical and thermal distortions as well as fabrication and deployment errors. A technique of describing nonanalytic surface configurations by a finite number of known (measured) points was successfully applied in a computer model to predict the RF radiation pattern of a reflector using aperture plane integration techniques. The accuracy of the results is shown to be both a function of the number of measured points used and of their distribution.

Moskowitz, S. M.↗
NASA NTRS1983

Antenna technology for orbital Very Long Baseline Interferometry (VLBI)

Since it is not economically feasible to construct steerable antennas much larger than 100 meters on Earth (400 meters for fixed telescopes), radio interferometry became a very useful technique for high resolution astronomy observations of quasars, galactic nuclei, and interstellar hydroxyl (OH) and water vapor (H2O) masers. The subsystems necessary to do the space VLBI experiment appear are available but require space qualifications. There are several 50-meter antenna concepts that could be used. Certainly there are problems to be solved. Feed positioning with respect to reflector, pointing such a large structure to accuracy indicated, and integration into the Shuttle control system are all significant engineering challenges. However, there are no problems that are insurmountable in the latter part of this decade.

Hamilton, E. 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 NTRS2021

Passive Ground-based Optical Techniques for Monitoring the On-Orbit ICESat-2 Altimeter Geolocation and Footprint Diameter

NASA launched its second Earth observing laser altimeter in 2018 with mission objectives of studying the changes in our climate by monitoring global elevations, particularly in the polar regions. Since the mission is focused on generating accurate elevations and elevation change, the geolocation (or geodetic position) of the measurements are of upmost importance to each of the scientific disciplines supported by these observations. Geolocation validation is required to ensure that the mission is meeting its objectives with the appropriate level of geolocation accuracy. One validation technique uses small optical reflectors placed in a specific pattern along one or more satellite ground-tracks. The optics provide a unique signal back to the satellite that can be used to compare the geolocation of these returns in the data to the known position on the surface. Results of the position comparison indicate the measurement locations are accurate to within 3.5 m with a standard deviation of 1.6 m. They also provide a method for determining a representative footprint diameter using geometric analysis, which resulted in an average value of 10.9 m +- 2.1 m.

ICESat-2↗
NASA NTRS1988

Advanced composite materials for precision segmented reflectors

The objective in the NASA Precision Segmented Reflector (PSR) project is to develop new composite material concepts for highly stable and durable reflectors with precision surfaces. The project focuses on alternate material concepts such as the development of new low coefficient of thermal expansion resins as matrices for graphite fiber reinforced composites, quartz fiber reinforced epoxies, and graphite reinforced glass. Low residual stress fabrication methods will be developed. When coupon specimens of these new material concepts have demonstrated the required surface accuracies and resistance to thermal distortion and microcracking, reflector panels will be fabricated and tested in simulated space environments. An important part of the program is the analytical modeling of environmental stability of these new composite materials concepts through constitutive equation development, modeling of microdamage in the composite matrix, and prediction of long term stability (including viscoelasticity). These analyses include both closed form and finite element solutions at the micro and macro levels.

Stein, Bland A.↗
NASA NTRS2012

Membrane Shell Reflector Segment Antenna

The mesh reflector is the only type of large, in-space deployable antenna that has successfully flown in space. However, state-of-the-art large deployable mesh antenna systems are RF-frequency-limited by both global shape accuracy and local surface quality. The limitations of mesh reflectors stem from two factors. First, at higher frequencies, the porosity and surface roughness of the mesh results in loss and scattering of the signal. Second, the mesh material does not have any bending stiffness and thus cannot be formed into true parabolic (or other desired) shapes. To advance the deployable reflector technology at high RF frequencies from the current state-of-the-art, significant improvements need to be made in three major aspects: a high-stability and highprecision deployable truss; a continuously curved RF reflecting surface (the function of the surface as well as its first derivative are both continuous); and the RF reflecting surface should be made of a continuous material. To meet these three requirements, the Membrane Shell Reflector Segment (MSRS) antenna was developed.

Fang, Houfei↗
NASA NTRS1978

On space deployable antennas and electronics: Plans and programs

Technology plans are presented for developing deployable reflectors having diameters of 30 to 300 meters and surface accuracies of several millimeters for L and X band applications, as well as for the electronic subsystems required for such large structures. An electromagnetic analysis method for predicting the radio frequency performance of large reflectors involves projecting field points onto an aperture plane. The data points in the aperture plane are quantized to produce contours of constant phase and amplitude. Far field patterns are then calculated using reduced computer storage.

Campbell, T. G.↗
NASA NTRS1982

Measurement of losses of mesh membrane material for reflector applications with an S-band radiometer

The spatial resolution, the frequency of revisits, and the accuracy requirements for the detection of Earth surface parameters from space force the satellite designers to consider large space structures for microwaves. Some Earth surface parameters are only detectable with radiometers. Because the large reflectors should be much lighter than solid and deployable reflectors, mesh membrane material is considered to be used as the reflector. It is essential to determine the emissivity of the reflecting material even when close to zero to estimate the accuracy of the radiometer measurement. An existing S-band radiometer was used to determine the loss of a 1 sq m pretensioned mesh first in a field experiment and later in a well shielded laboratory set-up. The models for retrieving the emissivity of the mesh are described in detail and the equivalent losses for different mesh positions were calculated.

Blume, H. J. C.↗