SEARCH · Search NASA

Results for “Reflector”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18

All sources NASA NTRS DOE OSTI

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 NTRS1990

Cheap Corner Reflectors For Radar

Corner reflectors for radar constructed easily and inexpensively. Wire mesh on plastic pipe forms retroreflective panels of triangular or square shape. Panels joined by bolts and wingnuts. Overlapping panel edges ensure mutual perpendicularity. Materials for new reflectors found in hardware and building-supply stores. No special skills or tools needed for assembly.

Caro, E. R.↗

NASA NTRS1990

Diffraction Analysis Of Distorted Reflector Antennas

Effects of systematic distortions of surfaces on radiation patterns predicted. Computer program for Diffraction Analysis of Reflector Antennas Subject to Systematic Distortions predicts performance of reflector antennas subject to sinusoidal, thermal, or gravitational distortions. Provides local interpolation algorithm readily applied to nonregular distribution of data. Developed in UNIVAC FORTRAN 77 for UNIVAC computer.

Rahmat-Samii, Yahya↗

NASA NTRS1990

Arc Reflector For Welding Ducts

Arc-light reflector for through-the-torch welding vision system designed expressly for use in welding ducts of small diameter. Cylindrical reflector positioned to reflect light diffusely from welding arc onto nearby surface of workpiece for most advantageous viewing along axis of welding torch.

Gilbert, Jeffrey L.↗

NASA NTRS1989

Unfurlable, continuous-surface reflector concept

Various concepts for large, deployable reflectors were developed and some have flown. In each case the surface material was either a continuous mesh of some sort or an assembly of rigid, continuous-surface facets or petals. Performance issues arise in each case. For mesh, reflectance diminishes with increasing frequency. For rigid sections, seams and relative positioning of the segments have to be dealt with. These two issues prompted the evolution of the concept of an unfurlable, continuous-surface reflector. The concept is described and what is learnt is presented, what is suspected will be learned, and also questions raised yet to be addressed.

Stumm, J. E.↗

NASA NTRS1989

Precision segmented reflector, figure verification sensor

The Precision Segmented Reflector (PSR) program currently under way at the Jet Propulsion Laboratory is a test bed and technology demonstration program designed to develop and study the structural and material technologies required for lightweight, precision segmented reflectors. A Figure Verification Sensor (FVS) which is designed to monitor the active control system of the segments is described, a best fit surface is defined, and an image or wavefront quality of the assembled array of reflecting panels is assessed

Manhart, Paul K.↗

NASA NTRS1990

Dual-shaped offset reflector antenna designs from solutions of the geometrical optics first-order partial differential equations

In obtaining solutions to the first-order nonlinear partial differential equations (PDEs) for synthesizing offset dual-shaped reflectors, it is found that previously observed computational problems can be avoided if the integration of the PDEs is started from an inner projected perimeter and integrated outward rather than starting from an outer projected perimeter and integrating inward. This procedure, however, introduces a new parameter, the main reflector inner perimeter radius p(o), when given a subreflector inner angle 0(o). Furthermore, a desired outer projected perimeter (e.g., a circle) is no longer guaranteed. Stability of the integration is maintained if some of the initial parameters are determined first from an approximate solution to the PDEs. A one-, two-, or three-parameter optimization algorithm can then be used to obtain a best set of parameters yielding a close fit to the desired projected outer rim. Good low cross-polarization mapping functions are also obtained. These methods are illustrated by synthesis of a high-gain offset-shaped Cassegrainian antenna and a low-noise offset-shaped Gregorian antenna.

Galindo-Israel, V.↗

NASA NTRS1989

Active wavefront control challenges of the NASA Large Deployable Reflector (LDR)

The 20-m Large Deployable Reflector will have a segmented primary mirror. Achieving diffraction-limited performance at 50 microns requires correction for the errors of tilt and piston of the primary mirror. This correction can be obtained in two ways, the use of an active primary or a correction at a demagnified pupil of the primary. A critical requirement is the means for measurement of the wavefront error and maintaining phasing during the observation of objects that may be too faint for determining the error. Absolute phasing can only be determined using a cooperative source. Maintenance of phasing can be done with an on-board source. A number of options are being explored as discussed below. The many issues concerning the assessment and control of an active segmented mirror will be addressed with an early construction of the Precision Segmented Reflector testbed.

Meinel, Aden B.↗

NASA NTRS1989

Support trusses for large precision segmented reflectors - Preliminary design and analysis

The Precision Segmented Reflector (PSR) primary structures plan is outlined. Geometries and design considerations for erectable and deployable reflector support structures are discussed. Support truss requirements and goals for the PSR are given, and the results of static and dynamic analyses of a prototype four meter diameter structure are presented. In addition, similar results are presented for two 20-meter diameter support trusses. Implications of the analyses for the PSR program are considered and the formulation and limitations of current PSR finite element models are discussed. It is shown that if the secondary optical system is supported by a simple tripod design, the first six vibration modes are likely to be dominated by the secondary system. The 20-meter diameter support trusses are found to be quite stiff for structures of such large size.

Collins, Timothy J.↗

NASA NTRS1989

Structures technologies for the Precision Segmented Reflector (PSR)

The PSR program is a first step in the development and validation of increasingly more precise and larger size lightweight segmented reflector technology that might ultimately be used in space on projects such as the Large Deployable Reflector (LDR). The LDR is described, and objectives of the PSR are discussed. Requirements for the PSR, including structure dimensions and geometric constraints, mass characteristics, erectable and deployable concepts, truss surface precision, and thermal and dynamic characteristics are discussed along with gravity deflections, secondary support characteristics, and removable members. Analytical development and system- and component-level tests are outlined.

Satter, C. M.↗

NASA NTRS1989

Interpolation solutions for the problem of synthesis of dual-shaped offset reflector antennas

Synthesis of dual-shaped offset reflector antennas to control the exit aperture distribution of amplitude and phase has received considerable attention in recent years. For a given feed illumination and desired aperture field distribution, an exact formulation of the problem of simultaneously synthesizing the shapes of the sub and main reflectors was presented recently by Galindo-Israel et al. (1987) in terms of a set of nonlinear first-order differential equations. In this paper, a numerical approach to solving these equations is discussed which circumvents some of the difficulties encountered by Galindo-Israel et al., particularly for small values of theta.

Jervase, Joseph A.↗

NASA NTRS1990

Analysis of near-field Cassegrain reflector - Plane wave versus element-by-element approach

A near-field Cassegrain reflector (NFCR) is an effective way to magnify a small phased array into a much larger-aperture antenna for limited scan applications. Traditionally the pattern analysis of NFCR is based on a plane wave approach, which simplifies the computation tremendously, but fails to provide design information about the most critical component of the whole antenna system, the feed array. Currently available computers make it possible to calculate the pattern of an NFCR by a more exact element-by-element approach. Each element in the feed array is considered individually, and the diffraction pattern from the subreflector is calculated by the geometrical theory of diffraction (including uniform theories at the shadow boundaries). The field contributions from all elements are superimposed at the curved main reflector surface, and a physical-optics integration is performed to obtain the secondary pattern.

Houshmand, Bijan↗

NASA NTRS1991

Semiconductor Laser With Multilayer Dielectric Reflector

Multilayer dielectric reflector included in proposed surface-emitting, distributed-feedback, grating semiconductor laser (e.g., a GaAlAs device). Contributes to efficiency and output power of laser by reducing amount of light entering substrate, where wasted by absorption. Index of refraction in reflector sublayers alternates between higher and lower value. Higher value less than effective index of refraction of waveguide layer.

Lang, Robert J.↗

NASA NTRS1991

Caustic Singularities Of High-Gain, Dual-Shaped Reflectors

Report presents study of some sources of error in analysis, by geometric theory of diffraction (GTD), of performance of high-gain, dual-shaped antenna reflector. Study probes into underlying analytic causes of singularity, with view toward devising and testing practical methods to avoid problems caused by singularity. Hybrid physical optics (PO) approach used to study near-field spillover or noise-temperature characteristics of high-gain relector antenna efficiently and accurately. Report illustrates this approach and underlying principles by presenting numerical results, for both offset and symmetrical reflector systems, computed by GTD, PO, and PO/GO methods.

Galindo, Victor↗

NASA NTRS1990

Analysis of blended rolled edge reflectors using numerical UTD

The uniform geometrical theory of diffraction (UTD) concept is used to predict the scattered fields in the target zones of compact-range blended rolled-edge reflectors. Since the necessary diffraction coefficients are not known in a closed form, a numerical method to calculate the diffraction coefficients is described. In the numerical method, the problem is reduced to two dimensions, and physical optics line integration is used to compute the diffraction coefficients. Thus, the method is computationally efficient. The method is used to analyze two compact-range reflectors. The results obtained using the numerical UTD show good agreement with the scattered fields obtained using a corrected physical optics surface integration.

Ellingson, Steven W.↗

NASA NTRS1991

The Precision Segmented Reflector program - On-orbit thermal behavior of the Submillimeter Imager and Line Survey telescope

The Precision Segmented Reflector program and the Submillimeter Imager and Line Survey mission are overviewed. The temperature requirements, thermal design and environment, as well as the on-orbit thermal performance of a 3.65-m-diameter passively-cooled submillimeter-wavelength telescope are discussed, and focus is placed on the geometric and thermal mathematical models employed in the study. Attention is given to an inflatable space-rigidized sunshade protecting the primary mirror thermally and the highly elliptical orbit chosen to reduce heat input from the earth. Primary-reflector temperature predictions are shown to indicate that a large spatial gradient can exist and the magnitude of the gradient is a strong function of the telescope pitch angle. It is suggested that the cryostat outer-shell temperature may be further lowered with the introduction of a rectangular shield between a solar array and the cryostat.

Tsuyuki, G.↗

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 NTRS1992

Paraboloidal Reflector With Movable Subreflector

Subreflector of 34-m-diameter paraboloidal radio-antenna reflector tilted and translated to compensate for gravitational distortions of antenna structure. Position and orientation of subreflector adjusted to focus with respect to phase center of radio-frequency feed horn and primary focus of computed paraboloid best fitting gravitationally distorted main paraboloidal reflector. Restores gain lost when antenna aimed at angle other than design optimum elevation.

Katow, Masakazu S.↗