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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
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 NTRS1989

Analysis and test of a 16-foot radial rib reflector developmental model

Analytical and experimental modal tests were performed to determine the vibrational characteristics of a 16-foot diameter radial rib reflector model. Single rib analyses and experimental tests provided preliminary information relating to the reflector. A finite element model predicted mode shapes and frequencies of the reflector. The analyses correlated well with the experimental tests, verifying the modeling method used. The results indicate that five related, characteristic mode shapes form a group. The frequencies of the modes are determined by the relative phase of the radial ribs.

Birchenough, Shawn A.↗
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 NTRS1989

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

Precision Segmented Reflector (PSR) technology is currently being developed for a range of future applications such as the Large Deployable Reflector. The structures activities at NASA-Langley are outlined in support of the PSR program. Design concepts are explored for erectable and deployable support structures which are envisioned to be the backbone of these precision reflectors. Important functional requirements for the support trusses related to stiffness, mass, and surface accuracy are reviewed. Proposed geometries for these structures and factors motivating the erectable and deployable designs are discussed. Analytical results related to stiffness, dynamic behavior, and surface accuracy are presented and considered in light of the functional requirements. Results are included for both a 4-meter-diameter prototype support truss which is currently being designed as the Test Bed for the PSR technology development program, and for two 20-meter support structures.

Collins, Timothy J.↗
NASA NTRS1990

Aperture taper determination for the half-scale accurate antenna reflector

A simulation is described of a proposed microwave reflectance measurement in which the half scale reflector is used in a compact range type of application. The simulation is used to determine an acceptable aperture taper for the reflector which will allow for accurate measurements. Information on the taper is used in the design of a feed for the reflector.

Lambert, Kevin M.↗
NASA NTRS1990

A soft actuation system for segmented reflector articulation and isolation

Segmented reflectors have been proposed for space based applications such as optical communication and large diameter telescopes. An actuation system for mirrors in a space based segmented mirror array was developed as part of NASA's Precision Segmented Reflector program. The actuation system, called the Articulated Panel Module (APM), provides 3 degrees of freedom mirror articulation, gives isolation from structural motion, and simplifies space assembly of the mirrors to the reflector backup truss. A breadboard of the APM was built and is described.

Agronin, Michael L.↗
NASA NTRS1989

Figure control concepts for segmented reflector telescopes

Control analysis activities related to the development of figure control technologies for large space telescopes with precision segmented actively controlled primary reflectors are reviewed. The Precision Segmented Reflector (PSR) configuration is described along with the development and use of the PSR models. Geometric and dynamic models, characterization of figure estimation errors and optimal sensor placement, and the development of quasi-static and dynamic control concepts are outlined. The structure of a quasi-static controller is presented, that utilizes edge sensor measurements to estimate displacement errors at the actuator level and generates figure correction commands. The second approach considers decentralization of the reflector system at the panel level, while the third considers decentralization at the actuator level.

Boussalis, D.↗
NASA NTRS1990

Single-ended output GaAs/AlGaAs single quantum well laser with a dry-etched corner reflector

GaAs/AlGaAs single quantum well lasers with integrated corner reflectors have been fabricated using chemically assisted ion beam etching. The air-GaAs interface is internally totally reflecting, and no coherent radiation is transmitted through the corner reflector. The corner reflector laser was compared with a conventional Fabry-Perot laser cleaved from the same wafer. An 11-percent reduction in threshold current and a reduction of the far-field angle from 4.4 deg to 0.7 deg was measured.

Hagberg, M.↗
NASA NTRS1991

System Would Keep Telescope Reflector Segments Aligned

Proposed actuation system maintains alignments of reflector segments of large telescope. Sensors measure positions and orientations of segments. Figure-control computer calculates orientation and figure of overall reflector surface from sensor data. Responding to computer output, servocontroller for each actuator corrects piston and tilt errors of each segment. Actuators adjust segments in response to sensed positions. Concept applicable to such large segmented space-based reflectors as those used in communication and in collection of solar energy.

Mettler, Edward↗
NASA NTRS1990

Measured performance of the half-scale accurate antenna reflector

A corrugated horn was designed and fabricated for use as a feed for the half-scale accurate antenna reflector. This feed allows the reflector to be used in a compact range configuration as part of a microwave reflectance measuring system. The horn design is described, and the measured farfield patterns of the horn are presented. The horn was installed at the focus of the reflector, and the nearfield of the antenna was measured. The results of these measurements are presented and discussed with respect to the compact range application.

Lambert, Kevin M.↗
NASA NTRS1991

Designs for the ATDRSS tri-band reflector antenna

Two approaches to design a tri-band reflector antenna for the Advanced TDRSS are examined. Two reflector antenna configurations utilizing frequency selective surfaces for operation in three frequency bands, S, Ku, and Ka, are proposed. Far-field patterns and the antenna feed losses were computed for each configuration. An offset-fed single reflector antenna configuration was adapted for conceptual spacecraft design. CADAM drawings were completed and a 1/13th scale model of the spacecraft was constructed.

Lee, Shung-Wu↗
NASA NTRS1990

The feasibility of solar reflector production from lunar materials for solar power in space

Science Applications International Corporation (SAIC) investigated the feasibility of producing solar reflectors from indigenous lunar materials for solar power production on the moon. First, lunar construction materials and production processes were reviewed, and candidate materials for reflector production were identified. At the same time, lunar environmental conditions were reviewed for their effect on production of concentrators. Next, conceptual designs and fabrication methods were proposed and studied for production of dish concentrators and heliostats. Finally, fabrication testing was performed on small-scale models using earth analogs of lunar materials. Findings from this initial investigation indicate that production of concentrators from lunar materials may be an attractive approach for solar energy production on the moon. Further design and testing are required to determine the best techniques and approaches to optimize this concept. Four materials were identified as having high potential for solar reflector manufacture. These baseline materials were foamed glass, concrete with glass-fiber reinforcement, a glass-fiber/glass-melt composite, and an iron-glass sintered material.

Source record↗
NASA NTRS1991

On the theory of the synthesis of offset dual-shaped reflectors - Case examples

In an earlier paper by Galindo-Israel et al. (1987), the geometrical optics (GO) principles, constraints, and requirements of the dual- and single-offset-shaped reflector synthesis problem were collected and developed into a set of nonlinear first-order PDEs. An extension of the methods by which solutions to the PDEs can be obtained is presented, together with several case examples. These examples are independently analyzed by GO and physical optics diffraction methods. The starting point for the integration over each reflector can be taken on the outer rim, at the center, or at an intermediate point-the intermediate starting point being the more general case. The utility of the speed of this synthesis method is demonstrated. For example, the program utilized completes a synthesis in less than 45 s on a 386/20 personal computer and within a fraction of a second on a mainframe Cray. This makes practical the incorporation of the synthesis into a search algorithm that can optimize one or more parameters of the reflector system. As an example, the optimization of the mapping equations for low cross polarization is discussed.

Galindo-Israel, Victor↗
NASA NTRS1991

Structural verification of an aged composite reflector

A structural verification program applied to qualifying two heritage composite antenna reflectors for flight on the TOPEX satellite is outlined. The verification requirements and an integrated analyses/test approach employed to meet these requirements are described. Structural analysis results and qualification vibration test data are presented and discussed. It was determined that degradation of the composite and bonding materials caused by long-term exposure to an uncontrolled environment had not severely impaired the integrity of the reflector structures. The reflectors were assessed to be structurally adequate for the intended TOPEX application.

Lou, Michael C.↗
NASA NTRS1992

Experimental code verification results for reflector antenna distortion compensation by array feeds

Electronic compensation of reflector surface distortion using array feed with individual amplitude and phase control of the array elements is becoming increasingly attractive because of the recent advances in monolithic microwave integrated circuit (MMIC) technology. An algorithm has been developed previously using the concept of focal plane conjugate field matching in the receive mode and a computer code has been generated that predicts the proper excitation coefficients for the elements of the reflector feed array to compensate the effects of reflector surface distortion. This paper presents the results of an experimental study to verify the above compensation algorithm and in general to demonstrate the effectiveness of the array feed compensation technique.

Zaman, A. J.↗
NASA NTRS1992

Extravehicular activity compatibility evaluation of developmental hardware for assembly and repair of precision reflectors

This report presents results of tests performed in neutral buoyancy by two pressure-suited test subjects to simulate Extravehicular Activity (EVA) tasks associated with the on-orbit construction and repair of a precision reflector spacecraft. Two complete neutral buoyancy assemblies of the test article (tetrahedral truss with three attached reflector panels) were performed. Truss joint hardware, two different panel attachment hardware concepts, and a panel replacement tool were evaluated. The test subjects found the operation and size of the truss joint hardware to be acceptable. Both panel attachment concepts were found to be EVA compatible, although one concept was judged by the test subjects to be considerably easier to operate. The average time to install a panel from a position within arm's reach of the test subjects was 1 min 14 sec. The panel replacement tool was used successfully to demonstrate the removal and replacement of a damaged reflector panel in 10 min 25 sec.

Heard, Walter L., Jr.↗
NASA NTRS1992

Composite materials for precision space reflector panels

One of the critical technology needs of large precision reflectors for future astrophysical and optical communications satellites lies in the area of structural materials. Results from a materials research and development program at NASA Langley Research Center to provide materials for these reflector applications are discussed. Advanced materials that meet the reflector panel requirements are identified, and thermal, mechanical and durability properties of candidate materials after exposure to simulated space environments are compared. A parabolic, graphite-phenolic honeycomb composite panel having a surface accuracy of 70.8 microinches rms and an areal weight of 1.17 lbm/sq ft was fabricated with T50/ERL1962 facesheets, a PAEI thermoplastic surface film, and Al and SiO(x) coatings.

Tompkins, Stephen S.↗