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At least 1,441 records · Page 80

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NASA NTRS1992

An optically controlled Ka-band phased array antenna

The design and development of a small, optically controlled phased array antenna suitable for communication satellite applications are discussed. A vertical integration architecture is used which minimizes the size of the array with its associated beamforming network (BFN). The antenna features a four-element linear microstrip array that uses aperture coupling of the antenna elements to the BFN; a modified Wilkinson power divider BFN; and 32 GHz, four-bit monolithic microwave integrated circuit (MMIC) phase shifters in customized quartz packages with corresponding optoelectronic interface circuits (OEIC's) for control signal reception.

Kunath, R. R.↗

NASA NTRS1991

Gain calibrating nonuniform image-array data using only the image data

An algorithm is developed for calibrating the spatial nonuniformity of image-array (CCD-type) detectors. Like other techniques this approach uses multiple, spatially displaced images. In circumstances where high-precision flat fields are not available by other means (i.e., sky flats) this technique is advantageous as it uses the data frames for gain calibration even when the array images extended, nonuniform, sources. Numerical experiments and direct observations with intrinsically uniform and quite nonuniform detectors show that this algorithm is useful when data frames are crowded with sources - circumstance where 'median filtering' flatfielding techniques often fail. The algorithm described is robust and efficiently uses information from multiple data frames to determine pixel gain variations, using visible and IR array observations of extended sources.

Kuhn, J. R.↗

NASA NTRS1991

100-micron array polarimetry from the Kuiper Airborne Observatory - Instrumentation, techniques, and first results

The University of Chicago far-infrared array polarimeter, 'STOKES', is the first multiple-beam polarimeter for far-infrared astronomy. Observations are made from the NASA Kuiper Airborne Observatory. Two orthogonal components of linear polarization are detected simultaneously by corresponding pairs of bolometers in two 32-detector arrays. Novel observing and data-analysis techniques are used to overcome the inherent difficulties of array polarimetry. Results from the first observing flights with the new instrument are reported for the molecular clouds W3 and W51. The measurements show that the magnetic-field structure in both clouds is nonuniform on the scale of 0.5-1.5 pc. This is consistent with molecular line and Zeeman observations that indicate the presence of turbulent velocities and significant small-scale structure. Preliminary results from the second flight series have yielded approximately 40 new measurements in the Sgr A complex. These results indicate that modifications made since the first flights have significantly improved the performance of STOKES.

Platt, S. R.↗

NASA NTRS1991

The Active Sun Telescope Array

The concept of the Active Sun Telescope Array (ASTA) designed as a part of the NASA Orbiting Solar Laboratory is described together with the details of the ASTA instrument package. The ASTA, which will investigate the phenomenology of the solar chromosphere and the corona, consists of six EUV/XUV solar telescopes designed to provide wide field solar images in narrow wavelength bands, high-resolution spectroheliograms, and line profiles of the solar plasma in the temperature range from 10,000 K to 30,000 K. The detectors used in the ASTA are of the multianode multichannel array photon-counting array detector type.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

The structure and development of streamwise vortex arrays embedded in a turbulent boundary layer

The results of an experimental investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer are presented. Measurements of secondary velocity in the crossplane are used to characterize the vortex array structure. Measurements in the crossplane at two streamwise locations characterize the influence of interactions among the vortices on the array structure when the initial spacing between vortices is varied. Evidence of the merging of counter-rotating cores is found in embedded arrays of closely spaced vortices. A model of vortex interaction and development is constructed from the experimental results. This model is based on the structure of the two dimensional Ossen vortex. The decay of vortex circulation due to the merging of the cores is correlated with the crossplane gradient in streamwise vorticity occurring between an embedded vortex and its adjacent counter-rotating neighbors.

Wendt, Bruce J.↗

NASA NTRS1992

Proposed Ka-band array-fed near field Cassegrain system for NASA's Polar Probe Mission

A Ka-band array-fed near-field Cassegrain antenna envisioned for NASA's Solar Probe Mission is the basis of the present spacecraft telecommunications system, which is designed for operation at X-band up/downlink and Ka-band downlink. The hexagonal array employed, which is located at the Cassegrain point of the 0.75-m reflector, encompasses 37 active elements; each of these contains 1/4-W HEMT amplifiers. Relative to a TWTA-based system, this active array feed reduces mass, increases dc power efficiency, enhanced reliability, and reduces volume requirements.

Kellogg, K.↗

NASA NTRS1992

A 5-18 micron array camera for high-background astronomical imaging

A new infrared array camera system using a Hughes/SBRC 58 x 62 pixel hybrid Si:Ga array detector has been successfully applied to high-background 5-18-micron astronomical imaging observations. The off-axis reflective optical system minimizes thermal background loading and produces diffraction-limited images with negligible spatial distortion. The noise equivalent flux density (NEFD) of the camera at 10 microns on the 3.0-m NASA/Infrared Telescope Facility with broadband interference filters and 0.26 arcsec pixel is NEFD = 0.01 Jy/sq rt min per pixel (1sigma), and it operates at a frame rate of 30 Hz with no compromise in observational efficiency. The electronic and optical design of the camera, its photometric characteristics, examples of observational results, and techniques for successful array imaging in a high- background astronomical application are discussed.

Gezari, Daniel Y.↗

NASA NTRS1992

A vertically integrated Ka-band phased array antenna

The design, development, and experimental demonstration of a small phased array antenna suitable for applications on communications satellites are discussed. Each of the vertical layers was optimized for performance, and MMICs on custom carriers were characterized prior to insertion. A vertical integration architecture is used which minimizes the size of the array with its associated beamforming network (BFN). The antenna features a four-element linear microstrip array that uses aperture coupling of the antenna elements to the BFN; a modified Wilkinson power divider BFN; and 32 Ghz, 4-bit MMIC phase shifters on customized alumina carriers. Performance data are presented for all components, and far-field antenna radiation patterns are given.

Kunath, R. R.↗

NASA NTRS1992

Real-time combining of residual carrier array signals using ML weight estimates

A real-time digital signal combining system for use with array feeds is proposed. The combining system attempts to compensate for signal-to-noise ratio (SNR) loss resulting from antenna deformations induced by gravitational and atmospheric effects. The combining weights are obtained directly from the observed residual carrier samples in each channel using a 'sliding-window' implementation of a maximum-likelihood (ML) parameter estimator. It is shown that with averaging times of about 0.1 s, combining loss for a seven-element array can be limited to about 0.1 dB in a realistic operational environment. This result suggests that the real-time combining system proposed here is capable of recovering virtually all of the signal power captured by the array feed, even in the presence of severe wind gusts and similar disturbances.

Vilnrotter, Victor A.↗

NASA NTRS1991

Structural scaling approximations for solar arrays

General scaling rules for a photovoltaic array structure are required in order to compare the effectiveness of different cell technologies. Important evaluation criteria for an array are moment of inertia, resonant frequency of vibrational modes, stiffness against acceleration, and resistance losses in the wiring. Approximate scaling relationships for these parameters for a generic solar array structure are presented.

Landis, Geoffrey A.↗

NASA NTRS1992

High-efficiency, high-output-power antiguide laser diode arrays

Antiguide laser arrays have been fabricated and operated up to peak pulsed powers of 7.7 W in a beam with a full-width at half-maximum in the main lobe of 0.7 deg. Up to 0.7 W of continuous wave power is emitted into a radiation pattern 2.5 times the diffraction limit. By varying the temperature of the array to vary the operating wavelength of the device, the threshold gain condition of the array modes is altered, allowing thermal tuning of the far field of the device.

Mehuys, D.↗

NASA NTRS1991

Design and optimization of a self-deploying PV tent array

A study was performed to design a self-deploying tent shaped PV (photovoltaic) array and optimize the design for maximum specific power. Each structural component of the design was analyzed to determine the size necessary to withstand the various forces it would be subjected to. Through this analysis the component weights were determined. An optimization was performed to determine the array dimensions and blanket geometry which produce the maximum specific power for a given PV blanket. This optimization was performed for both Lunar and Martian environmental conditions. The performance specifications for the array at both locations and with various PV blankets were determined.

Colozza, Anthony J.↗

NASA NTRS1991

The mini-dome Fresnel lens photovoltaic concentrator array - Current program status

Over the last seven years, NASA Lewis, ENTECH, and Boeing have been developing a high-efficiency, lightweight space photovoltaic concentrator array. The authors report the current status of the mini-dome Fresnel lens concentrator program, emphasizing the latest results on the fabrication and testing of a space-qualifiable version of the concentrator lens and panel structure. Calculations indicated that such an array can achieve 300 W/sq m at a specific power of 100 W/kg. The authors describe the current status of component and prototype panel testing and the preliminary development of a flight panel for the Photovoltaic Array Space Power Plus Diagnostics (PASP Plus) flight experiment.

Piszczor, Michael F.↗

NASA NTRS1993

Nonvolatile Array Of Synapses For Neural Network

Elements of array programmed with help of ultraviolet light. A 32 x 32 very-large-scale integrated-circuit array of electronic synapses serves as building-block chip for analog neural-network computer. Synaptic weights stored in nonvolatile manner. Makes information content of array invulnerable to loss of power, and, by eliminating need for circuitry to refresh volatile synaptic memory, makes architecture simpler and more compact.

Tawel, Raoul↗

NASA NTRS1992

The optical very large array and its moon-based version

An Optical Very Large Array (OVLA) is currently in early prototyping stages for ground-based sites, such as Mauna Kea and perhaps the VLT site in Chile. Its concept is also suited for a moon-based interferometer. With a ring of bi-dimensionally mobile telescopes, there is maximal flexibility in the aperture pattern, and no need for delay lines. A circular configuration of many free-flying telescopes, TRIO, is also considered for space interferometers. Finally, the principle of gaseous mirrors may become applicable for moon-based optical arrays. Fifteen years after the first coherent linkage of two optical telescopes, the design of an ambitious imaging array, the OVLA, is now well advanced. Two 1.5 m telescopes have been built and now provide astronomical results. Elements of the OVLA are under construction. Although primarily conceived for ground-based sites, the OVLA structure appears to meet the essential requirements for operation on the Moon.

Labeyrie, Antoine↗

NASA NTRS1993

Output data formatter for the Electronically Scanned Thinned Array Radiometer (ESTAR) instrument

A prototype Output Data Formatter (ODF) for the ESTAR (Electronically Scanned Thinned Array Radiometer) instrument has been designed and tested. It employs programmable logic devices to format and tag correlator data for transmission to Earth. After accepting 170 bits or correlator and error data in parallel, it appends an identification word and then serially passes the data to the Small Explorer Data System (SEDS) for transmission at a maximum rate of greater than 15 Mb/sec. Implemented with two reprogrammable field programmable gate arrays (FPGA's), each contained in a 132-pin plastic pin grid array (PGA) package, the design is cascadeable, fully testable, and low-power.

Chren, William A., Jr.↗

NASA NTRS1992

Monolithic millimeter-wave diode grid frequency multiplier arrays

Monolithic diode frequency multiplier arrays, including barrier-N-N(+) (BNN) doubler, multi-quantum-barrier-varactor (MQBV) tripler, Schottky-quantum-barrier-varactor (SQBV) tripler, and resonant-tunneling-diode (RTD) tripler arrays, have been successfully fabricated with yields between 85 and 99 percent. Frequency doubling and/or tripling have been observed for all the arrays. Output powers of 2.4-2.6 W (eta = 10-18 percent) at 66 GHz with the BNN doubler and 3.8-10 W (eta = 1.7-4 percent) at 99 GHz with the SQBV tripler have been achieved.

Liu, Hong-Xia L.↗

NASA NTRS1992

Developing an Inflatable Solar Array

Viewgraphs describing the development of an inflatable solar array as part of the Inflatable Torus Solar Array Technology (ITSAT) program are presented. Program phases, overall and subsystem designs, and array deployment are addressed.

Malone, Patrick K.↗