SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Test results obtained have confirmed the practicality of the solid state electro-optic filters as an optical control element in a television system. Neutral-density control range in excess of 1000:1 has been obtained on sample filters. Test results, measurements in a complete camera system, discussions of problem areas, analytical comparisons, and recommendations for future investigations are included.
Research on metal-barrier-metal structures is reviewed. Topics discussed include: demonstration of antenna coupling and rectification characteristics with high resistance evaporated structures at a wavelength of 10 microns; application of these devices to coherent conversion of laser radiation and infrared and optical circuit elements; and comparison of the point-contact type of diode structure and the newly developed photolithographic structures.
Two dimensional digital computers and computer devices operate in parallel on rectangular arrays of digital radiant energy optical signal elements which are arranged in ordered rows and columns. Logic gate devices receive two input arrays and provide an output array having digital states dependent only on the digital states of the signal elements of the two input arrays at corresponding row and column positions. The logic devices include an array of photoconductors responsive to at least one of the input arrays for either selectively accelerating electrons to a phosphor output surface, applying potentials to an electroluminescent output layer, exciting an array of discrete radiant energy sources, or exciting a liquid crystal to influence crystal transparency or reflectivity.
Initial work was concerned with determining whether the radiation emitted from a laser source could be sufficiently collimated to provide a suitable source for a nephelometer-type instrument. It was necessary to develop a standard scatterer that could be used to evaluate the performance of a nephelometer. The possible use of a gallium arsenide diode as a radiation source also was investigated. The first of these utilized a single lens to focus the light scattered from a target onto a ring detector. The second configuration used reflecting and refracting axicons as optical-system elements. The work performed in each of these areas is described.
The results of measurements made on a fully integrated optic RF spectrum analyzer (IOSA) are reported. The performance of the device acousto-optic bandwidth, single-tone RF resolution, two-tone RF resolution, single-tone dynamic range, two-tone dynamic range, and single-tone RF response are presented. The device parameters that control device performance are analyzed. These results demonstrate the viability of the IOSA for real time spectrum analysis of pulsed and CW RF signals. Improvements of RF bandwidth resolution can be obtained by the use of larger collimated optical beams which requires larger optical lens elements, and hence, larger crystals.
Ultraviolet spectra of supernova remnants obtained with the IUE satellite provide unique information concerning the shock conditions and elemental abundances in the optically bright filaments. High temperature species such as N V provide diagnostics for shock velocities above 100 k/s, and strong lines of carbon and silicon in the IUE spectral range make it possible to study the destruction of refractory grains in shocked interstellar gas. Observations of a nonradiative shock at the edge of the Cygnus Loop provide constraints on the physics of the shock front itself. Most of the very young remnants whose optical spectra show anomalous elemental abundances are too highly reddened for IUE observations, but extensive observations of the Crab Nebula and a spectrum of the supernova remnant in NGC 4449 yield carbon to oxygen ratios from which the mass of the progenitor may be estimated.
The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measure was about 8 s under a read beam intensity of 0.7 mW/sq cm with the grating periodicity being 0.63 microns. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to about 10 mW/sq cm and 4 microns, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements, for optical computing. In addition, the results suggest that the lifetime is sensitive to residual imperfections in the crystal.
Vacuum gas/tungsten-arc vapor-deposition process yields highly reflective, smooth films reproducing contours of surfaces on which deposited. Rate of deposition controlled precisely, and surface texture varied. Capable of deposition at rates double those of standard sputtering. Useful in making thin metallic coats to serve as electrical conductors, radio reflectors or antenna elements, or optical mirrors of partial or ultrahigh reflectivity, and in making semiconductor devices.
The aim of the project was to explore, define, and assess the possibilities of optical distributed sensing for feedback control. This type of sensor, which may have some impacts in the dynamic control of deformable structures and the monitoring of small displacements, can be divided into data acquisition, data processing, and control design. Analogue optical techniques, because they are noninvasive and afford massive parallelism may play a significant role in the acquisition and the preprocessing of the data for such a sensor. Assessing these possibilities was the aim of the first stage of this project. The scope of the proposed research was limited to: (1) the characterization of photorefractive resonators and the assessment of their possible use as a distributed optical processing element; and (2) the design of a control system utilizing signals from distributed sensors. The results include a numerical and experimental study of the resonator below threshold, an experimental study of the effect of the resonator's transverse confinement on its dynamics above threshold, a numerical study of the resonator above threshold using a modal expansion approach, and the experimental test of this model. A detailed account of each investigation, including methodology and analysis of the results are also included along with reprints of published and submitted papers.
The concept of two-stage optics, developed under a program to enhance the performance, lower the cost, and increase the reliability of the 20-m Large Deployable Telescope, is examined. The concept permits the large primary mirror to remain as deployed or as space-assembled, with phasing and subsequent control of the system done by a small fully assembled optical active element placed at an exit pupil. The technique is being applied to correction of the fabrication/testing error in the Hubble Space Telescope primary mirror. The advantages offered by this concept for very large space telescopes are discussed.
Preliminary experimental results on systems designed to demonstrate sensor operation in regenerative food production and crew air supply applications are presented. The systems use conventional fibers and sources in conjunction with custom wavelength division multiplexers in their optical signal processing sections and nonstandard porous optical fibers in the optical sensing elements. It is considered to be possible to create practical sensors for life-support system applications, and particularly, in regenerative food production environments, based on based on reversible sensors for oxygen, carbon monoxide, and humidity.
Bayesian a priori and a posteriori probability densities are employed to determine asteroid orbital elements from optical astrometric observations. For near-earth asteroids and Jupiter Trojans, the two-body approximation can yield grossly erroneous uncertainty estimates because of the scattering effect of close planetary encounters or prolonged weak planetary perturbations. For main-belt asteroids, the two-body approximation works efficiently, from which it is inferred that, although the ephemeris must be computed from an integrated orbit, only approximate partial derivatives are needed to attain sufficient accuracy in predicting ephemeris uncertainties. The semimajor and semiminor axes of the 2D 1-sigma sky-plane uncertainty ellipse during the years 1993 to 2005 in the many-body and two-body linear approximations are shown.
The objective of the Fourth Annual Conference on Advances in Smart Materials for Aerospace Applications was to provide a forum for technical dialogue on numerous topics in the area of smart materials. The proceedings presented herein represent the technical contributions of the participants of the workshop. Topics addressed include shape memory alloys, ferroelectrics, fiber optics, finite element simulation, and active control.
STIS has two MAMA detectors systems with distinctly different tube configurations. The first (designated BAND 1) has an opaque CsI photocathode deposited on the microchannel plate (MCP) providing wavelength coverage from 1150A to 1700A. The other MAMA (designated BAND 2) has a semitransparent CS2Te photocathode deposited on the faceplate in close proximity to the input of the MCP. It covers the 1650A to 3100A bandpass and serves as a backup for the short wavelength detector. Laboratory test data indicate that both of these detectors have good sensitivity, have good uniformity and provide stable response, making each capable of collecting data with a signal-to-noise ratio in excess of 100 per Space Telescope Imaging Spectrograph (STIS) optical resolution element. Over a multiyear development effort, a substantial body of laboratory test data (more than 6 GBytes spanning more than 6 years of collection) has accumulated on more than a dozen fabricated tubes. These tests even included a few destructive evaluations to examine the limitations and operating life. In addition, analyses where conducted regarding impact caused by the specified electronic tolerances and expected changes in the Hubble Space Telescope (HST) thermal environment. Perhaps the simplest test of stability is to collect a sequence of images, each with a uniform illumination, and use these individual "flat fields" to remove the pixel-to-pixel sensitivity in the other flat fields. These sequences typically spanned 3-5 weeks of time. The detectors are very stable, allowing the pixel-to-pixel sensitivity to be removed with good precision. The STIS specification for stability is 1% (sufficient for data with a S/N = 100) over a 1 week period and 2% over 30 days. All Engineering Model Units as well as Flight Detectors tested exceeded this specification.
Spatial Light Modulators (SLMs) are critical elements in optical processing systems used for imaging, displaying, data storage, communications, and other applications. By taking advantage of the natural properties of light beams, the devices process information at speeds unattainable by human operators and most machines, with high-resolution results.Boulder Nonlinear Systems, Inc., is one of the world s foremost SLM manufacturers. Applications of this technology are briefly described.
Systems and techniques for suppressing the carrier signal using an optical delay element and an electrical interferometer in an opto-electronic noise suppression module.
NASA's Technology Readiness Level (TRL)-6 is documented for the James Webb Space Telescope (JWST) Wavefront Sensing and Control (WFSC) subsystem. The WFSC subsystem is needed to align the Optical Telescope Element (OTE) after all deployments have occurred, and achieves that requirement through a robust commissioning sequence consisting of unique commissioning algorithms, all of which are part of the WFSC algorithm suite. This paper identifies the technology need, algorithm heritage, describes the finished TRL-6 design platform, and summarizes the TRL-6 test results and compliance. Additionally, the performance requirements needed to satisfy JWST science goals as well as the criterion that relate to the TRL-6 Testbed Telescope (TBT) performance requirements are discussed
The James Webb Space Telescope (JWST) consists of an infrared-optimized Optical Telescope Element (OTE) that is cooled down to 40 degrees Kelvin. A second adjacent component to the OTE is the Integrated Science Instrument Module, or ISIM. This module includes the electronic compartment, which provides the mounting surfaces and ambient thermally controlled environment for the instrument control electronics. Dissipating the 200 watts generated from the ISIM structure away from the OTE is of paramount importance so that the spacecraft's own heat does not interfere with the infrared light detected from distant cosmic sources. This technical challenge is overcome by a thermal subsystem unit that provides passive cooling to the ISIM control electronics. The proposed design of this thermal radiator consists of a lightweight structure made out of composite materials and low-emittance metal coatings. In this paper, we will present characterizations of the coating emittance, bidirectional reflectance, and mechanical structure design that will affect the performance of this passive cooling system.