SEARCH · Search NASA
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.
A silicon monolithic multispectral photosensor device is described. Fabrication techniques and preliminary spectral response data are presented. The device is designed to meet small size and weight requirements and to impose a reduced load upon cooling systems in use on satellites.
The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.
PIXTOOLS is software for Silicon Graphics IRIS consisting of thirteen programs plus library for operating on bit-map images. Enables user to create, edit, and save high-resolution images in forms in which displayed on video screens, resize them, and capture them. Eleven programs print information and read and write files. Two offer graphical interfaces. Menus enable manipulation of images and background color and saving of an image screen to file. Written in C.
The paper discusses imaging of Mars at 20 wavelengths in the spectral region from 0.35 to 1.10 microns performed during the 1973 opposition with a photometric imaging system that uses a silicon vidicon tube as the detector. The imaging system and data-reduction procedures are described in detail, and relative reflectance spectra for several small areas in the images are presented along with vidicon images obtained during early phases in the development of the 1973 dust storms. Several anomalous blue brightenings are examined and attributed to ground fog and H2O frost. It is suggested that anomalously large amounts of H2O were pulsed into the atmosphere from the regolith by the storm system. An apparent fading and recession of the north polar hood is noted, surface units revealed in contrast-enhanced ratio images are identified, and the need for higher-spatial-resolution orbital spectroscopy of dark areas is emphasized.
Quality control (QC) is critically important to tristructural-isotropic (TRISO) particle fuels owing to the complexity of and reliance on the fuel form to contain fission products during irradiation. Characterization methods for particle fuel QC have decades of history and have continued to develop as new insights into fuel performance inform revised fuel specifications and as advances in underlying technologies expand the possibilities of what may be characterized. Two relatively new methods for characterization of TRISO fuels have been published in open literature: optical microscopy image analysis for mixed uranium carbide/uranium oxide (UCO) kernel composition analysis and automated grain boundary detection in backscattered electron (BSE) images of the silicon carbide (SiC) layer in TRISO particles for grain size characterization. Suggestions and guidelines for the application of these methods to TRISO fuel qualification are provided in this report.
Five video systems - potentially useful for airborne surveillance of oil spills - were developed, flight tested, and evaluated. The systems are: (1) conventional black and white TV, (2) conventional TV with false color, (3) differential TV, (4) prototype Lunar Surface TV, and (5) field sequential TV. Wavelength and polarization filtering were utilized in all systems. Greatly enhanced detection of oil spills, relative to that possible with the unaided eye, was achieved. The most practical video system is a conventional TV camera with silicon-diode-array image tube, filtered with a Corning 7-54 filter and a polarizer oriented with its principal axis in the horizontal direction. Best contrast between oil and water was achieved when winds and sea states were low. The minimum detectable oil film thickness was about 0.1 micrometer.
The development of an improved capability photo sensor array imager for use in a Viking '75 type facsimile camera is presented. This imager consists of silicon photodiodes and lead sulfide detectors to cover a spectral range from 0.4 to 2.7 microns. An optical design specifying filter configurations and convergence angles is described. Three electronics design approaches: AC-chopped light, DC-dual detector, and DC-single detector, are investigated. Experimental and calculated results are compared whenever possible using breadboard testing and tolerance analysis techniques. Results show that any design used must be forgiving of the relative instability of lead sulfide detectors. A final design using lead sulfide detectors and associated electronics is implemented by fabrication of a hybrid prototype device. Test results of this device show a good agreement with calculated values.
Since the first introduction of charge-coupled devices (CCDs) in 1970, CCDs have been considered for applications related to memories, logic circuits, and the detection of visible radiation. It is pointed out, however, that the mass market orientation of CCD development has left largely untapped the enormous potential of these devices for advanced scientific instrumentation. The present paper has, therefore, the objective to introduce the CCD characteristics to the scientific community, taking into account prospects for further improvement. Attention is given to evaluation criteria, a summary of current CCDs, CCD performance characteristics, absolute calibration tools, quantum efficiency, aspects of charge collection, charge transfer efficiency, read noise, and predictions regarding the characteristics of the next generation of silicon scientific CCD imagers.
We report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility scale solar farm by nm-scale imaging of the local resistance at the Ag/Si interface of c-Si front metallization. Scanning spreading resistance microscopy imaging revealed that the number of point or small area electrical contacts decreased in a degraded cell compared to an unaffected cell, demonstrating the direct root cause of the Rs degradation. The degraded cell shows both a morphological and chemical difference in the screen-printed finger contact compared to the unaffected cell, which likely caused the degradation during the long-term field service. The reduction in electrical contact is likely caused by a structural change: The Ag particles in contact with the Si cell aggregate into bulk Ag, and a highly resistive ceramic oxide is formed in a "belt" shape at the Ag/Si interface. This resistive belt with a thickness of ~1 um blocks the current conduction from cell emitter to the Ag grid. Our results demonstrate an example of the multi-scale characterization approach for understanding degradation mechanisms in photovoltaics.
We report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility scale solar farm by nm-scale imaging of the local resistance at the Ag/Si interface of c-Si cell front metallization. Our previous work showed that the I-V measurement of individual cells demonstrated exclusively the cell Rs degradation, and the "beads pattern" of electroluminescence indicated the degradation at the Ag grid of front metallization. Scanning spreading resistance microscopy (SSRM) imaging, which is based on the contact mode of atomic force microscopy and taken on the cross-sections of Ag/Si contact, revealed the electrical conduction pathway of Ag particles in point or small area contact with Si cell emitter. The SSRM results illustrated that the number of electrical contacts in the degraded cell decreased largely compared with the unaffected cell, demonstrating the direct cause of the Rs degradation. This reduction in electrical contact in the degraded cell could be caused by a structural change in the Ag grid during long-term field service: The Ag particles in contact with Si aggregate into the Ag bulk and a highly resistive ceramic oxide is formed in a "belt" shape at the Ag/Si interface. This resistive belt with a thickness of ~1 m blocks the current conduction from cell emitter to the Ag grid. The degraded cell shows both a morphological and chemical difference in the screen-printed finger contact compared to the unaffected cell, which likely caused the different degradation susceptibility during the long-term field service. Our results demonstrate an example of the multi-scale characterization approach for understanding photovoltaic degradation mechanisms.
Subtopic 01-S1.06 requires mirrors with a diameter of 0.5-2.4 meters, areal density less than 20 kg/sq m, a figure specification of 0.02-0.005 waves root mean square (rms) at 633 nanometers, a surface roughness 0.5-1 nanometers rms, and a midfrequency error of 1.0-2.5 nanometers rms for use in the infrared (IR) to extreme ultra violet (EUV) waveband. Schafer's Phase II objective is to use Silicon Lightweight Mirrors (SLMS), a novel, all-silicon, foam-core, lightweight mirror technology, to build three imaging mirrors for the Next Generation Space Telescope Near Infrared Camera (NIRCam) Engineering Test Unit: M0 (a flat), M2 (a concave sphere) and M3R (an oblate spheroid). The surface figure error specification for the NIRCam imaging mirrors is 8 nanometers rms (0.013 waves rms at 633 nanometers), equivalent to that required for ultraviolet (UV) and EUV mirrors, and this figure must be maintained at the 35 K operational temperature of NGST. The surface roughness required is 30 A rms since NIRCam operates in the visible to infrared (VIS/IR) (0.65-5 microns). We will produce mounts for mirrors M2 and M3R using the complementary thermally matched C/SiC material demonstrated by Schafer under another NASA SBIR, NAS8-98137.
Solid-state, electronically scanned, linear detector arrays are now available which can be used in a pushbroom scan mode imaging system for high-resolution multispectral earth resource survey applications. These arrays provide high performance in the visible to near-IR region. Two performance criteria must be assessed in the choice of a detector array: signal-to-noise ratio and spectral response. Consideration of diffraction limitations shows that optics size cannot be significantly reduced by using very low-noise detectors. The required spectral response for a viable detector array should not have spectral ripples that cause a low-level, but significant, error in the detected effective reflectance of the target.
The fabrication of a photodiode transistor image sensor array in silicon, and tests on individual elements of the array are described along with design for a scanning system for an image sensor array. The spectral response of p-n junctions was used as a technique for studying the optical-absorption edge in silicon. Heterojunction structures of Sb2S3- Si were fabricated and a system for measuring C-V curves on MOS structures was built.
The optical and electronic design of the Halogen Occultation Experiment (Haloe) elevation sun sensor is described. The Haloe instrument is a gas-correlation radiometer now being developed at NASA Langley for the Upper Atmosphere Research Satellite. The system uses a Galilean telescope to form a solar image on a linear silicon photodiode array. The array is a self-scanned monolithic CCD. The addresses of both solar edges imaged on the array are used by the control/pointing system to scan the Haloe science instantaneous field of view (IFOV) across the vertical solar diameter during instrument calibration and then to maintain the science IFOV 4 arcmin below the top edge during the science data occultation event. Vertical resolution of 16 arcsec and a radiometric dynamic range of 100 are achieved at the 700-nm operating wavelength. The design provides for loss of individual photodiode elements without loss of angular tracking capability.
This article describes a single transducer ultrasonic imaging method that eliminates the effect of plate thickness variation in the image. The method thus isolates ultrasonic variations due to material microstructure. The use of this method can result in significant cost savings because the ultrasonic image can be interpreted correctly without the need for machining to achieve precise thickness uniformity during nondestructive evaluations of material development. The method is based on measurement of ultrasonic velocity. Images obtained using the thickness-independent methodology are compared with conventional velocity and c-scan echo peak amplitude images for monolithic ceramic (silicon nitride), metal matrix composite and polymer matrix composite materials. It was found that the thickness-independent ultrasonic images reveal and quantify correctly areas of global microstructural (pore and fiber volume fraction) variation due to the elimination of thickness effects. The thickness-independent ultrasonic imaging method described in this article is currently being commercialized under a cooperative agreement between NASA Lewis Research Center and Sonix, Inc.
The optical and electronic design of the Halogen Occultation Experiment (HALOE) elevation sunsensor is described. This system uses a Galilean telescope to form a solar image on a linear silicon photodiode array. The array is a self-scanned, monolithic charge coupled device. The addresses of both solar edges imaged on the array are used by the control/pointing system to scan the HALOE science instantaneous-field-of-view (IFOV) across the vertical solar diameter during instrument calibration, and then maintain the science IFOV four arcmin below the top edge during the science data occultation event. Vertical resolution of 16 arcsec and a radiometric dynamic range of 100 are achieved at the 0.7 micrometer operating wavelength. The design provides for loss of individual photodiode elements without loss of angular tracking capability. The HALOE instrument is a gas correlation radiometer that is now being developed by NASA Langley Research Center for the Upper Atmospheric Research Satellite.
On many shuttle missions, silicone contamination from unknown sources from within or external to the shuttle payload bay has been a chronic problem plaguing experiment payloads. There is currently a wide range of silicone usage on the shuttle. Silicones are used to coat the shuttle tiles to enhance their ability to shed rain, and over 100 kg of RTV 560 silicone is used to seal white tiles to the shuttle surfaces. Silicones are also used in electronic components, potting compounds, and thermal control blankets. Efforts to date to identify and eliminate the sources of silicone contamination have not been highly successful and have created much controversy. To identify the sources of silicone contamination on the space shuttle, the NASA Lewis Research Center developed a contamination camera. This specially designed pinhole camera utilizes low-Earth-orbit atomic oxygen to develop a picture that identifies sources of silicone contamination on shuttle-launched payloads. The volatile silicone species travel through the aperture of the pinhole camera, and since volatile silicone species lose their hydrocarbon functionalities under atomic oxygen attack, the silicone adheres to the substrate as SiO_x. This glassy deposit should be spatially arranged in the image of the sources of silicone contamination. To view the contamination image, one can use ultrasensitive thickness measurement techniques, such as scanning variable-angle ellipsometry, to map the surface topography of the camera's substrate. The demonstration of a functional contamination camera would resolve the controversial debate concerning the amount and location of contamination sources, would allow corrective actions to be taken, and would demonstrate a useful tool for contamination documentation on future shuttle payloads, with near negligible effect on cost and weight.