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Strain sensors that can be switched on and off were fabricated from p-channel IGFET on thin filament n-type silicon crystals with silicon dioxide layer sputtered over transistor for passivation. Applications include integration with microelectronic circuits for multiplexing.
The Advanced Software Development Workstation Project, funded by Johnson Space Center, is investigating knowledge-based techniques for software reuse in NASA software development projects. Two prototypes have been demonstrated and a third is now in development. The approach is to build a foundation that provides passive reuse support, add a layer that uses domain-independent programming knowledge, add a layer that supports the acquisition of domain-specific programming knowledge to provide active support, and enhance maintainability and modifiability through an object-oriented approach. The development of new application software would use specification-by-reformulation, based on a cognitive theory of retrieval from very long-term memory in humans, and using an Ada code library and an object base. Current tasks include enhancements to the knowledge representation of Ada packages and abstract data types, extensions to support Ada package instantiation knowledge acquisition, integration with Ada compilers and relational databases, enhancements to the graphical user interface, and demonstration of the system with a NASA contractor-developed trajectory simulation package. Future work will focus on investigating issues involving scale-up and integration.
In SPRAT XI, we proposed that p(sup +)n diffused junction InP solar cells should exhibit a higher conversion efficiency than their n(sup +)p counterparts. This was mainly due to the fact that our p(sup +)n (Cd,S) cell structures consistently showed higher V (sub OC) values than our n(sup +)p (S,Cd) structures. The highest V(sub OC) obtained with the p(sup +)n (Cd,S) cell configuration was 860 mV, as compared to the highest V(sub OC) 840 mV obtained with the n(sup +)p (S,Cd) configuration (AMO, 25 C). In this work, we present the performance results of our most recent thermally diffused cells using the p(sup +)n (Cd,S) structure. We have been able to fabricate cells with V(sub OC) values approaching 880 mV. Our best cell with an unoptimized front contact grid design (GS greater than or equal to 10%) showed a conversion efficiency of 13.4% (AMO, 25 C) without an AR coating layer. The emitter surface was passivated by a -50A P rich oxide. Achievement of such high V(sub OC) values was primarily due to the fabrication of emitter surfaces, having EPD densities as low as 2E2 cm(sup -2) and N(sub a)N(sub d) of about 3E18 cm (sup -3). In addition, our preliminary investigation of p(sup +)n structures seem to suggest that Cd-doped emitter cells are more radiation resistant than Zn-doped emitter cells against both high energy electron and proton irradiation.
Cylindrical (hyperbolic - parabolic Wolter I) mirrors have been electroformed from nickel over an electroless nickel-phosphorous (NiP) plated aluminum mandrel in support of the NASA AXAF-S x-ray spectrometer program. The electroless nickel was diamond turned and polished to achieve a surface finish of 10 angstroms rms or better. Gold was then plated on the nickel alloy after an electrochemical passivation step. Next a heavy layer of pure nickel was plated one millimeter thick with controlled stress at zero using a commercial PID program to form the actual mirror. This shell was removed from the NiP alloy coated mandrel by cryogenic cooling and contraction of the aluminum to release the mirror. It is required that the gold not adhere well to the NiP but all other plated coatings must exhibit good adherence. Four mirrors were fabricated from two mandrels prepared by this method. The area of each part is 0.7 square meters (7.5 square feet).
"Smart" structural components with sensors and/or actuators distributed throughout their volumes made of intraply hybrid composite materials, according to proposal. Strips of hybrid control material interspersed with strips of ordinary (passive) composite material in some layers, providing distributed control capability. For example, near and far edges of plate bent upward by commanding bottom control strips to expand and simultaneously commanding upper control strips to contract.
A distinct boundary between turbulent and non-turbulent regions in a fluid of otherwise constant properties is found in many laboratory and engineering turbulent flows, including jets, mixing layers, boundary layers and wakes. Generally, the flow has mean shear in at least one direction within t he turbulent zone, but the non-turbulent zones have no shear (adjacent laminar shear is a different case, e.g. transition in a boundary layer). There may be purely passive differences between the turbulent and non-turbulent zones, e.g. small variations in temperature or scalar concentration, for which turbulent mixing is an important issue. The boundary has several major characteristics of interest for the present study. Firstly, the boundary advances into the non-turbulent fluid, or in other words, nonturbulent fluid is entrained. Secondly, the change in turbulence properties across the boundary is remarkably abrupt; strong turbulent motions come close to the nonturbulent fluid, promoting entrainment. Thirdly, the boundary is irregular with a continually changing convoluted shape, which produces statistical intermittency. Its shape is contorted at all scales of the turbulent motion.
The passivating front and back window layer of the top cell has been chosen. We have chosen to use InGaAs as the tunnel junction interconnect compound since it is easily degenerately doped. All of the dual junction cell structures were grown on GaAs substrates. Time constraints prevented us from completing the development of the GaAs-on-Ge growth process. Analysis of the I-V and EQE data, and comparison with computer-modeled data, shows that the performance of the dual-junction cell is still being controlled by the bottom cell, in spite of top cell thinning. Further improvement in the dual-junction cell efficiency is possible by thinning the front window.
Interior noise and sonic fatigue are important issues in the development and design of advanced subsonic and supersonic aircraft. Conventional aircraft typically employ passive treatments, such as constrained layer damping and acoustic absorption materials, to reduce the structural response and resulting acoustic levels in the aircraft interior. These techniques require significant addition of mass and only attenuate relatively high frequency noise transmitted through the fuselage. Although structural acoustic coupling is in general very important in the study of aircraft fuselage interior noise, analysis of noise transmission through a panel supported in an infinite rigid baffle (separating two semi-infinite acoustic domains) can be useful in evaluating the effects of active/adaptive materials, complex loading, etc. Recent work has been aimed at developing adaptive and/or active methods of controlling the structural acoustic response of panels to reduce the transmitted noise1. A finite element formulation was recently developed to study the dynamic response of shape memory alloy (SMA) hybrid composite panels (conventional composite panel with embedded SMA fibers) subject to combined acoustic and thermal loads2. Further analysis has been performed to predict the far-field acoustic radiation using the finite element dynamic panel response prediction3. The purpose of the present work is to validate the panel vibration and acoustic radiation prediction methods with baseline experimental results obtained from an isotropic panel, without the effect of SMA.
A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.
Several experiments which have reported a delay of transition are analyzed in terms of the frequencies of the induced disturbances generated by different flow control elements. Two of the experiments employed passive stabilizers in the boundary layer, one leading-edge bluntness, and one employed an active spark discharge in the boundary layer. It is found that the frequencies generated by the various elements lie in the damping region of the associated stability curve. It is concluded that the creation of strong disturbances in the damping region stabilizes the boundary-layer and delays the transition from laminar to turbulent flow.
The ECOSystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) is a thermal infrared imaging multispectral scanner science mission. ECOSTRESS is designed and built by the NASA Jet Propulsion Laboratory and will be deployed on the International Space Station (ISS). ECOSTRESS will measure the water loss from growing leaves and the evaporation from the soil by measuring the temperature of plants and will gather data on the health of the agriculture system on Earth. The ISS orbit will allow ECOSTRESS to take observations at different times during each day over the seasons to provide coverage over the contiguous United States. The ECOSTRESS Thermal Control System (TCS) consists of a combination of active and passive components to maintain the ECOSTRESS components within the allowable flight temperature (AFT) limits. The active thermal control systems include mechanical cryocoolers, heaters and a single-phase pumped fluid loop for Instrument and Payload. The focal plane detector is cooled to 65K by a pair of mechanical cryocoolers and a third mechanical cryocooler cools an intermediate cold shield to 130K. The pumped fluid loop transfers the instrument waste heat to JAXA’s Japanese Exposed Module External Facility (JEM-EF) provided external fluid loop before rejection to space from the ISS radiators. The passive TCS includes multi-layer and single layer insulations, flexible thermal links and coatings on the radiometer. This paper describes the ECOSTRESS instrument TCS architecture, instrument thermal requirements and key design drivers, the top level thermal design and analysis approach, and reports preliminary test results.
The James Webb Space Telescope (JWST) is a large, infrared space telescope that has recently started its science program which will enable breakthroughs in astrophysics and planetary science. Notably, JWST will provide the very first observations of the earliest luminous objects in the universe and start a new era of exoplanet atmospheric characterization. This transformative science is enabled by a 6.6 m telescope that is passively cooled with a 5 layer sunshield. The primary mirror is comprised of 18 controllable, low areal density hexagonal segments, that were aligned and phased relative to each other in orbit using innovative image-based wave front sensing and control algorithms. This revolutionary telescope took more than two decades to develop with a widely distributed team across engineering disciplines. We present an overview of the telescope requirements, architecture, development, superb on-orbit performance, and lessons learned. JWST successfully demonstrates a segmented aperture space telescope and establishes a path to building even larger space telescopes.
The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is a joint NASA-CNES mission to study the Earth s cloud and aerosol layers. The satellite is composed of a primary payload (built by Ball Aerospace) and a spacecraft platform bus (PROTEUS, built by Alcatel Alenia Space). The thermal control subsystem (TCS) for the CALIPSO satellite is a passive design utilizing radiators, multi-layer insulation (MLI) blankets, and both operational and survival surface heaters. The most temperature sensitive component within the satellite is the laser system. During thermal vacuum testing of the integrated satellite, the laser system s operational heaters were found to be inadequate in maintaining the lasers required set point. In response, a solution utilizing the laser system s survival heaters to augment the operational heaters was developed with collaboration between NASA, CNES, Ball Aerospace, and Alcatel-Alenia. The CALIPSO satellite launched from Vandenberg Air Force Base in California on April 26th, 2006. Evaluation of both the platform and payload thermal control systems show they are performing as expected and maintaining the critical elements of the satellite within acceptable limits.
The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is a joint NASA-CNES mission to study the Earth's cloud and aerosol layers. The satellite is composed of a primary payload (built by Ball Aerospace) and a spacecraft platform bus (PROTEUS, built by Alcatel Alenia Space). The thermal control subsystem (TCS) for the CALIPSO satellite is a passive design utilizing radiators, multi-layer insulation (MLI) blankets, and both operational and survival surface heaters. The most temperature sensitive component within the satellite is the laser system. During thermal vacuum testing of the integrated satellite, the laser system's operational heaters were found to be inadequate in maintaining the lasers required set point. In response, a solution utilizing the laser system's survival heaters to augment the operational heaters was developed with collaboration between NASA, CNES, Ball Aerospace, and Alcatel-Alenia. The CALIPSO satellite launched from Vandenberg Air Force Base in California on April 26th, 2006. Evaluation of both the platform and payload thermal control systems show they are performing as expected and maintaining the critical elements of the satellite within acceptable limits.
The unsteady, compressible, thin-layer Navier-Stokes equations are used to numerically study the passive control of steady and unsteady supersonic asymmetric flows around circular and noncircular cones. The main computational scheme of the present study is an implicit upwind, flux-difference splitting, finite-volume scheme. Passive control of flow asymmetry is studied by using a vertical fin in the leeward plane of geometric symmetry and side strakes with and without thickness at different orientations. The study focuses on circular-section cones since they are the most likely section-shapes for strong flow asymmetry. Side-strake passive control is shown to be more efficient and practical than vertical-fin passive control.
Hybrid photoelectrodes, comprised of a light-absorbing semiconductor and a surface-integrated molecular catalyst, are attractive for applications in artificial photosynthesis, since they combine the advantages of broadband semiconductor light absorption with the selectivity of molecular catalysis. A widely used class of hybrid photoelectrodes is based on Si substrates passivated by a thin (<3 nm) layer of silicon oxide, which is commonly prepared by controlled chemical or thermal oxidation, resulting in chemical oxide (ChO) or thermal oxide (ThO) layers, respectively. However, the electrochemical stability of these oxide layers, and the chemical stability of the semiconductor-molecule assembly in hybrid photoelectrodes, are not well understood, with evidence that covalently-bound molecules detach from the oxide surface upon application of cathodic bias. We have examined the intrinsic electrochemical reactivity of silicon oxide layers and how it affects the attachment of molecular monolayers. We determined that the surface of Si|ThO is primarily terminated with hydrophobic siloxane moieties, whereas that of Si|ChO contains a higher concentration of hydrophilic silanol groups. Initial high current densities for Si|ChO under applied bias up to -2 V vs. Ag/AgCl, decrease during repeated cyclic voltammetry scans, due to the consumption of surface-bound water. This is manifested by a reversible wave around -0.5 V in CH 3 CN solution, and a similar pH-dependent wave in water, revealing the pK a of the silanol groups to be ~4. Here, our combined observations support the electrochemically-induced dehydration of the SiO 2 surface, which converts silanol groups to siloxanes and proceeds through an H-atom intermediate that is most likely stabilized by pentavalent Si. We propose that similar reactivity is responsible for the electrochemical loss of alkylsiloxane-attached molecules under cathodic bias, which has important implications for the choice of catalyst attachment strategy in hybrid photoelectrodes.
The microwave approaches for remote sensing of soil moisture centent, snowpack properties, surface water area, and the detection of precipitation over land are discussed. Both active (radar) and passive (radiometry) approaches are considered, and the advantages of microwave sensing are pointed out, including all-weather capability, especially at the longer wavelengths, and greater penetration depth with optical or infrared sensors. Results obtained from ground-based, aircraft, and spacecraft platforms show that microwave systems can monitor the moisture content in the surface soil layer (5 cm thick), and that passive microwave systems can discriminate between light and heavy snowcover, detect the presence of liquid water in the snow, and qualitatively estimate snow water equivalent.
This paper explores the potential of the negatively charged SiN x using plasma charge injection technology to passivate the front textured boron-diffused emitter of n-type Si solar cells. The high-x value single SiN x layer with x ≥ 1.30 (x = N/Si) previously developed for the planarized rear-side passivation of p-type silicon solar cells, with an excellent passivation and charge stability, was found to be unacceptable for the passivation on the front textured boron emitter of n-type cells due to a severe bulk lifetime degradation issue. Therefore, in this study, we investigated a new concept of depositing a dual-x SiN x with a low-x SiN x layer (x~1.01) on top of a high-x SiN x layer (x~1.30) for passivation of the front textured rough surface of boron diffused emitter in n-type cells. Here, the optimized dual-x SiN x stack reveals the promise of charge retention for more than 25 years in field operation as well as excellent passivation of boron-doped emitter without bulk lifetime degradation. N-type cells with the optimized dual-x SiN x after charge injection show comparable cell performance to Al 2 O 3 passivated reference cells. The results of cell-level light stability tests using one-cell minimodules exhibit cell performance decay characteristics similar to the traditional Al 2 O 3 /SiN x passivated reference module.