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At least 289 records · Page 16

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NASA NTRS1986

Development of flight ready fifty-micron-thick silicon solar cell array module technology

The development of ultrathin silicon solar cell array modules from initial design to flight testing is discussed. Three 80-cell modules were subjected to the thermal soak test, the LEO thermal cycle test, and the solar array flight experiment, and six 48-cell welded modules were evaluated in the geosynchronous orbit thermal cycle test. It is observed that the electrical performance of the modules was not affected by the different environmental conditions. The automatic assembly of the cell modules, in particular the welding and solar cell glassing operation, is described. The specific power capabilities of Kapton, Kapton-Kevlar-Kapton, Kapton-graphite-Kapton, and Kapton-graphite-aluminum honeycomb-graphite solar array designs are assessed.

Patterson, R. E.↗

NASA NTRS1985

The block program approach to photovoltaic module development

A series of photovoltaic module development activities, designated Blocks I through V, used increasingly refined requirements together with extensive testing and failure analysis to assist industry in developing the most advanced modules possible. The block program approach is described and the design details are given for all modules developed, highlighting the blockwise improvements. The success of this approach is demonstrated by the fact that most design details of the Block V modules have been adopted internationally. Instrumental to this success have been the steady improvements in design and test specifications that have guided module development. The experience gained since development of the Block-V specification is being incorporated into a Block VI Design and Test Specification, which includes upgraded and revised application-specific requirements. Highlights of this Block VI specification are also described.

Smokler, M. I.↗

NASA NTRS1987

Solar modulation of the cosmic radiation in the heliosphere

Changes in the solar modulation of galactic and anomalous component cosmic rays reflect changes in the structure and magnetic topology of the interplanetary medium. Therefore, to the extent that the modulation process is understood, the cosmic rays can be used as a probe of the medium to infer the extent and structure of the heliosphere in regions not directly sampled by spacecraft. The challenge to modulation theory and observation has been to determine which properties of the solar wind are most important for producing the observed modulation. Significant progress has been made in answering this question during the last solar cycle using observations from spacecraft at radii to 40 AU from the Sun and at latitudes up to 30 degrees with respect to the ecliptic. A brief summary of new results and observations (with specific attention to the STIP intervals XV-XIX) will be presented to illustrate the present state of our understanding of the relation between the solar wind and interplanetary magnetic field and the modulations of the cosmic radiation.

Mckibben, R. B.↗

NASA NTRS1989

Photovoltaic-Driven Multiple-Quantum-Well Modulator

Proposed high-performance spatial light modulator consists of multiple-quantum-well, strain-layer superlattice similar to one described in accompanying article, "Strain-Layer-Superlattice Light Modulator" (NPO-16915). Device differs from other one, operates in transmission rather than in resonant reflection and therefore includes only one stack of GaAs/InAs layers having total thickness less than penetration depth (1 to 2 micrometer) of optical modulating signal. Alternating, semitransparent semiconductor layers contain space-charge barriers forming quantum wells. Modulating light (with photon energy greater than semiconductor band gap) induces photovoltaic action, which affects transmission of modulated light (having photon energy less than band gap).

Maserjian, Joseph↗

NASA NTRS1989

Encapsulants And Corrosion In Photovoltaic Modules

Paper reports studies of effects of moisture on photovoltaic modules, presenting data useful in further quantitative studies of such phenomena. Measured data used in computer simulation of two-dimensional conduction to analyze ionic-conduction characteristics of PVB- and EVA-encapsulated modules. Notes encapsulant plays important role in electrochemical processes in photovoltaic module. Indicates how variations in design parameters affect levels of leakage currents in modules. Points out likely leakage-current paths in modules at various temperatures and humidities. Compares results of field and laboratory tests of same specimens and notes greater severity of outdoor environment.

Mon, Gordon R.↗

NASA NTRS1989

A low-loss linear analog phase modulator for 8415 MHz transponder application

A breadboard single-section low-loss analog phase modulator with good thermal stability for a spacecraft transponder application has been analyzed, fabricated, and evaluated. A linear phase shift of 70 degrees with a linearity tolerance of plus or minus 7 percent was measured for this modulator from 8257 to 8634 MHz over the temperature range -20 C to 75 C. The measured insertion loss and the static delay variation with temperature were within 2 plus or minus 0.3 dB and 0.16 ps/C, respectively. Four sections will be cascaded to provide the X-band (8415 MHz) phase modulator. The generic modulator design can also be utilized at 7950 to 8075 MHz followed by X4 multiplication to provide modulation of a Ka-band downlink signal.

Mysoor, N.↗

NASA NTRS1989

A multipurpose digital modulator

The theoretical basis and hardware implementation of a versatile device which uses digital signal-processing methods to achieve signal modulation are reported. The carrier-modulation process is formulated as a simple quadrature equation; a generalized description of the signal constellation to be processed is derived; the pulse-shaping scheme is explained; and the system architecture is described in detail and illustrated with diagrams. Experimental results obtained with a breadboard transmitter based on this modulation technique are presented in extensive graphs. The power spectra and eye diagrams generated for different QPSK, 8PSK, and MSK modulation schemes are shown to be in good agreement with theoretical predictions. It is suggested that this modulator could be readily implemented in VLSI and mass produced.

Davarian, Faramaz↗

NASA NTRS1988

Electromigration in thin-film photovoltaic module metallization systems

Electromigration as a possible thin-film module failure mechanism was investigated using several specially made, fully aluminized thin-film photovoltaic (TF-PV) modules. The effect of electromigration, as determined experimentally by measuring increases in electrical resistance across scribe lines, can be expressed as the product of a damage function, which correlates degradation rate with operating conditions such as current density and temperature, and a susceptibility function, which is defined by module design parameters, particularly aluminum purity and the configuration of the intercell region. Experimental measurements and derived acceleration factors suggest that open-circuit failure resulting from electromigration should not be a serious problem in present state-of-the-art TF-PV modules. Nevertheless, significant intercell resistance increases can result from long-term electromigration exposure, especially in future high-efficiency modules. The problem can be alleviated, however, by appropriate metallization applications and/or proper design of the intercell region.

Wen, L.↗

NASA NTRS1988

Electrical isolation design and electrochemical corrosion in thin-film photovoltaic modules

The development of a proposed wet insulation-resistance qualification test specification for production-line modules is presented. Laboratory research directed toward understanding and eliminating problems associated with electrical isolation of thin-film photovoltaic module circuitry is presented. Test results serve to measure module field life as limited by electrochemical corrosion degradation mechanisms. Current module-level research covering encapsulant voltage withstand capability is also described, and suggestions for improving module electrical isolation are offered.

Sugimura, R. S.↗

NASA NTRS1991

Utilization of common pressurized modules on the Space Station Freedom

During the preliminary design review of Space Station Freedom elements and subsystems, it was shown that reductions of cost, weight, and on-orbit integration and verification would be necessary in order to meet program constraints, particularly nominal Orbiter payload launch capability. At that time, the Baseline station consisted of four resource nodes and two 44 ft modules. In this study, the viability of a common module which maintains crew and payload accommodation is assessed. The size, transportation, and orientation of modules and the accommodation of system racks and user experiments are considered and compared to baseline. Based on available weight estimates, a module pattern consisting of six 28 ft. common elements with three radial and two end ports is shown to be nearly optimal. Advantageous characteristics include a reduction in assembly flights, dual egress from all elements, logical functional allocation, no adverse impacts to international partners, favorable airlock, cupola, ACRV (Assured Crew Return Vehicle), and logistics module accommodation, and desirable flight attitude and control characteristics.

Gould, Marston J.↗

NASA NTRS1992

Spatial Light Amplifier Modulators

Spatial light amplifier modulators (SLAM's) are conceptual devices that effect two-dimensional spatial modulation in optical computing and communication systems. Unlike current spatial light modulators, these provide gain. Optical processors incorporating SLAM's designed to operate in reflection or transmission mode. Each element of planar SLAM array is optical amplifier - surface-emitting diode laser. Array addressed electrically with ac modulating signals superimposed on dc bias currents supplied to lasers. SLAM device provides both desired modulation and enough optical gain to enable splitting of output signal into many optical fibers without excessive loss of power.

Eng, Sverre T.↗

NASA NTRS1991

Flexible digital modulation and coding synthesis for satellite communications

An architecture and a hardware prototype of a flexible trellis modem/codec (FTMC) transmitter are presented. The theory of operation is built upon a pragmatic approach to trellis-coded modulation that emphasizes power and spectral efficiency. The system incorporates programmable modulation formats, variations of trellis-coding, digital baseband pulse-shaping, and digital channel precompensation. The modulation formats examined include (uncoded and coded) binary phase shift keying (BPSK), quatenary phase shift keying (QPSK), octal phase shift keying (8PSK), 16-ary quadrature amplitude modulation (16-QAM), and quadrature quadrature phase shift keying (Q squared PSK) at programmable rates up to 20 megabits per second (Mbps). The FTMC is part of the developing test bed to quantify modulation and coding concepts.

Vanderaar, Mark↗

NASA NTRS1992

RF modulated fiber optic sensing systems and their applications

A fiber optic sensing system with an intensity sensor and a Radio Frequency (RF) modulated source was shown to have sensitivity and resolution much higher than a comparable system employing low modulating frequencies or DC mode of operation. Also the RF modulation with an appropriate configuration of the sensing system provides compensation for the unwanted intensity losses. The basic principles and applications of a fiber optic sensing system employing an RF modulated source are described. In addition the paper discusses various configurations of the system itself, its components, and modulation and detection schemes. Experimental data are also presented.

Adamovsky, Grigory↗

NASA NTRS1990

128 layer HYMOSS module fabrication issues

The fabrication of the first Z-technology module with 128 active layers of readout electronic circuitry is being pursued. Several issues which will be investigated regarding the 128-layer module build, such as photolithographic processing at the edge of the module (edge effects) and module buttability, are discussed in this paper. Other topics which are covered apply to future applications of fully populated HYMOSS modules. These topics include possible reductions of thermal mass for quick cool-down time applications and improvements of end-to-end yield for low-cost applications.

Ludwig, David E.↗

NASA NTRS1991

Optically addressed asymmetric Fabry-Perot modulator

A low power, high contrast optically addressed modulator, operating with normal incidence, has been fabricated. Optically controlled reflection modulation is achieved through optically induced absorption modulation in a periodically delta-doped InGaAs/GaAs multiple quantum well structure inserted in an integrated asymmetric Fabry-Perot resonator. A contrast ratio over 60:1 was measured using a spectrally matched low power InGaAs/GaAs quantum well laser to generate the write (control) signal. The insertion loss for the normally off modulator is 4.6 dB at the highest write signal power (30 mW) used. The device lends itself to the fabrication of arrays for optically addressed spatial light modulation.

Larsson, A.↗

NASA NTRS1992

The effect of small-wave modulation on the electromagnetic bias

The effect of the modulation of small ocean waves by large waves on the physical mechanism of the EM bias is examined by conducting a numerical scattering experiment which does not assume the applicability of geometric optics. The modulation effect of the large waves on the small waves is modeled using the principle of conservation of wave action and includes the modulation of gravity-capillary waves. The frequency dependence and magnitude of the EM bias is examined for a simplified ocean spectral model as a function of wind speed. These calculations make it possible to assess the validity of previous assumptions made in the theory of the EM bias, with respect to both scattering and hydrodynamic effects. It is found that the geometric optics approximation is inadequate for predictions of the EM bias at typical radar altimeter frequencies, while the improved scattering calculations provide a frequency dependence of the EM bias which is in qualitative agreement with observation. For typical wind speeds, the EM bias contribution due to small-wave modulation is of the same order as that due to modulation by the nonlinearities of the large-scale waves.

Rodriguez, Ernesto↗

NASA NTRS1991

Utilization of common pressurized modules on the Space Station Freedom

During the preliminary design review of Space Station Freedom elements and subsystems, it was shown that reductions of cost, weight, and on-orbit integration and verification would be necessary in order to meet program constraints, particularly nominal Orbiter payload launch capability. At that time, the Baseline station consisted of four resource nodes and two 44 ft modules. In this study, the viability of a common module which maintains crew and payload accommodation is assessed. The size, transportation, and orientation of modules and the accommodation of system racks and user experiments are considered and compared to baseline. Based on available weight estimates, a module pattern consisting of six 28 ft common elements with three radial and two end ports is shown to be nearly optimal. Advantageous characteristics include a reduction in assembly flights, dual egress from all elements, logical functional allocation, no adverse impacts to international partners, favorable airlock, cupola, ACRV (Assured Crew Return Vehicle), and logistics module accommodation, and desirable flight attitude and control characteristics.

Mazanek, Daniel D.↗

NASA NTRS1992

Development of a stable electro-optical modulator

The activity of the sun can be studied through the measurement of its magnetic field. The measurement of the polarization state of the sunlight in a narrow spectral bandwidth can be related to the magnetic fields strengths and directions over the active sunspots. Measuring the polarization state can be done using the vector magnetograph. The essential component of the vector magnetograph is the polarization modulators. Electro-optical modulators are used as dynamic retarders. KDP (potassium dideuterium phosphate) crystals provide variable retardation which can be controlled by the applied voltage. KDP's have a high contrast ratio but suffer some problems; they require a high voltage and have a limited modulation lifetime. The KDP modulator forms the heart of the polarimeter assembly which is used for carrying out accurate measurements of linear polarization of the sun. It is therefore important to study the optical and electrical behavior of the KDP crystals so that the ultimate goal of making stable electro-optical modulators in the laboratory is achieved. A number of activities were performed in coating and testing the KDP crystals. A summary of these activities is given.

Abushagur, Mustafa A. G.↗