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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Rotational modulation of the chromospheric activity in the young solar-type star, X-1 Orionis

The IUE satellite was used to observe one of the youngest G stars (GO V) for which Duncan (1981) derives an age of 6 x 10 to the 8th power years from the Li abundance. Rotational modulation was looked for in the emission flux in the chromospheric and transition region lines of this star. Variations in the Ca 11 K-lines profile were studied with the CHF telescope at Mauna Kea. Results show that the same modulation of the emission flux of Ca 11 due to stellar rotation is present in the transition region feature of C IV and probably of He II. For other UV lines the modulation is not apparent, due to a more complex surface distribution of the active areas or supergranulation network, or a shorter lifetime of the conditions which give rise to these features, or to the uncertainities in the measured line strengths. The Mg II emission flux is constant to within + or - 3.4% implying a rather uniform distribution of Mg II emission areas. The Ca II emission not only shows a measurable variation in intensity but also variations in detailed line profile shape when observed at high resolution.

Boesgaard, A. M.↗
NASA NTRS1983

Cosmic-ray modulation and the anamalous component

Advances in the theory and observation of cosmic ray modulation and in studies of the anomalous component in cosmic radiation are reviewed from reports that appeared in the open literature during the years 1979 to 1982. Entries, which are primarily the work of American researchers, are cited under the following categories: (1) microscopic diffusion theory; (2) global modulation theory; (3) anomalous component; and (4) general modulation observation.

Jones, F. C.↗
NASA NTRS1983

Photovoltaic module bypass diode encapsulation

The design and processing techniques necessary to incorporate bypass diodes within the module encapsulant are presented. The Semicon PN junction diode cells were selected. Diode junction to heat spreader thermal resistance measurements, performed on a variety of mounted diode chip types and sizes, have yielded values which are consistently below 1 deg C per watt, but show some instability when thermally cycled over the temperature range from -40 to 150 deg C. Three representative experimental modules, each incorporating integral bypass diode/heat spreader assemblies of various sizes, were designed. Thermal testing of these modules enabled the formulation of a recommended heat spreader plate sizing relationship. The production cost of three encapsulated bypass diode/heat spreader assemblies were compared with similarly rated externally mounted packaged diodes. It is concluded that, when proper designed and installed, these bypass diode devices will improve the overall reliability of a terrestrial array over a 20 year design lifetime.

Shepard, N. J., Jr.↗
NASA NTRS1982

Reliability and performance experience with flat-plate photovoltaic modules

Statistical models developed to define the most likely sources of photovoltaic (PV) array failures and the optimum method of allowing for the defects in order to achieve a 20 yr lifetime with acceptable performance degradation are summarized. Significant parameters were the cost of energy, annual power output, initial cost, replacement cost, rate of module replacement, the discount rate, and the plant lifetime. Acceptable degradation allocations were calculated to be 0.0001 cell failures/yr, 0.005 module failures/yr, 0.05 power loss/yr, a 0.01 rate of power loss/yr, and a 25 yr module wear-out length. Circuit redundancy techniques were determined to offset cell failures using fault tolerant designs such as series/parallel and bypass diode arrangements. Screening processes have been devised to eliminate cells that will crack in operation, and multiple electrical contacts at each cell compensate for the cells which escape the screening test and then crack when installed. The 20 yr array lifetime is expected to be achieved in the near-term.

Ross, R. G., Jr.↗
NASA NTRS1983

Cosmic-ray modulation and the anomalous component

Experimental and theoretical studies of cosmic-ray-modulation phenomena reported in the open literature by US researchers during the 1979-1982 period are reviewed. Areas covered include microscopic diffusion theory, gradient and curvature drift, global modulation theory, the anomalous component, and general modulation observations (such as the Pioneer-10 Forbush-decrease-propagation observations and studies on the time variation of the electron-to-proton ratio). An impressionistic overview of current and future trends in this area of study is also provided.

Jones, F.C.↗
NASA NTRS1983

Interplanetary flow systems associated with cosmic ray modulation in 1977 - 1980

The hydromagnetic flow configurations associated with cosmic ray modulation in 1977 to 1980 were determined using solar wind plasma and magnetic field data from Voyagers 1 and 2 and Helios 1. The modulation was related to two types of large scale systems of flows: one containing a number of transients such as shocks, post shock flows and magnetic clouds; the other consisting primarily of a series of quasi-stationary flows following interaction regions containing a stream interface and often bounded by a forward reverse shock pair. Each of the three major episodes of cosmic ray modulation was characterized by the passage of the system of transient flows. Plateaus in the cosmic ray intensity time profile were associated with the passage of systems of corotating streams.

Burlaga, L. F.↗
NASA NTRS1984

Operational modules for space station construction

Identification of an effective space construction concept is a current objective of NASA studies. One concept, described in this memorandum, consists of repetitive use of operational modules, which minimizes on-orbit stay time for the shuttle. A space station constructed of operational modules may benefit from fabrication and system checkout in ground-based facilities, and since the modules are the primary structure of the space station, a minimum of additional structure, and trips and on-orbit stay time of the shuttle are required.

Jackson, L. R.↗
NASA NTRS1984

Doppler radar having phase modulation of both transmitted and reflected return signals

A microwave radar signal is generated for transmission through an antenna. Before transmission, the signal is phase modulated by 0 deg or 90 deg amounts during each alternate half-cycles of an intermediate frequency (IF) clock signal. After transmission and return, the signal is again phase modulated the same amounts during each alternate half-cycles. The return phase modulated signal is mixed with a leakage signal component of the microwave signal, leaving an IF Doppler. The IF Doppler signal may then be amplified, removing any requirement that direct current level signals be amplified and also removing the effect of detector noise from the Doppler signal.

Kobayashi, H. S.↗
NASA NTRS1984

Safety-related requirements for photovoltaic modules and arrays

Safety requirements for photovoltaic module and panel designs and configurations for residential, intermediate, and large scale applications are investigated. Concepts for safety systems, where each system is a collection of subsystems which together address the total anticipated hazard situation, are described. Descriptions of hardware, and system usefulness and viability are included. A comparison of these systems, as against the provisions of the 1984 National Electrical Code covering photovoltaic systems is made. A discussion of the Underwriters Laboratory UL investigation of the photovoltaic module evaluated to the provisions of the proposed UL standard for plat plate photovoltaic modules and panels is included. Grounding systems, their basis and nature, and the advantages and disadvantages of each are described. The meaning of frame grounding, circuit groundings, and the type of circuit ground are covered.

Levins, A.↗
NASA NTRS1983

Qualification and testing of modules

The experience gained in procuring solar modules soon to be installed on the Photovoltaic Higher Education National Exemplar Facility (PHENEF) at Georgetown University is discussed. The 300 KE Photovoltaic Array consists of 4464, 2' X 4', polycrystalline solar cell modules. The performance requirements for the modules are described in a detailed procurement specification which defines physical and electrical characteristics and extensive quality assurance provisions including requirements for an interface control drawing and qualification and acceptance testing.

Cohen, D. B.↗
NASA NTRS1983

Large scale solar modulation of 500 MeV/N galactic cosmic rays seen from 1-30 AU

Using measurements of cosmic rays obtained by Cerenkov counters on Pioneer 10 and Pioneer 11 and neutron monitor data from Earth, the spatial and temperal development of cosmic ray modulation during the last solar maximum were observed. The large-scale features of modulation and recovery are similar at these three sites and thus appear rotationally symmetric near the ecliptic plane. Outward propagating features characterize the radial dependence. The decline of the old cosmic ray cycle is marked by steplike decreases that propagate outward at nearly the solar wind velocity. During the start of the new cosmic ray cycle, recovery occurs first in the inner heliosphere and, after a lag comparable with that of the declining phase, appears later farther out. However, the direction of diffusive propagation is still inward, because the gradient remains positive. Forbush decreases are common at all three sites, and are evidently of great importance in understanding modulation. The largest decrease occurred during a short series of events in the summer of 1982 and had half the amplitude of the eleven year cycle.

Fillius, W.↗
NASA NTRS1984

Interplanetary flow systems associated with cosmic ray modulation in 1977-1980

The hydromagnetic flow configurations associated with the cosmic ray modulation in 1977-1980 were determined using solar wind plasma and magnetic field data from Voyager 1 and 2 and Helios 1. The modulation was related to two types of large-scale systems of flows: one containing a number of transients such as shocks and postshock flows, the other consisting primarily of a series of quasi-stationary flows following interaction regions containing a stream interface and often bounded by a forward-reverse shock pair. Each of three major episodes of cosmic ray modulation was associated with the passage of a system of transient flows. Plateaus in the cosmic ray intensity-time profile were associated with the passage of systems of corotating streams.

Burlaga, L. F.↗
NASA NTRS1984

Advanced infrared laser modulator development

A parametric study was conducted to develop an electrooptic waveguide modulator for generating continuous tunable sideband power from an infrared CO2 laser. Parameters included were the waveguide configurations, microstrip dimensions device impedance, and effective dielectric constants. An optimum infrared laser modulator was established and was fabricated. This modulator represents the state-of-the-art integrated optical device, which has a three-dimensional topology to accommodate three lambda/4 step transformers for microwave impedance matching at both the input and output terminals. A flat frequency response of the device over 20 HGz or = 3 dB) was achieved. Maximum single sideband to carrier power greater than 1.2% for 20 W microwave input power at optical carrier wavelength of 10.6 microns was obtained.

Cheo, P. K.↗
NASA NTRS1984

Demonstration of transparent solar array module design

This report discusses the design, development, fabrication and testing of IR transparent solar array modules. Three modules, consisting of a baseline design using back surface reflector cells, and two modules using gridded back contact, IR transparent cells, were subjected to vacuum thermal balance testing to verify analytical predictions of lower operating emperature and increased efficiency. As a result of this test program, LMSC has verified that a significant degree of IR transparency can be designed into a flexible solar array. Test data correlates with both steady state and transient thermal analysis.

Pack, G. J.↗
NASA NTRS1984

Automated assembly of Gallium Arsenide and 50-micron thick silicon solar cell modules

The TRW automated solar array assembly equipment was used for the module assembly of 300 GaAs solar cells and 300 50 micron thick silicon solar cells (2 x 4 cm in size). These cells were interconnected with silver plated Invar tabs by means of welding. The GaAs cells were bonded to Kapton graphite aluminum honeycomb graphite substrates and the thin silicon cells were bonded to 0.002 inch thick single layer Kapton substrates. The GaAs solar cell module assembly resulted in a yield of 86% and the thin cell assembly produced a yield of 46% due to intermittent sticking of weld electrodes during the front cell contact welding operation. (Previously assembled thin cell solar modules produced an overall assembly yield of greater than 80%).

Mesch, H. G.↗
NASA NTRS1985

Satellite Module Design

The tethered satellite system (TSS) satellite is a multimission vehicle able to carry scientific payloads aways from the shuttle orbiter in the range of 130 to 330 km in altitude. The multimission capability is obtained adopting a modular concept of the satellite such to allow for: easy reconfiguration, easy refurbishment, and cost and schedule minimization. The modular concept is realized with: a payload module (PM), a service module (SM), and an auxiliary propulsion module (APM). The satellite configuration for the electrodynamic and atmospheric missions is described as well as its mechanized capabilities. Payload dedicated electrical facilities, satellite position determination accuracy; attitude control and measurement accuracy and attitude oscillation characteristics are summarized.

Vignoli, M.↗
NASA NTRS1985

Development of an Organic Rankine-Cycle power module for a small community solar thermal power experiment

An organic Rankine-cycle (ORC) power module was developed for use in a multimodule solar power plant to be built and operated in a small community. Many successful components and subsystems, including the reciever, power conversion subsystem, energy transport subsystem, and control subsystem, were tested. Tests were performed on a complete power module using a test bed concentrator in place of the proposed concentrator. All major single-module program functional objectives were met and the multimodule operation presented no apparent problems. The hermetically sealed, self-contained, ORC power conversion unit subsequently successfully completed a 300-hour endurance run with no evidence of wear or operating problems.

Kiceniuk, T.↗
NASA NTRS1984

Topics in electrochemical degradation of photovoltaic modules

Electrochemical degradation of photovoltaic modules was examined. It is found that the extent of electrochemical damage is dependent on the integrated leakage current. The PV electrochemical degradation mechanisms in the two polarities are different: (1) degradation rates in the two polarities are of the same order of magnitude; (2) center tapped grounded arrays are a preferred system configuration to minimize electrochemical degradation. The use of thicker pottant layers and polymer substrate films to reduce equilibrium leakage current values is suggested. A metallized substrate layer, if used, should be isolated from the pottant and the frame by polyester layers, and EVA modules appear to be consistent with 30 year life allocation levels for electrochemical damage. Temperature acceleration factors are well behaved and moderately well understood; humidity acceleration factors vary radically with module construction and materials and require additional research.

Mon, G. R.↗