Passive solar array orientation system /Thermal heliotrope/ Quarterly report, 23 Mar. - 23 Jun. 1969
Passive solar array orientation system in thermal heliotrope using bimetal elements
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Passive solar array orientation system in thermal heliotrope using bimetal elements
Buck-boost main bus voltage regulator for solar array battery space power system
The primary objective of the Low-cost Silicon Solar Array (LSSA) Project, which forms a major part of a national photovoltaic program, is the timely development of low-cost commercial-quality photovoltaic arrays through an active program of industrial and academic involvement. The definition of future array requirements is considered as a necessary step toward meeting this objective. An overview of array requirement trends which begin to evolve from the various ERDA activities is presented. For present terrestrial arrays the primary requirement is to generate power for small, often remote electric-power applications. To meet an objective of increased energy independence requires that photovoltaics become economically viable for the large energy consumption of the future. Various developments needed to achieve such an economic viability are discussed.
The results of a study for Task 3 of the Low Cost Solar Array Project, directed toward the development of a cost effective encapsulation system for photovoltaic modules using silicon based materials, are reported. Results of the following are discussed: (1) weather-ometer stressing vs. weathering history of silicon and silicon modified materials; (2) humidity/temperature cycling exposure; (3) exposure at high humidity/high temperature; (4) outdoor exposure stress; (5) thermal cycling stress; and (6) UV screening agents. The plans for the next quarter are outlined.
The use of concentrators to improve the performance of solar arrays in deep space was tested in a simulated deep space environment. The results of these tests are presented and discussed. Areas of discussion include cell temperature performance in a low temperature, low illumination environment with and without concentration, concentration ratios, and theoretical analysis versus test results. Tests were conducted on a series/parallel configuration and individual cells.
Issues affecting the long-term operational performance of the Advanced Photovoltaic Solar Array (APSA) are discussed, with particular attention given to circuit electrical integrity from shadowed and cracked cell modules. The successful integration of individual advanced array components provides a doubling of array specific performance from the previous NASA-developed advanced array (SAFE). Flight test modules both recently fabricated and under fabrication are described. The development of advanced high-performance blanket technology for future APSA enhancement is presented.
The Solar Array Module Plasma Interactions Experiment (SAMPIE), an approved Shuttle space flight experiment with a tentative launch date in July 1993, is intended to investigate plasma interactions of high-voltage space power systems. Solar cell modules, representing several technologies, will be biased to high voltages to characterize both arcing (negative potential) and current collection (positive potential). Other solar modules, specially modified in accordance with current theories of arcing and breakdown, will demonstrate the possibility of arc suppression. Finally, several additional test specimens will be included to study the basic nature of these interactions. The authors describe the rationale for the space flight experiment, the measurements to be made, the significance of the expected results, and the current design status of the flight hardware.
Solar cells in space plasma conditions are known to arc into the plasma when the interconnects are at a negative potential of a few hundred volts, relative to plasma potential. For cells with silver-coated interconnects, a threshold voltage for arcing exists at about -230 V, as found in both ground and LEO experiments. The arc rate beyond the threshold voltage depends nearly linearly on plasma density, but has a strong power-law dependence on voltage, such that for small increments in operating voltage there is a large increment in arc rate. The arcs generate broadband radio interference and visible light. In ground tests, interconnects have been damaged by arcs in cells having insufficient isolation from a source of high current. Models for the arcs are highly dependent on the choice of interconnect conductor material exposed to the plasma and possibly on the geometry and choice of adjacent insulator material. Finally, new technology solar cells use copper for the cell interconnects, a material which may have a lower arcing threshold voltage than silver. It is expected, from ground tests of simulated solar cells, that any junction of conductor and insulator exposed to space plasma conditions will arc into the plasma at a few hundred volts negative potential, relative to the local plasma.
Closed loop, integrated circuit voltage regulator for use in transmission of power from solar array to battery
Concentrator concepts which utilize Kapton mirror material were evaluated and selected for solar array use due to their zero mass. All concepts considered employed thin silicon solar cells. Design requirements for the concentrator were: the cell temperature was not to exceed 150 C; the concentrators were to produce illumination of the array within 15% of being perfectly uniform; the concentrators were to operate while misaligned as much as 5 degrees with the solar axis. Concentrator designs along with mirror structure and configurations are discussed and comparisons are made for optimal space applications.
This paper considers the effect of heat rejection devices (radiators) on the performance and cost of large concentrating solar arrays for space application. Overall array characteristics are derived from the weight, cost, and performance of four major components; namely primary structure, optics/secondary structure, radiator, and solar panel. An ideal concentrator analysis is used to establish general cost and performance trends independent of specific array design. Both passive and heat-pipe radiation are evaluated, with an incremental cost-of-power approach used in the evaluation. Passive radiators are found to be more cost effective with silicon than with gallium arsenide (GaAs) arrays. Representative concentrating arrays have been evaluated for both near-term and advanced solar cell technology. Minimum cost of power is achieved at geometric concentration ratios in the range 2 to 6.
The arcing that has been found to occur when negatively biased high-voltage solar arrays in LEO lie at a critical voltage with respect to the plasma environment is presently proposed to be due to a breakdown of gas emitted under electron bombardment from the solar cells' cover-glass. The elements of the model for this phenomenon include an electron current flow from the interconnect to a neighboring cover-glass, which desorbs neutral molecules under the electron bombardment. The neutral molecules form a gas over the interconnect, and this gas breaks down when the voltage over the interconnect is sufficiently high. Specific scaling predictions are made on the basis of the geometric structure and gas in question.
The goal of the Process Development Area, as part of the Flat-Plate Solar Array (FSA) Project, was to develop and demonstrate solar cell fabrication and module assembly process technologies required to meet the cost, lifetime, production capacity, and performance goals of the FSA Project. R&D efforts expended by Government, Industry, and Universities in developing processes capable of meeting the projects goals during volume production conditions are summarized. The cost goals allocated for processing were demonstrated by small volume quantities that were extrapolated by cost analysis to large volume production. To provide proper focus and coverage of the process development effort, four separate technology sections are discussed: surface preparation, junction formation, metallization, and module assembly.
Optimum charge regulator design evaluation for coupling spacecraft solar array to battery
Electronic commutator and rate-sensor for brushless direct-drive solar array reorientation systems
Tradeoff studies for fast response solar array simulator
The technology and economics of silicon ingot wafering for low cost solar arrays were discussed. Fixed and free abrasive sawing wire, ID, and multiblade sawing, materials, mechanisms, characterization, and innovative concepts were considered.
A theory is developed to account for the observed properties of discharges of solar arrays immersed in plasma. The theory is based on the assumption that a thin layer of insulating contaminant covers any metallic surface exposed to the plasma. Quantities derivable from the theory include a voltage threshold for arcing. The existence of the threshold and its predicted weak dependence on plasma density appear consistent with experimental results.