Technology for Small Spacecraft (1994) / Chapter Skim
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4 Spacecraft Electric Power
4 Spacecraft Electric Power
Pages 31-41
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POWER SOllRCES Solar Arrays For space missions that are sufficiently close to (and with an unobstructed view of the sun, solar cell arrays can meet most near-term space power needs for small, lightweight spacecraft by converting solar energy to electrical power. Solar cells can be mounted directly on the external surface of the spacecraft or on panels that are deployed once the spacecraft achieves orbit.
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From page 32... ...
LeRC is currently working on many advanced solar cells, such as copper indium diselenide cells, amorphous silicon cells, indium phosphide on germanium cells, cadmium telluride cells, and other multibandgap cells. LeRC is also performing research on ~ The multijunction approach utilizes the solar spectrum more efficiently by stacking several bandgap cells (e.g., a thin gallium arsenide cell stacked on top of a silicon cell)
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From page 33... ...
Prior to program termination, the midterm goal of the APSA program was to implement cell fabrication methods and array assembly procedures for thin-film solar cells that could increase array specific power to 190 watts per kilogram. As an example, advanced thin-f~im gallium arsenide or aluminum gallium arsenide cells produced by Kopin Corporations's Cleaved Lateral Epitaxy Films for Transfer (CLEFT)
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Although the design objectives for DoD concentrator technology generally focus on survivability rather than efficiency and high specfic power, there were several DoD technology advancements made in these programs that may hold promise for future NASA spacecraft. For example, the concentrator technology developed for the Survivable Concentrator Photovolta~c Array and the Survivable Power Subsystem Demonstration programs (mini-Cassagrainian arrays developed by TRW, minidome arrays developed by Boeing, and slats being developed by General Dynamics)
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These are the thinnest gallium arsenide solar cells flown to date (Nozette, 19931. Nuclear Technology Nuclear radioisotope power systems convert the heat from a radioisotope heat source into electricity.
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RIG for the Pluto Fast Flyby mission, based on silicon germanium unicouples, has a mass of 15 kilograms, with a cost of $51 million estimated by DOE for three fueled flight units. During the 1980s, a modular, radioisotope heat source module (the General Purpose Heat Source)
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From page 37... ...
with a radioisotope heat source and a heat rejection radiator. A recently completed system design study showed that replacement of the RIG with a thermophotovoltaic generator for the proposed Pluto Fast Flyby mission would reduce the required number of costly heat source modules by 60 percent, reduce the power source mass by over 50 percent, and triple or quadruple the system efficiency.
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From page 38... ...
The mission's power requirements are determined not by the length of the flyby but by the amount of stored data to be transmitted back to Earth from deep space. In the case of the proposed Pluto Fast Flyby mission, the power demand stipulated by the current design would have to be reduced by orders of magnitude to lower the battery mass to that of the radioisotope power system.
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The Pane! on Small Spacecraft Technology believes that developments in lowweight, high-efficiency solar cells and arrays would enhance not only the power generation capability of small spacecraft but also that of solar electric propulsion.
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Development times are probably too long to permit use in near-term planned programs such as the proposed Pluto Fast Flyby and Mars Pathfinder missions. However, for future deep space missions and Martian planetary surface investigations with small spacecraft and microrovers, especially at high latitudes, these technologies are enabling.
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From page 41... ...
For those missions, development of more efficient conversion systems to reduce heat source mass and cost would be beneficial. Radioisotope power system designs using Stirling, thermophotovoTtaic, and alkali metal thermal-to-electric converter conversion techniques should be jointly evaluated by NASA and DOE, and the ability of these techniques to satisfy various NASA missions should be assessed.
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