20Congreso Nacional 
Sociedad Mexicana de Ciencia de Superficies y Vacío A.C.

Space Photovoltaics - History, Progress and Promise

Dennis J. Flood
National Aeronautics and Space Administration (Ret.)
The John Glenn Research Center
Cleveland, Ohio 44135, U.S.A.

The first space solar array was carried aloft on Vanguard I on March 17, 1958.  Vanguard I was the second satellite successfully launched by the U.S. space program following the launch of Sputnik I by the (then) USSR on October 4, 1957.  The array on Vanguard I consisted of six photovoltaic panels mounted on the outer surface of the satellite.  The array produced about one watt of power for over six years.  The cells on that first array were single crystal silicon, each 2cm x 0.5cm in size, and about 10% efficient at 28C.  Solar arrays are now the primary source of power for all earth-orbiting satellites.  Space solar arrays and power systems have grown in size and complexity since 1958 and are now routinely several kilowatts in output.  The largest space solar array thus far will be on the International Space Station.  It is expected to reach a peak power of 200 kilowatts.

For over two decades geosynchronous orbit (GEO) communication satellite operational lifetimes have typically been about 7 years; now 15 year lifetimes are seriously being considered, driven in part by increased development and launch costs.  Among the keys to achieving longer operational life are lighter weight and more radiation resistant solar arrays, and improved, higher energy density batteries.  In addition to the GEO comsats, however, a new class of communication satellites is about to be deployed which will provide a worldwide portable telephone service.  Many of these proposed satellite constellations will be launched into low earth polar or near polar orbits, while some will be located at lower inclinations.  In many cases the power system on an individual satellite may exceed 10 kilowatts, and the large numbers of spacecraft required to complete the constellations place a premium on achieving low cost at every stage, from development to launch and operation.  Although cost savings can be obtained by employing as much commonality as possible for each satellite in a given constellation, an entirely new generation of low cost, high performance solar arrays will be required to enable such systems to meet their cost targets. This paper will provide an overview of a typical satellite power system along with the current status of solar cell technology development in the U.S. and some indications of technology yet to come.


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