Solar Today March April 2014 : Page 24
h i story of sol a r Hans Ziegler, power expert for the U.S. Army Signal Corps, championed the silicon cell for use in satellites. A U.S. Navy technician assembles the nose cone of a missile to test photo-voltaic cells in suborbital ﬂight. one application in particular where the solar cell made a perfect fit for a top secret program — the development of an artificial satellite. 11 Freed from terrestrial restraints on solar radiation — namely, inclement weather and nighttime — “operations above the earth’s atmosphere [would] provide ideal circumstances for solar energy converters,” the Signal Corps believed. Silicon solar cells theoretically would never run out of fuel since they ran on the sun’s energy. The other power option — batteries — would lose their charge in two to three weeks. The modular nature of photovoltaics also meant that cells could be tailored for the exact power requirement of a particular satellite. There would be no wasted weight or bulk. A tiny array could provide the small amount of power that the transistorized communication equipment on board a satellite needed, without encumbering the payload. The Signal Corps concluded, “For longer periods of operation and limited allowance for weight...the photovoltaic principle...appears most promising.” 12 The secrecy of America’s space plans ended on July 30, 1955, when President Dwight Eisenhower announced America’s plans to put a satellite into space. A drawing that accompanied Eisenhower’s front-page statement in the New York Times showed that it had a solar power source. 13 The civilian scientific panel overseeing America’s space program saw 24 MARCH/APRIL 2014 SOLAR TODAY powering satellites with photovoltaics as immensely important, since relying on batteries automatically condemned “most of the on-board apparatus...[to] an active life of only a few weeks.” They noted that “nearly all of the experiments will have enormously greater value if they can be kept operating for several months or more” and decided it was “of utmost importance to have a solar battery system” on board. 14 Based on the civilian panel’s recommendations, the Signal Corps was asked to take on the responsibility of designing a solar-cell power system for the program, called Project Vanguard. Its staff readily developed a prototype that clustered individual solar cells on the surface of the satellite’s shell. The group designed the modules to provide “mechanical rigidity against shock and vibration and to comply with thermal requirements of space travel.” 15 To test their reliability in space, the Signal Corps attached cell clusters to the nose cones of two high-altitude rockets. One rocket reached an altitude of 126 miles, the second 192 miles, both high enough to experience the vicissitudes of space. “In both firings, the solar cells operated perfectly,” Ziegler reported to an international conference on space activity held in the fall of 1957. 16 A U.S. Army Signal Corps press release added, “The power was sufficient for satellite instruments...[and they were] not affected by the temperatures of skin friction as the rockets passed through the atmosphere at more than a mile a second.” 17 Th e V an gu a r d : Th e F i rst Pr a ct i c a l U s e of th e B e ll S ol a r B a tt e ry The first satellite with solar cells aboard went into orbit on Saint Patrick’s Day in 1958. Nineteen days later, a headline in the New York Times revealed: “Radio Fails as Chemical Battery Is Exhausted: Solar-Powered Radio Still Functioning.” 18 Celebrating the first anniversary of the Vanguard launch, the Signal Corps let the public know that “the sun-powered Vanguard I...is still faithfully sending its radio message back to earth.” 19 By July 16, 1958, of the four satellites in the sky only the solar-powered Vanguard and Sputnik III, which was launched after Vanguard and also had solar cells aboard, Copyright © 2014 American Solar Energy Society. All rights reserved.