The first use of solar cells in space occurred on the satellite Vanguard I, which was launched on March 17, 1958. Eight tiny panels were installed symmetrically around the satellite to ensure power generation during the satellite's random tumbling. They delivered 50 to 100 milliwatts of power and provided secondary electricity for a beacon signal generator. Each panel had six square silicon cells, measuring 2 centimeters (0.79 inch) by 2 centimeters (0.79 inch) by 0.4 centimeters (0.16 inch), with a photovoltaic(PV) conversion efficiency of approximately 10 percent. The panels of solar cells were protected by a thick cover glass to avoid radiation damage from electrons and protons trapped in the Van Allen radiation belts that surround Earth.^* The longevity of Vanguard I's beacon signal surpassed all expectations—lasting until May 1964. As a result, future regulations required shutting down power supplies of satellites to avoid cluttering the radio wave spectrum with unwanted signals.

The early...