On Saint Patrick's Day in 1958, the U.S. Navy launched Vanguard 1, the first solar-powered satellite and the oldest artificial satellite currently orbiting the Earth. The main purpose of this mission was to test a new three-stage rocket. Vanguard 1 was the fourth satellite ever launched into space (following Sputniks 1 and 2 and Explorer 1). It looks a lot like a miniature version of Sputnik. Vanguard 1 was tiny compared to the satellites that came before it. It's about the size of a grapefruit and weighs only 3 pounds. Solar technology allowed the satellite to transmit signals to Earth for 7 years, while battery-powered satellites couldn't even last a month. Scientists think the satellite will deorbit by the year 2198 after spending 240 years in space.