Vanguard 1

Vanguard 1 was the first satellite to have solar electric power. Although communication with the satellite was lost in 1964, it remains the oldest man-made object still in orbit, together with the upper stage of its launch vehicle. Vanguard 1 was placed into a 654 × 3969 km 134.2-minute orbit inclined at 34.25 degrees by the three-stage Vanguard launch vehicle. Original estimates had the orbit lasting for 2000 years, but it was discovered that solar radiation pressure and atmospheric drag during high levels of solar activity produced significant perturbations in the perigee height of the satellite, which caused a significant decrease in its expected lifetime to only about 240 years. The battery-powered transmitter stopped operating in June 1958 when the batteries ran down. The solar-powered transmitter operated until May 1964 (when the last signals were received in Quito, Ecuador) after which the spacecraft was optically tracked from Earth.