Vanguard I is the oldest satellite still in orbit and the longest artificial satellite, having circled the planet more than 196,990 times since its launch in 1958. It was also the first satellite to be powered by solar energy and returned important information on geodesics and orbit dynamics.
Vanguard I was the fourth satellite launched into orbit and the second launched by the United States. (Others launched earlier were Soviet Sputniks I and II and American Explorer I.) Vanguard I was launched from Cape Canaveral, Florida on March 17, 1958, just over 5 months after the launch of the first satellite, Sputnik. Vanguard I was also the first satellite to be powered by solar energy.
Vanguard I’s biggest claim to fame is its status as the longest artificial satellite in orbit, having circled the planet more than 196,990 times since its launch. This equates to a distance of 5.7 billion nautical miles, the distance from Earth to dwarf planet Pluto and then halfway there. This is just over half the distance traveled by the Voyager 1 space probe, now far outside the confines of the solar system, making it one of the most distant man-made objects in history.
On March 17, 2008, American scientists celebrated the 50th year in orbit of Vanguard I. Vanguard I is the oldest satellite still in orbit. Its orbital path is an ellipse, 654×3969 km (406×2466 mi) in extent, inclined 34 degrees to the plane of the elliptical. This puts it into Mid-Earth Orbit (MEO). The satellite was initially launched on a trajectory thought to keep it in orbit for 2,000 years, but later analyses, accounting for solar radiation pressure and atmospheric drag, found that it will remain in orbit for a total of ‘suns’ 240 years . This erroneous estimate is the result of limited knowledge of space at the time of the satellite’s launch.
Vanguard I was quite small for a satellite: a 1.47 kg (3.2 lb) aluminum sphere 152 mm (6 in) in diameter. Because of its small size compared to an earlier Soviet-launched satellite, Sputnik (weighing 83.6 kg (about 183 pounds) and 2 feet in diameter), Soviet premier Nikita Khrushchev called it “the grapefruit satellite.” However, Vanguard I returned important information on geodesics and orbit dynamics, opening the window on space and paving the way for thousands of future satellites.
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