PAGEOS (Passive Geodetic Earth Orbiting Satellite) was a balloon satellite which was launched by NASA in 1966. It was placed into a polar orbit (inclination 85–86°) with a height of approximately 4000 km, which became gradually lower during its nine years of operation. The satellite partly disintegrated in July 1975, which was followed by a second break-up that occurred in January 1976 resulting in the release of a large number of fragments. Most of these re-entered the Earth's atmosphere during the following decade. This photograph shows a test inflation of a PAGEOS satellite in a blimp hangar at Weeksville, North Carolina, in 1965.Photograph credit: NASA