PAGEOS

PAGEOS (PAssive Geodetic Earth Orbiting Satellite) was a balloon satellite which was launched by NASA in June 1966. It was the first satellite specifically launched for use in geodetic surveying, or measuring the shape of the earth, by serving as a reflective and photographic tracking target. At the time, it improved on terrestrial triangulations of the globe by about an order of magnitude. The satellite, which carried no instrumentation, broke up between 1975 and 1976. One of the largest fragments of the satellite finally deorbited in 2016. PAGEOS was part of a larger program of inflatable satellites that grew from the original concept by William J. O'Sullivan of a 30-inch diameter inflatable satellite in 1956 to measure air drag at high altitudes, called the Sub-Satellite. While the Sub-Satellite failed, the idea of a visible US satellite became very attractive after Sputnik launched in the Cold War, resulting in a program of similar, larger satellites. These included satellites Echo 1 and Echo 2 under Project Echo, which were also used for experiments in geodetic surveying; several air-density-focused Explorer satellites; and finally PAGEOS.

PAGEOS (PAssive Geodetic Earth Orbiting Satellite) was a balloon satellite which was launched by NASA in June 1966. It was the first satellite specifically launched for use in geodetic surveying, or measuring the shape of the earth, by serving as a reflective and photographic tracking target. At the time, it improved on terrestrial triangulations of the globe by about an order of magnitude. The satellite, which carried no instrumentation, broke up between 1975 and 1976. One of the largest fragments of the satellite finally deorbited in 2016. PAGEOS was part of a larger program of inflatable satellites that grew from the original concept by William J. O'Sullivan of a 30-inch diameter inflatable satellite in 1956 to measure air drag at high altitudes, called the Sub-Satellite. While the Sub-Satellite failed, the idea of a visible US satellite became very attractive after Sputnik launched in the Cold War, resulting in a program of similar, larger satellites. These included satellites Echo 1 and Echo 2 under Project Echo, which were also used for experiments in geodetic surveying; several air-density-focused Explorer satellites; and finally PAGEOS.

Design

PAGEOS had a diameter of exactly , consisted of a thick mylar plastic film coated with vapour deposited aluminum enclosing a volume of about The metal coating both reflected sunlight and protected the satellite from damaging ultraviolet waves. The satellite was launched in a canister, which explosively separated as it was ejected from the rocket. Then, the balloon was inflated through a combination of residual internal air and a mixture of benzoic acid and anthraquinone placed inside, which turned to gas when the satellite was exposed to the heat of the sun. The satellite carried no instrumentation. The study and construction of PAGEOS was done by the Schjeldahl company, which also made Echo 1.

Orbit

The PAGEOS spacecraft was launched by a Thor-SLV2A Agena-D (Thor 473) on 24 June 1966, and placed into a polar orbit (inclination 85–86°) with an initial height of 4200km, which had gradually lowered during its 9 years of operation. The satellite first 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 during the following decade. In 2016, one of the largest fragments of PAGEOS de-orbited. The satellite's orbital period was approximately three hours. It was about as bright as Polaris, and appeared as a slow-moving star. Thanks to its high orbit and its polar inclination, it did not pass through the Earth's shadow and was visible any time of night, unlike lower-orbit satellites which had to be viewed exclusively just before sunrise and after sunset. Its high orbit also allowed it to be seen simultaneously by observers 2000-3000 km apart at optimum distances from the zenith.

See also

List of passive satellites Reference ellipsoid World Geodetic System (WGS84)

References

Text derived from https://en.wikipedia.org/w/index.php?oldid=1270040073 under CC BY-SA 4.0; modifications have been made.