PAGEOS

PAGEOS (Passive Geodetic Earth Orbiting Satellite) was a large, balloon-like satellite launched by NASA in 1966 as part of Project PAGE (Precise Range and Azimuth Geodetic Earth Orbit Satellite). Its primary purpose was to provide a high-altitude, easily visible target for ground-based triangulation.

PAGEOS was essentially a large, inflated sphere, 30 meters (98 feet) in diameter, constructed of a thin (0.0127 mm) mylar film coated with aluminum. This highly reflective surface made it visible to observers on Earth, even without the aid of telescopes under favorable conditions.

The satellite's orbit was chosen to be near-polar and at a high altitude (approximately 4,200 kilometers or 2,600 miles). This allowed for wide geographic coverage and reduced atmospheric drag.

By simultaneously photographing PAGEOS from widely spaced ground stations, scientists could accurately determine the relative positions of these stations. The triangulation method relied on knowing the precise location of the satellite in the sky at the time of each photograph. Using these observations, a global geodetic network was established, improving the accuracy of maps and allowing for a better understanding of the Earth's shape and gravitational field.

PAGEOS was a passive satellite, meaning it did not transmit or receive any signals. Its visibility depended solely on reflected sunlight. The satellite remained in orbit for several years, but eventually decayed due to atmospheric drag. While no longer operational, the data collected from PAGEOS observations significantly contributed to the advancement of geodesy and cartography. Its legacy lies in the enhanced accuracy of geodetic surveys and the improved understanding of the Earth's geoid.