PAGEOS

PAGEOS had a diameter of exactly {{convert|100|ft|m|sigfig=4}}, consisted of a {{convert|0.5|mil|μm|sigfig=3|lk=on}} thick mylar plastic film coated with vapour deposited aluminum enclosing a volume of about {{convert|524000|cuft|m3}}Teichman, L. A. (June 1, 1968). [https://ntrs.nasa.gov/citations/19680016348 "The fabrication and testing of Pageos 1"]. NASA Technical Reports Server 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.{{Cite web |date=19 June 1966 |title=Pageos Satellite to Girdle Globe for Earth Mapping |url=https://ntrs.nasa.gov/citations/19660022793 |website=NASA Technical Reports Server}} The satellite carried no instrumentation. The study and construction of PAGEOS was done by the Schjeldahl company, which also made Echo 1.

File:BC-4 World Primary Network.jpg

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PAGEOS was placed into a polar orbit, about 200 nautical miles above the earth, so that the U.S. Coastal and Geodetic Survey could practically apply triangulation techniques developed from experiments with Echo 1. This program was known as the "Worldwide Geometric Satellite Triangulation Program".{{Cite web |year=2007 |title=Entering the Space Age: The Evolution of Satellite Geodesy at the Coast and Geodetic Survey |url=https://celebrating200years.noaa.gov/foundations/satellite_geodesy/welcome.html#scene |access-date=2024-06-23 |website=NOAA 200th Celebration |publisher=National Oceanic and Atmospheric Administration |language=en}} Because of the satellite's high altitude, the sun illuminated it during the entirety of Earth night, allowing it to be picked out from a background of stars. Over five years, 16 groups conducted observations at 45 globally distributed stations, about 3000-4000 km apart from each other.{{Cite book |last=Seeber |first=Günter |url=https://books.google.com/books?id=qZTS6OI9NGoC |title=Satellite Geodesy: Foundations, Methods, and Applications |date=2008-08-22 |publisher=Walter de Gruyter |isbn=978-3-11-020008-9 |language=en}} 12 mobile tracking stations were used, which observed during favorable weather conditions during a few minutes of twilight each evening.{{Why|date=June 2024|reason=If the satellite was visible during the entire night, why were observations only taken during twilight?}}{{Clarification needed|reason=In addition to the 45 or forming part of them?|date=June 2024}} BC4 cameras were used to photograph the satellite. Observations were taken when the satellite was visible simultaneously to multiple stations at the same time. This resulted in the fixing of the precise locations of 38 different points around the world. This could be used to help determine the precise locations of the continents relative to each other, and to help determine the precise shape and size of the earth. Some unclassified data was used by scientists studying continental drift, and more classified data was used by US military planners studying intercontinental ballistic missiles. The observations were done with BC4 (Ballistic Camera-4) cameras, and could last more than a year at each station before satisfactory results were obtained. The network reached an accuracy about an order of magnitude better than terrestrial triangulations at the time, and was the first time that a scientific determination had been made with accuracy of a complete global polyhedron.

File:Thor-SLV2A Agena-D (Thor 473) with PAGEOS.jpg

The PAGEOS spacecraft was launched by a Thor-SLV2A Agena-D (Thor 473) on 24 June 1966,{{Cite web |last=Krebs |first=Gunter D |title=Thor-SLV2A Agena-D |url=https://space.skyrocket.de/doc_lau_det/thor-slv2a_agena-d.htm |access-date=2024-05-09 |website=Gunter's Space Page |language=en}}{{Better source needed|reason=The current source is insufficiently reliable (WP:NOTRS).|date=May 2024}} and placed into a polar orbit (inclination 85–86°) with an initial height of 4200km,{{Cite report |url=https://ntrs.nasa.gov/citations/19780003602 |title=National Geodetic Satellite Program, Part 1 |last=Henriksen |first=S. W. |date=1 January 1977 |access-date=5 August 2024}} which had gradually lowered during its 9 years of operation.{{Citation needed|date=March 2024}} 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.{{cite web |last=Krebs |first=Gunter D |title=PAGEOS 1 |url=http://space.skyrocket.de/doc_sdat/pageos.htm |accessdate=16 March 2017 |website=Gunter's Space Page}}{{Better citation needed|reason=The current source is insufficiently reliable (WP:NOTRS).|date=March 2024}} In 2016, one of the largest fragments of PAGEOS de-orbited.{{cite web|url=http://www.unoosa.org/documents/pdf/copuos/stsc/2017/tech-15E.pdf |title=USA Space Debris Environment, Operations, and Research Updates |publisher= 54th Session of the Scientific and Technical Subcommittee, Committee on the Peaceful Uses of Outer Space, United Nations, 30 January – 10 February 2017, Vienna |author=J.-C. Liou |date=February 1, 2017|access-date= February 5, 2017}}

The satellite's orbital period was approximately three hours. It was about as bright as Polaris, and appeared as a slow-moving star.{{Cite book |last=Dicati |first=Renato |url=https://books.google.com/books?id=O4LgDQAAQBAJ&dq=PAGEOS&pg=PA44 |title=Stamping the Earth from Space |date=2017-01-10 |publisher=Springer |isbn=978-3-319-20756-8 |language=en}} 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.

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

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Category:Geodetic satellites

Category:Satellites formerly orbiting Earth

Category:Passive satellites

Category:Spacecraft launched in 1966

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