View source for PAGEOS

{{Short description|Passive geodetic satellite launched by NASA in 1966}}
{{Use American English|date=March 2014}}
{{Use mdy dates|date=March 2014}}

{{Infobox spaceflight
| name               = Passive Geodetic Earth Orbiting Satellite (PAGEOS)
| names_list         = PAGEOS-A

<!--image of the spacecraft/mission-->| image              = Image:PAGEOS Satellite - GPN-2000-001896.jpg
| image_caption      = Test inflation of PAGEOS, 5 August 1965
| image_alt          = <!--image alt text-->
| image_size         = <!--Basic details-->
| mission_type       = <!--eg. Technology, Reconnaissance, ISS assembly, etc-->
| operator           = [[NASA]] Office of Space Applications
| Harvard_designation = 
| COSPAR_ID          = 1966-056A
| SATCAT             = 02253
| website            = <!--Homepage of the craft/mission, OFFICIAL PAGES ONLY-->
| mission_duration   = <!--How long the mission lasted-->
| distance_travelled = <!--How far the spacecraft travelled (if known)-->
| orbits_completed   = <!--number of times the spacecraft orbited the Earth - see below for spacecraft beyond Earth orbit-->
| suborbital_range   = <!--downrange distance reached if spacecraft did not enter orbit-->
| suborbital_apogee  = <!--altitude reached if spacecraft did not enter orbit-->

<!--Spacecraft properties-->| spacecraft         = <!--Spacecraft name/serial number (eg. Space Shuttle ''Discovery'', Apollo CM-118), etc-->
| spacecraft_type    = <!--eg. GPS Block II, Kobalt-M, US-K, etc-->
| spacecraft_bus     = <!--eg. A2100M, Star-2, etc-->
| manufacturer       = <!--company or companies who built the satellite-->
| launch_mass        = {{convert|56.7|kg|abbr=on}}
| BOL_mass           = <!--spacecraft mass in orbit at beginning of operational life, after LEOP phase-->
| landing_mass       = <!--Mass after landing (recovered spacecraft only)-->
| dry_mass           = <!--spacecraft mass in orbit without fuel-->
| payload_mass       = <!--Mass of cargo carried by spacecraft (eg. for Space Shuttle), or total mass of instrumentation/equipment/experiments for mission-->
| dimensions         = {{convert|30.48|m|abbr=on}}&nbsp;diameter<ref name="nssdca" />
| power              = <!--end-of-life power, in watts-->

<!--Launch details-->| launch_date        = {{start date|1966|06|24|00|14|00|7=Z}}
| launch_rocket      = Thrust augmented [[Thor-Agena#Versions|Thor-Agena D]]
| launch_site        = [[Vandenberg AFB]]
| launch_contractor  = <!--organisation(s) that conducted the launch (eg. United Launch Alliance, Arianespace, etc)-->
| deployment_from    = <!--place where deployed from-->
| deployment_date    = <!--date deployed-->
| entered_service    = <!--date on which the spacecraft entered service, if it did not do so immediately after launch-->
<!-- * - e.g. Proton-M/Briz-M not Proton-M, but Titan IV(401)A not Titan IV(401)A-Centaur-->

<!--end of mission-->| disposal_type      = <!--Whether the spacecraft was deorbited, decommissioned, placed in a graveyard orbit, etc-->
| deactivated        = <!--when craft was decommissioned-->
| destroyed          = partially disintegrated {{end date|1975|07}}
| last_contact       = <!--when last signal received if not decommissioned-->
| recovery_by        = <!--recovered by-->
| recovery_date      = <!--recovery date-->
| decay_date         = <!--when craft re-entered the atmosphere, not needed if it landed-->
| landing_date       = <!--when the spacecraft made a controlled landing, not needed if it did not return intact-->
| landing_site       = <!--where the craft landed; site/runway or coordinates-->
<!--
    The following template should be used for ONE of the three above fields "end_of_mission", "decay" or "landing" if the spacecraft is no longer operational.
    If it landed intact, use it for the landing time, otherwise for the date it ceased operations, or the decay date if it was still operational when it re-entered.
    {{end date|YYYY|MM|DD|hh|mm|ss|TZ=Z}} (for Zulu/UTC) or {{end date|YYYY|MM|DD}} (if time unknown) 
-->

<!--orbit parameters-->
<!--as science-related articles, SI units should be the principal units of measurement, however we usually use {{convert}} to display imperial units in parentheses after the initial values-->| orbit_reference    = [[Geocentric orbit|Geocentric]]<ref name="NSSDC Master Catalog">{{cite web|title=NSSDCA – PAGEOS 1 – Trajectory Details|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-056A|website=nssdc.gsfc.nasa.gov|publisher=[[NASA]]|accessdate=22 June 2016}}</ref>
| orbit_regime       = <!--high, low, medium, molniya, GSO - please link (e.g. [[Low Earth orbit|Low Earth]] - please don't use acronyms-->
| orbit_longitude    = <!--geosynchronous satellites only-->
| orbit_slot         = <!--Designation of orbital position or slot, if not longitude (e.g plane and position of a GPS satellite)-->
| orbit_semimajor    = <!--semimajor axis-->
| orbit_eccentricity = 0.00301
| orbit_periapsis    = {{convert|4207|km|abbr=on}}
| orbit_apoapsis     = {{convert|4271|km|abbr=on}}
| orbit_inclination  = 87.14°
| orbit_period       = 181.43&nbsp;min
| orbit_RAAN         = <!--right ascension of the ascending node-->
| orbit_arg_periapsis = <!--argument of perigee/periapsis-->
| orbit_mean_anomaly = <!--mean anomaly at epoch, only use in conjunction with an epoch value-->
| orbit_mean_motion  = <!--mean motion of the satellite, usually measured in orbits per day-->
| orbit_repeat       = <!--repeat interval/revisit time-->
| orbit_velocity     = <!--speed at which the spacecraft was travelling at epoch - only use for spacecraft with low orbital eccentricity-->
| orbit_epoch        = 24 June 1966
| orbit_rev_number   = <!--revolution number-->
| apsis              = gee

<!--Only use where a spacecraft/mission is part of a clear programme of sequential missions. 
If in doubt, leave it out-->| programme          = 
| previous_mission   = 
| next_mission       = <!--mission insignia or patch-->
| insignia           = <!--omit the "file" prefix-->
| insignia_caption   = <!--image caption-->
| insignia_alt       = <!--image alt text-->
| insignia_size      = <!--include px/em; defaults to 180px-->
}}

'''PAGEOS''' ('''PAssive Geodetic Earth Orbiting Satellite''') was a [[balloon satellite]] which was launched by [[NASA]] in June 1966.<ref name="nssdca">{{cite web|title=PAGEOS 1|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-056A|website=National Aeronautics and Space Administration|accessdate=16 March 2017}}</ref> It was the first satellite specifically launched for use in [[Geodesy|geodetic surveying]],<ref name=":1">{{Cite web |title=Modern Surveying |url=https://www.britannica.com/technology/surveying/Modern-surveying |access-date=2024-03-24 |website=Encyclopaedia Britannica |language=en}}</ref> or measuring the shape of the earth, by serving as a reflective and photographic tracking target. At the time, it improved on terrestrial [[Triangulation (surveying)|triangulations]] of the globe by about an order of magnitude.<ref name=":0">{{Cite web |last=Kleusberg |first=Alfred |date=2003 |title=Satelliten im Dienst der Geodäsie und Geoinformatik |url=https://www.uni-stuttgart.de/wechselwirkungen/ww2003/Kleusberg.pdf |url-status=dead |archive-url=https://web.archive.org/web/20060523075451/http://www.uni-stuttgart.de/wechselwirkungen/ww2003/Kleusberg.pdf |archive-date=23 May 2006 |website=University of Stuttgart}}</ref> The satellite, which carried no instrumentation, broke up between 1975 and 1976.<ref name=":2" /> One of the largest fragments of the satellite finally deorbited in 2016.<ref name="deorbit" />

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.<ref name=":3" /> 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.<ref name=":3" /> These included satellites Echo 1 and Echo 2 under [[Project Echo]], which were also used for experiments in geodetic surveying;<ref name=":1" /> several air-density-focused [[Explorers Program|Explorer satellites]]; and finally PAGEOS.<ref name=":3">{{Cite book |last=Hansen |first=James |url=https://ntrs.nasa.gov/citations/19950021264 |title=Spaceflight Revolution: NASA Langley Research Center from Sputnik to Apollo |date=12 March 2013 |publisher=Cia Publishing}}</ref>

==Design==
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 [[BoPET|mylar plastic film]] coated with [[Chemical vapor deposition|vapour deposited]] aluminum enclosing a volume of about {{convert|524000|cuft|m3}}<ref>Teichman, L. A. (June 1, 1968). [https://ntrs.nasa.gov/citations/19680016348 "The fabrication and testing of Pageos 1"]. ''NASA Technical Reports Server''</ref><ref name=":4" /> 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.<ref name=":4">{{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}}</ref> The satellite carried no instrumentation.<ref name=":4" /> The study and construction of PAGEOS was done by the [[Gilmore Schjeldahl|Schjeldahl company]], which also made [[Project Echo#Echo 1|Echo 1]].<ref name=":5" />

== Usage ==
[[File:BC-4 World Primary Network.jpg|thumb|Network of BC4 cameras used to establish the Worldwide Geometric Satellite Triangulation Network]]
[[File:BC4_camera_inside_observing_dome.jpg|thumb|A BC4 (Ballistic Camera-4) camera, inside its observing dome, with instrumentation shelter in background.]]{{Expert needed|spaceflight|section
| date = January 2025
| reason = Different sources on the topic appear to contradict each other
}}
PAGEOS was placed into a polar orbit, about 200 nautical miles above the earth, so that the [[United States Coast and Geodetic Survey|U.S. Coastal and Geodetic Survey]] could practically apply triangulation techniques developed from experiments with [[Project Echo#Echo 1|Echo 1]]. This program was known as the "Worldwide Geometric Satellite Triangulation Program".<ref name=":7">{{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}}</ref> 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.<ref name=":0" /><ref name=":5" /> Over five years, 16 groups conducted observations at 45 globally distributed stations, about 3000-4000 km apart from each other.<ref name=":0" /><ref name=":3" /><ref name=":6">{{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}}</ref> 12 mobile tracking stations were used, which observed during favorable weather conditions during a few minutes of twilight each evening.<ref name=":3" />{{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.<ref name=":6" /> Observations were taken when the satellite was visible simultaneously to multiple stations at the same time.<ref name=":6" /> This resulted in the fixing of the precise locations of 38 different points around the world.<ref name=":0" /> 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 missile|intercontinental ballistic missiles]].<ref name=":3" /> 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.<ref name=":7" /><ref name=":6" /> The network reached an accuracy about an order of magnitude better than terrestrial triangulations at the time,<ref name=":0" /> and was the first time that a scientific determination had been made with accuracy of a complete global polyhedron.<ref name=":6" />

==Orbit==
[[File:Thor-SLV2A Agena-D (Thor 473) with PAGEOS.jpg|thumb|Thor-SLV2A Agena-D launching PAGEOS ]]
The PAGEOS spacecraft was launched by a Thor-SLV2A Agena-D (Thor 473) on 24 June 1966,<ref>{{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}}</ref>{{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,<ref name=":8">{{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}}</ref> which had gradually lowered during its 9 years of operation.{{Citation needed|date=March 2024}} The satellite first partly disintegrated in July 1975,<ref name=":5" /> 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.<ref name=":2">{{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}}</ref>{{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.<ref name="deorbit">{{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}}</ref> 

The satellite's orbital period was approximately three hours.<ref name="NSSDC Master Catalog" /> It was about as bright as [[Polaris]], and appeared as a slow-moving star.<ref name=":5">{{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}}</ref> 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.<ref name=":5" /> Its high orbit also allowed it to be seen simultaneously by observers 2000-3000 km apart at optimum distances from the [[zenith]].<ref name=":8" />

==See also==
{{Portal|Spaceflight}}
* [[List of passive satellites]]
* [[Reference ellipsoid]]
* [[World Geodetic System]] (WGS84)

==References==
{{Reflist}}

{{Orbital launches in 1966}}

{{DEFAULTSORT:Pageos}}
[[Category:Geodetic satellites]]
[[Category:Satellites formerly orbiting Earth]]
[[Category:Passive satellites]]
[[Category:Spacecraft launched in 1966]]
[[Category:Balloon satellites]]