View source for Air Force Space Surveillance System

{{Short description|U.S. government radar system to detect orbital objects}}
{{Use American English|date=February 2021}}
{{Use dmy dates|date=February 2021}}

[[Image:NAVSPASUR Fence 2001.jpg|thumb|upright=1.3|right|Part of the master transmitter [[Antenna (radio)|antenna]] at Lake Kickapoo, [[Texas]] c.2001]]

The '''AN/FPS-133 Air Force Space Surveillance System''', colloquially known as the '''Space Fence''', was a [[Federal government of the United States|U.S. government]] [[multistatic radar]] system built to detect [[orbit]]al objects passing over the [[United States]]. It was a component of the [[United States Space Surveillance Network|U.S. Space Surveillance Network]], and according to the [[United States Navy|U.S. Navy]] was able to detect basketball sized ({{cvt|75|cm}}) objects at heights up to {{cvt|30000|km}}.<ref name="USN Transfer">{{citation-attribution|1={{cite news|first=Gary R.|last=Wagner|newspaper=Navy NewsStand
|url=http://www.navy.mil/search/display.asp?story_id=15597|archive-url=https://web.archive.org/web/20041104220630/http://www.navy.mil/search/display.asp?story_id=15597|url-status=dead|archive-date=4 November 2004|title=Navy Transfers Space Surveillance Mission to Air Force|date=October 24, 2004|access-date=September 13, 2014}} }}</ref>

The system ceased operation in September 2013. Plans for a [[Space Fence|new Space Fence]] began with sites at the [[Kwajalein Atoll]] in the [[Marshall Islands]], along with an option for another radar site in [[Western Australia]].<ref name=sfn-20140602>{{cite news|url=http://spaceflightnow.com/news/n1406/02spacefence/|title=Lockheed Martin wins contract for Space Fence|first=Stephen|last=Clark |publisher=Spaceflight Now|date=2 June 2014|access-date=3 June 2014}}</ref> It became operational on March 28, 2020.<ref name="operational">{{Cite web |url=https://spacenews.com/space-fence-surveillance-radar-site-declared-operational/ |last=Erwin |first=Sandra |date=March 28, 2020 |access-date=March 29, 2020 |title=Space Fence surveillance Radar Site Declared Operational}}</ref>

The operation's headquarters were at [[Dahlgren, Virginia]], and [[radar station]]s were spread out across the [[Contiguous United States|continental United States]] at roughly the level of the [[33rd parallel north]].

== Description ==
There were three [[transmitter]] sites in the system:<ref name="476CFR2.106">{{citation-attribution|1={{cite web|url=http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=2&SECTION=106&TYPE=TEXT|title=47CFR§2.106 Footnote US229|publisher=Access GPO.gov|access-date=May 24, 2006}} }}</ref>
* 216.983 [[Hertz|MHz]] at [[Lake Kickapoo|Lake Kickapoo, Texas]] ({{Coord|33|32|47|N|98|45|46|W|region:US}}) (Master transmitter)
* 216.970&nbsp;MHz at [[Maricopa, Arizona|Gila River, Arizona]] ({{Coord|33|06|32|N|112|01|45|W|region:US}})
* 216.990&nbsp;MHz at [[Jordan Lake (Alabama)|Jordan Lake, Alabama]] ({{Coord|32|39|33|N|86|15|52|W|region:US}})

The master transmitter at [[Lake Kickapoo]] was said to be the most powerful [[continuous wave]] (CW) station in the world, at 768&nbsp;kW [[Effective radiated power|radiated power]] on 216.97927&nbsp;MHz.

When the system became operational in 1961, the original frequency was '''108.50&nbsp;MHz''' (just above the FM broadcast band). In 1965, the "Fence" system was modernized with the operating frequency doubled to '''216.98&nbsp;MHz''' (just above Channel 13 in the VHF TV broadcast band) to obtain higher resolution and to locate smaller objects. This frequency was used until the Fence was decommissioned in 2013. Fill-in transmitter sites at Gila River and Jordan Lake used offset frequencies listed above from the early 1990s to 2013 to help better detect which transmitter "illuminated" an object in space, as multiple transmitters could have illuminated the same object at the same time. Overhead imagery (see coordinates given above) of the [[Gila River]] and [[Jordan Lake (Alabama)|Jordan Lake]] sites shows the original design at the lower frequency.

There were six receiving stations:<ref name="476CFR2.106"/>
* [[San Diego, California]] ({{Coord|32|34|42|N|116|58|11|W|region:US}})
* [[Elephant Butte, New Mexico]] ({{Coord|33|26|35|N|106|59|50|W|region:US}})
* [[Lewisville, Arkansas|Red River, Arkansas]] ({{Coord|33|19|48|N|93|33|01|W|region:US}})
* [[Hollandale, Mississippi|Silver Lake, Mississippi]] ({{Coord|33|08|42|N|91|01|16|W|region:US}}) 
* [[Hawkinsville, Georgia]] ({{Coord|32|17|20|N|83|32|10|W|region:US}})
* [[Tattnall County, Georgia|Tattnall, Georgia]] ({{Coord|32|02|35|N|81|55|21|W|region:US}})

The following receiving stations were placed in cold storage in April 2013:
* [[Hollandale, Mississippi|Silver Lake, Mississippi]] ({{Coord|33|08|42|N|91|01|16|W|region:US}})
* [[Tattnall County, Georgia|Tattnall, Georgia]] ({{Coord|32|02|35|N|81|55|21|W|region:US}})

The receiving stations at [[Elephant Butte, Sierra County, New Mexico|Elephant Butte]] and [[Hawkinsville]] were considered to be "High Altitude" stations with longer and more complex antenna systems that are designed to see targets at higher altitudes than the other four receiving stations.

== History ==
Author [[Curtis Peebles]] notes that the original "Space Fence" or Space Surveillance System began operations in 1959.<ref name="Peebles1997">{{cite book|first=Curtis|last=Peebles|title=High Frontier: The U.S. Air Force and the Military Space Program|url=https://books.google.com/books?id=cMgdYypcPc8C&pg=PA39|date=1 June 1997|publisher=DIANE Publishing|isbn=978-0-7881-4800-2|pages=39–}}</ref> The system predated the formation of [[NORAD]] and was known as the U.S. Navy Space Surveillance System (or SPASUR or NAVSPASUR).<ref>{{cite web|url=http://www.fas.org/spp/military/program/track/spasur_at.htm|title=U.S. Naval Space Command Space Surveillance System|publisher=Federation of American Scientists|access-date=September 13, 2014}}</ref> From 1960 until the early 1990s the system was used in conjunction with a network of [[Schmidt camera|Baker-Nunn cameras]] that could see "an object the size of a basketball at {{cvt|25000|mi}}".<ref name="Peebles1997"/><ref>{{cite news|url=https://news.google.com/newspapers?nid=336&dat=19770323&id=CdFSAAAAIBAJ&pg=5578,5712257|title=Hill AFB Repairs Cameras that Spy on Satellites|newspaper=The Deseret News|date=March 23, 1977|page=2D|access-date=September 13, 2014}}</ref>

The system was formerly operated by the [[United States Navy|U.S. Navy]] for [[North American Aerospace Defense Command|NORAD]] from 1961 until October 2004. Initially independent as NAVSPASUR, it was run by [[Naval Space Command]] from 1993, and finally by Naval Network and Space Operations Command from 2002 until command was passed to the [[United States Air Force|U.S. Air Force]] [[20th Space Control Squadron]] on 1 October 2004.<ref name="USN Transfer"/>

In 2009, the operations and maintenance contract for the day-to-day management and operation of the Fence was awarded to Five Rivers Services, [[Limited liability company|LLC]], based in [[Colorado Springs, Colorado]]. On 30 September 2011, Five Rivers Services was awarded a US$7,022,503 firm fixed price with cost reimbursable line items contract modification to manage, operate, maintain, and logistically support the nine Air Force Space Surveillance System field stations, presumably for Fiscal Year 2012.<ref>{{citation-attribution|1={{cite web|url=http://www.defense.gov/contracts/contract.aspx?contractid=4634|archive-url=https://web.archive.org/web/20111009022517/http://www.defense.gov/contracts/contract.aspx?contractid=4634|url-status=dead|archive-date=9 October 2011|title=Contracts, Defense Logistics Agency, No: 838-11|publisher=Defense.gov|date=September 30, 2011|access-date=September 13, 2014}} }}</ref>

=== Plans for system upgrade: 2009 – 2012 ===
The 850th Electronic Systems Group, [[Electronic Systems Center]] awarded 3 US$30-million contracts to [[Lockheed Martin]], [[Northrop Grumman]] and [[Raytheon Technologies]] on 11 June 2009.<ref name="afmil">{{citation-attribution|1={{cite news|newspaper=USAF News|url=https://www.hanscom.af.mil/News/story/id/123161236/|title=Space Fence program awards contracts for concept development|first=Monica D.|last=Morales|date=July 30, 2009|access-date= September 13, 2014|url-status=live|archive-url=https://web.archive.org/web/20160304060635/http://www.hanscom.af.mil/news/story.asp?id=123161236|archive-date=March 4, 2016}} }}</ref>

A new Space Fence is envisioned to be a system of two or three [[S band|S-band]] ground-based radars designed to perform uncued detection, tracking and accurate measurement of orbiting space objects. The Space Fence is intended to replace the Air Force Space Surveillance System, or VHF Fence, that was transferred from the [[United States Navy|U.S. Navy]] to the [[United States Air Force|U.S. Air Force]] in 2004. The shorter [[wavelength]] of the S-band Space Fence allows for detection of much smaller [[satellite]]s and [[Space debris|debris]].<ref name="afmil"/>

The [[2009 satellite collision|10 February 2009, collision]] of a U.S. [[Iridium satellite constellation|Iridium communications satellite]] ([[Iridium 33]]) and a [[Russia]]n [[Kosmos 2251|Cosmos 2251]] communications satellite, which added hundreds more pieces of debris to the [[atmosphere]], highlighted the need for more precise [[Space debris#Tracking and measurement|tracking of space objects]].<ref>{{cite news|newspaper=Aviation Week|title=Orbital Collision was the Worst Ever|url=http://aviationweek.com/awin/orbital-collision-was-worst-ever|date=February 11, 2009}} (article behind paywall)</ref>

Data collected from a new Space Fence's [[sensors]] would potentially feed into the [[Joint Space Operations Center]] Mission System, which is used to track objects orbiting the [[Earth]], monitor [[space weather]] and assess foreign launches. Used by operators at the [[614th Air and Space Operations Center]] at [[Vandenberg Air Force Base]], [[California]], the 614 AOC's 24-hour-a-day, seven-day-a-week support provides vigilance of global and theater operations and equips the Joint Functional Component Command for space operations with the tools to conduct command and control of space forces.<ref name="afmil"/>

Plans to award the final contract had been stalled by [[Federal government of the United States|U.S.]] [[budget sequestration in 2013|budget sequestration]] in early 2013 <ref>{{cite web |url=https://www.forbes.com/sites/davidewalt/2013/07/17/budget-cuts-threaten-the-air-forces-new-space-fence/|title=Budget Cuts Threaten The Air Force's New "Space Fence"|first=David M. |last=Ewalt|work=Forbes|date=July 17, 2013|access-date=September 13, 2014}}</ref> and the AFSSS system was scheduled to be discontinued in October 2013 due to budget cuts.<ref>{{citation-attribution|1={{cite news
|url=https://www.af.mil/News/Article-Display/Article/466832/air-force-space-command-to-discontinue-space-surveillance-system/|title=Air Force Space Command to discontinue space surveillance system |newspaper=USAF News|date=August 13, 2013|access-date=September 13, 2014}} }}</ref>

=== 2013 Shutdown ===
On 1 August 2013, General [[William L. Shelton]], commander of Air Force Space Command, directed that the Air Force Space Surveillance System (AFSSS) be closed and all sites vacated effective 1 October 2013.<ref>{{cite news|title=Shelton Orders Shutdown of Space Fence|first=Mike|last=Gruss|url=http://www.spacenews.com/article/military-space/36655shelton-orders-shutdown-of-space-fence|archive-url=https://archive.today/20130905201653/http://www.spacenews.com/article/military-space/36655shelton-orders-shutdown-of-space-fence|url-status=dead|archive-date=5 September 2013|website=spacenews.com |publisher=SpaceNews|date=6 August 2013|access-date=5 September 2013}}</ref> The main advantage of the system was its ability to provide uncued data on new objects as opposed to tracking objects based on existing information. However, the system was also said to be inherently inaccurate due to its dated design. Alternate operating modes for radars at [[Cavalier Space Force Station]] and [[Eglin Air Force Base|Eglin AFB]] were devised to fulfill the mission to provide uncued data for new objects. Shelton also noted the confusion between the planned new S-band space fence and the old UHF AFSSS, which was commonly called the "space fence".<ref>{{citation-attribution|1={{cite news|url=https://www.af.mil/News/Article-Display/Article/466832/air-force-space-command-to-discontinue-space-surveillance-system/|title=Air Force Space Command to discontinue space surveillance system|date=August 13, 2013|access-date=September 13, 2014}} }}</ref> The AFSSS was turned off September first.<ref>{{cite news|title=Technology: U.S. "Space Fence" Shut Down |url=http://www.arrl.org/arrlletter?issue=2013-09-05#toc06|newspaper=American Radio Relay League|date=5 September 2013|access-date=5 September 2013}}</ref> "It appears they pulled the plug at 00:00 [[Coordinated Universal Time|UTC]] (6 a.m. Local MDT) on September 1st", reports engineer Stan Nelson, who was monitoring the radar using an antenna in Roswell. The radar's final echoes came from a Russian satellite and a sporadic meteor".<ref>{{cite news|title=Space Fence Discontinued|url=http://spaceweather.com/archive.php?view=1&day=01&month=09&year=2013|website=spaceweather.com|publisher=SpaceWeather|date=1 September 2013|access-date=5 September 2013}}</ref> The shutdown only affects the original Space Fence, not the new one contracted to be built by [[Lockheed Martin]] for deployment in [[Australia]] and the [[Marshall Islands]].<ref>{{cite web|url=http://www.lockheedmartin.com.au/au/what-we-do/space-systems/space-fence.html|title=Space Debris & Space Fence - Tracking Space Debris|website=lockheed-martin.com.au
|publisher=Lockheed Martin|access-date=September 13, 2014|archive-url=https://web.archive.org/web/20140913171426/http://www.lockheedmartin.com.au/au/what-we-do/space-systems/space-fence.html|archive-date=September 13, 2014|url-status=dead}}</ref>

==New space fence==
A [[Space Fence|new space fence]] at [[Kwajalein Atoll]] in the [[Marshall Islands]] was declared operational on March 27, 2020.<ref>{{cite web| url = https://spacenews.com/space-fence-surveillance-radar-site-declared-operational/| title = Space News| date = 28 March 2020}}</ref> In 2014 [[Lockheed Martin]] won the contract to build the new [[S band]] space fence system at Kwajelein with an option for another radar site in [[Western Australia]].<ref name=sfn-20140602 />

== See also ==
{{Portal|Spaceflight}}
* [[Graves (system)|GRAVES]], in France
* [[Krona space object recognition station]], in North Caucasus, Russia
** [[Krona-N]], in the Russian Far East
* [[List of military electronics of the United States]]

== References ==
{{Reflist}}

== External links ==
{{refbegin}}
* [https://web.archive.org/web/20130824090217/http://www.inmaricopa.com/Article/2012/03/10/air-force-space-command-defense-surveillance Air Force uses invisible fence to protect skies] - an article about the Gila River, Arizona installation - InMaricopa Magazine, March 10, 2012
* [https://www.si.edu/object/archives/sova-nasm-2014-0048 Space Surveillance Fence Program Collection] at the [[Smithsonian Institution|Smithsonian]] [[National Air and Space Museum|Air and Space Museum]]
* [https://www.petersonschriever.spaceforce.mil/?id=4730 20th Space Control Squadron, Det 1] - Air Force Fact sheet about the Alternate Space Control Center and the AN/FPS-133 surveillance fence radar
* [http://www.fas.org/spp/military/program/track/spasur_at.htm US Naval Space Command Space Surveillance System] at the [[Federation of American Scientists|FAS]] website
* [https://www.usatoday.com/tech/science/space/2005-02-22-sat-track_x.htm Rural site part of USA's oldest sat-tracking system] from [[USA Today]]
* [https://web.archive.org/web/20140718204848/http://tattnalljournal.com/archives/041813_20pgs.pdf Tattnall Space Surveillance Station shut down due to sequestration], April 18, 2013, Ronald E. McCall, The Tatnall Journal
* [https://web.archive.org/web/20000118163538/http://www.au.af.mil/au/awc/awcgate/usspc-fs/navspace.htm Naval Space Command] - Maxwell-Gunter AFB
* http://www.fiveriversservices.com/ - former contractor for AFSSS
{{refend}}

{{USAF Weapons}}
{{USAF system codes}}

[[Category:Military radar networks]]
[[Category:Radars of the United States Air Force]]
[[Category:United States Space Surveillance Network]]
[[Category:Military equipment introduced in the 1960s]]
[[Category:Military electronics of the United States]]