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Eglin AFB Site C-6
transmitter/receiver building
The 45° angled side of the transmitter/receiver building at Eglin AFB Site C-6 faces southward in a direction that intercepts the 90 minute circular orbit altitude near the equator.
Country USA
State Florida
Region DoD Major Range Test Facility Base[2]
District Eglin Military Reservation
Municipality Walton County[3]
Part of USSSN
Main base Eglin AFB ~35 mi (56 km) away
Location elevated landform between Fox Branch, Little Alaqua, and Little Basin Creeks[4]
 - coordinates 30°34′24″N 86°12′54″W / 30.57333°N 86.215°W / 30.57333; -86.215 [5]
Length 318 ft (97 m), E-W [5]
Base depth 143 ft (44 m) [6]
Height 192 ft (59 m) [7]
Style phased array building
Material structural steel: 1,250 tons
concrete: 1,400 cubic yards[5]
Owner USAF
Access Restricted
Website: 21 Space Wing Fact Sheet 4730
Radar designations

Air Force Space Tracking Radar[8]
AN/FPS-85 Radar Set ( 496L)[9]
Phased Array Space Surveillance Radar[2]

Eglin AFB Site C-6 is an Air Force Space Command radar station with the AN/FPS-85 phased array radar, associated computer processing system(s), and radar control equipment (e.g., MIT Radar Calibration System in 1996).[10] The entire radar/computer system is located at a receiver/transmitter building and is supported by the site's power plant, fire station, 2 water wells (for 128 people),[11] and other infrastructure for the system to provide observations on space objects for "the Joint Space Operations Center satellite catalogue".[12]


Transmitter/receiver building
The antenna elements are mounted on the inclined faces of the transmitter/receiver building. and within the structure is the remainder of the radar, computer, and crew operations equipment. By 2012, the computer room had 2 "IBM ES-9000 mainframe computers, two RADAR and Interface Control Equipment cabinets, and two SunSparc workstations."[13] In the squadron Mission Operations Center,[14] "personnel use a screen[which?] with [space] objects assigned numbers, similar to an air traffic control screen."[15] An attached garage is on the building's east side.
Power building
The power building has an electrical generation system (cf. the earlier BMEWS "ELEC PWR PLANT" models AN/FPA-19 and -24.)[16]
Fire Station
In 2011, the site's fire station (30°34′24″N 086°12′52″W / 30.57333°N 86.21444°W / 30.57333; -86.21444) was added to the USGS's Geographical Names Information System (the transmitter/receiver building is not listed.)[3]
Recreation facilities
A softball field and gymnasium are avaiilable.
Monitoring station
A nearby monitoring station is used for processing a once-per-second calibration pulse transmitted by the radar.[17]


1950s missile testing over the Gulf of Mexico used radar sites on federal land assigned to Eglin AFB (e.g., the Anclote Missile Tracking Annex through 1969 at the mouth of the Anclote River near Tampa,[18] the 1959 Cudjoe Key Missile Tracking Annex, and the Carrabelle Missile Tracking Annex[where?] that "transferred from RADC to Eglin AFB" on 1 Ocrober 1962.)[19] "Following the launching of Sputnik I on 4 October 1957, the Air Force's Missile Test Center at Patrick AFB, Florida, set up·a project[specify]

to observe and collect data on satellites."[20]

Eglin AFB had its "first satellite tracking facility[where?]…operational fall 1957",[1] and the 496L System Program Office formed in early 1959.[21] Bendix Corporation was contracted and built a linear array at their Baltimore facility,[22] followed by a prototype "wideband phased array radar (EPS 46-XW 1)" with IBM computer from Spring 1959 through November 1960.[8] The Bendix AN/FPS-46 Electronically Steerable Array Radar (ESAR) using L-band[6] began transmitting in November 1960 as "the first full-size pencil-beam phased-array radar system."[19] "HQ AFSC decided to give full technical responsibility for the development of a sensor for the 496L Space Track System to RADC…after the Soviet lead in satellite technology in October 1957 and the subsequent failure to locate Explorer XII for six months after it was launched"[19] on August 16, 1961. Gen. J. Toomay was program manager after the phased array program transferred to RADC[8] and based on the Bendix Radio Division's[23] ESAR success, the FPS-85 contract was signed on 2 April 1962.[24]

Site construction

Site C-6 construction began in October 1962[13] for a system "providing for the possibilities of numerous tube failures by arranging for a large number of people to do replacements" during operations.[8] On 5 November 1964, DDR&E recommended the Site C-6 system be used for submarine-launched ballistic missile detection.[25] Before radar testing planned in May 1965, a 5 January 1965 fire due to arcing that ignitied dielectric material "almost totally destroyed"[20]:67 the transmitter/receiver building and contents (the system was insured.)[26] On 22 June 1965 the Joint Chiefs of Staff directed CONAD to prepare a standby plan to also use Site C-6 computer facilities "as a backup" to the NORAD/ADC Space Defense Center "prior to the availability of the AN/FPS-85."[27]

By December 1965 NORAD decided to use the future Site C-6 radar "for SLBM surveillance on an “on-call” basis"[28] "at the appropriate DEFCON",[29] and the specifications for the Avco 474N SLBM Detection and Warning System contracted 9 December 1965 required the AN/GSQ-89 processing system for networking the Fuzzy-7 mechanical radars to also process Site C-6 data.[27] By June 1966 the Site C-6 system was planned "to have the capability to operate in the SLBM [warning] mode simultaneously with the [space] surveillance and tracking modes".[28] Rebuilding of the "separate faces for transmitting and receiving" began in 1967,[30] with the destroyed analog phase shifters[specify]

and vacuum tube receivers replaced by low-loss[31] diode phase shifters and transistor receivers.[26]

Space Defense

Eglin Site C-6's squadron of the 9th Aerospace Defense Division activated in September 1968 (now the 20th Space Control Squadron)[32] and after "technical problems";[33] the site with radar and computer systems was completed[when?] in 1968,[34] were turned over to Air Force Systems Command on 20 September 1968,[35] and "became operational in December 1968,[7]

Eglin Site C-6 was assigned to Aerospace Defense Command on 20 December 1968,[35] and the site--using the FORTRAN computer language[36]--became operational during the week of Sunday, 9 February 1969.[37] Site C-6 was the 1971-84 location[13] of the Alternate Space Surveillance Center.[verification needed] In 1972 20% of the site's "surveillance capability…became dedicated to search for SLBMs"[38] (the USAF SLBM Phased Array Radar System was initiated In November 1972 by the JCS[39] while the Army's MSR and PAR phased arrays for missile defense were under construction.) The FPS-85 was expanded[specify]

in 1974,[30] and "a scanning program to detect" SLBM warheads[40] was installed in 1975.[41]  Alaska's AN/FPS-108 Cobra Dane phased array site was completed in 1976 and from 1979 until 1983, Site C-6 was assigned to Strategic Air Command's Directorate of Space and Missile Warning Systems (SAC/SX)--as were the new PAVE PAWS phased array sites operational in 1980.

Space Command

In 1983 Eglin Site C-6 transferred to Space Command (later renamed Air Force Space Command), and the "FPS-85 assumed a deep space role in November 1988 after receiving a range-extension upgrade enabling integration of many pulses."[42] After a contractor protest was denied in 1993,[43] a "new radar control computer" was installed at the site in 1994 (upgraded software was installed in 1999.)[44] The original central monitoring system that tested for failing transmitter modules was replaced by a PC-based system in March 1994.[17] In 1994 when the "amplifier and mixing functions on the existing transmitters" used six vacuum tubes for each module,[45] Southwest Research Institute was redesigning the transmitters[46] (5 tubes were replaced by solid-state components.)[47] By 1998, the site was providing space surveillance on "38 percent of the near-earth catalogue" of space objects (ESC's "SND C2 SPO was the System Program Office.)[48] "A complete modernization…of the 1960s signal-processing system was being studied in 1999",[49] and in 2002 Site C-6 was tracking "over 95 percent of all earth satellites daily."[7] In 2008, the site's squadron won the General Lance W. Lord Award for mission accomplishment (new "3-D modeling software" had been implemented.)[50] In 2009, the site had been included in a computer model of the February 2009 satellite collision,[51] and GCC Enterprises was contracted for completing "AntiTerrorism and Force Protection Improvements" to the site's infrastructure (perimeter fences, etc.),[52] By 2011 the site's "16 million observations of satellites per year" (rate of 30.4/minute) was "30 percent of the space surveillance network's total workload".[14] A 2012 Sensitive Compartmented Information Facility opened at the site[12] and in 2013, "new operating modes at Cavalier AFS and Eglin AFB [Site C-6 provided] more accuracy" than the 1961 VHF Space Surveillance Fence,[53] which could not detect space objects in low altitude/high eccentricity orbits[54] and was decommissioned[53] by November 2013.[55]



AN/FPS-85 Space Track Radar is a phased array radar at Eglin AFB Site C-6 with a beam steered from 155° to 205° in azimuth and is scanned at 35° elevation.[56] The radar tracks more than 16,000 near-earth and deep-space objects.[13]

External media
Figure 16-3 w/ teardrop outline of site on "Eglin Reservation"
construction video
"USAF Space Track Radar AN/FPS-85"


  1. 1.0 1.1 Mueller, Robert (1989). Air Force Bases (Report). Volume I: Active Air Force Bases Within the United States of America on 17 September 1982. Office of Air Force History. p. 136. ISBN 0-912799-53-6. Retrieved 2013-08-15. "complex surveillance and control system completed 1969" 
  2. 2.0 2.1 Joint Land Use Study - Draft (Report). 
  3. 3.0 3.1 "Eglin Air Force Base Fire Station C6 (2644695)". Geographic Names Information System, U.S. Geological Survey. Retrieved 2014-07-07. 
  4. Google terrain map at 30.564035,-86.214051
  5. 5.0 5.1 5.2 "Site C-6 AN/FPS-85 Spacetrack Radar". Retrieved 2014-07-13.  (citing
  6. 6.0 6.1 "AN/FPS-85 Spacetrack Radar". Retrieved 2013-07-13. 
  7. 7.0 7.1 7.2 AU Space Primer (Report). 2003-07-24. 
  8. 8.0 8.1 8.2 8.3 Reed, Sidney G.; Van Atta, Richard H.; Deitchman, Seymour J. (February 1990). DARPA Technical Accomplishments: An Historical Review of Selected Darpa Projects: Volume I (Report). Institute for Defense Analyses. Retrieved 2014-07-13. "In 1957 a President's Science Advisory Committee panel and many other experts had pointed out the need in ballistic missile defense (BMD) and space surveillance to detect, track and identify a large number of objects incoming or moving at very high speeds. … The recorded outlay for construction of ESAR and its testing, and also including the early experimental work extending bandwidth using the FPS-85, was about $20M. ARPA outlay for the phased array technology program appears to have been about $25M. The original FPS-85 cost about $30M, and its replacement after the fire, about $60M.24 The BTL phased arrays built for the Army's BMD project cost nearly $lB. … Air Force IR reconnaissance satellite studies apparently began in 1956. …BAMIRAC (Ballistic Missile Infrared Analysis Center… In the early 1970's the Air Force's geosynchronous-orbit early warning system, (SEWS), including IR scanning sensors, became operational.22 The present system includes three [Defense Support Program] satellites in geosynchronous orbit, one over the Atlantic and two over the Pacific areas, including, besides IR warning sensors, systems for detection of nuclear explosions. … The SEWS system cost is estimated as about $5 billion to FY 1988."  (citation 24 is "Discussion wilh MG Toomay, 1/90.")
  12. 12.0 12.1 "20th SPCS opens new SCIF". 10/5/2012. Retrieved 2014-07-13. 
  13. 13.0 13.1 13.2 13.3 Cite error: Invalid <ref> tag; name "Peterson" defined multiple times with different content
  14. 14.0 14.1
  17. 17.0 17.1 Major, J. Mark (Fall 1994). Upgrading the Nation's Largest Space Surveillance Radar (Report). Retrieved 2014-07-07. 
  18.,3371311 Anclote Tracking Site "phased down" from May 1 to July 1, 1969.
  19. 19.0 19.1 19.2 Smith, John Q.; Byrd, David A (c. 1991). Forty Years of Research and Development at Griffis Air Force Base: June 1951 – June 1991 (Report). Borky, Col. John M (Foreword). Rome Laboratory. Retrieved 2014-03-10. 
  20. 20.0 20.1 Cite NORAD Historical Summary |year=1964 |period=July–December
  23. " A man surveying and aligning each member on the 45DG scanner face with delicate optical equipment."
  24. Cite NORAD Historical Summary |year=1962 |period=January–July
  25. Cite NORAD Historical Summary |year=1965 |period=January–June
  26. 26.0 26.1 |quote=The original AN/FPS-85 radar used analog phase shifters (due to Prof. Huggins of Johns Hopkins) and vacuum tube receivers. On rebuilding, diode phase shifters and transistor receivers were employed.
  27. 27.0 27.1 Cite NORAD Historical Summary |year=1965 |period=July–December |quote=The Space Defense Center was established as an integrated NORAD/ADC center on 3 September 1965. …on 22 June the JCS directed CONAD to prepare a standby plan for use of the USAF AN/FPS-85 facility at Eglin AFB as a backup to the SDC, and an interim backup plan for use in the event of catastrophic failure prior to availability of the AN/FPS-85.
  28. 28.0 28.1 Cite NORAD Historical Summary |year=1966 |quote=AN/GSQ-89 (SLBM Detection and Warning System) … On 31 July 1964, NORAD concurred with the main conclusions of the study. NORAD recommended to USAF that funds for an austere interim system… DDR&E approved the interim line-of-sight system concept on 5 November 1964 and made $20.2 million available for development. The SLBM Contractor Selection Board, with NORAD representation, recommended the selection of the AVCO Corporation. In July 1965, DDR&E approved AVCO's plan to modify FPS-26 height finder radars at six sites and to install one at Laredo AFB, Texas (Laredo) would then be designated site Z-230). … The modified radars were to be termed AN/FSS-7's and the [signal processing] system was to be designated the AN/GSQ-89.
  29. Leonard, Barry (2009). History of Strategic Air and Ballistic Missile Defense. Volume II: 1955-1972. Fort McNair, DC: Center for Military History. ISBN 9781437921311. Retrieved date tbd. 
  30. 30.0 30.1 Photographs [and] Written Historical and Descriptive Data: Cape Cod Air Station Technical Facility/Scanner Building and Power Plant (Report). Retrieved 2014-06-10. "Technical Facility/Scanner Building (HAER No. MA-151-A), which houses the AN/FPS-1152 radar and related equipment… The first two PAVE PAWS sites in Massachusetts and California represented the first two-faced phased array radars deployed by the U.S." 
  31. Fenn et al. The Development of Phased-Array Radar Technology (Report). Lincoln Laboratories. Retrieved 2014-07-13. 
  33. "Brief History of Aerospace Defense Command" (web transcript of USAF document). Histories for HQ -Aerospace Defense Command, Ent AFB, Colorado. Unit Pages.,13506,704206%7C702985,00.html. Retrieved 2014-07-12. "In September 1959, the Chief of Naval Operations, Admiral Arleigh Burke suggested to the JCS the creation of a unified space command to control all DoD space assets and missions. The Army agreed, but the Air Force was unenthusiastic. … On 11 September 1978, Air Force Secretary John Stetson, at the urging of Under Secretary Hans Mark, had authorized a "Space Missions Organizational Planning Study" to explore options for the future. When published in February 1979, the study had offered five alternatives ranging from continuation of the status quo to creation of an Air Force command for space." 
  34. (citing: "J.E. Reed, “The AN/FPS-85 Radar System,” Proc. IEEE 57 (3), 1969, pp. 324–335."
  35. 35.0 35.1 Del Papa, Dr. E. Michael; Warner, Mary P (October 1987). A Historical Chronology of the Electronic Systems Division 1947-1986 (Report). Retrieved 2012-07-19. "the Space Defense Center combining the Air Force's Space Track and the Navy's Spasur." 
  36. "title tbd". Retrieved date tbd. "Litton/PRC needed a proof-of-concept demonstration to illustrate the cost effectiveness and feasibility of using automated transformation methods to modernize the J3 JOVIAL of BMEWS, SNX 360 Assembler of PARC radar facility, and FORTRAN of EGLIN radar facility into a common modern software language." 
  37. "The Old And The New In Radar Equipment" (Google News archive). February 19, 1969.,6124316. Retrieved 2014-07-09. 
  38. Jane's Radar and Electronic Systems, 6th edition, Bernard Blake, ed. (1994), p. 31 (cited by Winkler)
  39. Engineering Panel on the PAVE PAWS Radar System (1979). Radiation Intensity of the PAVE PAWS Radar System (Report). National Academy of Sciences. Retrieved 2014-06-05. 
  40. J. Toomay (1984). "Chapter 8: Warning and Assessment Sensors". In A. Zraket. Managing Nuclear Operations. Broomings. p. 297.  (cited by Reed)
  42. Nicholas L. Johnson, “U.S. Space Surveillance,” Advances in Space Research, pp. 8(5)-8(20) -- cited by
  49.,1647309 |quote=Site C-6 was test bed for PAVE PAWS
  51. LLNL-CONF-416345
  53. 53.0 53.1
  54. Burnham, W.F.; Sridharan, R.. Proceedings of the 1996 Space Surveillance Workshop (Report). Volume I. Lincoln Laboratory. Retrieved 2014-07-12. 
  56. "Space Surveillance Radar". Retrieved 21 February 2011. 

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