Air Force Space Surveillance System

The Air Force Space Surveillance System (AFSSS), historically known as the Space Fence, was a long-range radar network developed to detect and track objects in Earth orbit. As a central component of the United States Space Surveillance Network, it played a pivotal role in monitoring satellites, space debris and other orbital bodies. The system’s continental radar configuration created an electromagnetic “fence” that any object crossing its path would trigger, enabling uncued detection across a wide span of low-Earth orbit. Originally engineered by the United States Navy in the late 1950s, the AFSSS later became an Air Force–operated asset until its decommissioning in 2013, after which a new generation S-band Space Fence emerged to replace its capabilities.
The AFSSS formed part of the broader American strategy of maintaining situational awareness in space, supporting military, scientific and intelligence objectives during the Cold War and well into the twenty-first century.

Origins and Early Development

The system originated as the US Navy Space Surveillance System (NAVSPASUR), with experimental work underway by 1959. It began full operations in 1961. NAVSPASUR was designed to provide uninterrupted detection of satellites by emitting continuous-wave radio energy along a continental baseline. Any metallic orbital object travelling through this radar curtain would reflect a signal that could be recorded and analysed.
This early capability predated the formal creation of NORAD’s unified space surveillance apparatus. Through the 1960s and 1970s the system was augmented with optical instruments, including Schmidt cameras capable of recording objects as small as a basketball at considerable altitudes. This combination of radar and optical monitoring made NAVSPASUR one of the world’s most advanced surveillance networks of its time.

System Architecture and Technical Characteristics

The AFSSS consisted of a row of high-power transmitters and six receiving stations positioned approximately along the 33rd parallel north across the contiguous United States. Collectively, these installations formed an immense horizontal detection field.
Key elements included:

• Three main transmitter sites:
  • Lake Kickapoo, Texas (master transmitter), transmitting near 216.983 MHz with an exceptionally high continuous-wave output.
  • Maricopa, Arizona at roughly 216.970 MHz.
  • Jordan Lake, Alabama at about 216.990 MHz.
• Six receiving stations, including specialised high-altitude sites at Elephant Butte in New Mexico and Hawkinsville in Georgia. These installations featured extended antenna arrays for tracking objects at higher altitudes.

Originally operating at 108.5 MHz—just above the FM broadcast band—the system was modernised in 1965, doubling the frequency to approximately 216.98 MHz to enhance target resolution and allow detection of smaller objects. During the 1990s further complexity was added through offset-frequency fill-in transmitters, which enabled operators to distinguish signals from multiple illuminators.
The master transmitter at Lake Kickapoo was regarded as the most powerful continuous-wave radar station in the world, boasting a nominal output of 768 kW and an enormous effective radiated power due to its antenna design.

Operational Control and Administrative Changes

For most of its operational life, the system remained under Navy control. NAVSPASUR was managed by Naval Space Command from 1993 and by the Naval Network and Space Operations Command from 2002. On 1 October 2004, responsibility transferred to the United States Air Force’s 20th Space Control Squadron.
In 2009 the routine management and maintenance of the AFSSS field stations were contracted to Five Rivers Services, a Colorado-based company. Subsequent contract modifications supported continued operation of the network through the early 2010s.

Role in Space Surveillance

The system’s principal advantage was its ability to provide uncued detection, meaning that it could identify new or unexpected objects crossing the radar fence without prior tracking data. This capability was vital for cataloguing previously unknown satellites, monitoring foreign space launches and detecting newly generated debris, such as fragments resulting from collisions or explosions in orbit.
The urgency of improved debris monitoring became clear after several major orbital fragmentation events, including the 2009 collision between Iridium-33 and Kosmos-2251, which produced hundreds of new debris fragments. These incidents contributed to calls for a more precise, modern radar system.

Plans for Modernisation and the S-band Upgrade

Recognising the limitations of the ageing VHF system, the Air Force initiated efforts to develop a next-generation Space Fence. In 2009, design contracts were awarded to major defence companies, including Lockheed Martin, Northrop Grumman and Raytheon. The envisioned replacement used S-band radar, whose shorter wavelength allowed substantially greater resolution and the detection of far smaller objects.
The new system was also intended to feed data directly into the Joint Space Operations Center Mission System, which provides continuous operational support for space activities, including orbital tracking, space weather updates and foreign launch assessments.

2013 Shutdown of the AFSSS

Federal budget sequestration in 2013 delayed progress on the new system and also precipitated the closure of the AFSSS. On 1 August 2013 Air Force Space Command directed that all stations of the legacy system be shut down and vacated by 1 October. In practice, the radar was deactivated at 00:00 UTC on 1 September 2013.
The final recorded echoes reportedly originated from a Russian satellite and a sporadic meteor, marking the end of the original Space Fence’s operational life. Although valued for its uncued detection capability, the AFSSS was increasingly constrained by its dated architecture and limited measurement precision.

The New Space Fence and Continuing Legacy

A modern Space Fence system, built by Lockheed Martin, became operational on 27–28 March 2020 at Kwajalein Atoll in the Marshall Islands, with an optional second site planned for Western Australia. Using high-precision S-band radar, this installation significantly enhances global space situational awareness by detecting far smaller debris and contributing to safer orbital operations.
The legacy of the AFSSS endures in its foundational role in the development of American space surveillance. Its decades of continuous data collection provided a comprehensive baseline for modern tracking systems and helped establish the United States as a global leader in space situational awareness. The new S-band Space Fence builds upon this heritage, equipping operators with the tools necessary to manage an increasingly congested orbital environment