United States Space Surveillance Network

Space surveillance is a critical part of United States Strategic Command's (USSTRATCOM) mission and involves detecting, tracking, cataloging and identifying man-made objects orbiting Earth, i.e. active/inactive satellites, spent rocket bodies, or fragmentation debris. Space surveillance accomplishes the following:

Predict when and where a decaying space object will re-enter the Earth's atmosphere;
Prevent a returning space object, which to radar looks like a missile, from triggering a false alarm in missile-attack warning sensors of the U.S. and other countries;
Chart the present position of space objects and plot their anticipated orbital paths;
Detect new man-made objects in space;
Produce a running catalog of man-made space objects;
Determine which country owns a re-entering space object;
Inform NASA whether or not objects may interfere with the space shuttle or satellites and International Space Station orbits.

Space Surveillance Network

The command accomplishes these tasks through its Space Surveillance Network (SSN) of U.S. Army, Navy and Air Force operated, ground-based radar's and optical sensors at 25 sites worldwide.

The SSN has been tracking space objects since 1957 when the Soviet Union opened the space age with the launch of Sputnik I. Since then, the SSN has tracked more than 24,500 space objects orbiting Earth. Of that number, the SSN currently tracks more than 8,000 orbiting objects. The rest have re-entered Earth's turbulent atmosphere and disintegrated, or survived re-enty and impacted the Earth. The space objects now orbiting Earth range from satellites weighing several tons to pieces of spent rocket bodies weighing only 10 pounds (4.5 kg). About seven percent of the space objects are operational satellites, the rest are debris. USSPACECOM is primarily interested in the active satellites, but also tracks space debris. The SSN tracks space objects which are 10 centimeters in diameter (baseball size) or larger.

The Air Force Space Surveillance System

The Air Force Space Surveillance System (AFSSS), also known as the "space fence", is a very high frequency radar network located at sites across the southern United States (from California to Georgia) with a centralized data processing site at the Naval Network and Space Operations Command in Dahlgren, Virginia. The "fence" is now operated by the U.S. Air Force (20th Space Control Squadron Detachment 1).

The Satellite Detection and Reconnaissance Defense (the former designation of the NSSS) reached initial operating capability in 1961. Since then, the role of the "fence" has grown. The system detects space objects from new launches, maneuvers of existing objects, breakups of existing objects, and provides data to users from its catalog of space objects. Orbital parameters of more than 10,000 objects are maintained in this catalog -- which has now gained usage by NASA, weather agencies, and friendly foreign agencies. The information is essential to computing the collision avoidance information to de-conflict launch windows with known orbiting space objects.

Ground-based Electro-Optical Deep Space Surveillance (GEODSS)

There are three operational GEODSS sites that report to the 21st Operations Group: Socorro, New Mexico; Maui, Hawaii; and Diego Garcia, British Indian Ocean Territory. A site at Choe Jong San, South Korea was closed in 1993 due to weather and cost concerns. GEODSS is an optical system that uses telescopes, low-light level TV cameras, and computers. It replaced an older system of six 20 inch (half meter) Baker-Nunn cameras using photographic film.

GEODSS tracks objects in deep space, or from about 3,000 mi (4,800 km) out to beyond geosynchronous altitudes. GEODSS requires nighttime and clear weather tracking because of the inherent limitations of an optical system. Each site has three telescopes. The telescopes have a 40-inch (1.02 m) aperture and a two-degree field of view. The telescopes are able to "see" objects 10,000 times dimmer than the human eye can detect. This sensitivity, and sky background during daytime that masks satellites reflected light, dictates that the system operate at night. As with any ground-based optical system, cloud cover and local weather conditions directly influence its effectiveness. GEODSS system can track objects as small as a basketball more than 20,000 miles (30,000 km) in space, and is a vital part of USSTRATCOM’s Space Surveillance Network.

Air Force Fact Sheet

Space Based Visible (SBV) Sensor

The SSN includes one spaceborne sensor, the space-based visible (SBV) sensor, carried into orbit aboard the midcourse space experiment (MSX) satellite launched by the Ballistic Missile Defense Organization in 1996.

Space Control Center

The SCC in Cheyenne Mountain Air Station is the terminus for the SSN's abundant and steady flow of information. The SCC houses large, powerful computers to process SSN information and accomplish the space surveillance and space control missions.

The Air Force also provides the site and personnel for the Alternate SCC (ASCC). The ASCC would take over all operations in the event the SCC could not function. This capability is exercised frequently.

External links

U.S. Strategic Command Space Surveillance

J-Track 3D displays a globe and orbiting satellites.

Orbital Debris Quarterly News information on some of the latest events in orbital debris research.