United States Space Surveillance Network

The United States Space Surveillance Network (SSN) detects, tracks, catalogs and identifies artificial objects orbiting Earth, e.g. active/inactive satellites, spent rocket bodies, or fragmentation debris. The system is the responsibility of United States Space Command and operated by the United States Space Force and its functions are:

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 artificial objects in space;
Correctly map objects traveling in Earth orbit;
Produce a running catalog of artificial space objects;
Determine ownership of a re-entering space object;

The Space Surveillance Network includes dedicated, collateral, and contributing electro-optical, passive radio frequency (RF) and radar sensors. It provides space object cataloging and identification, satellite attack warning, timely notification to U.S. forces of satellite fly-over, space treaty monitoring, and scientific and technical intelligence gathering. The continued increase in satellite and orbital debris populations, as well as the increasing diversity in launch trajectories, non-standard orbits, and geosynchronous altitudes, necessitates continued modernization of the SSN to meet existing and future requirements and ensure their cost-effective supportability.

SPACETRACK also developed the systems interfaces necessary for the command and control, targeting, and damage assessment of a potential future U.S. anti-satellite weapon (ASAT) system. There is an Image Information Processing Center and Supercomputing facility at the Air Force Maui Optical Station (AMOS).

History

1957–1963

thumb|upright|Baker-Nunn satellite tracking camera

The first formalized effort by the US government to catalog satellites occurred at Project Space Track, later known as the National Space Surveillance Control Center (NSSCC), located at Hanscom Field in Bedford, Massachusetts. The procedures used at the NSSCC were first reported in 1959 and 1960 by Wahl, who was the technical director of the NSSCC. In 1960, under Project Space Track, Fitzpatrick and Findley developed detailed documentation of the procedures used at the NSSCC. Project Space Track began its history of satellite tracking from 1957 to 1961.

Early Space Track observations of satellites were collected at more than 150 individual sites, including radar stations, Baker–Nunn cameras, telescopes, radio receivers, and by citizens participating in the Operation Moonwatch program. Individuals at these Moonwatch sites recorded observations of satellites by visual means, but there were numerous observation types and sources, some automated, some only semi-automated. The observations were transferred to the NSSCC by teletype, telephone, mail, and personal messenger. There, a duty analyst reduced the data and determined corrections that should be made to the orbital elements before they were used for further predictions. After this analysis, the corrections were fed into an IBM 709 computer that computed the updated orbital data. The updated orbital data were then used in another phase of the same computer program to yield the geocentric ephemeris. From the geocentric ephemeris, three different products were computed and sent back to the observing stations for their planning of future observing opportunities.

Concurrent with Minitrack was the use of the Baker-Nunn satellite tracking cameras. These systems used modified Schmidt telescopes of great resolution to photograph and identify objects in space. The cameras first became operational in 1958 and eventually operated at sites worldwide. At their peak, the Air Force ran five sites, the Royal Canadian Air Force ran two, and the Smithsonian Institution's Astrophysics Observatory operated a further eight sites. The Baker-Nunn system, like Minitrack, provided little real-time data and was additionally limited to night-time, clear weather operations. A new S-band Space Fence is under construction at Kwajalein Atoll.

US Space Catalog

Since 1957, the United States Department of Defense (DoD) has maintained a database of satellites states known as the Space Object Catalog or simply the Space Catalog. Starting with the launch of Sputnik 1 as the second database entry and its booster listed as the first database entry. These satellite states are regularly updated with observations from the Space Surveillance Network, a globally distributed network of interferometer, radar and optical tracking systems. By the year 2024, the number of cataloged objects was past 31,000.

Different astrodynamics theories are used to maintain these catalogs. The General Perturbations (GP) theory provides a general analytical solution of the satellite equations of motion. The orbital elements and their associated partial derivatives are expressed as series expansions in terms of the initial conditions of these differential equations. The GP theories operated efficiently on the earliest electronic computing machines, and were therefore adopted as the primary theory for Space Catalog orbit determination. Assumptions must be made to simplify these analytical theories, such as truncation of the Earth's gravitational potential to a few zonal harmonic terms. The atmosphere is usually modeled as a static, spherical density field that exponentially decays. Third body influences and resonance effects are partially modeled. Increased accuracy of GP theory usually requires significant development efforts. The first installation, designated AN/FPS-17(XW-1) was at Diyarbakir (Pirinclik), Turkey, to detect Soviet launches. A second system, designated AN/FPS-17(XW-2), was installed at Laredo AFS (about northeast of Laredo AFB) in Texas, to track rockets launched from White Sands, New Mexico, and serve as a radar test bed. A third system, designated AN/FPS-17(XW-3), was installed on Shemya Island, Alaska, to detect Soviet launches. The Diyarbakir FPS-17 became operational in June 1955, the Laredo installation in February 1956, and Shemya in May 1960. The first two installations closed without replacements; the Shemya installation was replaced by the Cobra Dane (AN/FPS-108) radar.

The FPS-17 antenna featured a fixed parabolic torus section reflector that typically stood high and wide and was illuminated by an array of radar feed horns placed in front of it. The transmitters operated in the VHF band, sending out pulses at frequencies between approximately 180 to 220 MHz. The FPS-17 was unique in that, unlike most radar types, each site's version differed from the other sites. Differences included transmitter equipment, reflector size and number, and the number and arrangement of feed horns. Additionally, the FPS-17 was the first operational radar system to employ pulse compression techniques. There were two AN/FPS-17 antennas at Diyarbakir, Turkey, one antenna at Laredo, and three at Shemya in the Aleutians.

Blue Nine and Blue Fox

Blue Nine refers to a project which produced the AN/FPS-79 Tracking Radar Set built by General Electric, used with the 466L Electromagnetic Intelligence System (ELINT); US Air Force. Blue Fox refers to a modification of the AN/FPS-80 tracking radar to the AN/FPS-80(M) configuration. Shemya, AK, 1964. Both of these systems incorporated GE M236 computers.

AN/FPS-80

A 60-foot dish mechanical tracking radar built by General Electric. Deployed at Shemya Island, Alaska, as a UHF radar and upgraded to L-Band in 1964. Used as tracker radar for Spacetrack network measurements once target detected. Principally used for intelligence purposes to track Russian missiles. The advanced FPS-108 Cobra Dane phased array radar replaced the FPS-17 and FPS-80 radars in 1977.

Space Surveillance Network

thumb|400px|The Space Surveillance Network

The command accomplishes these tasks through its Space Surveillance Network (SSN) of U.S. Army, Navy and Space Force operated, 30+ ground-based radars and optical telescopes worldwide, plus 6 satellites in orbit.

, the catalog built using SSN data listed 44,336 objects including 8,558 satellites launched into orbit since 1957. 17,480 of them were actively tracked while 1,335 were lost. The rest have re-entered Earth's turbulent atmosphere and disintegrated, or survived re-entry and impacted the Earth. The SSN typically tracks space objects which are 10 centimeters in diameter (baseball size) or larger.

The Space Surveillance Network has numerous sensors that provide data. They are separated in three categories: dedicated sensors, collateral sensors and auxiliary sensors. Both the dedicated and collateral sensors are operated by the USSPACECOM, but while the former have a primary objective to acquire SSN data, the latter obtain SSN data as a secondary objective. The auxiliary sensors are not operated by the USSPACECOM and usually perform space surveillance collaterally. Additionally sensors are classified as Near-Earth (NE) tracking - observing satellites, space debris and other objects in lower orbits, or Deep Space (DS) - generally for asteroids and comets.

Dedicated sensors
Ground-based Electro-Optical Deep Space Surveillance (GEODSS) sites
Space Surveillance Telescope (SST)
MOSS - an Electro-Optical (E-O) surveillance system located at the Morón Air Base, Spain
GLOBUS II radar
AN/FPS-85 Space Track Radar
AN/FPS-133 Air Force Space Surveillance System, also known as the Space Fence and its replacement Space Fence
Midcourse Space Experiment (MSX) / Space Based Visible (SBV) satellites
Collateral sensors
Maui Space Surveillance System (MSSS) and Advanced Electro-Optical System (AEOS) telescope, co-located with a GEODSS station in Maui, Hawaii
Haystack Ultrawideband Satellite Imaging Radar (HUSIR), Haystack Auxiliary Radar (HAX) and Millstone Hill Radar
ALTAIR and ALCOR radars at the Ronald Reagan Ballistic Missile Defense Test Site, Kwajalein Atoll
Ascension Range Radar, locate at the Eastern Spacelift Range
Ground-Based Radar Prototype (GBR-P), located Ronald Reagan Ballistic Missile Defense Test Site, Kwajalein Atoll
Auxiliary sensors
Solid State Phased Array Radar System (SSPARS) / AN/FPS-132 Upgraded Early Warning Radar (UEWR) system of system, deployed at multiple sites
AN/FPS-108 Cobra Dane
AN/FPQ-16 Perimeter Acquisition Radar Characterization System (PARCS)

Ground-based Electro-Optical Deep Space Surveillance

thumb|GEODSS atop the Haleakala crater

thumb|right|[[Midcourse Space Experiment]]

Ground-based Electro-Optical Deep Space Surveillance, or GEODSS, is an optical system that uses telescopes, low-light level TV cameras, and computers. It replaced an older system of six Baker-Nunn cameras which used photographic film.

There are three operational GEODSS sites that report to the 20th Space Control Squadron:

Socorro, New Mexico
AMOS, Maui, Hawaii
Diego Garcia, British Indian Ocean Territory .

A site at Choe Jong San, South Korea was closed in 1993 due to nearby smog from the town, weather and cost concerns. Originally, the fifth GEODSS was planned to be operated from a site in Portugal, but this was never built.

Moron Optical Space Surveillance (MOSS), a transportable telescope that contributed to the GEODSS system was operational at Morón Air Base, Spain () from 1997 to 2012.

GEODSS tracks objects in deep space, or from about 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 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 in space or a chair at , and is a vital part of USSPACECOM's Space Surveillance Network. Each GEODSS site tracks approximately 3,000 objects per night out of 9,900 objects that are regularly tracked and accounted for. Objects crossing the International Space Station (ISS) orbit within will cause the ISS to adjust their orbit to avoid collision. The oldest object tracked is Object #4 (Vanguard 1), launched in 1958.

Space Based Visible (SBV) Sensor

The SSN included 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. It was retired from service on June 2, 2008.

The Space Based Space Surveillance (SBSS) pathfinder satellite now performs the mission previously handled by the MSX SBV.

The Canadian military satellite Sapphire, launched in 2013, also contributes data to the SSN.

Civil services

The USSPACECOM is primarily interested in the active satellites, but also tracks space debris. As the number of space debris and the value of satellites in space grew, it has become important to protect civil economic activity and help satellite operators avoid collisions with debris. In 2010, USSTRATCOM was given authority to provide space situational awareness services to commercial and foreign actors.

References

External links

The Space-Track website
U.S. Strategic Command Space Surveillance
Orbital Debris Quarterly News information on some of the latest events in orbital debris research.
A GEODSS Sourcebook