Naval Space Command

The Naval Space Command (NSC) was a military command of the United States Navy. It was headquartered at Dahlgren, Va., and began operations Oct. 1, 1983. Naval Space Command used the medium of space and its potential to provide essential information and capabilities to shore and afloat naval forces by a variety of means:
 * Operating surveillance, navigation, communication, environmental, and information systems;
 * Advocating naval warfighting requirements in the joint arena; and
 * Advising, supporting, and assisting the naval services through training, and by developing space plans, programs, policies, concepts, and doctrine.

The command was merged into Naval Network and Space Operations Command, itself part of Naval Network Warfare Command, about July 2002.

Overview
Naval Space Command's headquarters staff and operational element numbers approximately 350 Navy military and civilian personnel. Their component commands include the Naval Satellite Operations Center and the Fleet Surveillance Support Command.

Naval Space Command, a component of USSPACECOM, operates assigned space systems to provide surveillance and warning, and provides spacecraft telemetry and on-orbit engineering support. In addition, Naval Space Command serves as the Alternate Space Control Center [AASC] for USSPACECOM's primary centers located at Cheyenne Mountain AS.

ASCC missions include operational direction of the entire global space surveillance network (SSN) for commander in chief, USSPACECOM (USCINCSPACE). The ASCC also detects, tracks, identifies, and catalogs all man-made objects in space and provides position information on these objects to about 1,000 customers. In addition, ASCC is charged with monitoring the space environment and informing owners and operators of U.S. and allied space systems of potential threats to their assets by continuous liaison with the systems' operations centers.

The heartbeat of Naval Space Command revolves around providing space support to day-to-day operations of the Fleet and Fleet Marine Forces worldwide, whether for routine deployments, exercises, or actions in response to a crisis situation. This space support to terrestrial and naval forces can be categorized across a broad spectrum of activities that encompass communications, surveillance and indication, and warning, intelligence, navigation, and remote sensing.

Surveillance
Naval Space Command manages two distinct surveillance efforts in support of U.S. Navy ships, other U.S. Navy units, and Fleet Marine Forces: tracking satellites in orbit and monitoring over-the-horizon threats from sea and air forces.

First, Naval Space Command operates a surveillance network of nine field stations located across the southern U.S. Three transmitter sites in the network are located at Jordan Lake, Ala., Lake Kickapoo, Texas, and Gila River, Ariz. Six receiver sites are located at Tattnall, Ga., Hawkinsville, Ga., Silver Lake, Miss., Red River, Ark., Elephant Butte, N.M., and San Diego, Calif.

These surveillance stations produce a "fence" of electromagnetic energy that can detect objects out to an effective range of 15,000 nautical miles.

Over one million satellite detections, or observations, are collected by this surveillance network each month. Data gathered is transmitted to a computer center at Naval Space Command headquarters in Dahlgren, where it is used to constantly update a data base of spacecraft orbital elements. This information is reported to Fleet and Fleet Marine Forces to alert them when particular satellites of interest are overhead. The command also maintains a catalog of all earth-orbiting satellites and supports USSPACECOM as part of the nation's worldwide Space Surveillance Network.

Intelligence
Naval Space Command provides space intelligence support to deployed naval forces through an initiative dubbed "Chambered Round." The Chambered Round product is a message that provides deployed naval forces with tactical assessments of hostile space capabilities and specific reactions to their operations. This knowledge assists Fleet and Fleet Marine Force tactical units in reducing their vulnerability to space reconnaissance efforts...

http://www.spacecom.af.mil/usspace/fbnavspa.htm

History
The Minitrack system that was developed in the late 1950s for the NRL Vanguard Satellite Program used the signals emitted by Sputnik and later satellites to determine their positions and orbits. This pioneering tracking system led to the concept of tracking nonradiating, or noncooperative, satellites by signals reflected off them. An experiment using a transmitter in Fort Monmouth, New Jersey and Minitrack receivers demonstrated the concept, and from this experiment a larger and more elaborate system was developed by NRL. This system became known as the Naval Space Surveillance System (NAVSPASUR), which was commissioned as an operational command in 1961. Although the operational command is now integrated with the Naval Space Command, the sensor system is still in active use as a major component of the North American Aerospace Defense Command (NORAD), and has become the alternate Space Defense Computational Facility.

The system concept of NAVSPASUR is that of a continuous wave (CW) multistatic radar. A high-powered transmitter generates a large fan beam of energy, commonly called the "fence," which reflects signals from an orbiting object back to separate receiving stations. These receiving stations use large arrays of antennas as an interferometer to determine the angle and angle rates of arrival from the reflected signals. By observing the target satellite from several stations, the position can be determined; using multiple penetrations, the orbit can be inferred. This rather simple concept led to a highly reliable system that could detect virtually any satellite coming within the transmitter's illuminated field.

Even though the NAVSPASUR system performs the functions of detection and satellite orbit determination very well, there are limitations on coverage and time required to determine an orbit with the CW fence approach. NRL experiments into methods of improving the system included the idea of transmitting ranging signals as well as the primary CW signal, so that not only could the angles at the receiving sites be measured, but the distance to the target satellite as well (*). An experimental parallel fence with a ranging capability was begun in South Texas in 1960 to demonstrate system performance and early orbit determination. The three stations built in South Texas were a transmitter and two receiving stations.

SPASUR
The U.S. Navy Space Surveillance (SPASUR) System is a CW fence radar consisting of a chain of stations located on an east-west great-circle path across the southern United States. Three transmitter stations (one high-powered in the center of the chain and two low-powered on the ends for gap filling) and six receiving stations are used in the network. The system originally operated at 108 MHz [the Minitrack frequency] but was converted to 216 MHz in 1965, along with upgrading and expansion of the original experimental network.

The high-power transmitter consists of two 500-kW transmitters operating in parallel and feeding a north-south linear array 10,560 feet long.

The receiving stations are equipped with a number of linear antenna arrays for phase sensing and alerting. The north-south length of the phase-sensing antennas at two of the sites is 2,400 ft, and the east-west baseline (which sets the angular-accuracy limit) is 1,200 ft or approximately 260 wavelengths. Angular measurements from the various receiving sites are transmitted to a central computer facility located at Dahlgren, Va.

Control and Computation

Since angle measurements from at least two receiver stations are needed to determine position and to eliminate false alarms due to meteors or aircraft, the outputs must be collected at a central point and processed… One detection (encoded in digital form) requires a total of less than 100 bits. One telephone line from a receiving station to a central control could easily handle 70 or more detections per minute, a rate much higher than would be expected from any foreseeable space population.

The computation requirements for correlating the various receiver angle measurements and providing a detection report are relatively modest. Even [if orbital elements for new detections must be generated and correlated with objects in a catalog].. these computing requirements are well within the capability of a computer of the size of the IBM 7090 for space populations of a few thousand objects.