Navy Space Surveillance System [NAVSPASUR]

After the Soviet launch of Sputnik I in 1957, detecting and tracking foreign satellites orbiting over the U.S. became a major national security issue. As a result, the Navy Space Surveillance System (NavSpaSur) was developed (1958-1964) by NRL on a "crash basis" for the Advanced Research Projects Agency to detect and track such satellites. NRL was selected to develop this system primarily because of its success in developing the Minitrack satellite tracking network for project Vanguard. Unlike the Vanguard tracking system, NavSpaSur was designed to track both satellites that transmitted signals and those that were "quiet."

Design and construction of the Navy's "Fence" was begun by the Naval Research Laboratory in 1958. By February 1959, a network of six antenna sites stretching across the southern United States from Georgia to California was operational around the clock. Signals recorded at the sites as space objects passed through the high-energy radar were transmitted to the former Naval Ordnance Laboratory at Dahlgren. There, some of DoD's largest computers of that time calculated orbit predictions.

NavSpaSur consisted of nine radar sites stretching between southern California and Georgia and comprises a radar "fence" capable of detecting basketball-sized objects in orbit as high as 7,500 miles above Earth. The information gathered by this system is used to maintain and update the catalogs of orbiting objects, detect newly orbited objects, and warn U.S. military units of periods when they would be vulnerable to detection by foreign satellites.

On Feb. 1, 1961, NAVSPASUR was established at Dahlgren as the Navy's first operational space command after Navy leadership recognized that the service had a particular need for a space detection system to provide the Fleet with operational data on orbiting satellites. The initial surveillance network also included six field stations. Two trans-mitter sites were at Jordan Lake, Ala-bama and Gila River, Arizona. Four receiver stations were built: San Diego, California; Elephant Butte, New Mex-ico; Silver Lake, Mississippi and Fort Stewart, Georgia. Later additions to the NAVSPASUR network included a two-mile-long transmitter at Lake Kickapoo, Texas and two gap-filler receivers at Red River, Arkansas, and Hawkinsville, Georgia. These sites were built between 1961 and 1965, completing the system. By mid-1965, the system had reached its current configuration of nine field stations with three transmitter sites at Lake Kickapoo, Texas, Jordan Lake, Ala., and Gila River, Ariz., and six receiver sites at Fort Stewart, Ga., Hawkinsville, Ga., Silver Lake, Miss., Red River, Ark., Elephant Butte, N.M., and San Diego, Calif.

NAVSPASUR is a bi-static radar system with megawatt transmitters in Alabama, Texas (main site) and Arizona and receivers from South Carolina to San Diego. Since the transmitters are radiating a very narrow fan beam from the eastern horizon (91 deg azimuth) up through the zenith and down to the western horizon (271 deg azimuth) at all elevation angles to detect ALL possible objects in view instantaneously, this does spread out those megawatts to much less at any given angle on any given spacecraft. Thus there is a size below which this 80 Megawatt radar cannot detect objects.

Smaller objects can easily be tracked by other tracking radars because they can focus all of their energy at one instant on one very narrow beam at one point in the sky. But it is obvious that these scanning radars have to know exactly where to look and when, to be able to detect such small objects. Thus these radars have to be scheduled, and shared, and they will never replace the original mission of NAVSPASUR; that is, to detect "unpredicted" objects such as ICBM's heading towards the USA.

The system's network of field stations produces a "fence" of electromagnetic energy roughly 5,000 nautical miles long that extends across the continental U.S. and portions of the Atlantic and Pacific Oceans. In the North-South direction, the fence (Fig. 3-7) is about two miles wide and can detect payloads at a height of 15,000 nautical miles. Together, the system's nine field stations (Fig. 3-8) comprise one of the world's largest antenna systems. With a total length of over 15 miles, the antenna sites incorporate 150 miles of transmission lines, 10,000 feet of steel posts and 18,000 dipoles.

The three transmitters emit a fan of continuous wave radio energy at a fre-quency of 216.98 MHz. The largest transmitter, at Lake Kickapoo, has a two-mile long antenna array composed of 2,556 dipole elements. It has an out-put power of 766.8 kW divided into 18 separate segments, each of which can be operated independently. This pattern pro-vides a reliability over 99 percent, since a few segments can be inoperative with-out significantly affecting the opera-tional capability of the system. The two smaller transmitters at Gila River (40.5kW) and Jordan Lake (38.4kW) provide low-altitude coverage at the East and West extremities of the network.

Six receiver sites collect the transmit-ted energy reflected from satellites as they pass through the fence. Each re-ceiver site has individual antennas spaced at precise intervals. The longest antenna at each site is known as the "alert" antenna, as it is more sensitive and can detect a signal before the other antennas. It then electronically alerts the system controller to the presence of a target, which tunes the receiver to the precise frequency of the reflected energy from the satellite. Two receiver sites, Elephant Butte and Hawkinsville, are "high-altitude" sites. Their antenna arrays have higher gain and their electronics make them more sensitive to the reflected energy from higher altitudes.

The Naval Space Surveillance System field stations comprise a bi-static radar that points straight up into space and produces a "fence" of electromagnetic energy. The system can detect basketball-sized objects in orbit around the Earth out to an effective range of 15,000 nautical miles. Over 5 million satellite detections, or observations, are collected by the surveillance sensor each month. Data collected by the Fence is transmitted to a computer center at Dahlgren, where it is used to constantly update a database of spacecraft orbital elements. This information is reported to the fleet and Fleet Marine Forces to alert them when particular satellites of interest are overhead. The Navy's space surveillance system is one of about 20 sensors that together comprise the nation's worldwide Space Surveillance Network directed by U.S. Strategic Command in Omaha, Neb.

On September 30, 2002 Raytheon Company, Sudbury, Mass., was awarded a $17,173,912 cost-plus-award-fee, firm-fixed-price, cost-plus-fixed-fee contract for the modernization and upgrade of the U.S. Navy's Space Surveillance System, known as the Fence or Space Fence. The upgrade will replace the Very High Frequency radio transmitters and receivers currently in use with ones operating at S-band frequencies. This contract contains options, which if exercised, will bring the total cumulative value of this contract to a not-to-exceed value of $395,590,366. The work will be performed in Sudbury (60.2 percent); Andover, Mass. (34.8 percent); Burlington, Mass. (point nine percent); and Colorado Springs (four point one percent), and is to be completed by September 2004. Contract funds will not expire by the end of the current fiscal year. This contract was competitively procured via the Space & Naval Warfare Systems Command Business Opportunity Page and the Federal Business Opportunities website, with four offers received. The Space and Naval Warfare Systems Command, San Diego is the contracting activity (N00039-02-C-2201).

The Navy transferred operation of the former Naval Space Surveillance System, the nation's oldest sensor built to track satellites and debris in orbit around the Earth, to the Air Force during formal ceremonies 01 October 2004. The Secretary of Defense had directed the Navy to transfer program management of the system to the Air Force beginning in October 2003. The Air Force requested that the Navy continue to operate the space surveillance sensor, also known as the "Fence," through fiscal year 2004.

The transfer of Fence operations to the Air Force brought an end to more than 40 years of Navy control of the sensor from Dahlgren, first by the Naval Space Surveillance System (NAVSPASUR), then assumed by Naval Space Command in 1993, and finally by NNSOC when that organization was established in 2002. In addition to assuming operation of the Navy's space surveillance system, the 20th SPCS Det. 1 is also taking on the Alternate Space Control Center (ASCC) mission, which was first assigned to NAVSPASUR in 1987. In its ASCC role, NAVSPASUR - followed by Naval Space Command and finally NNSOC - served as the backup computational and command and control node for the Space Control Center at Cheyenne Mountain Air Force Base, Colo.