US Naval Space Command Space Surveillance System

(Allen Thomson)

One of the lesser-known assets of the US Space Command's world-wide space surveillance system is the 217 MHz NAVSPASUR "fence" across the southern US. The following items from various sources (indicated in italics) give some basic information about the system, its history and use.




Headquartered at Dahlgren, Va., Naval Space Command began operations Oct. 1, 1983. Naval Space Command uses the medium of space and its potential to provide essential information and capabilities to shore and afloat naval forces by a variety of means:


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.


A constant and vigilant surveillance of potentially hostile military threats is critical in preserving the operational effectiveness of our armed forces around the world. Naval Space Command manages two distinct surveillance efforts in support of Fleet 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...


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...


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 Monmoth, 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...

[For Timation satellite navigation experiments,] Two ground stations were initially used, at NRL [in Washington, D.C.] and the South Texas space surveillance site at Raymondville, Texas (**)

(*) Space Applications Branch, Ranging and Velocity Experimental Equipment, NRL Report 6633, 18 April 1968

(**) Gardner, I., Silverman, I., and Weaver, C., Timation I Ground Station, NRL Report 6876, 3 April 1969.

A History of Satellite Navigation
by Bradford W. Parkinson, Thomas Stansell, Ronald Beard and Konstantine Gromov

Navigation: Journal of the Institute of Navigation (ISSN 0028-1522), Vol.42, No.1; Spring 1995 Special Issue pp. 109-164



The U.S. Navy Spasur (Space Surveillance) 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 1,200ft 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 [General requirements for CW fence radars]

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.

(*) Easton, R.L., and J.J. Fleming: The Navy Space Surveillance System, Proc. IRE, vol.48, pp. 663-669, April, 1960

(**) Aviation Week and Space Technology, Aug.16, 1965
Satellite Surveillance Radar
Charles S. Lerch, Jr.
Chapter 32 of
Radar Handbook
Merrill I. Skolnik, editor
McGraw-Hill, 1970
Library of Congress Catalog Number 69-13615



A. Dedicated low-earth orbit (LEO) detection sensor; does not track.

B. Unique multi-static radar interferometer sensor system consisting of three transmitters and six receivers located across the US at 33N.
1. Covers 5000 nm (15% of earth's circumference).
2. Measures frequency, time and angle of detection
3. Transmits on 216.98 MHz:

C. Detection capabilities:
1. 0.1 m2 RCS @ 2,000 nm
2. 1.0 m2 RCS @ 10,000 nm
3. 200 m accuracy RMS

D. "Standing radar energy fence" is excellent sensor for break-ups and maneuvers.

E. Performance:
1. Detects 70% of catalog objects (100% of LEO objects with I > 33 deg).
2. Several (approx. 150) Space Surveillance Catalog objects only tracked by Fence.
3. Approx. 60K observations/day => 1.7M/month
12K triangulated obs/day => 360K/month
Provides approx. 21% of all SCC LEO observations.

4. Break-ups: > 48 first detects in last 10 yrs
Piece separations: > 59 first detects in last 6 yrs
Often the first sensor to detect a maneuver.

5. Fence has 99.9% operationally ready rate.

Naval Space Operations Center
25 June 1994


Lake Kickapoo Space Surveillance Station Archer City, Texas

The Lake Kickapoo Field Station, located on 180 acres of government owned land approximately thirty miles southwest of Wichita Falls, TX in Archer County is the primary Naval Space Command transmitter. It creates a fan of energy, "the fence", that is narrow in the north-south direction and extends from coast to coast over the southern United States. The Station is aligned on a great circle path inclined to the equator at approximately 33 degrees inclination. In conjunction with eight other field stations it forms the NAVSPACECOM satellite sensor system. Two small transmitters supplement the Lake Kickapoo generated "fence" and six receiver stations collect energy reflected from satellites crossing the beam. Lake Kickapoo is the largest continuous wave (CW) transmitter in the world with an average radiated power of 766.8 KW and operates at a frequency of 216.98 MHz.

The antenna is a single two mile long linear dipole array. The Station was built in two phases that resulted in halves once known as the North Site and South Site. Each had 9 antenna bays that were aligned end to end to form the full antenna array. Now the 18 bays have central control from the original South Site and 2556 dipole elements form the total antenna array.

The operation and maintenance of the Field Station is provided under contract by Rick Montoya Services Incorporated of McLean, VA. The Station is manned solely by contract personnel with only the Center at Dahlgren, VA utilizing civil service and military personnel.

The Lake Kickapoo Station is manned during the daytime work week by a Station Manager, Technical Supervisor, Senior Technician, two Shift Technicians, a Shift Assistant, two Maintenance Mechanics, a Maintenance Assistant and a Part-time Secretary. At other times, two Electronic Technicians and one Shift Assistant are on duty at the Station.

Total annual cost to operate this station is approximately $1.8M with $800K of this being the cost of electricity.

A new phase reference system using infrared fiber optics replaced the aged RF coaxial system in May 1993. This reference system monitors and maintains phase integrity for the 2 mile long Kickapoo antenna. Recent improvements at the Kickapoo site include a system controller upgrade to be completed by mid 1996.

General Information

1. Telephone: (817) 574-4526 phone
(817) 574-4527 fax
(817) 733-5800 cellular phone

2. Management: Station Manager Ardie O. Wood
Technical Supervisor Ralph T. Widner

3. Mailing Address: Naval Space Command Field Station

Lake Kickapoo Space Surveillance Station
P.O. Box 365
Archer City, TX 76351-0365

4. Shipping Address: Naval Space Command Field Station

Lake Kickapoo Space Surveillance Station
ATTN: Station Manager
Route 2178, 12 miles W of Archer City
Archer City, TX 76351

5. Station Coordinates: Latitude 33 32 48.079
Longitude 098 45 47.772

6. Nearest Airport: Wichita Falls Municipal Airport

7. Regional Airport: Dallas-Fort Worth Intl Airport

8. Lodging: Days Inn, Wichita Falls (817) 723-5541
La Quinta, Wichita Falls (817) 322-6971
Sheraton, Wichita Fall (817) 761-6000
Holliday Inn, Wichita Falls (817) 766-6000

9. Restaurants: McBride Land & Cattle Company
Uncle Len's Catfish House
El Chico Restaurant

10: Adjacent Stations(s): From Lake Kickapoo to Elephant Butte: (Approx. 615 miles, 11 hours driving time) From Olney, TX, Rt 114 to Seymour, US Rt 82 West to Las Cruces NM, and I-25 North to Truth or Consequences, NM

From Lake Kickapoo to Red River:
(Approx. 315 miles, 5 1/2 hours driving time)

From US Hwy 82 East to Lewisville

NAVSPACECOM fact sheet dated 23 January 1996



The Dahlgren Division of the Naval Surface Warfare Center, Dahlgren, Va is seeking sources on a competitive basis for an antenna verification testing and installation of replaced/installed spare components at the NAVSPACECOM Elephant Butte, New Mexico Field Station. These antennas are used in a one-of-a-kind earth satellite signal detection receiver. This receiver is in use at six NAVSPACOM Field Station. The antennas are constructed of Dipole Elements (144 per 600 foot array), coaxial transmission line combiners, tees, elbows, expansion joints and 7/8 inch, 3-1/8 inch transmission lines. The contractor will test fifty 600 foot arrays at the Elephant Butte, NMNAVSPACECOM Receiver Station...

Commerce Business Daily, April 17, 1997 PSA-1826



Spectrum Allocation

Footnote US239 [not available] provides for protection of the Navy's Space Surveillance (SPASUR) system operating in the southern part of the United States in the frequency band 216.88-217.08 MHz.[EN416] The Navy has modernized its SPASUR system, and has operated since 1965. The NAVSPASUR system provides data on satellites and other space objects as they pass over the continental United States. The system uses three transmitter sites and five receiver sites positioned on a great circle in the southern part of the United States. It is a bistatic system, locating objects by triangulation.[EN417]

[EN]417. A.R. Francoeur, Naval Space Surveillance System (NAVSPASUR) Solid State Transmitter Modernization, IEEE National Radar Conference, Institute of Electrical and Electronics Engineers, at 147 (1989).

U.S. National Spectrum Requirements: Projections and Trends
U.S. Department of Commerce
National Telecommunications and Information Administration
NTIA Special Publication 94-31
March, 1995
Chapter 4


Amateur Use of NAVSPASUR

Subject: Re: NAVSPASUR Fence - 216.980 Mhz
From: (Dave Perrussel)
Date: 1996/03/31
Message-Id: <4jn1di$>
Newsgroups: (Brian D Heaton) wrote:


> I am looking for info regarding the NAVSPASUR fence operating
>at 216.980 Mhz. I had been looking for info for the last couple
>months and just saw a mention of it in Popular Communications. There
>was some discussion (on DRIG) of experiments at using it to refine
>elsets for OSCAR birds.

First of all, its now called NAVSPACECOM fence (since late 1993)
but we still call it the SPASUR fence (grin)

A person from Florida (the name escapes me) had used the Lake Kickapoo transmitter for following satellites. Again, I'll have to look up the name at work on Monday.

> The article mentions transmitters in Texas (Kickapoo Lake I
>believe), Alabama and Arizona. The only thing I have been able to
>find thats even close is the AFSPACECOM PAVE PAWS phased array radar
>system. Its sites are listed as Mass, Calif, Texas, and Georgia.
>This is most likely a mircowave system, however.

The Fence has 3 frequencies: Gila River (Phoenix) Arizona - 216.97 MHz Lake Kickapoo (Archer City) Texas - 216.98 MHz Jordan Lake (Wetumpka) Alabama - 216.99 MHz receivers throughout the southern US (too many to mention here)

> I am interested in detecting satellites crossing the fence and
>would appreciate any data available on the subject. If there is
>enough interest I can try to put together a summary or possibly a FAQ
>if one doesn't already exist. Thanks in advance for your assistance..

Well, I'm in development of a web page (one of these days they'll put it on line!)

If you want more details, let me know. I work for the fence on a daily basis. E-mail me at the address below.


David Perrussel
Subject: Re: NAVSPASUR Fence - 216.980 MHz
From: (Gary Coffman)
Date: 1996/03/30
Message-Id: <>

[More Headers]

In article <> writes:

> I am looking for info regarding the NAVSPASUR fence operating
>at 216.980 MHz. I had been looking for info for the last couple
>months and just saw a mention of it in Popular Communications. There
>was some discussion (on DRIG) of experiments at using it to refine
>elsets for OSCAR birds.
> The article mentions transmitters in Texas (Kickapoo Lake I
>believe), Alabama and Arizona. The only thing I have been able to
>find that's even close is the AFSPACECOM PAVE PAWS phased array radar
>system. Its sites are listed as Mass, Calif, Texas, and Georgia.
>This is most likely a microwave system, however.

70cm actually. PAVE PAWS is an early warning radar. It is frequency agile and uses a steered phased array at very high power. It makes a raucous buzzing noise. The one in Georgia (Robbins AFB) is inactive, and likely to stay that way. The high ERP was determined to be actively dangerous to nearby aircraft, like the SAC B-52 bombers taking off and landing at Robbins. The other sites may or may not still be in use.

NAVSPASUR is a different animal. It is a CW signal (not Morse, a real continuos carrier) on 216.983 MHz aimed straight up in a fan pattern aligned with a line of latitude, IE east-west. There are three transmission sites, Jordan Lake AL, lat 32.659 long 86.264, Kickapoo Lake TX, lat 33.558 long 98.7367, and Gila River AZ, lat 33.11 long 112.03.

Phase slaved interferometers at remote receive sites give 3D position, and doppler measurements give range rate. With this information, an orbit for the object can be calculated. Because of the way the sites are staggered longitudinally, any satellite with an inclination of 33 degrees or more will show up on successive orbits through 2 or more of the fences. That allows the initial orbital element set to be refined.

You can use these signals to check and correct satellite element sets. Use your satellite prediction program to find out the time the satellite should cross one of these latitudes and be in a mutual footprint with your station and one of these sites, aim your antennas at the predicted position, and measure the actual AOS, LOS, and doppler of the reflected signal. The offset of this actual data from the predicted data can then be used to correct the element set.

Of course if the satellite has an active beacon, and you know its frequency precisely, you can do the same thing without resort to NAVSPASUR. It is most useful for locating passive targets.


Gary Coffman KE4ZV | You make it, | Due to provider problems Destructive Testing Systems | we break it. | with previous uucp addresses 534 Shannon Way | Guaranteed! | Email to Lawrenceville, GA 30244 | |

via DejaNews

Additional information on amateur and other "unofficial" use of the NAVSPASUR signal may be found at

Pictures of the Lake Kickapoo transmitter site may be found in Chapter 8 of Observing Earth Satellites, Desmond King-Helle, Van Nostrand Reinhold, 1983, ISBN 0-442-24877-6