American Geosynchronous SIGINT Satellites

by Major A. Andronov
Zarubezhnoye voyennoye obozreniye
(ISSN 0134-921X), No.12, 1993, pp. 37-43
Translated by Allen Thomson

Active use of equipment for collecting intelligence from radio signals began in the USA during the Second World War. The American admiral C. Nimitz in evaluating the role which such equipment played in the Pacific Theater said that having them was of equal value to having an additional fleet. However, the significance of SIGINT [radioelektronnaya razvedka (RER)] grew even more after the end of WW II. In 1952 the National Security Agency (NSA) was created, which served to concentrate all of the USA's efforts in SIGINT operations, development of the required equipment, and protection of information transmitted over national communications lines. Official data on the budget and staffing are lacking, but experts estimate that around 10 billion dollars are expended each year on the needs of the NSA, and that there are 50-100 thousand people on staff (of whom 80 percent are civilian specialists).

The special position of the NSA is explained by the exceptional importance of the intelligence it obtains on military, political and economic matters, which is then actively used by the US leadership in working out its political course or in undertaking actions of a military and economic nature. Timely creation of an organizational structure with wide-ranging powers and generous financing enabled the USA to deploy around the world a whole arsenal of SIGINT equipment, the most important and expensive of which were space systems.

In the 1950s American special services tried to solve the problem of collecting intelligence about radioelectronic equipment located deep within the territory of the Soviet Union and other socialistic countries by using reconnaissance aircraft which cries-crossed Soviet territory at high altitudes. These attempts, however, were not always successful. The reconnaissance aircraft were shot down by antiaircraft fire and by interceptors in the skies of the USSR, China, the GDR and Cuba (by some estimates, in the period 1950-1969 about 15 US and NATO reconnaissance aircraft were shot down).

The risk connected with the possibility of discovery of the high altitude reconnaissance flights, loss of crew, and the subsequent worsening of inter- government relations forced the American leadership to examine the possibility of using spacecraft, which were still in the future at that time. The WS-117L program (for the development of reconnaissance satellites for the Air Force and CIA), which was approved in 1954 by President Eisenhower also included the creation of satellite signal intercept equipment within the framework of an individual project called Pioneer Ferret.

The first ELINT [radiotekhnicheskaya razvedka] apparatus, called Scotop [? - Skotop]~ was put into space on board the experimental photoreconnalssance satellite Discoverer-13 in August 1960. The Scotop equipment was intended to record the signals of Soviet radars which were tracking the flight of American space objects. The launch of the first specialized ELINT satellites, which received the designation of "Ferret," was begun in the USA in 1962.

The tasks of space-based SIGINT were subdivided into two groups: ELINT against antiaircraft and ABM radars (discovery of their location, operating modes and signal characteristics) and SIGINT against C3 systems. In order to carry out these tasks the US developed Ferret-class satellites of two types: small ELINT satellites which were launched together with photoreconnaissance satellites into initially low orbits and then raised into a polar working orbit at an altitude of 300 to 800 km using on-board engines; and heavy (1 to 2 tonne mass) SIGINT satellites, which were put into orbit at an altitude of around 500 km using a Thor-Agena booster.

The Air Force continues to use ELINT satellites based on modernized Ferrets to the present day. The program of launching heavy SIGINT satellites was completed In 1971 after the orbiting of 15 spacecraft.

The experience of the first ten years of use of these satellites showed that effective intercept of communication channels required moving to higher geosynchronous (24-hour) and elliptical {12-hour) orbits, which would allow continuous monitoring of the operation of radio emitters. Operation of reconnaissance satellites in such orbits demanded that difficult engineering problems be solved, such as those associated with manufacturing large intercept antennas, sensitive radio receivers, and a radio system for covert transmission of intelligence data to Earth. However, the research which had been carried out in the 1960s by the CIA's Directorate of Science and Technology jointly with the firm Thompson-Ramo-Woolridge [TRW] (the main developer of reconnaissance systems in the USA) showed that the advantages were worth the costs, and that in the future high-orbit reconnaissance satellites would be able to carry out the tasks of both COMINT and ELINT (in the USA such combined reconnaissance is called SIGINT).

SIGINT satellites called "Jumpseat" were developed to be place into a 12-hour orbit of the Molniya type (39 thousand km apogee, 600 km perigee, 63 degree inclination). The basic task of these satellites, according to information in the open press, was to intercept radio communications transmitted through the Soviet Molniya communications satellites. From 1971 through 1987 seven satellites of the Jumpseat type were launched.

For the conduct of radio intercept from geosynchronous orbit there were satellites of the Spook Bird [? - Spuk Byord] type, which began to be launched in 1968. In the foreign literature one encounters the assertion that these were prototypes for IMEWS [proto-DSP] missile launch detection satellites, but this is not at all so. The external appearance of the Spook Bird satellites, in contrast to the IMEWS satellites have not yet been declassified or published in the press, which testifies to its space reconnaissance provenance.

Information on space reconnaissance technology is classified "Top Secret" in the US, in connection with which official publications are prohibited and all data on reconnaissance satellites appearing in the open press have only a unofficial character. Secrets pertaining to SIGINT satellites are especially carefully protected. Thus, for many years, Jumpseat satellites were launched as SDS relay satellites, which used the identical types of orbits and booster (the IMEWS missile warning satellites served as a similar "cover" for geosynchronous SIGINT satellites). After some information leaked out, the system of designations was changed.

The Spook Bird satellites developed by TRW under contract to the USAF were intended to monitor the radio communications of command posts and the staffs of higher-echelon commands in the Soviet armed forces, most importantly those of the strategic rocket forces, the powerful missiles of which evoked the most worry in the American leadership. The satellites had 3-meter intercept antennas which were deployed in space. Launch into geosynchronous orbit was accomplished with an Atlas-Agena rocket from Cape Canaveral, Florida.

A characteristic feature of American SIGINT satellites is the use of so- called quasistationary orbits, which were first "proved out" by the Spook Bird satellites. In distinction to the stationary orbits at 36,000 km altitude and zero degrees inclination which are used by the majority of communications and meteorological satellites, the SIGINT satellites' quasistationary orbits have an inclination of 3 to 10 degrees, an apogee of 39 to 42 thousand km, and a perigee of 30 to 33 thousand km. Thanks to these parameters, the satellite does not hang unmoving relative to the Earth, but moves in a complex elliptical trajectory. This enables it to view broad regions in the course of a day and to measure the direction to radio emitters (to take bearings) from various points of the orbit. For a terrestrial observer the path of the satellite has the form of a closed intersecting loop, elongated along the horizon, and having angular dimensions of around 30 degrees in azimuth and 5 to 6 degrees in elevation. (Fig. 1)

Quasistationary have a number of undoubted advantages for carrying out reconnaissance tasks: a large monitoring area, the possibility of taking multiposition bearings on radio emitters and a broadening of their electromagnetic accessibility.

In 1968-1969 two of the first experimental SIGINT satellites of the Spook Bird type (another name is Canyon) were put into quasistationary orbit. These were used for following the buildup of groupings of Soviet forces in the Far East during the period of deterioration of Soviet- Chinese relations in the end of the 1960s (after the conflict on Damanskiy Island). US intelligence services used these satellites to intercept, for example, communications in radio nets controlling the flight of Soviet bombers, the crews of which were at that time undergoing intensive training. In the early 1970s SIGINT satellites were also used for reconnaissance during local conflicts in Vietnam, and also between India and Pakistan.

It is evident that the results obtained by the first SIGINT satellites exceeded all expectations, since subsequent launches of production models [seriynyye obraztsy] were carried out practically every year up to 1978. Production SIGINT satellites of the first generation are known under the name "Rhyolite." Their development for the CIA and NSA was carried out by TRW in the mid 1960s.

Table 1 Characteristics of American SIGINT Satellites

Designator and NameLaunch Date
(International Number)
Booster type (Satellite mass, tonnes)Perigee
Inclination, deg
(period, min)
Experimental "Spook Bird" SIGINT Satellites
Atlas Agena
First Generation Rhyolite Production SIGINT Satellites
Atlas Agena
Atlas Agena
Modernized Rhyolite SIGINT Satellites
RER-1A-2 *23.5.77
Second Generation Chalet SIGINT Satellites
Modernized Vortex SIGINT Satellites (Chalet type)
Titan 34D
(1.4 - 1.6)
RER-2A-2 **2.9.88
Third Generation SIGINT Satellites of the Acquacade type
(3 - 3.5)
* Only the parameters of the transfer orbit were registered with the UN for these satellites. (This is one of the methods for concealing the satellite's true mission.)
** The satellite RER-2A-2 failed to reach operational orbit due to a failure in the Transtage upper stage.

The main efforts of American specialists in creating these satellites were concentrated on increasing the dimensions of the on-board antennas and, correspondingly, the amplification coefficient. Thanks to the use of the most advanced technology of those times for producing light, large-scale structures they succeeded in increasing the dimensions of the Rhyolite antennas to 15 to 20 meters. A possible deployment sequence of a large-scale antenna for a reconnaissance satellite is shown in Figure 2.

Towards the middle of the 1970s the first space-based SIGINT using satellites of the Rhyolite type was deployed on orbit. Judging from the frequency of launches and the mean lifetimes of satellites of those years, the system consisted of three to five satellites, on or two of which were usually placed on orbit in the region of the Indian Ocean and two or three over Africa and the Atlantic Ocean.

The terrestrial component of the system consisted of three large complexes for controlling the satellites and for reception and processing of data. These were located in Pine Gap (Alice Springs, Australia), Harrowgate (Menwith Hill, UK) and Fort Meade (NSA Headquarters, Maryland). The complexes are interconnected by secure satellite communications links, but the most valuable intercept material is regularly delivered to the US from Australia by military transport aircraft.

The largest complex in the system is Pine Gap (Fig. 3), which was completed in 1968, at the time of launch of the first Spook Bird Satellite. At present it has eight antenna systems under radomes of diameter from 2 to 33 meters. It is officially maintained that the facility is under joint use by the US and Australia (the open designation of the Pine Gap facility is the "Joint Defense Establishment for Space Research"). But, according to data in the Western press, the principal information processing tasks are carried out by CIA specialists, and Australian personnel are mostly used in auxiliary work and do not have access to all of the intercepted data. In the technical buildings are located apparatus for controlling the on-board systems of the satellite and preliminary processing of the radio intercept data using IBM and DEC computers. More detailed processing of the data in carried out at NSA and CIA centers in the US. For example, decryption of encoded communications is carried out at Fort Meade ("SIGINT City") using Cray supercomputers which can carry out several billion operations a second.

According to the foreign press, the SIGINT system may first have been used for support of combat operations during the Arab-Israeli war of 1974 for monitoring the air defense radars, staff and command posts of the Arab countries, and also for intercepting radio communications, including conversations of Arab pilots in the air.

As progress was made during the 1970s in the construction of large space structures out of composite materials, the US embarked on the design of a new SIGINT satellite of the Chalet type. The first such satellite, with a mass of around 1.2 tonnes, was launched in 1978 on a Titan 3C booster. The primary mission of this satellite was to intercept conversations carried on UHF [UKV] radio links which used antennas oriented in the direction of the stationary orbit, or antennas with wide main lobes. The technology then extant in the US allowed satellites to be placed in orbit with foldable [raskryvayemyye] parabolic antennas with dimensions of 30-45 m; antennas of other types (e.g., whip or yagi) could attain yet larger dimensions. In several foreign publications one finds assertions that the antennas of Chalet-class satellites are comparable to the dimensions of a soccer field.

In the period 1978-1981 three Chalet satellites were launched. Thanks to the construction of successful cover stories and strict adherence to secrecy during the launches, some foreign experts still identify these satellites with the IMEWS missile warning satellites which served as the cover for Chalet.

In 1984 there began to be launched more modern satellites of this same types which were called Vortex. Their basic distinguishing feature, judging by certain data, was the modernization of their on-board equipment for the purpose of expanding the range of interceptable radio frequencies in the direction of the centimetric band. This led to further growth in the mass of the satellite (to 1.4-1.6 tonnes). Titan 34D boosters lifted a total of three such satellites, but due to a failure in the Transstage transfer stage one of them did not reach its operational orbit.

Starting in 1985 third generation SIGINT satellites began to be deployed, and received the designation "Aquacade." They should have replaced Rhyolite satellites which had expended their consumables and, in distinction to the Chalet satellites, carried out a wider variety of missions in monitoring the radioelectronic situation in the USSR. In addition, they intercepted information transmitted through Soviet communications satellites located in adjoining sections of the synchronous orbit (by that time the USSR had Raduga and Gorizont communications satellites in synchronous orbit in addition to the Molniyas which American Jumpseats had been "stalking" in elliptical orbits).

Large-scale combat US operations were supported by the satellite system for the first time during the war with Iraq in 1990-1991. Despite the very long periods of operation of the satellites (some of the Chalet satellites had at that time been in orbit 11 or 12 years), at the time of the conflict they were put on a round-the clock schedule. The task of intercepting Iraqi radio conversations from space was made easier by the fact that they were for the most part using Soviet communications equipment of the sort the satellites had been designed against.

As a result of retargeting space-based SIGINT apparatus on the Iraqi radio nets, the volume of intercepted information significantly surpassed NSA's processing capability. Consequently the American command was forced to take urgent measures to increase the number of Arabic translators.

Along with carrying out the mission of strategic reconnaissance against Iraqi military C2 radio nets, the United States made special efforts to intercept information of tactical significance (e.g., the fact of airplanes taking off or the movement of tanks as revealed by the radio conversations of the crews) and to deliver it rapidly to users in the theater.

Table 2 shows data on the replacement of reconnaissance satellites in the system. The length of time they function is calculated on the basis of the mean lifetimes of communications satellites of that period and the frequency with which the SIGINT satellites are launched. From these data one can conclude that the SIGINT system based on Rhyolite satellites had four operational satellites and the Chalet system had three. Both groups were operating simultaneously at the beginning of the 1980s, evidently because they carried out different missions. The estimated lifetime on orbit of the SIGINT satellites was six to eight years. The system of Aquacade-class satellites (Magnum, Mentor) was deployed at the end of the 1980s and apparently supplanted the grouping of Rhyolite-class satellites as they reached the end of their operating lifetimes. All in all there were six to eight NSA SIGINT satellites with functional equipment constantly carrying out radio intercept missions in eosynchronous orbits during the 1980s and l990s. In connection with the Increased orbital lifetime of the satellites, and also with the growth in the cost and complexity of space hardware, the frequency of launches of SIGINT satellites dropped at the beginning of the l990s.

Table 2
Replacement Schedule of Geostationary Satellties
in the SIGINT System of the US NSA

Type of SatelliteDesignatorFunctional Lifetime
Spook BirdRER-1E-1
Rhyolite RER-1-1
1970-1975 (1976) #
1970-1977 (1978)
launch failure
1972-1977 (1978)
1973-1978 (1979)
1975-1981 (1982)
1977-1983 (1985)
1977-1984 (1988)
19781986 (1989)
Chalet RER-2-1
1984-1992 ( . ) #
MagnumRER-3-11985 -
MentorRER-3-21989 -
# Years in parentheses indicate dates up to which the satellite was in reserve.

The missions carried out by space-based SIGINT systems expand as satellite hardware is modernized consist of the following:

According to data in the foreign press, the band of radio frequencies which can be intercepted by SIGINT satellites stretches from 100 MHz to 25 GHz. This, however, is difficult to realize in practice as there would have to be a collection of large-scale antennas of differing forms on a satellite. The satellites probably employ the widely used modular principle for combining equipment to carry out specific reconnaissance missions. This is indicated by the simultaneous deployment on orbit of several different groupings of SIGINT satellites (Rhyolite and Chalet, Vortex and Aquacade), which conduct reconnaissance in different parts of the radio spectrum.

Intercepted radio data are transmitted to Earth on a 24 GHz downlink using a narrow-beam antenna. In designing the on-board equipment for the SIGINT satellites, there may have been used prototypes tested on the military communications satellites in the LES series. This equipment includes apparatus for intersatellite links in the millimeter wave band and thermoelectron generators [RTGs ?] which provide electrical power to the on-board systems for more than ten years.

The results of satellite reconnaissance over the past decades have been carefully concealed and only a few of them have been published in periodicals. One such result is the surveillance of Soviet rail-mobile missile complexes (the SS-24 ICBM). According to data in the Western press, the location of these complexes was revealed in the 1980s through intercepts of the exchange of encoded radio signals between the combat complexes and the missile forces' command centers.

Judging by some publications in the foreign press, the fact of the construction of the Soviet radar station at Abalakovo in Siberia also was initially discovered on the basis of radio conversations, and only afterward was a KH-9 photoreconnaissance satellite trained on the construction site.

The first word of the Chernobyl disaster in 1986 also was obtained from analysis of space-based intercept of radio conversations between Kiev and Moscow. Confirmation of the fact of the disaster was obtained subsequently by analysis of recordings of the Earth's infrared background made by an IMEWS missile warning satellite, and from meteorological images made by the military and civilian DMSP and NOAA meteorological satellites. Only on the third day after the disaster did a KH-11 electrooptical reconnaissance satellite take a picture of the ruined reactor.

Based on intercepts of telemetry signals from Soviet missiles, CIA specialists followed the development and testing in the USSR of new missile types and provided the US leadership with reliable information for conducting discussions on the limitation of strategic nuclear forces. For example, as a result of decrypting intercepted telemetry signals from the SS-20 missile, American specialists established that it was being tested with 900 kg of ballast and that its actual capabilities were greater than those demonstrated during testing. The first hint of the development of the heavy Soviet ICBM which came to be called the SS- 19 was obtained by the Americans as the result of intercepting and decrypting a radio conversation between members of the Politburo and missile designers which was being conducted over a automobile radiotelephones. In 1973-1974 SIGINT satellites also revealed tests of the Soviet SA-5 antiaircraft missile against ballistic missile warheads at the Sary Shagan test range.

The end of the Cold War and the reduction of US military budgets is having its effect on SIGINT systems. The current tendency to stretch out the development of new satellites and increase their cost has put American specialists in a difficult situation. The Chalet and Vortex satellites now in use have almost reached the end of their lifetimes. New satellites of the Vega type which supposedly should have replaced the older systems have been subject to sharp criticism in Congress due to their narrow technical focus on Soviet communications lines. This focus does not correspond to current demands for broadening the sphere of action of the American special services into the zones of regional conflicts and the area of economic intelligence.

A new satellite of the Aquacade type has already been at the Cape Canaveral complex for three years waiting to be launched. This satellite, in distinction to Magnum and Mentor which cost 350 million dollars weighed 3.5 tonnes, has better capabilities thanks to more modern equipment. Due to the payload's high cost (the mass will be around 4.5 tonnes), the Titan 4 booster and Centaur upper stage are required to be very reliable, but have not yet demonstrated such dependability. According to statements by the head of the USAF Space Command, each day of delay costs around 1 to two million dollars. The launch scheduled for the end of 1993 is unlikely to take place after the Titan-4 accident at Vandenberg AFB, which led to the loss of US Navy satellites intended for naval reconnaissance.

However, regardless of these difficulties, the US continues to exert serious efforts toward modernizing its space-based SIGINT system to meet the today's increased scope of the missions of the intelligence services. The demonstrated ability to obtain unique and operationally valuable technical, political and economic information will undoubtedly guarantee a leading place for the space-borne SIGINT system among the many resources of US technical intelligence.

Caption for Figure 1
Path of a satellite in "quasistationary" orbit with subsatellite point at 60 degrees East longitude and inclination of 10 degrees.

Caption for Figure 2
A possible sequence for opening a large-scale (100 m) antenna in space:
A - Antenna In folded form;
B - Extension of a telescopic masts with antenna feed unit
C - Opening of the supporting structure of the reflector (the membrane is held in place using cables);
D - Appearance of the antenna in its opened form
(1 - antenna feed unit; 2 - telescopic masts; 3 - system of cables; 4 - membrane which forms the reflective surface of the antenna; 5 - antenna support structure; 6 - radioelectronic equipment unit; 7 - solar batteries

Caption for Figure 3
Exterior view of the NSA SIGINT satellite receiving and data processing complex at Pine Gap (Australia)