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U.S. IMEWS Space System and Creation of an Advanced Ballistic Missile Launch Detection System

by Lieutenant Colonel A. Andronov and
Captain S. Garbuk, candidate of technical sciences

No 12, 1994 (signed to press 8 Dec 94) pp 34-40

The IMEWS [Integrated Missile Early Warning Satellite] space system was deployed in the early 1970's for giving the U.S. supreme military-political leadership early warning of a nuclear missile strike against U.S. territory. Its other name is DSP [Defense Support Program]. Compared with ground radar equipment, the system permitted detecting the launches of Soviet and Chinese ICBM's at an earlier stage.1

But in connection with changes in the military-political situation and the development of missile technology, a need arose for upgrading electronic equipment, making requirements tougher and broadening the range of missions assigned to the system. The principle of evolutionary modernization of onboard and ground gear with a gradual increase in the number of operational satellites and optimization of their orbital deployment (Fig. 1) was made the basis for this.

Three IMEWS satellites were deployed in geostationary orbit and two fixed receiving complexes were deployed during 1970-1974: in the United States at Buckley Air Force Base (Colorado) and in Australia (Woomera). The satellite deployed in the Indian Ocean zone (Indian) was intended for detecting Soviet and Chinese ICBM launches, and the two satellites (Atlantic and Pacific) situated over U.S. coastal waters were to keep an eye on launches of intermediate-range ballistic missiles from Soviet submarines (SLBM's) on alert duty off the U.S. coast.

In the latter half of the 1970's the main concern of the U.S. military leadership was caused by Soviet increased range SLBM's, which could reach U.S. territory from remote waters of the Pacific, Atlantic and Arctic oceans. The Pacific satellite was displaced almost 30° to the west of the American continent (in the vicinity of 132-136° West Longitude) to detect missile launches from these waters. But similar attempts to shift the Atlantic satellite closer to Europe in 1977 and 1980 proved unsuccessful inasmuch as the ground complex station at Buckley could not carry on dependable data reception from the satellite in the remote area of the Atlantic (36° West Longitude) due to the low elevation at which the satellite was visible, and the transportable SPS station (a total of two complexes were made) which was undergoing tests in that period required substantial modification.

Improved IMEWS satellites launched from 1976 on had an increased period of design functioning (it increased from 1.5 to 3 years, but in reality they operated for 5-7 years), which permitted creating an orbital reserve of satellites which had served their time but had serviceable onboard gear. One reserve satellite each was deployed in the Indian Ocean zone and over U.S. territory, which increased the reliability of the system as a whole (see table).

Characteristics of IMEWS Satellite Models Characteristics

IMEWS System Satellite Models Experimental (Phase 1)Improved (Phase 2)MOS/PIM SED DSP-I
Years launched1970-19731975-19771979-19841984-1987 Since 1989
Number of satellites launched (serial numbers)4 (1st through 4th)3 (5th through 7th)4 (8th through 11th)2 (12th and 13th) 3 (14th through 16th)
Design (actual) operating life, yrs 1.5 (3) 3 (5) 3 (5) 5 (7) 5-7 (7-9)
Satellite weight, t 0.9 1.04 1.2 1.68 2.38
Power supply system output, watts 400 480 500 705 1275
Number of telescope IR receiver detectors 2000 2000 2000 6000 6000
IR telescope operating wavelength, microns 2.7 2.7 2.7 2.7 and 4.32.7 and 4.3
Main system development stages determined by improvement of satellites Deployment of ICBM and SLBM detection system Expansion of zone for monitoring increased-range ICBM and SLBM launches Global monitoring of launches of ICBM's, SLBM's, operational-tactical missiles, tactical missiles and missiles of other classes

Special attention was given to Soviet SLBM basing areas in Arctic waters not viewed from a geostationary orbit. Four satellites of a new modification designated MOS/PIM (Multi Orbit Satellite/Payload Improvements) were developed in the mid-1970's and inserted into geostationary orbit during 1979-1984. In case of the appearance of crisis situations, the launch of new satellites to a highly elliptical Molniya type of orbit is possible for monitoring polar areas of the Arctic Ocean (in reality IMEWS satellites were not inserted into such orbits). MOS/PIM satellites now provided surveillance of the entire Earth's surface visible from orbit without dead spaces and were equipped with more powerful transmitters, which permitted receiving satellite data using small antennas of the SPS transportable stations. The diameter of SPS station antennas was 11 m and that of LPS fixed stations was 18 m.

In the early 1980's greatest concern for American experts was caused by new Soviet SS-20 intermediate-range missiles intended for employment in European TVD's [theaters of military operations]. One SPS station was deployed in Germany (Kapaun) in 1982 for operational notification of the U.S. European Command, and in 1984 the operations area of the Atlantic satellite was shifted 25° closer to Europe. Thus, Soviet ballistic missile basing areas in the European USSR were under dual monitoring of the Atlantic and Indian satellites.

The main problem in detecting operational-tactical missile launches is connected with the low intensity of engine exhaust flare glow and the short duration of engine operation. IMEWS satellites of a new generation designated DSP-I (DSP-Improved) were developed in the 1980's. Their onboard telescopes operated in two regions of the IR spectrum (mean wavelength values 2.7 and 4.3 microns instead of only 2.7 microns for the old satellites) and had 6,000 detectors (previously there were 2,000). The new band permitted detecting missiles with low exhaust flare glow intensity. The second problem, short duration of operation of operational-tactical missile engines, was remedied by increasing the number of operational satellites simultaneously monitoring areas with a missile danger. To ensure phased development of the new gear and modernization of the ground complex, two SED (Sensor Evaluationary Development) transition model satellites (IMEWS-12 and -13), which used the old design base but were equipped with new telescopes, were launched in 1984 and 1987.

Technical capabilities of the SED and DSP-I model satellites permitted detecting ballistic missile launches from any area of Earth. To realize the concept of global monitoring of ballistic missile launches, the system's orbital grouping had been reorganized by 1985 in such a way that three operational satellites were spaced 110-130° in longitude apart approximately evenly along the Equator.

The onboard gear of the new satellite models (three models were launched from 1989 through 1993--IMEWS-14, -15 and -16) permitted detecting ICBM's and operational-tactical missiles as well as tactical, surface-to-air, antiship and other missiles and even jet aircraft in an afterburning mode. In this connection the United States began accelerated development of gear for prompt communication of warning signals over satellite communication channels to the U.S. Armed Forces tactical echelon (for example, to command posts [CP's] of Air Force wings about mass takeoffs of aircraft, to naval ships about antiship missile launches, to CP's of Army units and formations about operational-tactical and tactical missile launches). On receiving such signals the theater [TVD] commanders can take retaliatory measures promptly in a combat situation. From the late 1980's to the early 1990's the IMEWS space system acquired the importance of a means for global tracking of launches of different classes of missiles, for conducting theater [TVD] area reconnaissance in the IR band, and for prompt warning of users at various Armed Forces command and control echelons from strategic to operational-tactical.

The expansion in range of missions performed by the system in support of command elements of U.S. theater [TVD] forces required changes in the organizational structure (the system is subordinate to the U.S. Armed Forces unified Space Command) and an increase in the number of operational satellites in orbit. A fourth operational satellite (European) began operation in 1988 in the vicinity of 8-10° East Longitude; it monitored ballistic missile launches on the European continent and transmitted data to a receiving station in Germany. A fifth operational satellite (Far Eastern) was placed in operation in the eastern Indian Ocean in 1991.

Thus, the system's present-day orbital grouping made up of five operational satellites provides threefold to fourfold monitoring of the main areas with missile danger (from the standpoint of the U.S. leadership) in Europe and Asia, including in the Near and Far East.

The first combat use of the IMEWS system for warning U.S. Armed Forces about launches of Iraqi operational-tactical missiles in 1991 was assessed in the U.S. press as very successful (98 percent of all launches were detected). It was asserted that the system was not intended for performing such missions, but modification of gear for detecting operational-tactical missiles already had been under way since the mid-1980's. For example, it was reported in the military press that work was carried out in Europe in 1990 for prompt communication of warning signals to Patriot SAM system command posts about Soviet operational-tactical missile launches. Contemporary articles contain more critical assessments of the system's functioning.

During the conflict Iraqi missile launches were detected by the Indian and European IMEWS-16 and -15 satellites (70° and 10° East Longitude respectively), and by the new IMEWS-12 launched in November 1990 and undergoing accelerated testing in the Far Eastern zone. In addition, the IMEWS-13 Atlantic satellite (39° West Longitude) could be used; by early 1991 it had limited capabilities due to nine long years of operation. Essentially all the system's ground equipment processed data from the satellites: the complex in Woomera (from the Indian and Far Eastern), the station in Kapaun (from the European) and the Buckley complex (from the Atlantic). Depending on the volume of data received, either a full launch report containing data on time, launch coordinates, type of ballistic missile and estimated impact area would be transmitted to consumers after processing (the accuracy of determining the launch point was 3-5 km and warning time was 1-5 minutes), or only a warning signal about a ballistic missile launch would be transmitted.

The alarm signal came in place of a full report, for example, with the launch of the missile which hit the U.S. barracks in the city of Dhahran, which led to the greatest loss of Americans in the entire war with Iraq (28 personnel died). A full report just was not transmitted to the troops despite the fact that the missile launch was detected by three satellites (IMEWS-12, -13 and -15 made 2-3 fixes each).

The mission of issuing preliminary target designations on operational-tactical missiles to Patriot system radars also did not manage to be accomplished in the course of the war. The IMEWS space system essentially was the first echelon of the ABM defense system deployed by the multinational forces command in the Near Eastern Theater [TVD], and also included air, ground and space imaging and electronic reconnaissance assets, a U.S. ground radar in Turkey, communications equipment, and the Patriot systems. Intercepting Iraqi ballistic missiles over populated areas led to victims and to destruction even if the interceptor missiles hit the target. Thus, according to data of Israeli military specialists, the first missile attacks against Israeli cities not protected by these systems led to fewer victims and destruction than approximately the very same number of attacks after deployment of Patriot batteries.

Consequences of missile strikes would have been less serious if, based on rough target designations back before the moment approaching Iraqi ballistic missiles were detected by Patriot system radars, preliminary interceptor missile launches were made to intercept these ballistic missiles at a maximum distance from the defended installation.

Despite use of data from four satellites, U.S. specialists did not succeed in calculating the azimuth of the plane of departure and coordinates of warhead impact areas with an accuracy and promptness sufficient for making preliminary launches. Moreover, because of organizational and technical disorders, data on the azimuth of ballistic missile launches were not transmitted to combat complexes of interceptor missiles, and some army brigades operating outside the zone of responsibility of corps air defense weapons did not even receive warning signals of missile strikes.

The problem of vectoring airstrike elements to Iraqi mobile ballistic missile launchers based on satellite data also was not solved. Warning signals would arrive at air wing CP's 5-7 minutes after launch and airstrike elements appeared in the presumed ballistic missile launch areas 15-30 minutes later, when the launchers already had managed to abandon them.

The problem of detecting mobile launchers even under moderate desert terrain conditions proved enormously more difficult than previously assumed, and although large aerial and space reconnaissance forces in addition to the IMEWS system were involved in solving it, Iraq continued to deliver missile attacks until the end of the war.

In the opinion of the most critical U.S. experts, combat employment of the IMEWS system might have proven fully ineffective "had there not been elements of luck and Iraqi military mistakes." An analysis of its results in the course of the Persian Gulf conflict lent new impetus to upgrading the space warning system.

The principal shortcomings of the existing system are considered to be the following: low periodicity of scanning the Earth's surface (one scan in 10 seconds), which is connected with low photodetector sensitivity; presence of centralized data processing, which diminishes promptness in communicating data to theater [TVD] consumers; and the existence of periods when onboard satellite gear is "blinded" by reflected solar radiation. The U.S. command anticipates purchasing another seven DSP-I model satellites (from IMEWS-17 to IMEWS-23) and, from satellite No 19 on, to considerably modernize their onboard gear for processing and transmitting data to Earth, including to a theater [TVD] on operational-tactical missile launches, inasmuch as increasing the promptness of these processes continues to be a key issue. Those satellites will support system functioning after 2000.

The MGT mobile systems developed in the mid-1980's for receiving and processing satellite data and intended above all for increasing the survivability of the system's ground element were connected directly with the NORAD CP and were not adapted for prompt notification of theater [TVD] consumers. New receiving stations being developed jointly by the U.S. Army and Navy under the TSD (Tactical Surveillance Demonstration), TAGS (Tactical Ground Station) and Radiant Ivory programs will be stationed in a theater [TVD] and will transmit processed data directly to consumers at the operational-tactical echelon. It is expected that around $48.4 million will be spent on these programs up to 1995. During 1993-1994 tests of the first two prototypes of receiving stations were conducted in the United States and FRG. The Navy command plans to procure two sets of stations and the Army five on condition that a sufficient amount of funds is allocated.

The concept of the new receiving station's operation in detecting low-signature targets is based on several innovations: a lowering of thresholds for activating satellite telescope IR detectors, which increases the likelihood of detection and the duration of tracking of targets with a low-intensity engine exhaust flare glow; simultaneous processing of target fixes made by several satellites from different points of a geostationary orbit (stereo images), which increases fix accuracy; and processing of received data using ballistic missile ballistic models for a more precise forecast of the parameters of operational-tactical missile trajectories.

A concept on which Air Force specialists are working within the scope of the Talon Shield program provides for an alternative centralized scheme of processing data from IMEWS satellites at the NORAD CP with subsequent transmission of warning signals to theater [TVD] installations.

In 1992 the Air Force command let a $24.5 million contract with Aerojet to develop the CTPE (Central Tactical Processing Element) system for processing data from IMEWS satellites and other assets (including theater [TVD] radars) on low-signature targets such as aircraft and missiles with low-intensity engine exhaust flare emission and with prompt issuance of data to theater [TVD] consumers. The system is based on a 12-processor computer system with parallel architecture developed by Silicon Graphics and installed at the NORAD CP. System speed is 60 million operations per second, clock frequency is 100 MHz, and subsequently it is planned to increase it to 150 MHz.

In late 1993 it was planned to conduct the first actual tests of the CTPE system with "stereo processing" of measurement data from several IMEWS satellites and with output of warning signals in near-real time. Work under the Talon Shield program is planned to be completed by 1997.

The United States connects a further quality leap, which will permit expanding the class of targets detected and tracked and increasing sensitivity and reliability of the space warning system, with development of new-generation satellites, which will replace existing satellites after 2005.

Work to create a new ballistic missile launch warning system has been under way since 1979 in parallel with modernization of the IMEWS system. U.S. specialists believe that possibilities for further improving onboard gear of existing satellites have been exhausted to a considerable extent. The potential sensitivity of sensors and accuracy of a fix on missiles being launched are limited by the design scheme adopted in the late 1960's in developing satellites (scanning by rotating the telescope) and by the low rate of scan of the Earth's surface.

Advanced satellites were being created in various years under the AWS (Advanced Warning System), BSTS (Boost Surveillance and Tracking System) and FEWS (Follow-On Early Warning System) programs, but these projects did not get to the stage of full-scale development due to the high cost and risk connected with the introduction of new technologies for creating multiple-element, matrix photodetectors which perform a continuous scan or high-speed scan of the entire Earth's surface and with the introduction of light, large optics and data processing systems aboard satellites.

Research under the AWS program was conducted on order of the U.S. Air Force during 1979-1984. The possibility was studied for the first time of tracking the operation of several ballistic missile stages with the help of matrix photodetectors with tunable optical filters simultaneously in several frequency bands of the optical spectrum. Data were to be transmitted directly to theater [TVD] consumers after onboard processing. As an additional task, it was planned to accomplish the detection and tracking of airborne targets in the medium-wave region of the IR spectrum.

After work began under the SDI (Strategic Defense Initiative) Program, the AWS was reoriented in 1984 for creating the BSTS system, which was viewed as the first element of a multi-echelon ABM defense system. It was proposed that the new system would support the detection of a mass ICBM launch under conditions of wide use of countermeasures, including nuclear countermeasures, and would output preliminary target designation data to the ABM defense battle management and communications system with an accuracy of around 1 km. Onboard processing gear would have a high degree of radiation protection and would reduce the data flow rate from several hundred megabits per second to tens of kilobits per second.

Two groups of firms headed by Lockheed and Grumman respectively were conducting competitive development of new satellites, on which around one billion dollars were spent. The first project envisaged use of a less expensive scanning telescope. Grumman rejected the scanning principle and developed a focal matrix of 2,000 modules, each of which contains around a million sensing elements. Both firms used mercury and cadmium tellurides in fabricating the matrix, and ceramics, beryllium, and silicon carbide for the telescope mirror, which was around 1 m in diameter. It was planned to make wide use of ultraspeed radiation-resistant microcircuits as onboard processors.

An external view of the satellite developed by Grumman under the BSTS program is shown in Fig. 2. A characteristic feature of the satellite, which weighs 5.4 t, is use of a triple-axis stabilization system, an optical system with three-mirror telescope, and a unified module combining photodetectors, processor and thermal regulation system radiator. The program was shut down in the early 1990's due to duplication of main functions by the BSTS and Brilliant Eyes systems and due to its high cost, which was unacceptable after the cold war ended. But the main engineering solutions obtained in the course of the work have been preserved in subsequent projects.

Competitive design of the new FEWS system began in July 1992 by order of the U.S. Air Force; it was carried on by two groups of firms headed by Thomson-Ramo-Wooldridge and Lockheed (the contracts are worth $240 million each).

Requirements for the new system now were formulated with consideration of the experience of the war against Iraq and the wide proliferation of intermediate-range missile weapons expected in the world by the end of the 1990's. It was presumed that the advanced system, whose deployment was supposed to begin in the 2000's, would support detection of ICBM and operational-tactical missile launches on a global scale and full onboard data processing and prompt data transmission to the theater [TVD]. Specialists believe that because of the application of the stereo processing principle, the area where the system calculates a mobile operational-tactical missile launcher is located will be the size of a "stadium, and not a city," as is the case for the present-day IMEWS. The onboard processors also are intended for eliminating background emissions and false returns, and the use of intersatellite communications gear will permit rejecting the use of ground systems outside of U.S. territory.

The FEWS advanced satellite system project developed by Thomson-Ramo-Wooldridge and by Grumman (Fig. 3) weighs 3.1 t and, like the BSTS program satellite, has a triple-axis stabilization system and multiple-element photodetector matrix installed in the focal plane of a telescope with a three-mirror optical system. Competitive design of the FEWS system was stopped in November 1993 at the request of the U.S. Defense Department because of high cost (around $11.7 billion for the period 1995-2019), lack of conformity to specifications and performance characteristics placed on it, and the changed military-strategic situation in the world.

In 1995 the U.S. Defense Department proposes to begin development of the new ALARM (Alert, Locate and Report Missiles) space system for detecting ballistic missile launches, intended for detecting the launches not only of ICBM's and SLBM's, but also tactical, operational-tactical and cruise missiles as well as flights of high-altitude aircraft. U.S. experts believe that in the next few years this will become one of the main tasks for the advanced space system for missile launch detection, which is to provide prompt communication of data to consumers in support of the theater [TVD] ABM defense organization.

According to the concept being advanced by the Pentagon, the advanced ALARM system is to hold an intermediate position in characteristics between the existing IMEWS and rejected FEWS systems, with the possibility of phased improvement of its gear as new technological solutions are worked out and characteristics of the FEWS system are brought up to design characteristics.

It is presumed that ALARM satellites will have less cost and capabilities compared with FEWS, but better characteristics than present-day IMEWS satellites for detecting operational-tactical and tactical missiles. The following are the principal directions for lowering its cost:
  • combining ALARM and IMEWS ground systems, as a result of which the need for creating costly ground stations disappears; supporting detection of tactical and operational-tactical missile launches only in two regions of the Earth instead of global coverage as for the FEWS system;
  • rejecting the installation of instruments aboard the advanced satellites for detecting nuclear explosions (accommodated on NAVSTAR satellites) and gear for onboard data processing and intersatellite communications (which satellites of the first models have);
  • using medium class booster rockets instead of costly Titan IV heavy rockets (around $300 million).

As a result of the proposed measures, the cost of developing the ALARM system can be around one billion dollars during 1995-1999 instead of the five billion planned to be allocated for creating the FEWS system in this same period. In case of U.S. Congressional approval of the ALARM project, it is planned to carry out competitive preliminary design work during 1995-1997 and to begin full-scale development in October 1997, as a result of which the first satellite may be inserted into geosynchronous orbit in 2004.

The ALARM project already now is coming under harsh criticism. According to U.S. Congressional Budget Office estimates, the cumulative cost of the life cycle of the ALARM and FEWS systems during 1995-2019 is approximately $11.3 and 11.7 billion respectively, and the former's capabilities are substantially lower. U.S. Defense Department specialists assert that the main saving (compared with FEWS) will be achieved in the next decade beginning with the fourth model (after 2007) as a result of the technology of manufacturing onboard gear having been upgraded. The U.S. Congress will make the final decision on work under the ALARM program at the end of the current year. Questions of operation and upgrading of the space missile launch detection system presently are acquiring political coloration. In view of the fact that such costly systems, created only in the United States and Russia, are losing importance as the first echelon of a strategic warning system with the end of the cold war, the American side is examining questions of presenting satellite data to other countries for detecting operational-tactical missile launches during local conflicts.

IMEWS system data already have been transmitted to Israel in 1993, for example, during the delivery of strikes by U.S. cruise missiles against Iraqi targets (for timely detection of possible retaliatory launches of operational-tactical missiles by Iraq against Israel). Options are being considered for presenting warning data to South Korea, Japan and European countries in case a threat of delivery of missile strikes appears on the part of North Korea, China or the Arab states. Such data will be provided along with deliveries to these countries of very costly components of theater [TVD] ABM defense systems (Patriot systems or their more advanced versions). As the missile launch detection system is developed further, its ground receiving complexes will become an important part of advanced theater [TVD] ABM defense systems.


1. For more detail on the IMEWS system see ZARUBEZHNOYE VOYENNOYE OBOZRENIYE, No 6, 1992, pp 51-57--Ed.

Fig. 1. Diagram of IMEWS
satellite deployment:
1. IMEWS-14 (Pacific)
2. IMEWS-13 (Atlantic)
3. IMEWS-15 (European)
4. IMEWS-16 (Indian)
5. IMEWS-12 (Far Eastern)
A vertical line denotes deployment areas of operational
satellites, a broken vertical line denotes deployment areas of
reserve satellites, and a broken horizontal line denotes a
transfer to other orbits

Fig. 2. External view of BSTS satellite:
1. Module with photodetector matrix and subsystems for thermal regulation and data processing and transmission
2. Payload module with optical telescope
3. Service subsystems model
4. Motor compartment

Fig. 3. Advanced FEWS program satellite:
1. Focal plane with photodetector matrix
2. Telescope hood
3. Secondary telescope mirror
4. Primary telescope mirror
5. Tertiary telescope mirror
6. Intersatellite communications radio link antenna
7. Service subsystems compartment
8. Radio link antenna for data transmission to Earth
9. Solar battery panels

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