by Jos Heyman, Tiros Space Information

The military services of the United States and its NATO allies have been and remain extensive users of satellite technology to support their military communications requirements. The purpose of this article is to provide a historical overview of the military communications satellites and its NATO allies.

Early Research and Development
Much of the early research with communications satellite undertaken by the USA was conducted by the military services or NASA. As a result, a number of such satellites deserve consideration in this overview.

The Signal Corps Orbiting Relay Experiment (Score) was the first satellite used for investigating communications between Earth orbit and the surface. Launched on December 18, 1958, the satellite was placed in an orbit of 185 x 1484 km at an inclination of 32.3°, remaining attached to the final stage of the launch vehicle. It carried a tape recorder and transmitted a recorded message spoken by President Eisenhower at 132 MHz. The batteries became exhausted after 13 days, during which period the feasibility of such communications had been proven.

The Echo program investigated the use of a reflective surface in radio communications. After suborbital tests with the balloon from Wallops Island on October 28, 1959, February 27, 1959, and May 31, 1960, and a launch failure on May 13, 1960, Echo-1, launched on 12 August 1960. It successfully provided the first space communications link between two ground stations. It was a 30-meter diameter balloon with an aluminized surface that reflected radio signals back to Earth. It was in a near-circular orbit of 1524 x 1684 km at an inclination of 47.2° and remained in orbit for almost eight years. After initial taped messages from Goldstone (California) to Holmdel (New Jersey), the first two way communication took place on August 13, 1960, between Cedar Rapids (Iowa) and Richardson (Texas). Also, the first pictures were transmitted between the same stations on August 19, 1960.

Echo-2, launched on January 25, 1964, and was larger than Echo-1, measuring 46 meters in diameter. It was placed in a polar orbit of 1029 x 1316 km and an inclination of 81.5°, enabling the first joint experimental program to be carried out by the United States and the U.S.S.R. Although the two Echo satellites provided valuable experience in space communications, they proved to be unsuitable for long-term use. The lack of signal amplification was a severe handicap. Their large size was also a factor as the pressure of solar radiation caused the balloons to drift erratically.

Reference must be made to the Westford project. This was a military program that envisaged the placing of 400 million copper needles in orbit, which would then be used as a passive reflector for communications. The needles were launched on board the Midas-4 early warning satellite on October 21, 1961, but failed to disperse properly. The experiment was repeated on May 9, 1963, with the launch of the Midas-7 early warning satellite — 400 million metal fibers needles were released. Only a few of the needles were catalogued and, although in 1966 it had been suggested that most of the needles had re-entered with a few clusters expected to re-enter by 1968, in reality most of the needles remain in orbit.

Courier-1B, launched on October 4, 1960, (after a failure on August 18, 1960) was the first ‘repeater’ satellite, amplifying the signals and then re-transmitting them to Earth. It was placed in a 938 x 1237 km orbit with an inclination of 28.3°. The satellite was built by Philco and carried four transmitters operating in the 1700/2300 MHz band, as well as a repeater system that consisted of five tape recorders with a five minutes capacity each. Its batteries lasted for 17 days during which time much information was acquired about the operation of repeaters in space, propagation conditions and ground-station operations.

Syncom-1 (February 14, 1963) was the first attempt to place a satellite into geostationary orbit but, due to communications problems, this orbit was not achieved. Syncom-2 was intended to be placed in a geostationary orbit at 55° W on July 26, 1963 but only achieved a near-synchronous orbit of 35,584 x 35,693 km with a period of 24 hours and 14 minutes but with an inclination of 30.3°.

In spite of this incorrect orbit, the satellite, which was used for military communications over the Indian Ocean until April 1969, provided valuable experience. The satellite was built by Hughes and was spin-stabilized and carried two transponders operating in the 7.3/1.8 GHz band.

Syncom-3 was identical to Syncom-2 and was the first satellite to achieve a near-geostationary orbit on August 19, 1964 — the orbit was 38 minutes short of being geostationary. The satellite was used for communications over the Pacific Ocean, including the relay of television broadcasts of the 1964 Olympic Games from Tokyo to the United States. Syncom-3 was taken out of service in April 1969.

The U.S. Air Force conducted another experiment involving passive communications systems with Orbiting Vehicle (OV) 1-8. The OV consisted of a wire mesh sphere with a diameter of 914 cm that contained a balloon inside, which was launched on July 14, 1966.

In 1965, the U.S. Air Force commissioned the Lincoln Laboratories of the Massachusetts Institute of Technology to develop and build a series of experimental satellites to test and evaluate advanced space communications devices and systems.

Experiments included satellite-to-satellite transmissions over long distances and communications with a variety of small ground terminals. The satellites, designated as Lincoln Experimental Satellites (LES), were placed in synchronous orbits of various inclinations. The last two in the series were powered by radioisotope thermo-electric generators (RTG) and were three-axis stabilized. Eight LES satellites were launched between February 11, 1965, and March 15, 1976.

A follow-on to the LES series was known as Tactical Communications Satellite (Tacsat) and was launched on February 9, 1969. The satellite, which was built by Hughes, was positioned over the Galapagos Islands in the Pacific Ocean and was the most powerful communications satellite in orbit at that time. It provided a link between ground-based mobile receivers with 30 cm antennas and aircraft and operated in the 225/400 MHz and 7/8 MHz bands.

DSCS
The first operational U.S. military communications satellite system was the Initial Defense Satellite Communications System (IDSCS), which commenced as a research and development project but was converted into a global operational network for high volume communications in 1968 (see Table 1, Table 2 and Table 3 on page 18). It was originally known as the Initial Defense Communications Satellite Program (IDCSP). The satellites were placed in an equatorial, near-geostationary orbit at altitudes of approximately 33,800 km in which they drifted app. 30° each day. They were built by Philco and carried a single transponder operating in the 8/7 GHz band.

The second generation of satellites was named Defense Satellite Communications System (DSCS) II, and featured increased capacity with two transponders operating in 8/7 GHz. The operational system consisted of four satellites located over the Atlantic Ocean at 12° W, the Indian Ocean at 60° E, the West Pacific Ocean at 135° W and the East Pacific Ocean at 175° E with an additional two satellites as in-orbit spares. The DSCS II satellites were built by TRW and were spin-stabilized.

The third generation was DSCS III and the 14 satellites launched between October 30, 1982, and August 29, 2003, were built by General Electric (and their successors). They were equipped with seven transponders which operated in the 7/8 GHz band and were also fitted with anti-jamming devices.

Milstar
The next generation of military communications satellites, designated as Military Strategic Tactical and Relay (Milstar), consisted of three satellites in geostationary orbit. Built by Lockheed Martin, the satellites were equipped with up to 32 transponders operating in the 45/21 GHz, to service mobile military terminals, 225/400 MHz and 60 GHz bands, the latter for satellite-to-satellite communications.

Initially it was planned to augment the system with three satellites in highly elliptical polar orbits as well as a number of satellites in much higher orbits as spares, but the constellation remained restricted to geostationary satellites of which five were launched. Milstar is the current primary system for the U.S. military.

WGS
Designed by Boeing and based on the Boeing 702 satellite bus, the geostationary orbiting Wideband Global Satcom system (also referred to as Wideband Gapfiller System) augmented the Defense Satellite Communication System (DSCS) III, which it will eventually replace. See Table 5.

The 5987 kg satellites will be fitted with transponders operating in the 5-10 GHz band and the 45/21 GHz band to provide a wide range of communications capabilities to the military services by the ability of connecting users between any and all of the 18 proposed coverage areas even when users are operating on different frequency bands. The capacity of the satellites will be 10 times that of the DSCS III series of satellites. The first three satellites will be Block I satellites, to be followed by three Block II satellites —the last one will be funded by Australia in exchange for access to the entire system. The Block II version will include a radio frequency bypass capability designed to support airborne intelligence, surveillance, and reconnaissance platforms with data rates of up to 311 megabits per second.

FLTSATCOM
The Fleet Satellite Communications System (FLTSATCOM) network provided global communications for the U.S. defense forces, but primarily for the U.S. Navy. See Table 6.

Each satellite was equipped with a single transponder operating in the 8/7 GHz and 23 transponders in the 240/400 MHz band. Other channels included 25 KHz and 125 KHz. Ten channels were for the exclusive use of the U.S. Navy and provided mainly ship-to-ship and ship-to-shore communications. The satellites, which were three-axis stabilized, have been built by TRW. Four satellites provided a worldwide coverage except for the Polar Regions.

UHF
The UHF Follow-on series of satellites replaced the FLTSATCOM satellites. They were built by Hughes and the operational system consisted of nine satellites in a geostationary orbit. Each satellite carried 11 transponders operating in the UHF band. Commencing with UHF-4, an EHF transponder operating at 44/20 GHz was added, offering a further 11 communications channels, while UHF-7 carried two additional EHF transponders operating at 44/20 GHz offering a further 20 communications channels. See Table 7.
AEHF
The Advanced Extremely High Frequency (AEHF) military communications satellite system will be a cross-linked constellation in geosynchronous orbit that will provide secure, survivable, and protected communications systems for the U.S. military.

To be built by Lockheed Martin, using the A2100 spacecraft bus, the system will replace the Milstar 2 communications system. The satellites will deliver a 10 times total capacity and channel data rates six times higher than that of Milstar 2. The design includes a sophisticated payload and phased array antennas as well as an electric propulsion system. The first launch is scheduled for 2009. Initially it was planned to have six satellites but that was reduced to three in 2004. The option to launch a further two satellites remains open.

Syncom IV
For some time, the U.S. Navy leased a series of communications satellites from Hughes. Designated Leasat, or Syncom IV, the satellites were equipped with eight transponders that operated in the 240/400 MHz band and one transponder in the 7/8 GHz band. See Table 8.

SDS
The Satellite Data Systems series of satellites, which evolved from the Code 313 and then the Data Relay Satellite System, were initially built by Hughes and were used for communications by the strategic forces in the UHF frequencies. In particular they were used to transmit images from surveillance satellites.

They were placed in highly elliptical orbits with an inclination of 63° to cover the polar regions which cannot be adequately covered by geostationary satellites. Three separate generations of SDS satellites have been identified.

North Atlantic Treaty Organization (NATO)
To provide a communications network between NATO headquarters in Belgium and the various capitals of the member nations, as well as the NATO command centers on land and at sea, a satellite system was brought into operation in 1970.

The satellites of the first generation, NATO-1 and -2, each carried two transponders operating in the 375/400 MHz bands. They were built by Philco-Ford, and were spin-stabilized. They provided voice, wide-band, telegraph and facsimile services and were designed to be compatible with the United States’ IDCSP and the British Skynet satellite systems, except that the antennas had been optimized for operation in the Northern Hemisphere only. Separate channels were provided for communications with fixed ground stations with large antennas or ship-borne receivers with small antennas. The second generation of satellites (NATO-3 series) were more powerful versions, and the three transponders operated in the 8/7 GHz band. The NATO-4 generation was based on the Skynet-4 satellite and carried three transponders that operated in the 8/7 GHz band and two transponders in the 1470/1530 MHz band.

United Kingdom:
Skynet
The United Kingdom, through its military commitments overseas, undertook early development of a military communications satellite system under the designation of Skynet. By means of a satellite stationed over the Indian Ocean, reliable communications were possible between the United Kingdom and military establishments in Western Europe, the Middle East and the Far East, as well as ship-based terminals. Skynet-1 and -2, which were built by Philco-Ford were spin-stabilized, and equipped with one transponder operating in the 8/7 GHz bands.

Skynet-2A and -2B were built by Marconi, were also spin-stabilized, and had one transponder operating in the 8/7 GHz band. The Skynet-3 series was a mid-seventies proposal that was cancelled due to the reduction of the overseas military activities of the United Kingdom. The fourth generation of Skynet satellites operated within a NATO framework and consisted of six separate satellites. The satellites, built by British Aerospace, carried three transponders in the 8/7 GHz band and two transponders in the 310/255 MHz band.

The Skynet-5 series were a 4725 kg military communications satellite fitted with 9 UHF and 15 SHF transponders as well as anti-jamming capabilities. They were built by EADS Astrium using the Eurostar 3000 platform. The satellites are owned and operated by Paradigm Secure Communications on a lease to the military.

Experimental Satellites
In addition to the operational systems described above, the U.S. military services have been responsible for several experimental communications satellites designed to test new technologies.

The Global Low Orbiting Message Relay Satellite (Glomar) was launched on October 30, 1985, to demonstrate the feasibility of a small satellite to send on/off commands to small sensors on the ground, record the data transmitted from these sensors and dump such data, on command, to a ground station.

The Glomar satellite, launched on April 5, 1990, was an experimental communications satellite for the U.S. Navy—two Multiple Access Communications (Macsat) satellites, launched on May 9, 1990, were experimental satellites for the Defense Research Agency, DARPA. The seven Microsat satellites, which were launched on July 17, 1991, were also for experimental military communications of a store-dump nature.

Cancelled Proposals
The designation AFSATCOM was originally used for a proposed series of satellites optimized for use by the U.S. Air Force. The satellites never materialized as the requirements were met by other transponders carried on DSCS, FLTSATCOM and SDS satellites. Other systems that did not materialize included; the Strategic Polar Communications Satellite System, to consist of four satellite in polar orbit; the Advanced Polar Communications Satellite (carrying codename Tackle); and the Decree system, a code name for the Global Communications Satellite for Instantaneous Message Relay.

About the author
Jos Heyman is the Managing Director of Tiros Space Information, a Western Australian consultancy specializing in the dissemination of information on the scientific exploration and commercial application of space for use by educational as well as commercial organisations. An accountant by profession, Jos is the editor of the TSI News Bulletin and is also a regular contributor to the British Interplanetary Society’s Spaceflight journal.