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Intelsat IV

Fifth Generation Commercial Communications Satellite

Intelsat IV (Neg#: DVD-1089-2)

Diameter: 2.38 m (7 ft 9 in.)
Overall Height: 5.31 m (17 ft 5 in.)
Weight in Orbit:
595 kg (1313 lb)
beginning of life

The Intelsat IV series of communications satellites, launched from Cape Canaveral during the early 1970's, marked the fifth generation of geostationary communications satellites developed by Hughes Aircraft Company, today known as Boeing Satellite Systems, since the 1963 launching of Syncom II, the world's first synchronous satellite. Syncom II, 15 inches high and 28 inches in diameter, weighed 78 pounds in orbit. In contrast, the Intelsat IVs weighed over 1300 pounds (595 kg) in orbit and were more than 17 feet (5.31 meters) in diameter. Launch vehicles for the satellites were the Atlas-Centaur rockets. Eight flight spacecraft and one prototype were built for the International Telecommunications Satellite Organization (INTELSAT). Communications Satellite Corporation (COMSAT) managed the Intelsat IV program for the then 109-nation organization. Seven of the huge satellites were successfully launched between January 1971 and May 1975.


Companies from 10 nations representing Europe, Japan, and Canada participated with Hughes in building the satellites.

Each Intelsat IV satellite could relay 6000 two-way telephone calls or transmit 12 simultaneous color television programs or varied combinations of communications traffic, including data and facsimile.

The communications subsystem consisted of global receive and both global and spot beam transmit antennas connected to a microwave 12-channel repeater that provided high power amplification for each channel. Six antennas--two global receive, two global transmit, and two spot beam transmit--were provided.

The spot beam feed horns illuminated the parabolic reflectors, which focused and redirected the energy toward earth. Each spot beam antenna was individually steerable, and its beam center could be pointed anywhere over the visible portion of the earth in incremental steps of less than 0.01 degrees.

The satellite had 12 broadband communications channels. Each channel had a bandwidth of 40 MHz and provided about 500 communications circuits. Four of the repeaters were dedicated to earth coverage antennas, and eight could be switched to either earth coverage or spot beam transmit antennas. All seven spacecraft exceeded their design lives and have been retired from active service, the last of which, Intelsat IV F-1 was retired in October 1987.

F-1 flight model in early stages of assembly.
Engineers examine Intelsat IV spacecraft following anechoic chamber test.

Intelsat IV Launch Summary

  • Intelsat IV (F-2)--Launched 25 January 1971. Entered commercial service over Atlantic Ocean 26 March 1971.
  • Intelsat IV (F-3)--Launched 19 December 1971. Entered commercial service over Atlantic Ocean 18 February 1972.
  • Intelsat IV (F-4)--Launched 22 January 1972. Entered commercial service over Pacific Ocean 14 February 1972.
  • Intelsat IV (F-5)--Launched 13 June 1972. Entered commercial service over Indian Ocean 30 July 1972.
  • Intelsat IV (F-7)--Launched 23 August 1973. Entered commercial service over Atlantic Ocean 14 September 1973.
  • Intelsat IV (F-8)--Launched 21 November 1974. Entered commercial service over Pacific Ocean 14 December 1974.
  • Intelsat IV (F-6)--Launched 20 February 1975. Mission terminated by range safety officer after booster malfunction.
  • Intelsat IV (F-1)--Launched 22 May 1975. Entered commercial service over Indian Ocean 13 July 1975.
SCG 890953A/2500/7-89