Intelsat
In 1964, 11 nations signed the agreement establishing the International Telecommunications Satellite Consortium (Intelsat), an intergovernmental organization created to operate a global commercial satellite network. Membership grew rapidly, eventually exceeding 100 countries. Each member state designated a communications authority to act as its “signatory”; in the United States, this role was held by COMSAT, which also managed the consortium until 1979. On 18 July 2001, Intelsat was privatized and became Intelsat Ltd.
The first commercial geostationary communications satellite to provide routine international service, Intelsat 1 (Early Bird), was launched on 6 April 1965 over the Atlantic Ocean region. Early Bird provided 240 telephone circuits or one TV channel, marking the start of routine commercial satellite communications on 28 June 1965. Although technically similar to NASA’s Syncom 3, Early Bird operated in the commercial C-band (6/4 GHz) rather than the 8/2 GHz military frequencies used in contemporary US defense systems. Early Bird had a launch mass of 68 kg (dry mass 34 kg), a spacecraft power of 40–45 W from 6,000 silicon solar cells providing 45 W in sunlight and two 21-cell NiCd batteries. The spacecraft provided 240 voice channels with one 50-MHz transponder with a TWTA output power of 6 W. Uplinks/downlinks were centered on 6.3/4.2 GHz for Europe and 6.4/4.1 GHz for the US. Mounted on the top of the satellite was the mast-like C-band antenna which consisted of collinear slotted dipoles, providing about 9 dB (8×) gain. The radiation pattern was a toroid (doughnut) symmetrical about the spin axis. Despite having an original design life of only two years, Early Bird remained active until 1969 1.
Intelsat 2 was launched in 1967 with a launch mass of 162 kg (dry mass 76 kg), a power of 85 W, and two 25-MHz transponders providing 240 voice channels, which was increased to a launch mass of 293 kg (dry mass 152 kg) and a power of 183 W, with two 40-MHz transponders for Intelsat 3.
Intelsat 4 represented a significant increase in capability with a launch mass of 1,414 kg (dry mass 730 kg) with a power of 600 W providing 12×36-MHz transponders. The new spacecraft introduced a modification to spin stabilization as well as the concept of frequency reuse through which the satellite’s 500-MHz bandwidth could be doubled by transmitting two independent, shaped, hemispherical beams. Since then, modern communication satellites employ a number of beams to increase capacity and to maximize power onto subscriber communities. Eight Intelsat 4 satellites were launched (with one failure on launch) providing service between 1971 and 1985.
The Intelsat 5 series, first launched in 1980, represented a major advance in capacity and flexibility. Each spacecraft had a launch mass of 1,928 kg (dry mass ~1,020 kg) and generated 1,800 W of power. The payload consisted of 21×C-band transponders (36 MHz each) and 4×Ku-band transponders (72 MHz each). To address the growing congestion of C-band, Intelsat 5 introduced polarization discrimination, which doubled frequency re-use compared to the Intelsat 4 generation. It also pioneered the use of Ku-band spot beams, enabling smaller Earth stations and improved regional coverage. Another key innovation was the transition from spin stabilization to three-axis stabilization, allowing more precise antenna pointing and higher power. The Intelsat 5-A variant included a dedicated maritime communications package, similar to that of COMSAT’s Marisat system. In total, 15 Intelsat 5 and 5-A satellites were launched; none remain in service today.
The Intelsat 6 series, launched between 1989 and 1991, marked another quantum leap in satellite capability. With a launch mass of ~4,300 kg and payload power of 2,600 W, these satellites carried 38×C-band and 10×Ku-band transponders, supporting a wide range of international services. Three were deployed in the Atlantic Ocean Region and two in the Indian Ocean Region. Intelsat 6 is also remembered for a dramatic rescue mission: Intelsat 603, stranded in an unusable orbit due to launch vehicle failure, was retrieved and refitted by astronauts during the maiden flight of the Space Shuttle Endeavour (STS-49) in May 1992, before being successfully redeployed. Although none of the Intelsat 6 satellites remain in service, they established the scale and power levels that defined modern geostationary platforms.
Seven Intelsat 7-7/A satellites were launched between 1993 and 1997 into the Atlantic Ocean Region (three), the Indian Ocean Region (two), and the Pacific Ocean Region (two). No Intelsat 7 satellites remain in service. The satellites had a mass of ~3,700 kg, had power of 3,600 W and 26×C-band and 14×Ku-band transponders.
Six Intelsat 8 satellites were launched in 1997–1998 into the Atlantic Ocean Region (two), the Indian Ocean Region (two), and Pacific Ocean Region (two) with an increased platform mass of between 3,350 kg and 3,500 kg, and a power of 5,600 W with 38×C-band and 6×Ku-band transponders. The Intelsat 8-8/A series incorporated six-fold C-band frequency re-use. All are now out of service.
The Intelsat 9 series included seven satellites, four over the Atlantic and three over the Indian Ocean, with a launch mass of 4,723 kg, a power of 6,400 W and 44×C-band and 12×Ku-band transponders. Because of their high power, Intelsat 9 satellites could operate to smaller Earth stations and had sufficient power to facilitate services such as satellite news gathering (SNG), DAMA, Internet, DTH and VSAT networks. All seven satellites are now out of service.
Three Intelsat 10 satellites were launched in 2004 to cover the Atlantic Ocean (one) and Indian Ocean (two) Regions. The satellite launch mass increased to 5,600 kg and had a spacecraft power of 8,000 W carrying 70 C-band and 36 Ku-band transponders. All are now out of service.
Since the Intelsat 10 series, some 39 Intelsat satellites have been launched (several of them rebranded). In particular, the first of the HTS, Intelsat 29e, which was launched in January 2016, had 20 C-band transponders with a bandwidth 864 MHz (equivalent to 24×36-MHz transponders), 56×Ku-band transponders with a bandwidth of 9,395 MHz (equivalent to 249×36-MHz transponders), and a Ka-band payload of 450 MHz. Intelsat 32e was launched in February 2017, Intelsat 33e in 2017, Intelsat 35e in June 2017, and Horizons 3e (a joint venture with SKY Perfect JSAT)) in August 2018. Until a recent merger with SES, Intelsat operated a fleet of 70 C-, Ku- and Ka-band geostationary satellites, including about 20 that are customer-owned. After the merger, the SES-Intelsat combination is in excess of 120 satellites 2.