The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

During the 1960s and 1970s, message capacity and
transmission power of the Intelsat 2, 3, and 4 generations
were progressively increased by segmenting the voice circuits
into more and more transponder (transmitterreceiver)
units, each having a certain bandwidth. The first
of the Intelsat 4 series, launched in 1971, provided 4,000
voice circuits. With the Intelsat 5 series (1980), the introduction
of multiple beams directed at the Earth resulted
in even greater capacity. A satellite’s power could now be
concentrated on small regions of the planet, making possible
lower-cost ground stations with smaller antennas. An
Intelsat 5 satellite could typically carry 12,000 voice circuits.
The Intelsat 6 satellites, which entered service in
1989, can carry 24,000 circuits and feature dynamic
onboard switching of telephone capacity among six
beams, using a technique called SS/TDMA (satellite
switched/time-division multiple access). Intelsat 7 satellites
provide up to 112,500 voice circuits and three TV circuits
each, depending on the market needs in the orbital
location. Satellites in the most recently completed series,
Intelsat 8 and 8A, launched in the late 1990s, can simultaneously
handle 112,500 phone calls, or 22,000 phone
calls plus three color TV broadcasts. These are now being
joined by a 10-strong fleet of the even more powerful
Intelsat 9, each carrying 76 C-band and 24-Ku-band
transponders (see frequency bands). When the new fleet
Intelsat Series
Interbol 197
is in place by 2003–2004, Intelsat expects to have a constellation
of 24 operational satellites supplemented by
over 600 Earth stations. (See table, “Intelsat Series.”)
Interbol
Two pairs of spacecraft designed to measure different
parts of Earth’s magnetic field: one pair with orbits of
500 km by 200,000 km (tail probes), the other with orbits
Launch
Vehicle: Molniya-M
Site: Plesetsk
of 500 km by 20,000 km (auroral probes). Originally an
Intercosmos project with a launch planned for the late
1980s, Interbol was delayed until 1995 and 1996 following
the breakup of the Soviet Union. Each pair of spacecraft
consists of a Russian Prognoz-M (1,250-kg tail probe
and 1,400-kg auroral probe) and a Czech Magion (50 kg)
satellite. Both Prognoz probes carried a variety of plasma
and charged particle detectors, including Swedish,
French, and Canadian instruments. The Magion subsatellites
can fly in close proximity to the Prognoz or
maneuver to as much as 10,000 km from the mother
craft. (See table, “Interbol Missions.”)
Spacecraft No. Dates
Launch
Vehicle Circuit Capacity Mass (kg)
Intelsat 1 1 Apr. 1965 Delta D 240 voice or 1 TV 39
Intelsat 2 3 Jan. 1966–Sep. 1967 Delta E 240 voice or 1 TV 87
Intelsat 3 5 Dec. 1968–Apr. 1970 Delta M 1,500 voice or 4 TV 287
Intelsat 4 7 Jan. 1971–May 1975 Atlas-Centaur 4,000 voice or 2 TV 1,410
Intelsat 4A 6 Sep. 1975–Mar. 1978 Atlas-Centaur 7,250 voice or 2 TV 1,520
Intelsat 5 8 Dec. 1980–Jun. 1984 Atlas-Centaur, Ariane 1,
Atlas G
12,000 voice + 2 TV 2,000
Intelsat 5A 6 Mar. 1985–Jan. 1989 Atlas G, Ariane 2/3 15,000 voice + 2 TV 2,013
Intelsat 6 4 Oct. 1989–Oct. 1991 Ariane 4 24,000 voice + 3 TV 4,300
Intelsat K 1 Jun. 10, 1992 Atlas IIA 32 TV 2,930
Intelsat 7 6 Oct. 1993–Jun. 1996 Ariane 4, Atlas IIAS 18,000 voice + 3 TV 4,200
Intelsat 7A 3 May 1995–Feb. 1996 Ariane 4, CZ-3B 18,000 voice + 3 TV 4,500
Intelsat 8 4 Mar. 1997–Dec. 1997 Ariane 4, Atlas IIAS 22,000 voice + 3 TV 3,400
Intelsat 8A 2 Feb.–Jun. 1998 Atlas IIAS 22,000 voice + 3 TV 3,520
Intelsat 9 7 Jun. 2001– Ariane 4, Proton-K 76 C-band + 24 Ku-band
transponders
4,723