important role in communication fields. A large number of satellite communication
systems are designed or under construction now [4].
The remainder of this paper is organized as follows. In Sect. 2, several typical
communication satellite systems are briefly introduced. Section 3 identifies some
development prospects. Finally, Sect. 4 comes the conclusion.
2 Typical Commercial Communication Satellite Systems
2.1 Iridium-NEXT
The Iridium constellation was conceived in the late 1980s by several engineers in
Motorola. An early computation revealed that 77 satellites would be needed to achieve
full global coverage including the polar regions. Since the number of satellites is the
same as the number of electron circling the Iridium nucleus, the project handled by
Motorola was named Iridium. The name retained although the number of active
satellites composing the constellation reduced to 66 at last.
Iridium satellites began to be launched in 1997. The full constellation was established in May 1998, and the satellite system started offering services in November
1998. Due to the unexpected fast development of the ground mobile communication, it
was difficult for the Iridium to attract enough users. As a result, the company went
bankrupt in 2000. In 2007, Iridium Satellite LLC (the commercial entity that took over
the assets of the original bankrupt Iridium consortium) announced the Iridium-NEXT
plan for replenishing the Iridium constellation to provide higher data rates, increase
capacity, and introduce new services.
The constellation of the Iridium-NEXT is the same as the original Iridium system
with 66 active satellites in six orbital planes. There are nine spare satellites at the same
time. The altitude and inclination of the orbits are 780 km and 86.4°. The orbital period
is 100.5 min. Except for planes 1 and 6, the adjacent orbital planes are co-rotating and
spaced 31.6°. The planes 1 and 6 are counter-rotating at a spacing of 22°.
The Iridium-NEXT satellite establishes L-Band and satellite-ground links to mobile
and OpenPort terminals at data speeds of up to 128 kbit/s and 1.5 Mbit/s, respectively.
For fixed and transportable terminals, the service speed is higher, up to 8 Mbit/s. Each
Iridium-NEXT satellite establishes 23.18–23.38 GHz inter-satellite links to four
satellites, two in front and behind within the same orbital plane and the other two in
neighboring planes to either side, at data speeds of 12.5 Mbps [5].
2.2 LeoSat
The LeoSat system is developed by LeoSat Enterprises together with Thales Alenia
Space. A constellation of up to 108 low earth orbit (LEO) communications satellites is
going to be launched to form a mesh network interconnected with laser inter-satellite
links. The altitude of the orbits is about 1400 km. A total of 108 satellites will be
deployed in six orbital planes.
LeoSat’s system adopts optical inter-satellite links, flat panel antennas, optimized
Ka-band communications, and semiconductor processing. Each satellite in the LeoSat
532
J. Huang and J. Cao
systems are designed or under construction now [4].
The remainder of this paper is organized as follows. In Sect. 2, several typical
communication satellite systems are briefly introduced. Section 3 identifies some
development prospects. Finally, Sect. 4 comes the conclusion.
2 Typical Commercial Communication Satellite Systems
2.1 Iridium-NEXT
The Iridium constellation was conceived in the late 1980s by several engineers in
Motorola. An early computation revealed that 77 satellites would be needed to achieve
full global coverage including the polar regions. Since the number of satellites is the
same as the number of electron circling the Iridium nucleus, the project handled by
Motorola was named Iridium. The name retained although the number of active
satellites composing the constellation reduced to 66 at last.
Iridium satellites began to be launched in 1997. The full constellation was established in May 1998, and the satellite system started offering services in November
1998. Due to the unexpected fast development of the ground mobile communication, it
was difficult for the Iridium to attract enough users. As a result, the company went
bankrupt in 2000. In 2007, Iridium Satellite LLC (the commercial entity that took over
the assets of the original bankrupt Iridium consortium) announced the Iridium-NEXT
plan for replenishing the Iridium constellation to provide higher data rates, increase
capacity, and introduce new services.
The constellation of the Iridium-NEXT is the same as the original Iridium system
with 66 active satellites in six orbital planes. There are nine spare satellites at the same
time. The altitude and inclination of the orbits are 780 km and 86.4°. The orbital period
is 100.5 min. Except for planes 1 and 6, the adjacent orbital planes are co-rotating and
spaced 31.6°. The planes 1 and 6 are counter-rotating at a spacing of 22°.
The Iridium-NEXT satellite establishes L-Band and satellite-ground links to mobile
and OpenPort terminals at data speeds of up to 128 kbit/s and 1.5 Mbit/s, respectively.
For fixed and transportable terminals, the service speed is higher, up to 8 Mbit/s. Each
Iridium-NEXT satellite establishes 23.18–23.38 GHz inter-satellite links to four
satellites, two in front and behind within the same orbital plane and the other two in
neighboring planes to either side, at data speeds of 12.5 Mbps [5].
2.2 LeoSat
The LeoSat system is developed by LeoSat Enterprises together with Thales Alenia
Space. A constellation of up to 108 low earth orbit (LEO) communications satellites is
going to be launched to form a mesh network interconnected with laser inter-satellite
links. The altitude of the orbits is about 1400 km. A total of 108 satellites will be
deployed in six orbital planes.
LeoSat’s system adopts optical inter-satellite links, flat panel antennas, optimized
Ka-band communications, and semiconductor processing. Each satellite in the LeoSat
532
J. Huang and J. Cao