The Inmarsat-4 (I-4) series
of satellites are the most advanced commercial mobile communications
spacecraft of their kind. The three satellites that make
up the global I-4 constellation are part of an 11-strong
fleet of spacecraft owned and operated by Inmarsat. All
the Inmarsat satellites, including the Inmarsat-2 and Inmarsat-3
generations, fly in geosynchronous orbit 35,786km (22,240
statute miles) above the Earth.
Spot beams
Inmarsat's first wholly owned satellites, the Inmarsat-2s,
were launched in the early 1990s, and the Inmarsat-3s -
the first generation to use spot beam technology - followed
later in the decade.
The I-4s set a new benchmark
for mobile satellite communications in terms of their power,
capacity and flexibility when they first went into orbit
in 2005. One I-4 satellite is 60 times more powerful than
an Inmarsat-3.
The I-4 series is expected to continue in commercial operation
until about 2020.
Alphasat
In the meantime, Inmarsat has entered into agreement with
the European Space Agency (ESA) to become the commercial
operator of a new satellite called Alphasat.
The satellite is part of an ESA initiative to develop a
new spacecraft platform capable of carrying a large communications
payload.
Alphasat is scheduled for completion in 2012 and will supplement
the existing I-4 satellites. It will provide service over
Europe, the Middle East and Africa.
