Inside the I-4 satellites

Spot beams focus power

The Inmarsat-4 satellites are unique in their ability to generate hundreds of high-power spot beams.

Each I-4 can generate 19 wide beams and more than 200 narrow spot beams. These can quickly be reconfigured and focused anywhere on Earth to provide extra capacity where needed.

Some of the spacecraft's impressive features include:

• The I-4 body - approaching the size of a double-decker bus at 7m x 2.9m x 2.3m
• Solar arrays - approaching the width of a football pitch, with an immense wing span of 45 metres
• Solar panels - combining conventional silicon with advanced gallium arsenide (GaAs) cells for optimum efficiency
• Digital signal processor - controlling the antennas, beam forming and channel allocation
• Reflector - 9 metres wide and designed to unfurl in orbit like a giant flower
• Antennas - 120 helix elements combined in a single flexible array
• Thrusters - both chemical and plasma ion for orbital station keeping