THE INMARSAT-4S. The most advanced commercial spacecraft for mobile communications?
Posted on Jul 28 2011 at 08:40:02 AM in Technology
For many years, Inmarsat has been the leading name in commercial mobile communication satellite technology. Inmarsat currently owns and operates 11 communication spacecraft of different classes flying in geosynchronous orbit 35,786km (22,240 statute miles) above the Earth. Amongst these is our focus, three satellites referred to as the Inmarsat-4 or I-4. These satellites set a landmark in mobile satellite communications. They are revered for their power, capacity and flexibility.
Before the I-4s, Inmarsat had and still have in operation the I-2s and I-3s. These were Inmarsat�s first fully owned satellites and were at the time really impressive. The I-3s being the first generation satellites to use spot beam technology. Today one I-4 satellite is 60 times more powerful than an I-3 satellite. The I-4 series is expected to be in commercial operation until the year 2020.
The I-4 satellite programme cost Inmarsat US$1.5 billion and involved an international team of space technologists from the United Kingdom, France, Germany, the USA and Canada with EADS Astrium as the lead contractor. The I-4�s main body was constructed in Britain including:
The Bus: this is the part of the satellite that holds the onboard rocket engine that positions the spacecraft in geostationary orbit. The body was built at the EADS Astrium facility in Stevenage, Hertfordshire.
The Payload: this is the satellite�s communications electronics and it was assembled at the company�s facility in Portsmouth, Hampshire.
The other main elements of the spacecraft which consist of the antenna, the solar arrays and the 9-metre reflector � were manufactured in Canada, Germany, and the United States and were then transported to the EADS Astrium Facility in Toulouse, France, for final integration with the bus and payload.
Just like its older brother, the I-4 use spot beam technology only, the can generate hundreds of high-power spot beams. A single I-4 can generate 19 wide beams and over 200 narrow spot beams which can be quickly reconfigured and focused anywhere on the Earth to provide extra capacity where needed.
� 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