Feature

Communications


Hylas-1 in operation
 
 
 
 
Fans of the 1960s TV series Star Trek were amazed when they saw Captain Kirk flip open a tiny hand-help phone to speak to the crew of his starship. Today, mobile phones are no longer science fiction. Wherever you go on Earth, from the polar regions to the middle of the ocean, it is possible to keep in touch by phone. With the latest models it is also possible to send e-mails and search the internet.
 
This revolution in communications has been made possible through the introduction of satellite technology. Until the mid-1960s, telephone messages were handled by land-based radio links and cables. However, there were limits on how many messages could be handled.

Then along came the first communications satellites. Flying in geostationary orbit, about 36,000 km above the equator, satellites were able to work without an expensive network of transmitters and cables. They could easily link callers on either side of an ocean or a mountain range. Early Bird, launched in 1965, could handle 240 telephone calls at any one time. Today, a large communications satellite can handle hundreds of thousands of phone calls.

Another revolution has taken place in recent years, with the introduction of fleets of small satellites in low or medium Earth orbits. With dozens of them flying along different paths, there are always several satellites above the horizon to receive calls from mobile devices. Each call is then sent to a ‘gateway’ station on the ground, which passes it on to the receiver. These satellites are also used for personal tracking, messaging and emergency location.
 
 
 
Last update: 5 July 2011


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