The Earth from the sky

3rd October 2003 at 01:00
Satellites help with everything from phone calls to weather forecasts, but the future of communications may be a lot closer to Earth. Brady Haran reports

It all started with a metal sphere about the size of a basketball. Launched by the Soviet Union on October 4, 1957, the world's first artificial satellite, Sputnik 1, was extremely simple and was equipped with a radio transmitter to give off a constant beeping noise.

It had a short life, falling from orbit before the year was out, but Sputnik, which loosely means "fellow traveller", had changed the world forever.

Five years later, on July 11, 1962, the UK played a role in another space milestone. At BT's Goonhilly Satellite Earth Station in Cornwall a large radio dish, since nicknamed Arthur, was pointed across the Atlantic Ocean and received the first television signal to be beamed from the US to Britain. The pictures were relayed via Telstar 1, the world's first commercial communication satellite.

Both Sputnik1 and Telstar 1 suffered fiery deaths long ago having been incinerated by friction when they fell back into the Earth's atmosphere.

But they have been replaced over the years by a new generation of satellites that soar higher and contain increasingly sophisticated equipment.

Today thousands of satellites (some inoperative) are orbiting the Earth, helping with everything from weather forecasts to telephone calls. Some of them can handle about 500 TV channels, a marked improvement on Telstar 1, which could only handle one.

Des Prouse, who is a satellite expert and head of operations design for BT, based at Goonhilly, says today's satellites are highly sophisticated and can be as tall as double-decker buses. They can orbit the Earth at a range of altitudes, but BT deals with satellites in geostationary orbit. These are sophisticated craft which circle 22,370 miles above the equator, moving at the same speed as Earth's rotation to ensure they remain at a fixed point above planet's surface. An advantage of these satellites is they don't "rise and set" relative to the horizon, like satellites in lower orbits. This means Earth stations can maintain a constant link. These stations act as the conduit between Earth-based networks and the satellites.

If a signal is to be transmitted large distances by "bouncing" off a satellite, Earth stations are the places where these signals are either "thrown" into space or "caught" when they return to Earth, says Des Prouse.

He says some people are unaware how widespread satellite usage has become: "The man in the street knows he gets his satellite TV from there, but he probably doesn't know that we are using it for ship and aircraft communications."

"Another major use of satellites is for multi-national corporate communications. A typical use is credit card validation for credit card companies. For example, if someone in Africa pays for something, their card is swiped through a processor and chances are the information will come back to the UK via satellite for validation, then back to Africa to say the card has passed the test."

Futurologist Ian Pearson, who helps BT predict technology trends, says satellites will continue to be used for TV, but they will be used less for personal communications. He says an alternative way to relay signals over large distances may be helium balloons.

"There was a trial done recently with a huge great blimp, which the Japanese put up into the stratosphere, hundreds of thousands of feet up.

You could use those as effectively as satellites and the advantage of that is you don't have to wait such a large amount of time for the signal to go up and come down again.

"When people are trying to do interviews across the world via satellite there is a very noticeable delay... it comes across as the guy being evasive and not bothering to answer the question. A balloon, rather than a satellite, is going to be just a couple of hundred thousand feet up - it takes next to no time to get there and back."

Using the bottom of aircraft could be another method of bouncing signals over shorter distances. "If you look out a window in London you can always see three or four aeroplanes, and because you can see them that means you can get a signal to and from them, whereas you might not be able to see a mobile phone mast."

Yet another option is relaying signals via high-altitude planes operating on solar power. "There are lots of different ways of skinning the cat," says Ian Pearson.

"Satellites don't look like the way to go for the future of communications at all. There's an awful lot of clutter in space and there a lots of things that you do need space for."

However, he says satellites will remain fundamental for TV broadcasting:

"They can cover several very large countries of even the whole of Europe because they are so high up.

"That's not an advantage for telephone communications, but it is for broadcasting."

Other areas where satellites remain valuable are environmental monitoring, weather forecasting and positioning systems. "The larger the areas you are covering, the more useful a satellite is," he says.


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