New satellite schemes promise -- or threaten -- instant communications from mountain-tops and desert islands. Mike Holderness reports

And thou beside me in the wilderness

You're celebrating the millennium with the holiday of a lifetime. Getting to the Himalayas was a nightmare, but at last you've found some peace -- and a chance to read Shakespeare. On the screen of your Personal Digital Assistant -- a bit flash for the mountains, but so much easier to carry than the book -- Puck's promise to "put a girdle round the earth" is rudely and ironically interrupted.

Your company computer network's electronic mail menu appears on the screen. Your boss is demanding that you read and respond to a crisis report this afternoon. She didn't even know where you were. She simply requested a connection to your personal number, and the phone system tracked you down.

You may see this story as a dream of freedom -- to be and work wherever you choose -- or as a nightmare of compulsive communication. Some companies see it as a potential gold-mine, and are investing thousands of millions to make it come true. With Apple having finally announced its Newton hand-held Personal Digital Assistant (PDA) computer last week, all the pieces are in place. Any two computers, anywhere on Earth, will be able to exchange information at any time.

Probably the most advanced and innovative scheme is Motorola's Iridium project. This involves launching 66 small communications satellites into low orbits, starting in 1996. Last week Motorola announced that it had raised US $800 million (540Mpound) first-stage funding for Iridium.

The previous week Inmarsat, the maritime communications co- operative of 67 countries' phone companies, announced that it had ruled out Low-Earth Orbit (LEO) satellites for its hand-held sat- phone system. Instead, it is awarding contracts to investigate systems based in intermediate and geo-synchronous (GEO) orbits.

Inmarsat already supports personal sat-phones, using its existing four operational satellites. Such systems have revolutionised life for foreign correspondents. Many radio reports from the demonstrations in Beijing's Tiananmen Square in 1989, for example, were telephoned direct via satellite, with China's phone authorities powerless to intervene.

Inmarsat says it already has 25,000 users, most in its traditional market of ship-to-shore communications. The smallest Inmarsat sat-phone on the market now, however, is the size of a suitcase. It plans to have hand-held sat-phones on the market between 1998 and 2000. These, at a predicted price of pounds_1000, will offer 2400 bits per second data communication as well as voice and paging.

If the sat-phone can find a compatible cellular phone network, and if it has a free line, it'll use it. With the number of cellular phones world-wide expected to grow from 15 million to 100 million by the end of the century, congestion will remain rife. When necessary, your sat-phone will beam your voice and data directly to a satellite.

Jai Singh, Inmarsat executive vice-president in charge of the project, sees the market as "business people who travel across cellular zones and across coverage gaps... and governments and wealthy individuals in countries which are not expected to have wide cellular coverage."

The decision to go for intermediate or GEO satellites was, Jai Singh says, based on user convenience. "In central London, to make a call through a LEO you might have to wait minutes for it to come into view, and then you might be interrupted as it went behind a building... to get line of sight to a GEO you might have to walk 20 metres, but then you have the link as long as you want." GEO satellites, 36,000km (22,500 miles) up, orbit the Earth in exactly 24 hours and thus remain fixed over one spot on the surface. However, sophisticated equipment is needed to receive a quarter-watt signal -- the strongest which safety allows -- at a range of 36,000km.

The Iridium satellites will be only 777km (485 miles) up and thus individually much simpler. Each of the 66 will at any time be in sight of several others: messages will be passed between satellites to reach an appropriate ground station. A link from Pitcairn Island to Rockall might be set up entirely between satellites.

Motorola predicts that its cheapest hand-set will cost around pounds_1700. It will also use cellular networks where possible, and will have a built-in data link. The cost of a call anywhere on earth should be around $3 (pounds_2) a minute; speeds of up to 64,000 bits per second will be possible. Motorola hopes to have two million customers four years after the system goes operational in 1998.

Iridium is an extraordiarily large space project. The name is derived from the number of satellites in the original proposal -- 77, the atomic number of the element Iridium. One-third of the satellite launches are due to be on ex-Soviet Proton rockets.

Iridium spokesperson John Windolph says that they are talking with Personal Digital Assistant manufacturers about building in Iridium equipment, and Motorola plans to make its own PDAs. A PDA with a high-speed satellite link and simple software could operate as a terminal of any other computer, anywhere.

Political problems may crop up. Some countries are chary of a communication channel which competes with their telephone monopolies, and over which they have no control. India, for example, officially won't allow you to use a modem without a government license. In many Indian states a license won't do much good, because the phone system is unusable for computer communications -- making the country a major potential market for sat-phones.

Some are sceptical of the business prospects. David Lewin of consultancy Ovum says "PDAs are more likely to have some sort of cellular interface... LEOs may be the perfect solution, but the perfect solution doesn't always win, it's the one that gets there first."

Between the Inmarsat and Iridium schemes -- and three or four others waiting in the wings -- some sort of world-wide satellite network will happen in the next decade. Then, the only place to get absolutely out of reach of the office will be in a submarine under water. Watch the holiday brochures...