A new satellite network to satisfy our need to keep in touch may mean signals from the heavens cannot get through. Robert McKie reports
In a few days, the world will shrink irrevocably. Engineers will switch on a flotilla of 66 communication satellites allowing telephone users – from Antarctica to the Atlantic, and from the Sahara to Sidcup – to talk to each other.
No place on Earth will ever be out of communication. It is a gossip’s dream come true – and astronomers are livid.
They say the new satellites – part of the Iridium network – will flood the skies with radio waves. Signals that have taken aeons to reach us from distant stars and galaxies will be drowned. A window on the universe is being curtained over.
“In three weeks, when they turn on these satellites, a great chunk of the spectrum will be blotted out. It’s galling,” said Cambridge radio astronomer Dr Paul Scott.
Radio astronomy, pioneered by United Kingdom scientists such as Sir Bernard Lovell, has transformed our understanding of the cosmos and shown that the universe was created in a Big Bang explosion 15-billion years ago.
These discoveries have been made with instruments sensitive enough to detect emissions that have less than a trillionth of a watt of energy, signals equivalent to the ripple of energy generated by a falling snowflake.
But as devices have become ever more sophisticated, so the airwaves have been polluted through mushrooming television, radio and telephone transmissions. Radio astronomers have had to negotiate to keep thin slices of the electromagnetic spectrum protected for their research.
Slowly they have been hemmed in. Then the $5-billion Iridium network was established. It will allow the possessors of small, hand-held devices, little bigger than standard cellular phones, to talk – either with other Iridium users, or with standard phone owners – no matter where they are on the planet.
Proximity to radio masts will be unnecessary because transmissions will be picked up on one of 66 satellites flying 800km overhead. Their signals will then be relayed from one satellite to another before being beamed back down to Earth to a local ground station.
International phone calls are already relayed by satellites that orbit in deep space where their velocities exactly match the speed of Earth’s rotation, allowing them to hover over one area.
However, this geostationary orbit is so high – 35 200km – that only telephones linked to powerful transmitters can use them. Iridium phone signals will need no boosting because they will be picked up by low- orbiting satellites. On the other hand, dozens of satellites are needed to ensure proper blanket coverage of the sky.
Iridium phones are expected to cost about 1 500 in the United Kingdom. Business travellers, and mining and offshore industrialists working in Third World countries are expected to be the first users.
The company’s chief executive, Edward Staiano, says he expects Iridium to break even in cash flow in a year, and to pay off its $3-billion debt by 2002.
By that time, however, Iridium will face stiff competition. The Globalstar $2,6-billion system of 56 satellites – which is already being assembled in space – should be in operation, as should the rival British-based ICO system of 12 higher-orbiting satellites.
And if that is not enough, there is the gargantuan $9-billion network of 288 satellites being planned by a consortium led by Bill Gates. It is expected to carry most of the Internet data that will be exchanged between computer users in the next decade.
In short, our skies are being filled up with communication satellites and radio waves. However, it is not the volume of traffic that upsets astronomers; it is the chunks of radio spectrum that are to be used to carry this data.
“A satellite in heavy use will leak radio waves from one part of the spectrum into neighbouring areas,” said Jodrell Bank’s Dr James Cohen. “For instance, Iridium’s transmissions will spill over into an area of the spectrum called the hydroxyl region.”
Hydroxyl ions – made up of single atoms of hydrogen and oxygen – emit radio waves at a precise wavelength (1 612MHz) when heated up, and are created by dying stars.
“These emissions are vital for studying star deaths, but come November 1, when Iridium – which transmits messages between 1 616MHz to 1 625MHz – is switched on, they will be drowned out,” he said.
Iridium has pledged to rectify the problem when it replaces its satellites – in the year 2006. “Frankly, that’s not much comfort,” he said. “If it is Iridium today, it will be someone else tomorrow.”
This point is backed by Scott. “We cannot choose the wavelengths of the universe’s most important emission bands. These are dictated by nature. But we can choose the frequencies we use to transmit phone calls and TV programmes. Unfortunately we are not making a very good job of it at present.”
That’s not all, says Cohen. “These wavelengths represent a sort of common language of the radio waves, and some researchers believe they are the most likely ones that will be adopted by alien civilisations when trying to communicate across the galaxy. We may be obscuring the one medium by which we could discover worlds with intelligent life on them.”
The problem is similar to the one that is faced by Earth’s environment. Just as forests are being ripped up for farming, and oceans are being overfished, so our electromagnetic environment is being exploited for cash. It is reckoned that a single megahertz section of the radio spectrum is worth about $1-billion.
“Given that kind of cash, it is not surprising we have problems,” said Cohen. “What we need is protection, some system of electromagnetic national parks. To get that, we need commitment from Western governments, however.”