The Fountains of Paradise

Fortunately, the old orbital forts were superbly equipped for this task. Their radars – designed to locate oncoming missiles at extreme ranges with no advance warning – could easily pin-point the debris of the early space age. Then their lasers vapourised the smaller satellites, while the larger ones were nudged into higher and harmless orbits. Some, of historic interest, were recovered and brought back to Earth. During this operation there were quite a few surprises – for example, three Chinese astronauts who had perished on some secret mission, and several reconnaissance satellites constructed from such an ingenious mix of components that it was quite impossible to discover what country had launched them. Not, of course, that it now mattered a great deal, since they were at least a hundred years old.

The multitude of active satellites and space stations – forced for operational reasons to remain close to Earth – all had to have their orbits carefully checked, and in some cases modified. But nothing, of course, could be done about the random and unpredictable visitors which might arrive at any minute from the outer reaches of the Solar System. Like all the creations of mankind, the Tower would be exposed to meteorites. Several times a day its network of seismometers would detect milligram impacts; and once or twice a year minor structural damage might be expected. And sooner or later, during the centuries to come, it might encounter a giant which could put one or more tracks out of action for a while. In the worst possible case, the Tower might even be severed somewhere along its length.

That was about as likely to happen as the impact of a large meteorite upon London or Tokyo – which presented roughly the same target area. The inhabitants of those cities did not lose much sleep worrying over this possibility. Nor did Vannevar Morgan. Whatever problems might still lie ahead, no one doubted now that the Orbital Tower was an idea whose time had come.

V – ASCENSION

38. A Place of Silent Storms

(Extract from Professor Martin Sessui's address, on receiving the Nobel Prize for Physics, Stockholm, 16 December 2154.)

Between Heaven and Earth lies an invisible region of which the old philosophers never dreamed. Not until the dawn of the twentieth century – to be precise, on 12 December 1901 – did it make its first impact upon human affairs.

On that day, Guglielmo Marconi radioed the three dots of the Morse letter "S" across the Atlantic. Many experts had declared this to be impossible, as electromagnetic waves could travel only in straight lines, and would be unable to bend round the curve of the globe. Marconi's feat not only heralded the age of world-wide communications, but also proved that, high up in the atmosphere, there exists an electrified mirror, capable of reflecting radio waves back to earth.

The Kennelly-Heaviside Layer, as it was originally named, was soon found to be a region of great complexity, containing at least three main layers, all subject to major variations in height and intensity. At their upper limit they merge into the Van Allen Radiation Belts, whose discovery was the first triumph of the early space age.

This vast region, beginning at a height of approximately fifty kilometres and extending outwards for several radii of the Earth, is now known as the ionosphere; its exploration by rockets, satellites and radio waves has been a continuing process for more than two centuries. I should like to pay a tribute to my precursors in this enterprise – the Americans Tuve and Breit, the Englishman Appleton, the Norwegian Størmer – and, especially, the man who, in 1970, won the very award I am now so honoured to accept, your countryman Hannes Alfvén…

The ionosphere is the wayward child of the sun; even now, its behaviour is not always predictable. In the days when long-range radio depended upon its idiosyncrasies it saved many lives – but more men than we shall ever know were doomed when it swallowed their despairing signals without trace.

For less than one century, before the communications satellites took over, it was our invaluable but erratic servant – a previously unsuspected natural phenomenon, worth countless billions of dollars to the three generations who exploited it.

Only for a brief moment in history was it of direct concern to mankind. And yet – if it had never existed, we should not be here! In one sense, therefore, it was of vital importance even to pre-technological humanity, right back to the first ape-man – indeed, right back to the first living creatures on this planet. For the ionosphere is part of the shield that protects us from the sun's deadly X-ray and ultra-violet radiations. If they had penetrated to sea level, perhaps some kind of life might still have arisen on earth; but it would never have evolved into anything remotely resembling us…