Then the Tower would grow in two opposite directions – down to Earth, and simultaneously up to the orbital mass-anchor, the whole process being adjusted so that it would always be in balance. Its cross-section would decrease steadily from orbit, where it would be under the maximum stress, down to Earth; it would also taper off towards the anchoring counterweight.
When its task was complete, the entire construction complex would be launched into a transfer orbit to Mars. This was a part of the contract which had caused some heartburning among terrestrial politicians and financiers now that, belatedly, the space elevator’s potential was being realised.
The Martians had driven a hard bargain. Though they would wait another five years before they had any return on their investment, they would then have a virtual construction monopoly for perhaps another decade. Morgan had a shrewd suspicion that the Pavonis tower would merely be the first of several; Mars might have been designed as a location for space elevator systems, and its energetic occupants were not likely to miss such an opportunity. If they made their world the centre of interplanetary commerce in the years ahead, good luck to them; Morgan had other problems to worry about, and some of them were still unsolved.
The Tower, for all its overwhelming size, was merely the support for something much more complex. Along each of its four sides must run thirty-six thousand kilometres of track, capable of operation at speeds never before attempted. This had to be powered for its entire length by superconducting cables, linked to massive fusion generators, the whole system being controlled by an incredibly elaborate, fail-safe computer network.
The Upper Terminal, where passengers and freight would transfer between the Tower and the spacecraft docked to it, was a major project in itself. So was Midway Station. So was Earth Terminal, now being lasered into the heart of the sacred mountain. And in addition to all this, there was Operation Cleanup…
For two hundred years, satellites of all shapes and sizes, from loose nuts and bolts to entire space villages, had been accumulating in Earth orbit. All that came below the extreme elevation of the Tower, at any time, now had to be accounted for, since they created a possible hazard. Three-quarters of this material was abandoned junk, much of it long forgotten. Now it had to be located, and somehow disposed of.
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 worldwide 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 St�rmer – and, especially, the man who, in 1970, won the very award I am now so honoured to accept, your countryman Hannes Alfv�n…
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…
Because the ionosphere, like the atmosphere below it, is ultimately controlled by the sun, it too has its weather. During times of solar disturbance it is blasted by planet-wide gales of charged particles, and twisted into loops and whirls by the earth’s magnetic field. On such occasions it is no longer invisible, for it reveals itself in the glowing curtains of the aurora – one of Nature’s most awesome spectacles, illuminating the cold polar nights with its eerie radiance.
Even now, we do not understand all the processes occurring in the ionosphere. One reason why it has proved difficult to study is because all our rocket and satellite-borne instruments race through it at thousands of kilometres an hour; we have never been able to stand still to make observations! Now, for the very first time, the construction of the proposed Orbital Tower gives us a chance of establishing fixed observatories in the ionosphere. It is also possible that the Tower may itself modify the characteristics of the ionosphere – though it will certainly not, as Dr. Bickerstaff has suggested, short-circuit it!
Why should we study this region, now that it is no longer important to the communications engineer? Well, apart from its beauty, its strangeness and its scientific interest, its behaviour is closely linked with that of the sun – the master of our destiny. We know now that the sun is not the steady, well-behaved star that our ancestors believed; it undergoes both long and short-period fluctuations. At the present time it is still emerging from the so-called “Maunder Minimum” of 1645 to 1715; as a result, the climate now is milder than at any time since the Early Middle Ages. But how long will this upswing last? Even more important, when will the inevitable downturn begin, and what effect will this have upon climate, weather and every aspect of human civilization – not only on this planet, but on the others as well? For they are all children of the sun…