For a moment there was an uncharacteristic silence. Then Maxine Duval answered quietly: “Not as lonely as Yuri Gagarin must have been, a hundred kilometres higher still. Van, you have brought something new into the world. The sky may still be cruel – but you have tamed it. There may be some people who could never face this ride: I feel very sorry for them.”

37 . The Billion-Ton Diamond

In the last seven years much had been done, yet there was still so much to do. Mountains – or at least asteroids – had been moved. Earth now possessed a second natural moon, circling just above synchronous altitude. It was less than a kilometre across, and was rapidly becoming smaller as it was rifled of its carbon and other light elements. Whatever was left – the core of iron, tailings and industrial slag – would form the counterweight that would keep the Tower in tension. It would be the stone in the forty-thousand-kilometre-long sling that now turned with the planet once every twenty-four hours.

Fifty kilometres eastwards of Ashoka Station floated the huge industrial complex which processed the weightless – but not mass-less – megatons of raw material and converted them into hyperfilament. Because the final product was more than ninety percent carbon, with its atoms arranged in a precise crystalline lattice, the Tower had acquired the popular nickname “The Billion Ton Diamond”. The Jeweller's Association of Amsterdam had sourly pointed out that (a) hyperfilament wasn't diamond at all (b) if it was, then the Tower weighed five times ten to the fifteen carats.

Carats or tons, such enormous quantities of material had taxed to the utmost the resources of the space colonies and the skills of the orbital technicians. Into the automatic mines, production plants and zero-gravity assembly systems had gone much of the engineering genius of the human race, painfully acquired during two hundred years of spacefaring. Soon all the components of the Tower – a few standardised units, manufactured by the million – would be gathered in huge floating stock-piles, waiting for the robot handlers.

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 counter-weight.

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 super-conducting 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 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.