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All this had mellowed her, though it had not slowed her down. She was no longer the sometimes fiery chauvinist who had once remarked: Since women are better at producing babies, presumably Nature has given men some talent to compensate. But for the moment I can't think of it. However, she had only recently embarrassed a hapless panel chairman with the loud aside: I'm a newswoman, dammit not a newsperson.

Of her femininity there had never been any doubt; she had been married four times, and her choice of REMS was famous. Whatever their sex, Remotes were always young and athletic, so that they could move swiftly despite the encumbrance of up to twenty kilos of communications gear. Maxine Duval's were invariably very male and very handsome; it was an old joke in the trade that all her REMs were also RAMS. The jest was completely without rancour, for even her fiercest professional rivals liked Maxine almost as much as they envied her.

Sorry about the race, said Rajasinghe, but I note that Marlin III won very handily without you. I think you'll admit that this is rather more important But let Morgan speak for himself.

He released the PAUSE button on the projector, and the frozen statue came instantly to life.

My name is Vannevar Morgan. I am Chief Engineer of Terran Construction's Land Division. My last project was the Gibraltar Bridge. Now I want to talk about something incomparably more ambitious.

Rajasinghe glanced round the room. Morgan had hooked them, just as he had expected.

He leaned back in his chair, and waited for the now familiar, yet still almost unbelievable, prospectus to unfold. Odd, he told himself, how quickly one accepted the conventions of the display, and ignored quite large errors of the Tilt and Level controls. Even the fact that Morgan moved while staying in the same place, and the totally false perspective of exterior scenes, failed to destroy the sense of reality.

"The Space Age is almost two hundred years old. For more than half that time, our civilisation has been utterly dependent upon the host of satellites that now orbit Earth. Global communications, weather forecasting and control, land and ocean resources banks, postal and information services if anything happened to their space-borne systems, we would sink back into a dark age. During the resultant chaos, disease and starvation would destroy much of the human race.

"And looking beyond the Earth, now that we have self-sustaining colonies on Mars, Mercury and the Moon, and are mining the incalculable wealth of the asteroids, we see the beginnings of true interplanetary commerce. Though it took a little longer than the optimists predicted, it is now obvious that the conquest of the air was indeed only a modest prelude to the conquest of space.

But now we are faced with a fundamental problem an obstacle that stands in the way of all future progress. Although generations of research have made the rocket the most reliable form of propulsion ever invented -

("Has he considered bicycles?" muttered Sarath.)

" space vehicles are still grossly inefficient. Even worse, their effect on the environment is appalling. Despite all attempts to control approach corridors, the noise of take-off and re-entry disturbs millions of people. Exhaust products dumped in the upper atmosphere have triggered climatic changes, which may have very serious results. Everyone remembers the skin-cancer crisis of the twenties, caused by ultra-violet break-through and the astronomical cost of the chemicals needed to restore the ozonosphere.

"Yet if we project traffic growth to the end of the century, we find that Earth-to-orbit tonnage must be increased almost fifty percent. This cannot be achieved without intolerable costs to our way of life perhaps to our very existence. And there is nothing that the rocket engineers can do; they have almost reached the absolute limits of performance, set by the laws of physics.

What is the alternative? For centuries, men have dreamed of anti-gravity or of 'spacedrives'. No-one has ever found the slightest hint that such things are possible; today we believe that they are only fantasy. And yet, in the very decade that the first satellite was launched, one daring Russian engineer conceived a system that would make the rocket obsolete. It was years before anyone took Yuri Artsutanov seriously. It has taken two centuries for our technology to match his vision.

Each time he played the recording, it seemed to Rajasinghe that Morgan really came alive at this point. It was easy to see why; now he was on his own territory, no longer relaying information from an alien field of expertise. And despite all his reservations and fears, Rajasinghe could not help sharing some of that enthusiasm. It was a quality which, nowadays, seldom impinged upon his life.

"Go out of doors any clear night," continued Morgan, "and you will see that commonplace wonder of our age the stars that never rise or set, but are fixed motionless in the sky. We and our parents and their parents have long taken for granted the synchronous satellites and space stations, which move above the equator at the same speed as the turning earth, and so hang forever above the same spot.

"The question Artsutanov asked himself had the childlike brilliance of true genius. A merely clever man could never have thought of it or would have dismissed it instantly as absurd.

"If the laws of celestial mechanics make it possible for an object to stay fixed in the sky, might it not be possible to lower a cable down to the surface and so to establish an elevator system linking Earth to space?

"There was nothing wrong with the theory, but the practical problems were enormous. Calculations showed that no existing materials would be strong enough; the finest steel would snap under its own weight long before it could span the thirty-six thousand kilometres between Earth and synchronous orbit.

"However, even the best steels were nowhere near the theoretical limits of strength. On a microscopic scale, materials had been created in the laboratory with far greater breaking strength. If they could be mass-produced, Artsutanov's dream could become reality, and the economics of space transportation would be utterly transformed.

"Before the end of the twentieth century, super-strength materials hyperfilaments had begun to emerge from the laboratory. But they were extremely expensive, costing many times their weight in gold. Millions of tons would be needed to build a system that could carry all Earth's outbound traffic; so the dream remained a dream.

Until a few months ago. Now the deep-space factories can manufacture virtually unlimited quantities of hyperfilament. At last we can build the Space Elevator or the Orbital Tower, as I prefer to call it. For in a sense it is a tower, rising clear through the atmosphere, and far, far beyond

Morgan faded out, like a ghost that had been suddenly exorcised. He was replaced by a football-sized Earth, slowly revolving. Moving an arm's-breadth above it, and keeping always poised above the same spot on the equator, a flashing star marked the location of a synchronous satellite.

From the star, two thin lines of light started to extend-one directly down towards the earth, the other in exactly the opposite direction, out into space.

When you build a bridge, continued Morgan's disembodied voice, you start from the two ends and meet in the middle. With the orbital tower, it's the exact opposite. You have to build upwards and downwards simultaneously from the synchronous satellite, according to a careful programme. The trick is to keep the structure's centre of gravity always balanced at the stationary point; if you don't, it will move into the wrong orbit, and start drifting slowly round the earth.

The descending line of light reached the equator; at the same moment, the outward extension also ceased.

"The total height must be at least forty thousand kilometres and the lowest hundred, going down through the atmosphere, may be the most critical part, for there the tower may be subject to hurricanes. It won't be stable until it's securely anchored to the ground.