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20. The Bridge that Danced

Even in this age of instantaneous communications and swift global transport, it was convenient to have a place that one could call one's office. Not everything could be stored in patterns of electronic charges; there were still such items as good old-fashioned books, professional certificates, awards and honours, engineering models, samples of material, artists' rendering of projects (not as accurate as a computer's, but very ornamental), and of course the wall-to-wall carpet which every senior bureaucrat needed to soften the impact of external reality.

Morgan's office, which he saw on the average ten days per month, was on the sixth or LAND floor of the sprawling Terran Construction Corporation Headquarters in Nairobi. The floor below was SEA, that above it ADMINISRATI0N-meaning Chairman Collins and his empire. The architect, in a fit of nave symbolism, had devoted the top floor to SPACE. There was even a small observatory on the roof, with a thirty-centimetre telescope that was always out of order, because it was only used during office parties, and frequently for most non-astronomical purposes. The upper rooms of the Triplanetary Hotel, only a kilometre away, were a favourite target, as they often held some very strange forms of life or at any rate of behaviour.

As Morgan was in continuous touch with his two secretaries one human, the other electronic he expected no surprises when he walked into the office after the brief flight from ANAR. By the standards of an earlier age, his was an extraordinarily small organisation. He had less than three hundred men and women under his direct control; but the computing and information-processing power at their command could not be matched by the merely human population of the entire planet.

Well, how did you get on with the Sheik? asked Warren Kingsley, his deputy and long time friend, as soon as they were alone together.

Very well; I think we have a deal. But I still can't believe that we're held up by such a stupid problem. What does the legal department say?

We'll definitely have to get a World Court ruling. If the Court agrees that it's a matter of overwhelming public interest, our reverend friends will have to move though if they decide to be stubborn, there would be a nasty situation. Perhaps you should send a small earthquake to help them make up their minds.

The fact that Morgan was on the board of General Tectonics was an old joke between him and Kingsley; but GT perhaps fortunately had never found a way of controlling and directing earthquakes, nor did it ever expect to do so. The best that it could hope for was to predict them, and to bleed off their energies harmlessly before they could do major damage. Even here, its record of success was not much better than 75 percent.

A nice idea, said Morgan, I'll think it over. Now, what about our other problem?

All set to go do you want it now?

O.K. let's see the worst.

The office windows darkened, and a grid of glowing lines appeared in the centre of the room.

Watch this, Van, said Kingsley. Here's the regime that gives trouble.

Rows of letters and numbers materialised in the empty air velocities, payloads, accelerations, transit times Morgan absorbed them at a glance. The globe of the earth, with its circles of longitude and latitude, hovered just above the carpet; and rising from it, to little more than the height of a man, was the luminous thread that marked the position of the orbital tower.

Five hundred times normal speed; lateral scale exaggeration fifty. Here we go.

Some invisible force had started to pluck at the line of light, drawing it away from the vertical. The disturbance was moving upwards as it mimicked, via the computer's millions of calculations a second, the ascent of a payload through the earth's gravitational field.

What's the displacement? asked Morgan, as his eyes strained to follow the details of the simulation.

Now about two hundred metres. It gets to three before -

The thread snapped. In the leisurely slow-motion that represented real speeds of thousands of kilometres an hour, the two segments of the severed tower began to curl away from each other one bending back to earth, the other whipping upwards to space

But Morgan was no longer fully conscious of this imaginary disaster, existing only in the mind of the computer; superimposed upon it now was the reality that had haunted him for years.

He had seen that two-century-old film at least fifty times, and there were sections that he had examined frame by frame, until he knew every detail by heart. It was, after all, the most expensive movie footage ever shot, at least in peacetime. It had cost the State of Washington several million dollars a minute.

There stood the slim (too slim!) and graceful bridge, spanning the canyon. It bore no traffic, but a single car had been abandoned midway by its driver. And no wonder, for the bridge was behaving as none before in the whole history of engineering.

It seemed impossible that thousands of tons of metal could perform such an aerial ballet; one could more easily believe that the bridge was made of rubber than of steel. Vast, slow undulations, metres in amplitude, were sweeping along the entire width of the span, so that the roadway suspended between the piers twisted back and forth like an angry snake. The wind blowing down the canyon was sounding a note far too low for any human ears to detect, as it hit the natural frequency of the beautiful, doomed structure. For hours, the torsional vibrations had been building up, but no-one knew when the end would come. Already, the protracted death-throes were a testimonial that the unlucky designers could well have foregone.

Suddenly, the supporting cables snapped, flailing upwards like murderous steel whips. Twisting and turning, the roadway pitched into the river, fragments of the structure flying in all directions. Even when projected at normal speed, the final cataclysm looked as if shot in slow motion; the scale of the disaster was so large that the human mind had no basis of comparison. In reality, it lasted perhaps five seconds; at the end of that time, the Tacoma Narrows Bridge had earned an inexpungable place in the history of engineering. Two hundred years later there was a photograph of its last moments on the wall of Morgan's office, bearing the caption One of our less successful products.

To Morgan that was no joke, but a permanent reminder that the unexpected could always strike from ambush. When the Gibraltar Bridge was being designed, he had gone carefully through von Krmn's classic analysis of the Tacoma Narrows disaster, learning all he could from one of the most expensive mistakes of the past. There had been no serious vibrational problems even in the worst gales that had come roaring in from the Atlantic, though the roadway had moved a hundred metres from the centre line precisely as calculated.

But the space elevator was such a leap forward into the unknown that some unpleasant surprises were a virtual certainty. Wind forces on the atmospheric section were easy to estimate, but it was also necessary to take into account the vibrations induced by the stopping and starting of the payloads and even, on so enormous a structure, by the tidal effects of the sun and moon. And not only individually, but acting all together; with, perhaps, an occasional earthquake to complicate the picture, in the so-called worst case analysis.

All the simulations, in this tons-of-payload-per-hour regime, give the same result. The vibrations build up until there's a fracture at around five hundred kilometres. We'll have to increase the damping drastically.

I was afraid of that. How much do we need?

Another ten megatons.

Morgan could take some gloomy satisfaction from the figure. That was very close to the guess he had made, using his engineer's intuition and the mysterious resources of his subconscious. Now the computer had confirmed it; they would have to increase the anchor mass in orbit by ten million tons.

Even by terrestrial earth-moving standards, such a mass was hardly trivial; it was equivalent to a sphere of rock about two hundred metres across. Morgan had a sudden image of Yakkagala, as he had last seen it, looming against the Taprobanean sky. Imagine lifting that forty thousand kilometres into space! Fortunately, it might not be necessary; there were at least two alternatives.

Morgan always let his subordinates do their thinking for themselves; it was the only way to establish responsibility, it took much of the load off him and, on many occasions, his staff had arrived at solutions he might have overlooked.

What do you suggest, Warren? he asked quietly.

We could use one of the lunar freight launchers, and shoot up ten megatons of moon-rock. It would be a long and expensive job, and we'd still need a large space-based operation to catch the material and steer it into final orbit. There would also be a psychological problem -

Yes, I can appreciate that; we don't want another San Luiz Domingo -

San Luiz had been the fortunately small South American village that had received a stray cargo of processed lunar metal intended for a low-orbit space station. The terminal guidance had failed, resulting in the first man-made meteor crater and two hundred and fifty deaths. Ever since that, the population of planet Earth had been very sensitive on the subject of celestial target practice.

A much better answer is to catch an asteroid; we're running a search for those with suitable orbits, and have found three promising candidates. What we really want is a carbonaceous one then we can use it for raw material when we set up the processing plant. Killing two birds with one stone.

A rather large stone, but that's probably the best idea. Forget the lunar launcher a million 10-ton shots would tie it up for years, and some of them would be bound to go astray. If you can't find a large enough asteroid, we can still send the extra mass up by the elevator itself though I hate wasting all that energy if it can be avoided.

It may be the cheapest way. With the efficiency of the latest fusion plants, it will take only twenty dollars' worth of electricity to lift a ton up to orbit.

Are you sure of that figure?

It's a firm quotation from Central Power.

Morgan was silent for a few minutes. Then he said: The aerospace engineers really are going to hate me. Almost as much, he added to himself, as the Venerable Parakarma.

No that was not fair. Hate was an emotion no longer possible to a true follower of the Doctrine. What he had seen in the eyes of ex-Doctor Choam Goldberg was merely implacable opposition; but that could be equally dangerous.

19. By the Shores of Lake Saladin | The Fountains of Paradise | 21. Judgement