the unlucky designers could well have foregone.
Suddenly, the supporting cables snapped, flailing upward 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 inexpungible 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 the more expensive 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 Theodore von Kármán’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 meters from the centerline—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 in 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 the 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 kilometers. 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 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 meters across. Morgan had a sudden image of Yakkagala, as he had last seen it, looming against the Taprobanean sky. Imagine lifting that forty thousand kilometers into space! Fortunately, it might not be necessary; there were 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 arrived at solutions he had 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 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 celestrial 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 ten-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 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