It was not only the tensions in the beanstalk cable that were growing as the fly-in continued. Rob could feel a mounting discomfort, like a rock sitting in the pit of his stomach. Nothing on the bridge construction projects had prepared him for this, for the convoluted juggling of multiple forces implied by the landing of the stalk. Although the control panel gave him nominal control of operations, Rob knew that he was actually helpless. Everything depended on the accuracy of the calculations and the realism of the simulations they had done. Nothing that he — that any human — did now could improve the pattern of approach. He was at the center of the Control System, with only one decision left to make: abort, or continue the landing? The simple flip of a binary switch, that was what it all came down to. Rob was feeling less and less able to comprehend all the factors that would guide the decision. After the physical and mental turmoil of the past two weeks his brain felt numbed and slow, incapable of accurate evaluation. He bit his lip until it hurt, focused all his attention on the displays, and waited for the next datum point on his decision tree.
He had never expected to be so isolated. In all his plans, all his thoughts about the landing and tether, Regulo would be in close radio contact, assessing, advising, reassuring. No matter what the record books might show, this project was not Rob Merlin’s; it belonged to Darius Regulo, its originator, its designer, its only begetter.
Rob felt alone in his worries. He was not. In hundreds of outrider ships along the length of the stalk, in other vessels that matched the course of the great ballast weight, and in the hot and cramped offices of Tether Control, men and women sweated over the same display images, frowned at the same incoming data streams, and thanked Fortune that the final abort decision was not theirs to make.
All around the world, people were beginning to watch the sky. It was too soon to see anything; but logic did not control their actions.
Contact minus 600.
With ten minutes to contact, the diving head of the beanstalk reached the upper atmosphere. It entered the ionosphere and began to feel the first effects of frictional heating. Now it was starting to slow in its descent. The long tail, way out beyond synchronous altitude, was already tugging upward to provide a colossal outward tension that would slow all downward motion. The cup that hung at the very end of the beanstalk was moving higher and higher, sling-shotting out from the first approach spiral to stretch away from Earth. Eighty-five thousand kilometers above the surface, it formed the final point of a stalk that reared steadily closer to the vertical.
Looking down from the outer cup, an observer would see the shape of the beanstalk gradually straightening beneath, moving to make a clean line that dropped endlessly away to the distant Earth. The same observer, looking far out ahead of the swinging cable, would see the ballast asteroid, still thousands of kilometers away but rapidly coming closer.
The tension in the load-bearing cable had increased by two orders of magnitude in as many hours. It was still less than the final figure for the installed beanstalk, but already the stored energy exceeded that of any fusion weapon. Longitudinal waves of compression and tension rippled constantly along the length of the load cable, transmitting balancing forces from the out-flying higher end to the downward plummet of the lower cable.
Observers in Quito had heard the crack as the head passed through supersonic speed. Now they waited for the first sight of it. Along the equator, far to the west of Tether Control, a thin line of contrail at last became visible. It spread from the speeding head of the stalk in a wake of turbulent ice crystals. The shadow formed a dark swath on the equator, neatly bisecting the globe into north and south hemispheres. There was a steady rumble like approaching thunder.
High in the Andes, Indian peasants paused in their daily work of scratching the stubborn soil, long enough to offer their prayers to the old gods of the storm. Luis Merindo watched the scopes in Tether Control and sought the same reassurances from the newer deities of aerodynamics and electronics. The head of the beanstalk was a millisecond off at the first triangulation point. How much would that become when it reached the pit? He was relieved to see an estimate from Santiago flashing up onto his display. Just a few meters. They had more than enough margin for that at the pit.
As soon as atmospheric entry was initiated, Rob’s attention moved to the temperature sensors set throughout the length of the stalk. The change in gravitational potential as the beanstalk dropped would appear partly as kinetic energy and partly as dissipated energy within the stressed interior of the cable. That stretching and flexing would appear as adiabatic heating and cooling, driving the local temperature up and down differentially along the length. A thousand degrees was the limit. With ample strength at normal temperatures, the cable would weaken drastically above a thousand. The calculation had been one of the trickiest parts of stalk design, a bewildering maze of orbital dynamics, nonlinear elasticity and thermal diffusion.
Rob was relieved to see that his estimates were on the conservative side.
Contact minus 60.
The cupped upper end of the beanstalk, moving almost tangentially to the curve of the Earth’s surface, engulfed the ballast asteroid. The mesh of silicon threads that formed the cup began to take the strain as the ballast sought to continue its upward path. After one second, the stresses stabilized. The trajectory of the upper end of the beanstalk now became geostationary, moving to remain vertically above Quito ’s tether point. The tension in the cable was close to the design maximum value of eighty million newtons per square centimeter. Although the head still descended, that movement was less and less rapid.
The blunt lower end of the beanstalk was visible now from Tether Control. Its movement seemed almost leisurely. It descended like a sluggish, questing blind-worm seeking the pit that would house the tether. Luis Merindo watched his displays as the head disappeared behind the towering piles of rock around the hole. He checked his read-outs. In-filling would begin in thirty seconds. After that, only one question meant anything: Would the tether hold, against the billions of tons of upward force created when the ballast swung wide and high above synchronous orbit?
In the secondary viewing room at Santiago, Howard Anson was also watching the head of the beanstalk. He had no feeling for engineering, and the sight for him brought memories from another time of apocalypse. “Then will I headlong run into the Earth,” he whispered to himself. “Earth gape. Oh no, it will not harbor me. Mountains and hills, come, come and fall on me, and hide me from the heavy wrath of God.”
That earned him a peculiar look from the senate aide sitting next to him. Anson wondered if the man was objecting to his liberties with Marlowe’s classic text. He smiled and shrugged in an embarrassed way, and the other turned his attention back to the screens.
All opportunities for abort were now past. The remaining question centered on the tether. Unless that held, the beanstalk would be dragged from its temporary lodging north of Quito and swing up and away again, out past the Moon. The huge inertia of the system meant that even this question would take many seconds to answer by eye; the smart sensors on the beanstalk would know it in less than a heartbeat.
Contact.
The base of the beanstalk touched the bottom of the pit, five kilometers below ground level. As it did so, mountains began to move. Landslides were following the broad head of the beanstalk into the depths of the prepared chasm. The rumble of detonations, placed carefully around the edge of the pit, merged into the continuous roar of a billion tons of rock as it fell into the pit and packed down under the pressure as more earth and boulders followed.