One hour. Contact minus 4,000.

The first abort option had passed. The beanstalk was moving faster now, arcing in towards Earth along the smooth curve of an Archimedean spiral. From a head moving along at ten kilometers a second, the thin filament curved around through more than three hundred degrees to its bulbous tail. Three billion tons of inertia began to make their presence felt. As the beanstalk swung in toward Earth impact, the elements of the cable could not follow their natural free-fall pattern. Instead, tensions were building along the whole length, constraining the diving head to follow an approach path that would turn gradually to the planned landing point at Quito.

Stored elastic energy was growing within the load cable. Already it matched that of a medium-sized fission bomb. If the cable snapped, the energy would release as a shock wave along the length of it.

Rob looked at the readings from the strain gauges set all along the axis of the beanstalk. They still shared low values, negligible compared with their final planned maxima. He switched to the screen that monitored the orbit of the ballast asteroid. Soon it would reach perigee. In thirty minutes it would begin to swing out again, away from Earth. For the moment nothing needed to be done. Rob checked the Doppler broadening from the asteroid observations, confirming that they showed an acceptably low rotation rate for the ballast.

There was still plenty of time for an abort option. The beanstalk had not yet started its final straightening. High-reaction drives attached to the head could swing it away from Earth and curve it clear. When the drives were jettisoned in another forty minutes, at least some part of the stalk must enter Earth’s atmosphere.

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.