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.