After that the process was quite simple, for many years. The principal factory on New Clarke made a cable of carbon nanotube filaments. The nanotubes were made of carbon atoms linked in chains so that the bonds holding them together were as strong as any that humans could manufacture. The filaments were only a few score meters long, but were bundled in clusters with their ends overlapping, and then the bundles were bundled, until the cable was nine meters in diameter. The factories could create the filaments and bundle them at speeds that allowed them to extrude the cable at a rate of about four hundred meters an hour, ten kilometers a day, for hour after hour, day after day, year after year.

While this thin strand of bundled carbon spun out into space, robots on another facet of the asteroid were constructing a mass driver, an engine that would use the deuterium from the indigenous water to fire crushed rock away from the asteroid at speeds of 200 kilometers a second. Around the asteroid smaller engines and conventional rockets were also being constructed and stocked with fuels, waiting for the time when they would fire, and perform the work of attitude jets. Other factories constructed long wheeled vehicles capable of running back and forth on the growing cable, and as the cable continued to appear out of the planet, small rocket jets and other machinery were attached to it.

The mass driver fired. The asteroid began to move into a new orbit.

Years passed. The asteroid’s new orbit intersected the orbit of Mars such that the asteroid came within ten thousand kilometers of Mars, and the collection of rockets on the asteroid fired in a way that allowed the gravity of Mars to capture it, in an orbit at first highly elliptical. The jets continued to fire off and on, regularizing the orbit. The cable continued to extrude. More years passed.

A little over a decade after the landers had first touched down, the cable was approximately thirty thousand kilometers long. The asteroid’s mass was about eight billion tons, the cable’s mass was about seven billion. The asteroid was in an elliptical orbit with a periapsis of around fifty thousand kilometers. But now all the rockets and mass drivers on both New Clarke and the cable itself began to fire, some continuously but most in spurts. One of the most powerful computers ever made sat in one of the payload bays, coordinating the data from sensors and determining what rockets should fire when. The cable, at this time pointing away from Mars, began to swing around toward it, as in the pivoting of some delicate part of a timepiece. The asteroid’s orbit became smaller and more regular.