Ten minutes later, the first reception vehicle halted outside the Operations Control building and an extending tube telescoped out to dock with its airlock. Major Stanislow, Colonel Peters, and a handful of aides walked through into the outer access chamber, where they were met by Mills and a few other officers. Mutual introductions were concluded, and without further preliminaries the party ascended to the first floor and proceeded through an elevated walkway into the adjacent dome, constructed over the head of number-three shaft. A labyrinth of stairs and walkways brought them eventually to number-three high-level airlock anteroom. A capsule was waiting beyond the airlock. For the next four minutes they plummeted down, down, deep into the ice crust of Ganymede.

They emerged through another airlock into number-three low-level anteroom. The air vibrated with the humming and throbbing of unseen machines. Beyond the anteroom, a short corridor brought them at last to the low-level control room. It was a maze of consoles and equipment cubicles, attended by perhaps a dozen operators, all intent on their tasks. One of the longer walls, constructed completely from glass, gave a panoramic view down over the workings in progress outside the control room. Lieutenant Cameron joined them as they lined up by the glass to take in the spectacle beyond.

They were looking out over the floor of an enormous cathedral, over nine hundred feet long and a hundred feet high, hewn and melted out of the solid ice. Its rough-formed walls glistened white and gray in the glare of countless arc lights. The floor was a litter of steelmesh roadways, cranes, gantries, girders, pipes, tubes, and machinery of every description. The left-side wall, stretching away to the far end of the tunnel, carried a lattice of ladders, scaffolding, walkways, and cabins that extended up to the roof. All over the scene, scores of figures in ungainly heavy-duty space suits bustled about in a frenzy of activity, working in an atmosphere of pressurized argon to eliminate any risk of explosion from methane and the other gases released from the melted ice. But all eyes were fixed on the right-hand wall of the tunnel.