"Ice Hole to Ganymede Main." Cameron addressed screen three, which showed Foster at Main Base, situated seven hundred miles away to the south.

"Clear."

"Ice Hole to Jupiter Four. Report, please."

"All channels clear and checking positive." The last acknowledgment came from the deputy mission director on screen four, speaking from his nerve center in the heart of the mile-long Jupiter Mission Four command ship, at that moment orbiting over two thousand miles up over Ganymede.

"All channels positive and ready to proceed, sir," Cameron called to Mills.

"Carry on, then, Lieutenant"

"Aye, aye, sir."

Cameron passed the order to Stracey, and out by the hull the ponderous figures lumbered into action, swinging forward a rock-drill supported from an overhead gantry. The group by the window watched in silence as the bit chewed relentlessly into the inner wall. Eventually the drill was swung back.

"Initial penetration complete," Stracey's voice informed them. "Nothing visible inside."

An hour later, a pattern of holes adorned the exposed expanse of metal. When lights were shone through and a TV probe inserted, the screen showed snatches of a large compartment crammed with ducts and machinery. Shortly afterward, Stracey's team began cutting out the panel with torches. Mills invited Peters and Stanislow to come and observe the operations first-hand. The trio left the control room, descended to the lower floor, and a few minutes later emerged, clad in space suits, through the airlock onto the tunnel floor. As they arrived at the aperture, the rectangle of metal was just being swung aside.

The spotlights confirmed the general impression obtained via the drill holes. When preliminary visual examinations were completed, two sergeants who had been standing by stepped forward. Communications lines were plugged into their backpacks and they were handed TV cameras trailing cables, flashlights, and a pouch of tools and accessories. At the same time, other members of the team were smoothing over the jagged edges of the hole with pads of adhesive plastic to prevent tearing of the lines. An extending aluminum ladder was lowered into the hole and secured. The first sergeant to enter turned about on the edge of the hole, carefully located the top rung with his feet, and inch by inch disappeared down into the chamber. When he had found a firm footing, the second followed.