But he could not understand why anyone would go to the trouble to mine an asteroid from the inside. The cutters on a prospecting ship could slice all but the densest nickel-iron asteroids into bite-sized chunks for the leviathan processing centers. No ore Derec knew of was worth the expense of tunnel-and-shaft mining on this scale. Even with the energy-and-raw-materials economics which applied with robot labor, it would have to be something a hundred times more precious than the rarest element-unless the value of secrecy was part of the equation.
Who am I dealing with?Derec wondered. Newly sobered, he stepped back onto the lift.
“Level Three,” he said.
The next two levels were just as silent and finished-looking as Two. Derec could notdecide whether they were finished-waiting-to-be-used, like the spare parts in the great chamber, or finished-and-abandoned.
But Level Five was another story. The rumble of heavy machinery assaulted his ears even before the platform reached the lighted zone. When he stepped off the lift, he could feel rolling, low-frequency vibrations in the floor and ceiling of the tunnel.
I’m getting closer, he thought. Now-which way? The sound surrounded him, offering no clue as to which of the tunnels had the most promise.
While he stood there equivocating, a double platform arrived and disgorged a porter robot. On impulse, Derec climbed onto its half-full cargo pad. He was counting on its ignoring him, as the picker had. He was not disappointed. Neither cradling him in its arms nor trying to dislodge him, the porter started down the south tunnel.
For the first two minutes of the ride, wind noise and the whine of the robot’s own mechanisms masked the distant work noise. But before long Derec could sort the separate elements: irregular thumping sounds like muffled explosions, a highpitched grinding that made his skin crawl, and a steady background rumble that suggested great masses of rock and ice being moved about.
Presently the end of the tunnel came in sight as a black patch in the distance. Shortly after, Derec began to detect a whiff of ammonia in the air. The moment he did, another piece of the puzzle fell into place.
He had wondered from the start why the complex outside the E-cell was filled with nitrogen. The robots did not require it. Strictly speaking, robots did not require an atmosphere at all. And keeping the complex sealed and pressurized had to be more complicated than simply opening it to space.
But maintaining a standard two-gas atmosphere in the proper proportions through the vast complex was even more complicated. Derec had concluded that the nitrogen atmosphere and “open” breathers were a compromise between the inconvenience of full pressure suits and the complexity of a dual-gas E-system. The nitrogen allowed humans to speak and hear normally and to move about without safesuits, without the fire and explosion risk posed by free oxygen.
But Derec had overlooked something important. The ices which made up a large fraction of the asteroid’s bulk were not water, but compounds like methane and ammonia. The mining processes would inevitably release them as gases into the work area, where they might react with the high energies and circuits of the mining machinery or with each other.
I should have seen it sooner, he thought. Without an atmosphere comprised of some relatively inert gas, there would be no way to dilute the unwelcome compounds or efficiently flush them out. So of course, an atmosphere. Of course, nitrogen. The atmosphere accommodated a human presence, but was not primarily for human convenience.
The porter slowed as they neared the end of the tunnel, and Derec took that opportunity to jump off. Ahead of him were several robots, gathered near the end of the tunnel, and the gateway to what he presumed was the work chamber. Through the gateway he caught glimpses of a ragged rock wall, equipment booms, and an occasional flash of bright light.
The gateway itself was an enormous boxlike machine which filled the tunnel flush to the walls, floor, and ceiling. The only path through to the work chamber was a narrow walkway between columns of bright green chemical storage tanks. That was where he had to go.
As Derec drew closer, he saw that the gateway was actually crawling slowly forward. Like some mechanical larva, the gateway was burrowing through the asteroidal mass and leaving a finished tunnel in its wake. Everything-the raw material of the walls, the covering of reinforcing synthemesh, even the overhead lamps-was being handled in one continuous operation. The gateway was a four-surface paving machine.
But Derec’s real interest was in the excavation beyond. He stepped up onto the gateway and threaded his way between the shoulder-high cylinders, aware as he did that one of the humanoid robots was following him. There was a strong draft through the walkway, from the tunnel to the chamber beyond. Even so, the odor of ammonia was almost strong enough to make him gag.
At the forward end, the narrow walkway widened into a control cabin, where two humanoid robots sat behind a bank of transparent panels looking out into the excavation chamber that surrounded the gateway on three sides. Derec stopped a few steps short of the ramp into the excavation and tried to sort out the functions of the equipment that filled it.
The uncut face of the asteroidal material was some thirty meters away. A two-headed boom cutter was working it, one boom bearing rotary grinders, the other microwave lasers. They moved back and forth like weaving cobras, and the ice and rock wall crumbled before them.
The lasers seemed to be doing most of the damage. Suddenly released from its icy glue, loose rock sloughed off the face with a cracking sound. More resistant deposits were gouged off by the rotating teeth of the grinder. The gases boiling off the face were being sucked into the wide-mouthed exhaust vents that loomed over the work face.
As he studied the work rig, a metallic hand touched his shoulder.
“You may not enter the processing zone during operations,” the robot said.
The robot’s edict stirred a flash of annoyance. “I will if I want to,” Derec snapped back over his shoulder.
The robot tightened its grip pointedly. “You may not enter the processing zone during operations,” the robot repeated. “Untrained personnel are to be considered at risk.”
Shrugging off its touch, Derec turned his back on the robot and looked once more into the excavation. Like the gateway, the mining unit was slowly advancing toward an ever-receding rock face. The motion brought the jumble of loose rock within reach of scuttling scooper arms, which funneled it up a ramp to an enormous hopper. A pair of high-sided conveyors carried material away from the hopper, one to the left and one to the right. While on the conveyor it passed through an N-ray station, an X-ray station, and a magnetometer.
From that point on, things got confusing. It was as though after having gone to all that trouble to mine the asteroid, the robots had forgotten to sort out the part of it they wanted to keep.
Some of the tailings were diverted to a spur conveyor, run through a crusher, and then used as the raw material for the fifteen-centimeter thick walls of the tunnel. To Derec’s astonishment, the rest was carried to the back wall of the work chamber, reunited with the captured methane and ammonia, and built up into a wall of ice and rock again. The excavation never got any larger.
But what about the tunnel? Derec wondered. They have to be taking something out-
Closer study showed him otherwise. The empty volume of the ever-lengthening access tunnel meant only that the asteroidal material surrounding it was being replaced in a more compressed state than it was in when mined. Nothing was being extracted. Nothing was being carried away for later refining or shipment.
It just didn’t make sense.
The depletion alarm on Derec’s first cartridge pack began to sound, and he transferred the delivery tube to the backup. He would have to leave soon or risk dying of nitrogen poisoning before he could return to the E-cell. But it was hard to tear himself away from the incomprehensible sight of a dozen robots and a few million dollars worth of heavy equipment engaged in a task as senseless as trying to dig a hole in water. And how many other excavations just like this
were underway elsewhere in the complex? Ten? Fifty? Five hundred?
Trying to understand, Derec focused his attention on the robots. Three of the armored type patrolled the hopper, breaking up snags with their grapples. A fourth stood on a small platform under the booms of the cutter, shattering oversized rocks as they fell from the face with blasts from its chest-mounted laser. Two humanoids stood at the N-ray stations, intently studying the scanning screen.
Derec’s guardian angel was still standing within arm’s reach behind him, and he turned and sought the robot’s eyes. “What are you mining here?” he demanded. “What’s the point of all this?”
But the robot said nothing, gazing back with its expressionless eyes.
“Get out of the way,” Derec said disgustedly, and the robot stepped aside into the control booth to let him pass.
His annoyance spilling over into anger, Derec stalked down the narrow walkway and jumped down to the tunnel. It was then he realized his mistake: there were no porter robots there to carry him back to the lift.
“I need a ride,” Derec said sharply to the nearest humanoid robot. “Can you tell me when the next porter robot will be making a delivery?”
“What is your need?”
“I need a ride.”
“That is not an approved allocation of resources.”
Derec did not even bother to argue. Turning away, he stalked away northward, his mind unsettled, churning with unconnected thoughts. He felt as though the answer to all his questions was already in his grasp, except he couldn’t recognize it. How did it all add up? What was wrong with the picture?
As he hand-walked along the tunnel, his thoughts kept carrying him back to the robots. There was something about the way they behaved, the way they worked together. Throughout the complex, all the routine, repetitive jobs were being done by the nonhumanoid robots. The blue-skinned humanoid robots were supervisors, trouble-shooters, technicians, repair specialists. But they could have just as easily done the repetitive jobs as well, even tending the front line in the excavation. Instead, there were a half-dozen specialized varieties, porters and pickers and miners that didn’t act like robots at all-
Derec stopped short and turned to stare back down the tunnel toward the excavation. Of course. Of course. The picker and the custodians, the tenders and the portersweren’t specialized robots working with the blue robots. They weretools beingused by the blue robots. Their intelligence was limited-perhaps not even positronic in nature. The real intelligence resided in the humanoid robots, which might well be more sophisticated than any Derec had previously known of.
But why were they all here?
Derec thought of all the levels, all the tunnels that had already been bored out, all the mass of the asteroid still waiting undisturbed. Could he have stumbled on an industrial test site? It might explain much-the secrecy, the distinctive stamp of the unknown designer, the unending but pointless excavation.
Focus on the robots, Derec told himself. The tasks they’re handling themselves are the ones they consider critical-
In a flash of memory, he saw the two humanoid robots tending the scanning instruments on the conveyor line, and suddenly Derec knew. The realization staggered him, and yet there was no pushing the notion away once it had formed in his mind.
The robots weren’t mining the asteroid at all. They weresifting it. They were searching for something, something lost or buried or hidden, something so unique and valuable that it was worth any price, any effort.
What that something was, Derec could not imagine. And just at that moment, he was not sure that he ever wanted to find out.
Chapter 4. You Can’t Get There From Here
It was a very long way back to the lift. How fast had the porter gone when carrying him to the excavation? Forty kilometers per hour? Then the shaft lay ten kilometers away. Sixty? Then a fifteen-kilometer hike awaited him, at a thousand strides, a thousand arm-swings to a kilometer. Even in a gravity field this weak, that was asking a lot from his body.
He did not turn back only because he was sure that the Supervisors, as he had begun to think of the humanoid robots, knew where he was and how much oxygen he had. At some point the two changing variables would intersect at a value which said that he was in danger, and they would send a porter to fetch him and whisk him back to the E-cell.
Each time he saw a robot coming toward him, or heard one closing on him from behind, he began to anticipate relief for his weary arms and legs. But each time, the robot sped past without even slowing. He considered trying to stop a porter by blocking the tunnel, but the only porters that came by were burdened with a full load of chemical tanks or machine parts. There was no room for him.
Because there was no choice, Derec pressed on. For a time he tried counting the yellow ceiling lamps to prove to himself that he was making progress, but his mind wandered and he lost count. There was a terrible sameness to the tunnel, with its unrelieved stretches of white. It seemed as though he were caught in limbo, trapped on a subterranean treadmill.
As it turned out, he was not wrong in thinking that the Supervisors were aware of him. But he was quite wrong about the form their help would take.
He had sat down to rest, his back against the west wall, when a picker came racing up and stopped half a meter away. From its cargo basket it plucked a pair of fresh cartridge packs, laying them at his feet. Before he could react, it backed up, pivoted, and raced away. The timing was so perfect that the pack Derec was using began to sound its depletion alarm just as the picker vanished from sight in the distance.
“Consistent,” he said crossly, addressing the absent Supervisors as he swapped the depleted packs for the new ones. “You’ve done as little as possible to help me right from the start. And this really is the very least you could do.”
Hours later, he reached the E-cell with barely enough energy to fold down one of the bunks before he collapsed in it. He was asleep in minutes, his body claiming its rest. But his troubles pursued him even in his dreams, which were full of silent blue robots moving through dark places ripe with the cold scent of danger.
When he awoke, Derec began to think about escaping. For it was clear now that the most likely message for the Supervisor to have sent was something on the order of, “We have an intruder. What shall we do with him?” And Derec did not like most of the possible answers to that question.
He did not think the Supervisor robots, independent as they might be, were capable of killing him. The First Law was too deeply rooted in the basic structure of a positronic brain. To remove it or tamper with it was to guarantee trouble, up to and including complete intellectual disintegration.
But the recipient of the message was probably human, and therefore quite capable of using violence in service of his or her self-interest. They would want to know how he had discovered the installation, and what he had wanted there, and he would have nothing to tell them.
Perhaps they would accept that at face value, and help him return to wherever he had come from. But considering the circumstances, the stronger possibility was that they would insist on answers. Derec sensed that it would take a long time to convince them he had none. Even so, afterward they would want to make sure that he could never tell anyone what he had stumbled on.
No, he did not want to wait around for the Supervisors’ masters to arrive. The key to escaping was Darla. The pod’s thrusters were almost certainly rated for a much stronger gravity field than the one the asteroid boasted. If so, then there should be more than enough fuel remaining to lift off the asteroid again and put some distance between it and himself-if only he could convince Darla of the wisdom of that act.
But first, he had to find her. Measuring from memory, Derec suspected that the pod was too large to have been brought down the lift. The robots must have removed him from the pod somewhere on the surface-inside an entry dome, perhaps-and left the pod behind.
So he began by riding the lift in search of the place where he had been brought into the as
teroid. It turned out to be called Level Zero. At the top of the lift shaft a disclike pressure door scissored out of the way to allow the platform to pass, and the lift carried Derec up into a high-ceilinged circular room a hundred meters across.
Most of the chamber was filled with neatly aligned rows of machines-buglike augers and borers, tracked carriers, and flying globes like the one Derec had seen when the robots were carrying him and his pod away. On the far side of the room, a steep ramp enclosed by a transparent material led up and out onto the surface.
There was a Supervisor there as well, seated at a control station with its back to Derec. Though it gave no such sign, Derec was sure the robot was aware of his presence.
Stepping off the lift, Derec began to wander among the idle machines. This must be some of the equipment that was used to survey the outer crust of the asteroid, he thought. The flying globes were probably scanning platforms, while the other machines could be used to dig up any promising sites.
It seemed just as obvious to Derec that the surface survey was complete. It was not only the appearance of the machines that led to that conclusion. Searching the surface first made sense. Why even begin the underground excavation before you were sure that the object of your search wouldn’t be turned up by a much faster and far less complicated aerial survey?
But Derec was less interested in sorting out the remaining mysteries about this world than he was in finding Darla and saying good-bye to it. A quick catalog of the chamber turned up no sign of the pod or of his safesuit. But he did find a rack with three pearl-white augmented worksuits. They were too large for use in the lower levels or to allow him to climb into the pod if he found it, but he could still use one for an excursion to the surface.
Moving behind the nearest suit, Derec grabbed the crossbar and vaulted himself feet first through the access door on the back. As he settled in the saddlelike seat, he felt the feedback pads snugging up against his feet. He inserted his arms into the suit’s arms, and the controllers for the external manipulator came into his hands. A sloping display screen reflected the status of the suit’s systems on the bubblelike canopy before him.
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