The Sentinel

by Arthur C. Clarke

  “You’ve often asked me about our long-term plans,” he continued. “The foundation of the World State is, of course, only the first step. You will live to see its completion—but the change will be so imperceptible that few will notice it when it comes. After that there will be a pause for thirty years while the next generation reaches maturity. And then will come the day which we have promised. I am sorry that you will not be there.”

  Stormgren’s eyes were open, but his gaze was fixed far beyond the dark barrier of the screen. He was looking into the future, imagining the day he would never see, when the great ships of the Overlords came down at last to Earth and were thrown open to the waiting world.

  “On that day,” continued Karellen, “the human mind will experience one of its very rare psychological discontinuities. But no permanent harm will be done: the men of that age will be more stable than their grandfathers. We will always have been part of their lives, and when they meet us we will not seem so—strange—as we would do to you.”

  Stormgren had never known Karellen in so contemplative a mood, but this gave him no surprise. He did not believe that he had ever seen more than a few facets of the Supervisor’s personality: the real Karellen was unknown and perhaps unknowable to human beings. And once again Stormgren had the feeling that the Supervisor’s real interests were elsewhere, and that he ruled Earth with only a fraction of his mind, as effortlessly as a master of three-dimensional chess may play a game of checkers.

  Karellen continued his reverie, almost as if Stormgren were not there.

  “Then there will be another pause, only a short one this time, for the world will be growing impatient. Men will wish to go out to the stars, to see the other worlds of the Universe and to join us in our work. For it is only beginning: not a thousandth of the suns in the Galaxy have ever been visited by the races of which we know. One day, Rikki, your descendants in their own ships will be bringing civilization to the worlds that are ripe to receive it—just as we are doing now.”

  Faintly across the gulf of centuries Stormgren could glimpse the future of which Karellen dreamed, the future towards which he was leading mankind. How far ahead? He could not even guess: there was no way in which he could measure Man’s present stature against the standards of the Overlords.

  Karellen had fallen silent and Stormgren had the impression that the Supervisor was watching him intently.

  “It is a great vision,” he said softly. “Do you bring it to all your worlds?”

  “Yes,” said Karellen, “all that can understand it.”

  Out of nowhere, a strangely disturbing thought came into Stormgren’s mind.

  “Suppose, after all, your experiment fails with Man? We have known such things in our own dealings with other races. Surely you have had your failures too?”

  “Yes,” said Karellen, so softly that Stormgren could scarcely hear him. “We have had our failures.”

  “And what do you do then?”

  “We wait—and try again.”

  There was a pause lasting perhaps ten seconds. When Karellen spoke again, his words were muffled and so unexpected that for a moment Stormgren did not react.

  “Goodbye, Rikki!”

  Karellen had tricked him—probably it was already too late. Stormgren’s paralysis lasted only for a moment. Then in a single swift, well-practiced movement, he whipped out the flash-gun and jammed it against the screen.

  The pine trees came almost to the edge of the lake, leaving along its border only a narrow strip of grass a few yards wide. Every evening when it was warm enough Stormgren would walk slowly along this strip to the landing-stage, watch the sunlight die upon the water, and then return to the house before the chill evening wind came up from the forest. The simple ritual gave him much contentment, and he would continue it as long as he had the strength.

  Far away over the lake something was coming in from the west, flying low and fast. Aircraft were uncommon in these parts, unless one counted the transpolar liners which must be passing overhead every hour of the day and night. But there was never any sign of their presence, save an occasional vapor trail high against the blue of the stratosphere. This machine was a small helicopter, and it was coming towards him with ominous determination. Stormgren glanced along the beach and saw that there was no chance of escape. Then he shrugged his shoulders and sat down on the wooden bench at the end of the jetty.

  The reporter was so deferential that Stormgren found it surprising. He had almost forgotten that he was not only an elder statesman but, outside his own country, almost a mythical figure.

  “Mr. Stormgren,” the intruder began, “I’m very sorry to bother you, but I wonder if you would mind answering a few questions about the Overlords?”

  Stormgren frowned slightly. After all these years, he still shared Karellen’s dislike for the word.

  “I do not think,” he said, “that I can add a great deal to what has already been written elsewhere.”

  The reporter was watching him with a curious intentness.

  “I thought that you might,” he answered. “A rather strange story has just come to our notice. It seems that, nearly thirty years ago, one of the Science Bureau’s technicians made some remarkable pieces of equipment for you. We wondered if you could tell us anything about it.”

  For a moment Stormgren was silent, his mind going back into the past. He was not surprised that the secret had been discovered: indeed it was amazing that it had taken so long. He wondered how it had happened, not that it mattered now.

  He rose to his feet and began to walk back along the jetty, the reporter following a few paces behind.

  “The story,” he said, “contains a certain amount of truth. On my last visit to Karellen’s ship I took some apparatus with me, in the hope that I might see the Supervisor. It was rather a foolish thing to do but—well, I was only sixty at the time.”

  He chuckled to himself and then continued.

  “It’s not much of a story to have brought you all this way. You see, it didn’t work.”

  “You saw nothing?”

  “No, nothing at all. I’m afraid you’ll have to wait—but after all, there are only twenty years to go.”

  Twenty years to go. Yes, Karellen had been right. By then the world would be ready, as it had not been when he had spoken that same lie to Duval thirty years before.

  Yet was it a lie? What had he really seen? No more, he was certain, than Karellen had intended. He was as sure as he could be of anything that the Supervisor had known his plan from the beginning, and had foreseen every moment of its final act.

  Why else had that enormous chair been already empty when the circle of light blazed upon it? In the same moment he had started to swing the beam, but he was too late. The metal door, twice as high as a man, was closing swiftly when he first caught sight of it—closing swiftly, yet not quite swiftly enough.

  Karellen had trusted him, had not wished him to go down into the long evening of his life still haunted by a mystery he could never solve. Karellen dared not defy the unknown powers above him (were they of that same race too?) but he had done all that he could. If he had disobeyed Them, They could never prove it.

  “We have had our failures.”

  Yes, Karellen, that was true: and were you the one who failed, before the dawn of human history? It must have been a failure indeed, for its echoes to roll down all the ages, to haunt the childhood of every race of man. Even in fifty years, could you overcome the power of all the myths and legends of the world?

  Yet Stormgren knew there would be no second failure. When the two races met again, the Overlords would have won the trust and friendship of Mankind, and not even the shock of recognition could undo that work. They would go together into the future, and the unknown tragedy that had darkened the past would be lost forever down the dim corridors of prehistoric time.

  And Stormgren knew also that the last thing he would ever see as he closed his eyes on life would be that swiftly turning door, and the long b
lack tail disappearing behind it.

  A very famous and unexpectedly beautiful tail.

  A barbed tail.

  BREAKING

  STRAIN

  “Breaking Strain” was written in the summer of 1948, and although its deliberately low-key treatment was neither thrilling nor wondrous, it appeared in Thrilling Wonder Stories for December 1949. (To justify his existence, the editor changed the title to the unexciting and unimaginative “Thirty Seconds—Thirty Days.” And to make matters even more confused, he later republished it in The Best From Startling Stories.)

  The story caused one friendly critic to remark that I was apparently aspiring to the “Kipling of the spaceways”—a noble but (at least in 1948)—somewhat premature ambition. And on going through my records I am Thrilled and Startled to see that it was sold to CBS in 1955. I wonder if it was ever used . . .

  GRANT WAS WRITING UP the Star Queen’s log when he heard the cabin door opening behind him. He didn’t bother to look around—it was hardly necessary for there was only one other man aboard the ship. But when nothing happened, and when McNeil neither spoke nor came into the room, the long silence finally roused Grant’s curiosity and he swung the seat round in its gimbals.

  McNeil was just standing in the doorway, looking as if he had seen a ghost. The trite metaphor flashed into Grant’s mind instantly. He did not know for a moment how near the truth it was. In a sense McNeil had seen a ghost—the most terrifying of all ghosts—his own.

  “What’s the matter?” said Grant angrily. “You sick or something?”

  The engineer shook his head. Grant noticed the little beads of sweat that broke away from his forehead and went glittering across the room on their perfectly straight trajectories. His throat muscles moved, but for a while no sound came. It looked as though he was going to cry.

  “We’re done for,” he whispered at last. “Oxygen reserve’s gone.”

  Then he did cry. He looked like a flabby doll, slowly collapsing on itself. He couldn’t fall, for there was no gravity, so he just folded up in mid-air.

  Grant said nothing. Quite unconsciously he rammed his smoldering cigarette into the ash tray, grinding it viciously until the last tiny spark had died. Already the air seemed to be thickening around him as the oldest terror of the spaceways gripped him by the throat.

  He slowly loosed the elastic straps which, while he was seated, gave some illusion of weight, and with an automatic skill launched himself toward the doorway. McNeil did not offer to follow. Even making every allowance for the shock he had undergone, Grant felt that he was behaving very badly. He gave the engineer an angry cuff as he passed and told him to snap out of it.

  The hold was a large hemispherical room with a thick central column which carried the controls and cabling to the other half of the dumbbell-shaped spaceship a hundred meters away. It was packed with crates and boxes arranged in a surrealistic three-dimensional array that made very few concessions to gravity.

  But even if the cargo had suddenly vanished Grant would scarcely have noticed. He had eyes only for the big oxygen tank, taller than himself, which was bolted against the wall near the inner door of the airlock.

  It was just as he had last seen it, gleaming with aluminum paint, and the metal sides still held the faint touch of coldness that gave the only hint of the contents. All the piping seemed in perfect condition. There was no sign of anything wrong apart from one minor detail. The needle of the contents gauge lay mutely against the zero stop.

  Grant gazed at the silent symbol as a man in ancient London, returning home one evening at the time of the Plague, might have stared at a rough cross newly scrawled upon his door. Then he banged half a dozen times on the glass in the futile hope that the needle had stuck—though he never really doubted its message. News that is sufficiently bad somehow carries its own guarantee of truth. Only good reports need confirmation.

  When Grant got back to the control room, McNeil was himself again. A glance at the opened medicine chest showed the reason for the engineer’s rapid recovery. He even assayed a faint attempt at humor.

  “It was a meteor,” he said. “They tell us a ship this size should get hit once a century. We seem to have jumped the gun with ninety-five years still to go.”

  “But what about the alarms? The air pressure’s normal—how could we have been holed?”

  “We weren’t,” McNeil replied. “You know how the oxygen circulates night-side through the refrigerating coils to keep it liquid? The meteor must have smashed them and the stuff simply boiled away.”

  Grant was silent, collecting his thoughts. What had happened was serious—deadly serious—but it need not be fatal. After all, the voyage was more than three quarters over.

  “Surely the regenerator can keep the air breathable, even if it does get pretty thick?” he asked hopefully.

  McNeil shook his head. “I’ve not worked it out in detail, but I know the answer. When the carbon dioxide is broken down and the free oxygen gets cycled back there’s a loss of about ten percent. That’s why we have to carry a reserve.”

  “The space suits!” cried Grant in sudden excitement. “What about their tanks?”

  He had spoken without thinking, and the immediate realization of his mistake left him feeling worse than before.

  “We can’t keep oxygen in them—it would boil off in a few days. There’s enough compressed gas there for about thirty minutes—merely long enough for you to get to the main tank in an emergency.”

  “There must be a way out—even if we have to jettison cargo and run for it. Let’s stop guessing and work out exactly where we are.”

  Grant was as much angry as frightened. He was angry with McNeil for breaking down. He was angry with the designers of the ship for not having foreseen this God-knew-how-many-million-to-one chance. The deadline might be a couple of weeks away and a lot could happen before then. The thought helped for a moment to keep his fears at arm’s length.

  This was an emergency, beyond doubt, but it was one of those peculiarly protracted emergencies that seem to happen only in space. There was plenty of time to think—perhaps too much time.

  Grant strapped himself in the pilot’s seat and pulled out a writing-pad.

  “Let’s get the facts right,” he said with artificial calmness. “We’ve got the air that’s still circulating in the ship and we lose ten percent of the oxygen every time it goes through the generator. Chuck me over the Manual, will you? I can never remember how many cubic meters we use a day.”

  In saying that the Star Queen might expect to be hit by a meteor once every century, McNeil had grossly but unavoidably oversimplified the problem. For the answer depended on so many factors that three generations of statisticians had done little but lay down rules so vague that the insurance companies still shivered with apprehension when the great meteor showers went sweeping like a gale through the orbits of the inner worlds.

  Everything depends, of course, on what one means by the word meteor. Each lump of cosmic slag that reaches the surface of the Earth has a million smaller brethren that perish utterly in the no-man’s-land where the atmosphere has not quite ended and space has yet to begin—that ghostly region where the weird Aurora sometimes walks by night.

  These are the familiar shooting stars, seldom larger than a pin’s head, and these in turn are outnumbered a millionfold again by particles too small to leave any visible trace of their dying as they drift down from the sky. All of them, the countless specks of dust, the rare boulders and even the wandering mountains that Earth encounters perhaps once every million years—all of them are meteors.

  For the purposes of space-flight, a meteor is only of interest if, on penetrating the hull of a ship, it leaves a hole large enough to be dangerous. This is a matter of relative speeds as well as size. Tables have been prepared showing approximate collision times for various parts of the Solar System—and for various sizes of meteors down to masses of a few milligrams.

  That which had struck the Star Qu
een was a giant, being nearly a centimeter across and weighing all of ten grams. According to the table the waiting-time for collision with such a monster was of the order of ten to the ninth days—say three million years. The virtual certainty that such an occurrence would not happen again in the course of human history gave Grant and McNeil very little consolation.

  However, things might have been worse. The Star Queen was 115 days on her orbit and had only thirty still to go. She was traveling, as did all freighters, on the long tangential ellipse kissing the orbits of Earth and Venus on opposite sides of the Sun. The fast liners could cut across from planet to planet at three times her speed—and ten times her fuel consumption—but she must plod along her predetermined track like a streetcar, taking 145 days, more or less, for each journey.

  Anything more unlike the early-twentieth-century idea of a spaceship than the Star Queen would be hard to imagine. She consisted of two spheres, one fifty and the other twenty meters in diameter, joined by a cylinder about a hundred meters long. The whole structure looked like a match-stick-and-Plasticine model of a hydrogen atom. Crew, cargo, and controls were in the larger sphere, while the smaller one held the atomic motors and was—to put it mildly—out of bounds to living matter.

  The Star Queen had been built in space and could never have lifted herself even from the surface of the Moon. Under full power her ion drive could produce an acceleration of a twentieth of a gravity, which in an hour would give her all the velocity she needed to change from a satellite of the Earth to one of Venus.

  Hauling cargo up from the planets was the job of the powerful little chemical rockets. In a month the tugs would be climbing up from Venus to meet her, but the Star Queen would not be stopping for there would be no one at the controls. She would continue blindly on her orbit, speeding past Venus at miles a second—and five months later she would be back at the orbit of the Earth, though Earth itself would then be far away.