Expedition to Earth

by Arthur C. Clarke

  To the layman, knowing nothing of the finer details of astronautics, the plan would have seemed quite suicidal. The Doradus was armed with the latest in ultra-scientific weapons: moreover, the twenty kilometers which separated her from her prey represented less than a second’s flight at maximum speed. But Commander Smith knew better, and was already feeling rather unhappy. He realized, only too well, that of all the machines of transport man has ever invented, a cruiser of space is far and away the least maneuverable. It was a simple fact that K.15 could make half a dozen circuits of his little world while her commander was persuading the Doradus to make even one.

  There is no need to go into technical details, but those who are still unconvinced might like to consider these elementary facts. A rocket-driven spaceship can, obviously, only accelerate along its major axis—that is, “forward.” Any deviation from a straight course demands a physical turning of the ship, so that the motors can blast in another direction. Everyone knows that this is done by internal gyros or tangential steering jets, but very few people know just how long this simple maneuver takes. The average cruiser, fully fueled, has a mass of two or three thousand tons, which does not make for rapid footwork. But things are even worse than this, for it isn’t the mass, but the moment of inertia that matters here—and since a cruiser is a long, thin object, its moment of inertia is slightly colossal. The sad fact remains (though it is seldom mentioned by astronautical engineers) that it takes a good ten minutes to rotate a spaceship through 180 degrees, with gyros of any reasonable size. Control jets aren’t much quicker, and in any case their use is restricted because the rotation they produce is permanent and they are liable to leave the ship spinning like a slow-motion pinwheel, to the annoyance of all inside.

  In the ordinary way, these disadvantages are not very grave. One has millions of kilometers and hundreds of hours in which to deal with such minor matters as a change in the ship’s orientation. It is definitely against the rules to move in ten-kilometer radius circles, and the commander of the Doradus felt distinctly aggrieved. K.15 wasn’t playing fair.

  At the same moment that resourceful individual was taking stock of the situation, which might very well have been worse. He had reached the hills in three jumps and felt less naked than he had out in the open plain. The food and equipment he had taken from the ship he had hidden where he hoped he could find it again, but as his suit could keep him alive for over a day that was the least of his worries. The small packet that was the cause of all the trouble was still with him, in one of those numerous hiding places a well-designed space-suit affords.

  There was an exhilarating loneliness about his mountain eyrie, even though he was not quite as lonely as he would have wished. Forever fixed in his sky, Mars was waning almost visibly as Phobos swept above the night side of the planet. He could just make out the lights of some of the Martian cities, gleaming pin-points marking the junctions of the invisible canals. All else was stars and silence and a line of jagged peaks so close it seemed he could almost touch them. Of the Doradus there was still no sign. She was presumably carrying out a careful telescopic examination of the sunlighted side of Phobos.

  Mars was a very useful clock: when it was half full the sun would rise and, very probably, so would the Doradus. But she might approach from some quite unexpected quarter: she might even—and this was the one real danger—she might even have landed a search party.

  This was the first possibility that had occurred to Commander Smith when he saw just what he was up against. Then he realized that the surface area of Phobos was over a thousand square kilometers and that he could not spare more than ten men from his crew to make a search of that jumbled wilderness. Also, K.15 would certainly be armed.

  Considering the weapons which the Doradus carried, this last objection might seem singularly pointless. It was very far from being so. In the ordinary course of business, side-arms and other portable weapons are as much use to a space-cruiser as are cutlasses and crossbows. The Doradus happened, quite by chance—and against regulations at that—to carry one automatic pistol and a hundred rounds of ammunition. Any search party would therefore consist of a group of unarmed men looking for a well concealed and very desperate individual who could pick them off at his leisure. K.15 was breaking the rules again.

  The terminator of Mars was now a perfectly straight line, and at almost the same moment the sun came up, not so much like thunder as like a salvo of atomic bombs. K.15 adjusted the filters of his visor and decided to move. It was safer to stay out of the sunlight, not only because here he was less likely to be detected in the shadow but also because his eyes would be much more sensitive there. He had only a pair of binoculars to help him, whereas the Doradus would carry an electronic telescope of twenty centimeters aperture at least.

  It would be best, K.15 decided, to locate the cruiser if he could. It might be a rash thing to do, but he would feel much happier when he knew exactly where she was and could watch her movements. He could then keep just below the horizon, and the glare of the rockets would give him ample warning of any impending move. Cautiously launching himself along an almost horizontal trajectory, he began the circumnavigation of his world.

  The narrowing crescent of Mars sank below the horizon until only one vast horn reared itself enigmatically against the stars. K.15 began to feel worried: there was still no sign of the Doradus. But this was hardly surprising, for she was painted black as night and might be a good hundred kilometers away in space. He stopped, wondering if he had done the right thing after all. Then he noticed that something quite large was eclipsing the stars almost vertically overhead, and was moving swiftly even as he watched. His heart stopped for a moment: then he was himself again, analyzing the situation and trying to discover how he had made so disastrous a mistake.

  It was some time before he realized that the black shadow slipping across the sky was not the cruiser at all, but something almost equally deadly. It was far smaller, and far nearer, than he had at first thought. The Doradus had sent her television-homing guided missiles to look for him.

  This was the second danger he had feared, and there was nothing he could do about it except to remain as inconspicuous as possible. The Doradus now had many eyes searching for him, but these auxiliaries had very severe limitations. They had been built to look for sunlit spaceships against a background of stars, not to search for a man hiding in a dark jungle of rock. The definition of their television systems was low, and they could only see in the forward direction.

  There were rather more men on the chessboard now, and the game was a little deadlier, but his was still the advantage.

  The torpedo vanished into the night sky. As it was traveling on a nearly straight course in this low gravitational field, it would soon be leaving Phobos behind, and K.15 waited for what he knew must happen. A few minutes later, he saw a brief stabbing of rocket exhausts and guessed that the projectile was swinging slowly back on its course. At almost the same moment he saw another flare far away in the opposite quarter of the sky, and wondered just how many of these infernal machines were in action. From what he knew of Z-class cruisers—which was a good deal more than he should—there were four missile-control channels, and they were probably all in use.

  He was suddenly struck by an idea so brilliant that he was quite sure it couldn’t possibly work. The radio on his suit was a tunable one, covering an unusually wide band, and somewhere not far away the Doradus was pumping out power on everything from a thousand megacycles upward. He switched on the receiver and began to explore.

  It came in quickly—the raucous whine of a pulse transmitter not far away. He was probably only picking up a sub-harmonic, but that was quite good enough. It D/F’ed sharply, and for the first time K.15 allowed himself to make long-range plans about the future. The Doradus had betrayed herself: as long as she operated her missiles, he would know exactly where she was.

  He moved cautiously forward toward the transmitter. To his surprise the signal faded, then increase
d sharply again. This puzzled him until he realized that he must be moving through a diffraction zone. Its width might have told him something useful if he had been a good enough physicist, but he couldn’t imagine what.

  The Doradus was hanging about five kilometers above the surface, in full sunlight. Her “non-reflecting” paint was overdue for renewal, and K.15 could see her clearly. As he was still in darkness, and the shadow line was moving away from him, he decided that he was as safe here as anywhere. He settled down comfortably so that he could just see the cruiser and waited, feeling fairly certain that none of the guided projectiles would come so near the ship. By now, he calculated, the commander of the Doradus must be getting pretty mad. He was perfectly correct.

  After an hour, the cruiser began to heave herself round with all the grace of a bogged hippopotamus. K.15 guessed what was happening. Commander Smith was going to have a look at the antipodes, and was preparing for the perilous fifty-kilometer journey. He watched very carefully to see the orientation the ship was adopting, and when she came to rest again was relieved to see that she was almost broadside on to him. Then, with a series of jerks that could not have been very enjoyable aboard, the cruiser began to move down to the horizon. K.15 followed her at a comfortable walking pace—if one could use the phrase—reflecting that this was a feat very few people had ever performed. He was particularly careful not to overtake her on one of his kilometer-long glides, and kept a close watch for any missiles that might be coming up astern.

  It took the Doradus nearly an hour to cover the fifty kilometers. This, as K.15 amused himself by calculating, represented considerably less than a thousandth of her normal speed. Once she found herself going off into space at a tangent, and rather than waste time turning end over end again fired off a salvo of shells to reduce speed. But she made it at last, and K.15 settled down for another vigil, wedged between two rocks where he could just see the cruiser and he was quite sure she couldn’t see him. It occurred to him that by this time Commander Smith might have grave doubts as to whether he really was on Phobos at all, and he felt like firing off a signal flare to reassure him. However, he resisted the temptation.

  There would be little point in describing the events of the next ten hours, since they differed in no important detail from those that had gone before. The Doradus made three other moves, and K.15 stalked her with the care of a big-game hunter following the spoor of some elephantine beast. Once, when she would have led him out into full sunlight, he let her fall below the horizon until he could only just pick up her signals. But most of the time he kept her just visible, usually low down behind some convenient hill.

  Once a torpedo exploded some kilometers away, and K.15 guessed that some exasperated operator had seen a shadow he didn’t like—or else that a technician had forgotten to switch off a proximity fuse. Otherwise nothing happened to enliven the proceedings: in fact, the whole affair was becoming rather boring. He almost welcomed the sight of an occasional guided missile drifting inquisitively overhead, for he did not believe that they could see him if he remained motionless and in reasonable cover. If he could have stayed on the part of Phobos exactly opposite the cruiser he would have been safe even from these, he realized, since the ship would have no control there in the moon’s radio-shadow. But he could think of no reliable way in which he could be sure of staying in the safety zone if the cruiser moved again.

  The end came very abruptly. There was a sudden blast of steering jets, and the cruiser’s main drive burst forth in all its power and splendor. In seconds the Doradus was shrinking sunward, free at last, thankful to leave, even in defeat, this miserable lump of rock that had so annoyingly balked her of her legitimate prey. K.15 knew what had happened, and a great sense of peace and relaxation swept over him. In the radar room of the cruiser, someone had seen an echo of disconcerting amplitude approaching with altogether excessive speed. K.15 now had only to switch on his suit beacon and to wait. He could even afford the luxury of a cigarette.

  “Quite an interesting story,” I said, “and I see now how it ties up with that squirrel. But it does raise one or two queries in my mind.”

  “Indeed?” said Rupert Kingman politely.

  I always like to get to the bottom of things, and I knew that my host had played a part in the Jovian War about which he very seldom spoke. I decided to risk a long shot in the dark.

  “May I ask how you happen to know so much about this unorthodox military engagement? It isn’t possible, is it, that you were K.15?”

  There was an odd sort of strangling noise from Carson. Then Kingman said, quite calmly: “No, I wasn’t.”

  He got to his feet and went off toward the gun room.

  “If you’ll excuse me a moment, I’m going to have another shot at that tree-rat. Maybe I’ll get him this time.” Then he was gone.

  Carson looked at me as if to say: “This is another house you’ll never be invited to again.” When our host was out of earshot he remarked in a coldly cynical voice:

  “You’ve done it. What did you have to say that for?”

  “Well, it seemed a safe guess. How else could he have known all that?”

  “As a matter of fact, I believe he met K.15 after the War: they must have had an interesting conversation together. But I thought you knew that Rupert was retired from the service with only the rank of lieutenant commander. The Court of Inquiry could never see his point of view. After all, it just wasn’t reasonable that the commander of the fastest ship in the Fleet couldn’t catch a man in a space-suit.”

  Expedition to Earth

  It was in the last days of the Empire. The tiny ship was far from home, and almost a hundred light-years from the great parent vessel searching through the loosely packed stars at the rim of the Milky Way. But even here it could not escape from the shadow that lay across civilization: beneath that shadow, pausing ever and again in their work to wonder how their distant homes were faring, the scientists of the Galactic Survey still labored at their never-ending task.

  The ship held only three occupants, but between them they carried knowledge of many sciences, and the experience of half a lifetime in space. After the long interstellar night, the star ahead was warming their spirits as they dropped down toward its fires. A little more golden, a trifle more brilliant than the sun that now seemed a legend of their childhood. They knew from past experience that the chance of locating planets here was more than ninety per cent, and for the moment they forgot all else in the excitement of discovery.

  They found the first planet within minutes of coming to rest. It was a giant, of a familiar type, too cold for protoplasmic life and probably possessing no stable surface. So they turned their search sunward, and presently were rewarded.

  It was a world that made their hearts ache for home, a world where everything was hauntingly familiar, yet never quite the same. Two great land masses floated in blue-green seas, capped by ice at either pole. There were some desert regions, but the larger part of the planet was obviously fertile. Even from this distance, the signs of vegetation were unmistakably clear.

  They gazed hungrily at the expanding landscape as they fell down into the atmosphere, heading toward noon in the subtropics. The ship plummeted through cloudless skies toward a great river, checked its fall with a surge of soundless power, and came to rest among the long grasses by the water’s edge.

  No one moved: there was nothing to be done until the automatic instruments had finished their work. Then a bell tinkled softly and the lights on the control board flashed in a pattern of meaningful chaos. Captain Altman rose to his feet with a sigh of relief.

  “We’re in luck,” he said. “We can go outside without protection, if the pathogenic tests are satisfactory. What did you make of the place as we came in, Bertrond?”

  “Geologically stable—no active volcanoes, at least. I didn’t see any trace of cities, but that proves nothing. If there’s a civilization here, it may have passed that stage.”

  “Or not reached it yet?�
�

  Bertrond shrugged. “Either’s just as likely. It may take us some time to find out on a planet this size.”

  “More time than we’ve got,” said Clindar, glancing at the communications panel that linked them to the mother ship and thence to the Galaxy’s threatened heart. For a moment there was a gloomy silence. Then Clindar walked to the control board and pressed a pattern of keys with automatic skill.

  With a slight jar, a section of the hull slid aside and the fourth member of the crew stepped out onto the new planet, flexing metal limbs and adjusting servo motors to the unaccustomed gravity. Inside the ship, a television screen glimmered into life, revealing a long vista of waving grasses, some trees in the middle distance, and a glimpse of the great river. Clindar punched a button, and the picture flowed steadily across the screen as the robot turned its head.

  “Which way shall we go?” Clindar asked.

  “Let’s have a look at those trees,” Altman replied. “If there’s any animal life we’ll find it there.”

  “Look!” cried Bertrond. “A bird!”

  Clindar’s fingers flew over the keyboard: the picture centered on the tiny speck that had suddenly appeared on the left of the screen, and expanded rapidly as the robot’s telephoto lens came into action.