The Sentinel

by Arthur C. Clarke

  It is surprising how long it takes to do a simple addition when your life depends on the answer. Grant ran down the short column of figures half a dozen times before he finally gave up hope that the total would change. Then he sat doodling nervously on the white plastic of the pilot’s desk.

  “With all possible economies,” he said, “we can last about twenty days. That means we’ll be ten days out of Venus when . . . ” His voice trailed off into silence.

  Ten days didn’t sound much—but it might just as well have been ten years. Grant thought sardonically of all the hack adventure writers who had used just this situation in their stories and radio serials. In these circumstances, according to the carbon-copy experts—few of whom had ever gone beyond the Moon—there were three things that could happen.

  The popular solution—which had become almost a cliché—was to turn the ship into a glorified greenhouse or a hydroponic farm and let photosynthesis do the rest. Alternatively one could perform prodigies of chemical or atomic engineering—explained in tedious technical detail—and build an oxygen manufacturing plant which would not only save your life—and of course the heroine’s—but also make you the owner of fabulously valuable patents. The third or deus ex machina solution was the arrival of a convenient spaceship which happened to be matching your course and velocity exactly.

  But that was fiction and things were different in real life. Although the first idea was sound in theory there wasn’t even a packet of grass seed aboard the Star Queen. As for feats of inventive engineering, two men—however brilliant and however desperate—were not likely to improve in a few days on the work of scores of great industrial research organizations over a full century.

  The spaceship that “happened to be passing” was almost, by definition, impossible. Even if other freighters had been coasting on the same elliptic path—and Grant knew there were none—then by the very laws that governed their movements they would always keep their original separations. It was not quite impossible that a liner, racing on its hyperbolic orbit, might pass within a few hundred thousand kilometers of them—but at a speed so great that it would be as inaccessible as Pluto.

  “If we threw out the cargo,” said McNeil at last, “would we have a chance of changing our orbit?”

  Grant shook his head.

  “I’d hoped so,” he replied, “but it won’t work. We could reach Venus in a week if we wished—but we’d have no fuel for braking and nothing from the planet could catch us as we went past.”

  “Not even a liner?”

  “According to Lloyd’s Register Venus has only a couple of freighters at the moment. In any case it would be a practically impossible maneuver. Even if it could match our speed how would the rescue ship get back? It would need about fifty kilometers a second for the whole job!”

  “If we can’t figure a way out,” said McNeil, “maybe someone on Venus can. We’d better talk to them.”

  “I’m going to,” Grant replied, “as soon as I’ve decided what to say. Go and get the transmitter aligned, will you?”

  He watched McNeil as he floated out of the room. The engineer was probably going to give trouble in the days that lay ahead. Until now they had got on well enough—like most stout men McNeil was good-natured and easy going. But now Grant realized that he lacked fiber. He had become flabby—physically and mentally—living too long in space.

  A buzzer sounded on the transmitter switchboard. The parabolic mirror out on the hull was aimed at the gleaming arc-lamp of Venus, only ten million kilometers away and moving on an almost parallel path. The three-millimeter waves from the ship’s transmitter would make the trip in little more than half a minute. There was bitterness in the knowledge that they were only thirty seconds from safety.

  The automatic monitor on Venus gave its impersonal Go ahead signal and Grant began to talk steadily, and he hoped, quite dispassionately. He gave a careful analysis of the situation and ended with a request for advice. His fears concerning McNeil he left unspoken. For one thing he knew that the engineer would be monitoring him at the transmitter.

  As yet no one on Venus would have heard the message, even though the transmission time-lag was over. It would still be coiled up in the recorder spools, but in a few minutes an unsuspecting signal officer would arrive to play it over.

  He would have no idea of the bombshell that was about to burst, triggering trains of sympathetic ripples on all the inhabited worlds as television and newssheet took up the refrain. An accident in space has a dramatic quality that crowds all other items from the headlines.

  Until now Grant had been too preoccupied with his own safety to give much thought to the cargo in his charge. A sea captain of ancient times, whose first thought was for his ship, might have been shocked by the attitude. Grant, however, had reason on his side.

  The Star Queen could never founder, could never run upon uncharted rocks or pass silently, as so many ships have passed, forever from the knowledge of man. She was safe, whatever might befall her crew. If she was undisturbed she would continue to retrace her orbit with such precision that men might set their calendars by her for centuries to come.

  The cargo, Grant suddenly remembered, was insured for over twenty million dollars. There were not many goods valuable enough to be shipped from world to world and most of the crates in the hold were worth more than their weight—or rather their mass—in gold. Perhaps some items might be useful in this emergency and Grant went to the safe to find the loading schedule.

  He was sorting the thin, tough sheets when McNeil came back into the cabin.

  “I’ve been reducing the air pressure,” he said. “The hull shows some leaks that wouldn’t have mattered in the usual way.”

  Grant nodded absently as he passed a bundle of sheets over to McNeil.

  “Here’s our loading schedule. I suggest we both run through it in case there’s anything in the cargo that may help.”

  If it did nothing else, he might have added, it would at least give them something to occupy their minds.

  As he ran down the long columns of numbered items—a complete cross-section of interplanetary commerce—Grant found himself wondering what lay behind these inanimate symbols. Item 347—1 book—4 kilos gross.

  He whistled as he noticed that it was a starred item, insured for a hundred thousand dollars, and he suddenly remembered hearing on the radio that the Hesperian Museum had just bought a first edition Seven Pillars of Wisdom.

  A few sheets later was a very contrasting item, Miscellaneous books—25 kilos—no intrinsic value.

  It had cost a small fortune to ship those books to Venus, yet they were of “no intrinsic value.” Grant let his imagination loose on the problem. Perhaps someone who was leaving Earth forever was taking with him to a new world his most cherished treasures—the dozen or so volumes that above all others had most shaped his mind.

  Item 564—12 reels film.

  That, of course, would be the Neronian super-epic, While Rome Burns, which had left Earth just one jump ahead of the censor. Venus was waiting for it with considerable impatience.

  Medical supplies—50 kilos. Case of cigars—1 kilo. Precision instruments—75 kilos. So the list went on. Each item was something rare or something which the industry and science of a younger civilization could not yet produce.

  The cargo was sharply divided into two classes—blatant luxury or sheer necessity. There was little in between. And there was nothing, nothing at all, which gave Grant the slightest hope. He did not see how it could have been otherwise, but that did not prevent him from feeling a quite unreasonable disappointment.

  The reply from Venus, when it came at last, took nearly an hour to run through the recorder. It was a questionnaire so detailed that Grant wondered morosely if he’d live long enough to answer it. Most of the queries were technical ones concerning the ship. The experts on two planets were pooling their brains in the attempt to save the Star Queen and her cargo.

  “Well, what do you think of it?” Gr
ant asked McNeil when the other had finished running through the message. He was watching the engineer carefully for any further sign of strain.

  There was a long pause before McNeil spoke. Then he shrugged his shoulders and his first words were an echo of Grant’s own thoughts.

  “It will certainly keep us busy. I won’t be able to do all these tests in under a day. I can see what they’re driving at most of the time, but some of the questions are just plain crazy.”

  Grant had suspected that, but said nothing as the other continued.

  “Rate of hull leakage—that’s sensible enough, but why should anyone want to know the efficiency of our radiation screening? I think they’re trying to keep up our morale by pretending they have some bright ideas—or else they want to keep us too busy to worry.”

  Grant was relieved and yet annoyed by McNeil’s calmness—relieved because he had been afraid of another scene and annoyed because McNeil was not fitting at all neatly into the mental category he had prepared for him. Was that first momentary lapse typical of the man or might it have happened to anyone?

  Grant, to whom the world was very much a place of blacks and whites, felt angry at being unable to decide whether McNeil was cowardly or courageous. That he might be both was a possibility that never occurred to him.

  There is a timelessness about space-flight that is unmatched by any other experience of man. Even on the Moon there are shadows that creep sluggishly from crag to crag as the sun makes its slow march across the sky. Earthward there is always the great clock of the spinning globe, marking the hours with continents for hands. But on a long voyage in a gyro-stabilized ship the same patterns of sunlight lie unmoving on wall or floor as the chronometer ticks off its meaningless hours and days.

  Grant and McNeil had long since learned to regulate their lives accordingly. In deep space they moved and thought with a leisureliness that would vanish quickly enough when a voyage was nearing its end and the time for braking maneuvers had arrived. Though they were now under sentence of death, they continued along the well-worn grooves of habit.

  Every day Grant carefully wrote up the log, checked the ship’s position and carried out his various routine duties. McNeil was also behaving normally as far as could be told, though Grant suspected that some of the technical maintenance was being carried out with a very light hand.

  It was now three days since the meteor had struck. For the last twenty-four hours Earth and Venus had been in conference and Grant wondered when he would hear the result of their deliberations. He did not believe that the finest technical brains in the Solar System could save them now, but it was hard to abandon hope when everything still seemed so normal and the air was still clean and fresh.

  On the fourth day Venus spoke again. Shorn of its technicalities, the message was nothing more or less than a funeral oration. Grant and McNeil had been written off, but they were given elaborate instructions concerning the safety of the cargo.

  Back on earth the astronomers were computing all the possible rescue orbits that might make contact with the Star Queen in the next few years. There was even a chance that she might be reached from Earth six or seven months later, when she was back at aphelion, but the maneuver could be carried out only by a fast liner with no payload and would cost a fortune in fuel.

  McNeil vanished soon after this message came through. At first Grant was a little relieved. If McNeil chose to look after himself that was his own affair. Besides there were various letters to write—though the last-will-and-testament business could come later.

  It was McNeil’s turn to prepare the “evening” meal, a duty he enjoyed for he took good care of his stomach. When the usual sounds from the galley were not forthcoming Grant went in search of his crew.

  He found McNeil lying in his bunk, very much at peace with the universe. Hanging in the air beside him was a large metal crate which had been roughly forced open. Grant had no need to examine it closely to guess its contents. A glance at McNeil was enough.

  “It’s a dirty shame,” said the engineer without a trace of embarrassment, “to suck this stuff up through a tube. Can’t you put on some ‘g’ so we can drink it properly?”

  Grant stared at him with angry contempt, but McNeil returned his gaze unabashed.

  “Oh, don’t be a sourpuss! Have some yourself—what does it matter now?”

  He pushed across a bottle and Grant fielded it deftly as it floated by. It was a fabulously valuable wine—he remembered the consignment now—and the contents of that small crate must be worth thousands.

  “I don’t think there’s any need,” said Grant severely, “to behave like a pig—even in these circumstances.”

  McNeil wasn’t drunk yet. He had only reached the brightly lighted anteroom of intoxication and had not lost all contact with the drab outer world.

  “I am prepared,” he said with great solemnity, “to listen to any good argument against my present course of action—a course which seems eminently sensible to me. But you’d better convince me quickly while I’m still amenable to reason.”

  He pressed the plastic bulb again and a purple jet shot into his mouth.

  “Apart from the fact that you’re stealing Company property which will certainly be salvaged sooner or later—you can hardly stay drunk for several weeks.”

  “That,” said McNeil thoughtfully, “remains to be seen.”

  “I don’t think so,” retorted Grant. Bracing himself against the wall, he gave the crate a vicious shove that sent it flying through the open doorway.

  As he dived after it and slammed the door he heard McNeil shout, “Well, of all the dirty tricks!”

  It would take the engineer some time—particularly in his present condition—to unbuckle himself and follow. Grant steered the crate back to the hold and locked the door. As there was never any need to lock the hold when the ship was in space McNeil wouldn’t have a key for it himself and Grant could hide the duplicate that was kept in the control cabin.

  McNeil was singing when, some time later, Grant went back past his room. He still had a couple of bottles for company and was shouting:

  “We don’t care where the oxygen goes.

  If it doesn’t get into the wine. . . .”

  Grant, whose education had been severely technical, couldn’t place the quotation. As he paused to listen he suddenly found himself shaken by an emotion which, he did not for a moment recognize.

  It passed as swiftly as it had come, leaving him sick and trembling. For the first time, he realized that his dislike of McNeil was slowly turning to hatred.

  It is a fundamental rule of space-flight that, for sound psychological reasons, the minimum crew on a long journey shall consist of not less than three men.

  But rules are made to be broken and the Star Queen’s owners had obtained full authority from the Board of Space Control and the insurance companies when the freighter set off for Venus without her regular captain.

  At the last moment he had been taken ill and there was no replacement. Since the planets are disinclined to wait upon man and his affairs, if she did not sail on time she would not sail at all.

  Millions of dollars were involved—so she sailed. Grant and McNeil were both highly capable men and they had no objection at all to earning double their normal pay for very little extra work. Despite fundamental differences in temperament, they got on well enough in regular circumstances. It was nobody’s fault that circumstances were now very far from ordinary.

  Three days without food, it is said, it is long enough to remove most of the subtle differences between a civilized man and a savage. Grant and McNeil were still in no physical discomfort. But their imaginations had been only too active and they now had more in common with two hungry Pacific Islanders in a lost canoe than either would have cared to admit.

  For there was one aspect of the situation, and that the most important of all, which had never been mentioned. When the last figures on Grant’s writing-pad had been checked and rechecked, the cal
culation was still not quite complete. Instantly each man had made one further step, each had arrived simultaneously at the same unspoken result.

  It was terribly simple—a macabre parody of those problems in the first-year arithmetic that begin, “If six men take two days to assemble five helicopters, how long . . .”

  The oxygen would last two men for about twenty days, and Venus was thirty days away. One did not have to be a calculating prodigy to see at once that one man, and one man only, might yet live to walk the metal streets of Port Hesperus.

  The acknowledged deadline was twenty days ahead, but the unmentioned was only ten days off. Until that time there would still be enough air for two men—and thereafter for one man only for the rest of the voyage. To a sufficiently detached observer the situation would have been very entertaining.

  It was obvious that the conspiracy of silence could not last much longer. But it is not easy, even at the best of times, for two people to decide amicably which one of them shall commit suicide. It is still more difficult when they are no longer on speaking terms.

  Grant wished to be perfectly fair. Therefore the only thing to do was to wait until McNeil sobered up and then to put the question to him frankly. He could think best at his desk, so he went to the control cabin and strapped himself down in the pilot's chair.

  For a while he stared thoughtfully into nothingness. It would be better, he decided, to broach the matter by correspondence, especially while diplomatic relations were in their present state. He clipped a sheet of notepaper on the writing pad and began, “Dear McNeil . . .” Then he tore it out and started again, “McNeil . . .”

  It took him the best part of three hours and even then he wasn’t wholly satisfied. There were some things it was so darned difficult to put down on paper. But at last he managed to finish. He sealed the letter and locked it away in his safe. It could wait for a day or two.

  Few of the waiting millions on Earth and Venus could have any idea of the tensions that were slowly building up aboard the Star Queen. For days press and radio had been full of fantastic rescue schemes. On three worlds there was hardly any other topic of conversation. But only the faintest echo of the planet-wide tumult reached the two men who were its cause.