The Space Trilogy

by Arthur C. Clarke

  They could not understand that the law of celestial mechanics admit of no appeal. The Pegasus was barely clear of Earth, and still weeks from her intended goal. But she had reached her orbiting speed, and had launched herself like a giant projectile on the path that would lead inevitably to Mars, under the guidance of the sun's all-pervading gravity. There could be no turning back: that would be a manoeuvre involving an impossible amount of propellant. The Pegasus carried enough dust in her tanks to match velocity with Mars at the end of her orbit, and to allow for reasonable course corrections en route. Her nuclear reactors could provide energy for a dozen voyages—but sheer energy was useless if there was no propellant mass to eject. Whether she wanted to or not, the Pegasus was headed for Mars with the inevitability of a runaway streetcar. Captain Halstead did not anticipate a pleasant trip.

  The words MAYDAY, MAYDAY came crashing out of the radio and banished all other preoccupations of the Pegasus and her crew. For three hundred years, in air and sea and space, these words had alerted rescue organizations, had made captains change their course and race to the aid of stricken comrades. But there was so little that the commander of a space-ship could do; in the whole history of astronautics, there have been only three cases of a successful rescue operation in space.

  There are two main reasons for this, only one of which is widely advertised by the shipping lines. Any serious disaster in space is extremely rare; almost all accidents occur during planet-fall or departure. Once a ship has reached space, and has swung into the orbit that will lead it effortlessly to its destination, it is safe from all hazards except internal, mechanical troubles. Such troubles occur more often than the passengers ever know, but are usually trivial and are quietly dealt with by the crew. All space-ships, by law, are built in several independent sections, any one of which can serve as a refuge in an emergency. So the worst that ever happens is that some uncomfortable hours are spent by all while an irate captain breathes heavily down the neck of his engineering officer.

  The second reason why space-rescues are so rare is that they are almost impossible, from the nature of things. Spaceships travel at enormous velocities on exactly calculated paths, which do not permit of major alterations—as the passengers of the Pegasus were now beginning to appreciate. The orbit any ship follows from one planet to another is unique; no other vessel will ever follow the same path again, among the changing patterns of the planets. There are no "shipping-lanes" in space, and it is rare indeed for one ship to pass within a million kilometres of another. Even when this does happen, the difference of speed is almost always so great that contact is impossible.

  All these thoughts flashed through Captain Halstead's mind when the message came down to him from Signals. He read the position and course of the distressed ship—the velocity figure must have been garbled in transmission, it was so ridiculously high. Almost certainly, there was nothing he could do—they were too far away, and it would take days to reach them.

  Then he noticed the name at the end of the message. He thought he was familiar with every ship in space, but this was a new one to him. He stared in bewilderment for a moment before he suddenly realized just who was calling for his assistance…

  Enmity vanishes when men are in peril on sea or in space. Captain Halstead leaned over his control desk and said: "Signals! Get me their captain."

  "He's on circuit, sir. You can go ahead."

  Captain Halstead cleared his throat. This was a novel experience, and not a pleasant one. It gave him no sort of satisfaction to tell even an enemy that he could do nothing to save him.

  "Captain Halstead, Pegasus, speaking," he began. "You're too far away for contact. Our operational reserve is less than ten kilometres a second. I've no need to compute—I can see it's impossible. Have you any suggestions? Please confirm your velocity; we were given an incorrect figure."

  The reply, after a four-second time-lag that seemed doubly maddening in these circumstances, was unexpected and astonishing.

  "Commodore Brennan, Federal cruiser Acheron. I can confirm our velocity figure. We can contact you in two hours, and will make all course corrections ourselves. We still have power, but must abandon ship in less than three hours. Our radiation shielding has gone, and the main reactor is becoming unstable. We've got manual control on it, and it will be safe for at least an hour after we reach you. But we can't guarantee it beyond then."

  Captain Halstead felt the scalp crawl at the back of his neck. He did not know how a reactor could became unstable—but he knew what would happen if one did. There were a good many things about the Acheron he did not understand—her speed, above all—but there was one point that emerged very clearly and upon which Commodore Brennan must be left in no doubt.

  "Pegasus to Acheron," he replied. "I have three hundred passengers aboard. I cannot hazard my ship if there is danger of an explosion."

  "There is no danger—I can guarantee that. We will have at least five minutes' warning, which will give us ample time to get clear of you."

  "Very well—I'll get my airlocks ready and my crew standing by to pass you a line."

  There was a pause longer than that dictated by the sluggish progress of radio waves. Then Brennan replied:

  "That's our trouble. We're cut off in the forward section. There are no external locks here, and we have only five suits among a hundred and twenty men."

  Halstead whistled and turned to his navigating officer before answering.

  "There's nothing we can do for them," he said. "They'll have to crack the hull to get out, and that will be the end of everyone except the five men in the suits. We can't even lend them our own suits—there'll be no way we can get them aboard without letting down the pressure." He flicked over the microphone switch.

  "Pegasus to Acheron. How do you suggest we can assist you?"

  It was eerie to be speaking to a man who was already as good as dead. The traditions of space were as strict as those of the sea. Five men could leave the Acheron alive—but her captain would not be among them.

  Halstead did not know that Commodore Brennan had other ideas, and had by no means abandoned hope, desperate though the situation on board the Acheron seemed. His chief medical officer, who had proposed the plan, was already explaining it to the crew.

  "This is what we're going to do," said the small, dark man who a few months ago had been one of the best surgeons on Venus. "We can't get at the airlocks, because there's vacuum all round us and we've only got five suits. This ship was built for fighting, not for carrying passengers, and I'm afraid her designers had other matters to think about besides Standard Spaceworthiness Regs. Here we are, and we have to make the best of it.

  "We'll be alongside the Pegasus in a couple of hours. Luckily for us, she's got big locks for loading freight and passengers: there's room for thirty or forty men to crowd into them, if they squeeze tight—and aren't wearing suits. Yes, I know that sounds bad, but it's not suicide. You're going to breathe space, and get away with it! I won't say it will be enjoyable, but it will be something to brag about for the rest of your lives.

  "Now listen carefully. The first thing I've got to prove to you is that you can live for five minutes without breathing—in fact, without wanting to breathe. It's a simple trick: Yogis and magicians have known it for centuries, but there's nothing occult about it and it's based on common-sense physiology. To give you confidence, I want you to make this test."

  The M.O. pulled a stop watch out of his pocket, and continued:

  "When I say 'Now!' I want you to exhale completely—empty your lungs of every drop of air—and then see how long you can stay before you have to take a breath. Don't strain—just hold out until it becomes uncomfortable, then start breathing again normally. I'll start counting the seconds after fifteen, so you can tell what you managed to do. If anyone can't take the quarter minute, I'll recommend his instant dismissal from the Service."

  The ripple of laughter broke the tension, as it had been intended to; then the MO held up
his hand, and swept it down with a shout of "Now!" There was a great sigh as the entire company emptied its lungs; then utter silence.

  When the MO started counting at "Fifteen," there were a few gasps from those who had barely been able to make the grade. He went on counting to "Sixty" accompanied by occasional explosive pants as one man after another capitulated. Some were still stubbornly holding out after a full minute.

  "That's enough," said the little surgeon. "You tough guys can stop showing off—you're spoiling the experiment."

  Again there was a murmur of amusement; the men were rapidly regaining their morale. They still did not understand what was happening, but at least some plan was afoot that offered them a hope of rescue.

  "Let's see how we managed," said the M.O. "Hands up all those who held out for fifteen to twenty seconds… Now twenty to twenty-five… Now twenty-five to thirty—Jones, you're a damn liar—you folded up at fifteen!… Now thirty to thirty-five…"

  When he had finished the census, it was dear that more than half the company had managed to hold their breath for thirty seconds, and no one had failed to reach fifteen seconds.

  "That's about what I expected," said the M.O. "You can regard this as a control experiment, and now we come on to the real thing. I ought to tell you that we're now breathing almost pure oxygen here, at about three hundred millimetres. So although the pressure in the ship is less than half its sea-level value on Earth, your lungs are taking in twice as much oxygen as they would on Earth, and still more than they would on Mars or Venus. If any of you have sneaked off to have a surreptitious smoke in the toilet, you'll already have noticed that the air was rich, as your cigarette will only have lasted a few seconds.

  "I'm telling you all this because it will increase your confidence to know what is going on. What you're going to do now is to flush out your lungs and fill your system with oxygen. It's called hyperventilation, which is simply a ten dollar word for deep breathing. When I give the signal, I want you all to breathe as deeply as you can, then exhale completely, and carry on breathing in the same way until I tell you to stop. I'll let you do it for a minute—some of you may feel a bit dizzy at the end of that time, but it'll pass. Take in all the air you can with every breath; swing your arms to get maximum chest expansion.

  "Then, when the minute's up, I'll tell you to exhale, then stop breathing, and I'll begin counting seconds again. I think I can promise you a big surprise. OK—here we go!"

  For the next minutes, the overcrowded compartments of the Acheron presented a fantastic spectacle. More than a hundred men were flailing their arms and breathing stertorously, as if each was at his last gasp. Some were too closely packed together to breathe as deeply as they would have liked, and all had to anchor themselves somehow so that their exertion would not cause them to drift around the cabins.

  "Now!" shouted the MO "Stop breathing—blow out all your air—and see how long you can manage before you've got to start again. I'll count the seconds, but this time I won't begin until half a minute has gone."

  The result, it was obvious, left everyone flabbergasted. One man failed to make the minute, otherwise almost two minutes elapsed before most of the men felt the need to breathe again. Indeed, to have taken a breath before then would have demanded a deliberate effort. Some men were still perfectly comfortable after three or four minutes; one was holding out at five when the doctor stopped him.

  "I think you'll all see what I was trying to prove. When your lungs are flushed out with oxygen, you just don't want to breathe for several minutes, any more than you want to eat again after a heavy meal. It's no strain or hardship; it's not a question of holding your breath. And if your life depended on it, you could do even better than this, I promise you.

  "Now we're going to tie up right alongside the Pegasus; it will take less than thirty seconds to get over to her. She'll have her men out in suits to push along any stragglers, and the air lock doors will be slammed shut as soon as you're all inside. Then the lock will be flooded with air and you'll be none the worse except for some bleeding noses."

  He hoped that was true. There was only one way to find out. It was a dangerous and unprecedented gamble, but there was no alternative. At least it would give every man a fighting chance for his life.

  "Now," he continued, "you're probably wondering about the pressure drop. That's the only uncomfortable part, but you won't be in a vacuum long enough for severe damage. We'll open the hatches in two stages; first we'll drop pressure slowly to a tenth of an atmosphere, then we'll blow out completely in one bang and make a dash for it. Total decompression's painful, but not dangerous. Forget all that nonsense you may have heard about the human body blowing up in a vacuum. We're a lot tougher than that, and the final drop we're going to make from a tenth of an atmosphere to zero is considerably less than men have already stood in lab tests. Hold your mouth wide open and let yourself break wind. You'll feel your skin stinging all over, but you'll probably be too busy to notice that."

  The MO paused, and surveyed his quiet, intent audience. They were all taking it very well, but that was only to be expected. Every one was a trained man—they were the pick of the planets' engineers and technicians.

  "As a matter of fact," the surgeon continued cheerfully, "you'll probably laugh when I tell you the biggest danger of the lot. It's nothing more than sunburn. Out there you'll be in the sun's raw ultra-violet, unshielded by atmosphere. It can give you a nasty blister in thirty seconds, so we'll make the crossing in the shadow of the Pegasus. If you happen to get outside that shadow, just shield your face with your arm. Those of you who've got gloves might as well wear them.

  "Well, that's the picture. I'm going to cross with the first team just to show how easy it is. Now I want you to split up into four groups, and I'll drill you each separately…"

  Side by side, the Pegasus and the Acheron raced toward the distant planet that only one of them would ever reach. The airlocks of the liner were open, gaping wide no more than a few meters from the hull of the crippled battleship. The space between the two vessels was strung with guide ropes, and among them floated the men of the liner's crew, ready to give assistance if any of the escaping men were overcome during the brief but dangerous crossing.

  It was lucky for the crew of the Acheron that four pressure bulkheads were still intact. Their ship could still be divided into four separate compartments, so that a quarter of the crew could leave at a time. The airlocks of the Pegasus could not have held everyone at once if a mass escape had been necessary.

  Captain Halstead watched from the bridge as the signal was given. There was a sudden puff of smoke from the hull of the battleship, then the emergency hatch—certainly never designed for an emergency such as this—blew away into space. A cloud of dust and condensing vapour blasted out, obscuring the view for a second. He knew how the waiting men would feel the escaping air sucking at their bodies, trying to tear them away from their handholds.

  When the cloud had dispersed, the first men had already emerged. The leader was wearing a space-suit, and all the others were strung on the three lines attached to him. Instantly, men from the Pegasus grabbed two of the lines and darted off to their respective airlocks. The men of the Acheron, Halstead was relieved to see, all appeared to be conscious and to be doing everything they could to help.

  It seemed ages before the last figure on its drifting line was towed or pushed into an airlock. Then the voice from one of those spacesuited figures out there shouted, "Close Number Three!" Number One followed almost at once; but there was an agonizing delay before the signal for Two came. Halstead could not see what was happening; presumably someone was still outside and holding up the rest. But at last all the locks were closed. There was no time to fill them in the normal way—the valves were jerked open by brute force and the chambers flooded with air from the ship.

  Aboard the Acheron, Commodore Brennan waited with his remaining ninety men, in the three compartments that were still unsealed. They had formed their groups
and were strung in chains of ten behind their leaders. Everything had been planned and rehearsed; the next few seconds would prove whether or not in vain.

  Then the ship's speakers announced, in an almost quietly conversational tone:

  "Pegasus to Acheron. We've got all your men out of the locks. No casualties. A few haemorrhages. Give us five minutes to get ready for the next batch."

  They lost one man on the last transfer. He panicked and they had to slam the lock shut without him, rather than risk the lives of all the others. It seemed a pity that they could not all have made it, but for the moment everyone was too thankful to worry about that.

  There was only one thing still to be done. Commodore Brennan, the last man aboard the Acheron, adjusted the timing circuit that would start the drive in thirty seconds. That would give him long enough; even in his clumsy spacesuit he could get out of the open hatch in half that time. It was cutting it fine, but only he and his engineering officer knew how narrow the margin was.

  He threw the switch and dived for the hatch. He had already reached the Pegasus when the ship he had commanded, still loaded with millions of kilowatt-centuries of energy, came to life for the last time and dwindled silently toward the stars of the Milky Way.

  The explosion was easily visible among all the inner planets. It blew to nothingness the last ambitions of the Federation, and the last fears of Earth.

  Twenty

  Every evening, as the sun drops down beyond the lonely pyramid of Pico, the shadow of the great mountain reaches out to engulf the metal column that will stand in the Sea of Rains as long as the Sea itself endures. There are 527 names on that column, in alphabetical order. No mark distinguishes the men who died for the Federation from those who died for Earth, and perhaps this simple fact is the best proof that they did not die in vain.