Project Solar Sail

by Arther C. Clarke

  There was a long pause while the two skippers digested this bad news. Merton wondered who was to blame; perhaps one yacht had been trying to shadow the other, and had not completed the maneuver before they were both caught in darkness. Now there was nothing that either could do; they were slowly but inexorably converging, unable to change course by a fraction of a degree.

  Yet, sixty-five minutes! That would just bring them out into sunlight again, as they emerged from the shadow of Earth. They still had a slim chance, if their sails could snatch enough power to avoid a crash. There must be some frantic calculations going on, aboard Arachne and Santa Maria.

  Arachne answered first; her reply was just what Merton had expected.

  “Number Six calling Control. We don’t need assistance, thank you. We’ll work this out for ourselves.”

  I wonder, thought Merton. But at least it will be interesting to watch. The first real drama of the race was approaching—exactly above the line of midnight on sleeping Earth.

  For the next hour, Merton’s own sail kept him too busy to worry about Arachne and Santa Maria. It was hard to keep a good watch on that fifty million square feet of dim plastic out there in the darkness, illuminated only by his narrow spotlight and the rays of the still distant moon. From now on, for almost half his orbit around Earth, he must keep the whole of this immense area edge-on to the sun. During the next twelve or fourteen hours, the sail would be a useless encumbrance; for he would be heading into the sun, and its rays could only drive him backward along his orbit. It was a pity that he could not furl the sail completely, until he was ready to use it again. But no one had yet found a practical way of doing this.

  Far below, there was the first hint of dawn along the edge of Earth. In ten minutes, the sun would emerge from its eclipse; the coasting yachts would come to life again as the blast of radiation struck their sails. That would be the moment of crisis for Arachne and Santa Maria—and, indeed, for all of them.

  Merton swung the periscope until he found the two dark shadows drifting against the stars. They were very close together—perhaps less than three miles apart. They might, he decided, just be able to make it . . .

  Dawn flashed like an explosion along the rim of Earth, as the sun rose out of the Pacific. The sail and shroud lines glowed a brief crimson, then gold, then blazed with the pure white light of day. The needles of the dynamometers began to lift from their zeros—but only just. Diana was still almost completely weightless, for with the sail pointing toward the sun, her acceleration was now only a few millionths of a gravity.

  But Arachne and Santa Maria were crowding on all the sail they could manage, in their desperate attempt to keep apart. Now, while there was less than two miles between them, their glittering plastic clouds were unfurling and expanding with agonizing slowness, as they felt the first delicate push of the sun’s rays. Almost every TV screen on Earth would be mirroring this protracted drama; and even now, at this very last minute, it was impossible to tell what the outcome would be.

  The two skippers were stubborn men. Either could have cut his sail, and fallen back to give the other a chance; but neither would do so. Too much prestige, too many millions, too many reputations were at stake. And so, silently and softly as snowflakes falling on a winter night, Arachne and Santa Maria collided.

  The square kite crawled almost imperceptibly into the circular spider’s web; the long ribbons of the shroud lines twisted and tangled together with dreamlike slowness. Even aboard Diana, busy with his own rigging, Merton could scarcely tear his eyes away from this silent, long-drawn-out disaster.

  For more than ten minutes the billowing, shining clouds continued to merge into one inextricable mass. Then the crew capsules tore loose and went their separate ways, missing each other by hundreds of yards. With a flare of rockets, the safety launches hurried to pick them up.

  That leaves five of us, thought Merton. He felt sorry for the skippers who had so thoroughly eliminated each other, only a few hours after the start of the race; but they were young men, and would have another chance.

  Within minutes, the five had dropped to four. From the very beginning, Merton had had doubts about the slowly rotating Sunbeam. Now he saw them justified.

  The Martian ship had failed to tack properly; her spin had given her too much stability. Her great ring of a sail was turning to face the sun, instead of being edge-on to it. She was being blown back along her course at almost her maximum acceleration.

  That was about the most maddening thing that could happen to a skipper—worse even than a collision, for he could blame only himself. But no one would feel much sympathy for the frustrated colonials, as they dwindled slowly astern. They had made too many brash boasts before the race, and what had happened to them was poetic justice.

  Yet it would not do to write off Sunbeam completely. With almost half a million miles still to go, she might still pull ahead. Indeed, if there were a few more casualties, she might be the only one to complete the race. It had happened before.

  However, the next twelve hours were uneventful, as Earth waxed in the sky from new to full. There was little to do while the fleet drifted around the unpowered half of its orbit, but Merton did not find the time hanging heavily on his hands. He caught a few hours’ sleep, ate two meals, wrote up his log, and became involved in several more radio interviews. Sometimes, though rarely, he talked to the other skippers, exchanging greetings and friendly taunts. But most of the time he was content to float in weightless relaxation, beyond all the cares of Earth, happier than he had been for many years. He was—as far as any man could be in space—master of his own fate, sailing the ship upon which he had lavished so much skill, so much love, that she had become part of his very being.

  The next casualty came when they were passing the line between Earth and sun, and were just beginning the powered half of the orbit. Aboard Diana, Merton saw the great sail stiffen as it tilted to catch the rays that drove it. The acceleration began to climb up from the microgravities, though it would be hours yet before it would reach its maximum value.

  It would never reach it for Gossamer. The moment when power came on again was always critical, and she failed to survive it.

  Blair’s radio commentary, which Merton had left running at low volume, alerted him with the news: “Hello, Gossamer has the wriggles!” He hurried to the periscope, but at first could see nothing wrong with the great circular disk of Gossamer’s sail. It was difficult to study it, as it was almost edge-on to him and so appeared as a thin ellipse; but presently he saw that it was twisting back and forth in slow, irresistible oscillations. Unless the crew could damp out these waves, by properly timed but gentle tugs on the shroud lines, the sail would tear itself to pieces.

  ###

  They did their best, and after twenty minutes it seemed that they had succeeded. Then, somewhere near the center of the sail, the plastic film began to rip. It was slowly driven outward by the radiation pressure like smoke coiling upward from a fire. Within a quarter of an hour, nothing was left but the delicate tracery of the radial spars that had supported the great web. Once again there was a flare of rockets, as a launch moved in to retrieve the Gossamer’s capsule and her dejected crew.

  “Getting rather lonely up here, isn’t it?” said a conversational voice over the ship-to-ship radio.

  “Not for you, Dimitri,” retorted Merton. “You’ve still got company back there at the end of the field. I’m the one who’s lonely, up here in front.” It was not an idle boast. By this time Diana was three hundred miles ahead of the next competitor, and his lead should increase still more rapidly in the hours to come.

  Aboard Lebedev, Dimitri Markoff gave a good-natured chuckle. He did not sound, Merton thought, at all like a man who had resigned himself to defeat.

  “Remember the legend of the tortoise and the hare,” answered the Russian. “A lot can happen in the next quarter-million miles.”

  It happened much sooner than that, when they had completed their first orb
it of Earth and were passing the starting line again—though thousands of miles higher, thanks to the extra energy the sun’s rays had given them. Merton had taken careful sights on the other yachts, and had fed the figures into the computer. The answer it gave for Woomera was so absurd that he immediately did a recheck.

  There was no doubt of it—the Australasians were catching up at a fantastic rate. No solar yacht could possibly have such an acceleration, unless—

  A swift look through the periscope gave the answer. Woomera’s rigging, pared back to the very minimum of mass, had given way. It was her sail alone, still maintaining its shape, that was racing up behind him like a handkerchief blown before the wind. Two hours later it fluttered past, less than twenty miles away. But long before that, the Australasians had joined the growing crowd aboard the Commodore’s launch.

  So now it was a straight fight between Diana and Lebedev—for though the Martians had not given up, they were a thousand miles astern and no longer counted as a serious threat. For that matter, it was hard to see what Lebedev could do to overtake Diana’s lead. But all the way around the second lap—through eclipse again, and the long, slow drift against the sun—Merton felt a growing unease.

  He knew the Russian pilots and designers. They had been trying to win this race for twenty years, and after all, it was only fair that they should, for had not Pyotr Nikolayevich Lebedev been the first man to detect the pressure of sunlight, back at the very beginning of the twentieth century? But they had never succeeded.

  And they would never stop trying. Dimitri was up to something—and it would be spectacular.

  Aboard the official launch, a thousand miles behind the racing yachts, Commodore van Stratten looked at the radiogram with angry dismay. It had traveled more than a hundred million miles, from the chain of solar observatories swinging high above the blazing surface of the sun, and it brought the worst possible news.

  The Commodore—his title, of course, was purely honorary; back on Earth he was Professor of Astrophysics at Harvard—had been half-expecting it. Never before had the race been arranged so late in the season; there had been many delays, they had gambled, and now it seemed they might all lose.

  Deep beneath the surface of the sun, enormous forces were gathering. At any moment, the energies of a million hydrogen bombs might burst forth in the awesome explosion known as a solar flare. Climbing at millions of miles an hour, an invisible fireball many times the size of Earth would leap from the sun and head out across space.

  The cloud of electrified gas would probably miss Earth completely. But if it did not, it would arrive in just over a day. Spaceships could protect themselves, with their shielding and their powerful magnetic screen. But the lightly built solar yachts, with their paper-thin walls, were defenseless against such a menace. The crews would have to be taken off, and the race abandoned.

  John Merton still knew nothing of this as he brought Diana around Earth for the second time. If all went well, this would be the last circuit, both for him and for the Russians. They had spiraled upward by thousands of miles, gaining energy from the sun’s rays. On this lap, they should escape from Earth completely—and head outward on the long run to the moon. It was a straight race now. Sunbeam’s crew had finally withdrawn, exhausted, after battling valiantly with their spinning sail for more than a hundred thousand miles.

  Merton did not feel tired; he had eaten and slept well, and Diana was behaving herself admirably. The autopilot, tensioning the rigging like a busy little spider, kept the great sail trimmed to the sun more accurately than any human skipper. Though by this time the two square miles of plastic sheet must have been riddled by hundreds of micrometeorites, the pin-head-sized punctures had produced no falling off to thrust.

  He had only two worries. The first was shroud line number eight, which could no longer be adjusted properly. Without any warning, the reel had jammed; even after all these years of astronautical engineering, bearings sometimes seized up in vacuum. He could neither lengthen nor shorten the line, and would have to navigate as best he could with the others. Luckily, the most difficult maneuvers were over. From now on, Diana would have the sun behind her as she sailed straight down the solar wind. And as the old-time sailors often said, it was easy to handle a boat when the wind was blowing over your shoulder.

  His other worry was Lebedev, still dogging his heels three hundred miles astern. The Russian yacht had shown remarkable maneuverability thanks to the four great panels that could be tilted around the central sail. All her flip-overs as she rounded Earth had been carried out with superb precision; but to gain maneuverability she must have sacrificed speed. You could not have it both ways. In the long, straight haul ahead, Merton should be able to hold his own. Yet he could not be certain of victory until, three or four days from now, Diana went flashing past the far side of the moon.

  And then, in the fiftieth hour of the race, near the end of the second orbit around Earth, Markoff sprang his little surprise.

  “Hello, John,” he said casually, over the ship-to-ship circuit. “I’d like you to watch this. It should be interesting.”

  Merton drew himself across to the periscope and turned up the magnification to the limit. There in the field of view, a most improbable sight against the background of the stars, was the glittering Maltese cross of Lebedev, very small but very clear. And then, as he watched, the four arms of the cross slowly detached themselves from the central square and went drifting away, with all their spars and rigging, into space.

  Markoff had jettisoned all unnecessary mass, now that he was coming up to escape velocity and need no longer plod patiently around Earth, gaining momentum on each circuit. From now on, Lebedev would be almost unsteerable—but that did not matter. All the tricky navigation lay behind her. It was as if an old-time yachtsman had deliberately thrown away his rudder and heavy keel—knowing that the rest of the race would be straight downwind over a calm sea.

  “Congratulations, Dimitri,” Merton radioed. “It’s a neat trick. But it’s not good enough—you can’t catch up now.”

  “I’ve not finished yet,” the Russian answered. “There’s an old winter’s tale in my country, about a sleigh being chased by wolves. To save himself, the driver has to throw off the passengers one by one. Do you see the analogy?”

  Merton did, all too well. On this final lap, Dimitri no longer needed his co-pilot. Lebedev could really be stripped down for action.

  “Alexis won’t be very happy about this,” Merton replied. “Besides, it’s against the rules.”

  “Alexis isn’t happy, but I’m the captain. He’ll just have to wait around for ten minutes until the Commodore picks him up. And the regulations say nothing about the size of the crew—you should know that.”

  Merton did not answer. He was too busy doing some hurried calculations, based on what he knew of Lebedev’s design. By the time he had finished, he knew that the race was still in doubt. Lebedev would be catching up with him at just about the time he hoped to pass the moon.

  But the outcome of the race was already being decided, ninety-two million miles away.

  ###

  On Solar Observatory Three, far inside the orbit of Mercury, the automatic instruments recorded the whole history of the flare. A hundred million square miles of the sun’s surface suddenly exploded in such blue-white fury that, by comparison, the rest of the disk paled to a dull glow. Out of that seething inferno, twisting and turning like a living creature, in the magnetic fields of its own creation, soared the electrified plasma of the great flare. Ahead of it, moving at the speed of light, went the warning flash of ultraviolet and x-rays. That would reach Earth in eight minutes, and was relatively harmless. Not so the charged atoms that were following behind at their leisurely four million miles an hour—and which, in just over a day, would engulf Diana, Lebedev, and their accompanying little fleet in a cloud of lethal radiation.

  The Commodore left his decision to the last possible minute. Even when the jet of plasma had been trac
ked past the orbit of Venus, there was a chance that it might miss Earth. But when it was less than four hours away, and had already been picked up by the moon-based radar network, he knew that there was no hope. All solar sailing was over for the next five or six years until the sun was quiet again.

  A great sigh of disappointment swept across the solar system. Diana and Lebedev were halfway between Earth and moon, running neck and neck—and now no one would ever know which was the better boat. The enthusiasts would argue the result for years; history would merely record: race cancelled owing to solar storm.

  When John Merton received the order, he felt a bitterness he had not known since childhood. Across the years, sharp and clear, came the memory of his tenth birthday. He had been promised an exact scale model of the famous spaceship Morning Star, and for weeks had been planning how he would assemble it, where he would hang it up in his bedroom. And then, at the last moment, his father had broken the news. “I’m sorry, John—it costs too much money. Maybe next year . . .”

  Half a century and a successful lifetime later, he was a heartbroken boy again.

  For a moment, he thought of disobeying the Commodore. Suppose he sailed on, ignoring the warning? Even if the race were abandoned, he could make a crossing to the moon that would stand in the record books for generations.

  But that would be worse than stupidity. It would be suicide—and a very unpleasant form of suicide. He had seen men die of radiation poisoning, when the magnetic shielding of their ships had failed in deep space. No—nothing was worth that . . .

  He felt as sorry for Dimitri Markoff as for himself; they both deserved to win, and now victory would go to neither. No man could argue with the sun in one of its rages, even though he might ride upon its beams to the edge of space.

  Only fifty miles astern now, the Commodore’s launch was drawing alongside Lebedev, preparing to take off her skipper. There went the silver sail, as Dimitri—with feeling that he would share—cut the rigging. The tiny capsule would be taken back to Earth, perhaps to be used again—but a sail was spread for one voyage only.