The Sentinel - Arthur C. Clarke [83]
“T minus ten seconds. All recording cameras ON.”
Something so huge, yet so frail, was hard for the mind to grasp. And it was harder still to realize that this fragile mirror could tow him free of Earth merely by the power of the sunlight it would trap.
“ . . . five, four, three, two, one, CUT!”
Seven knife blades sliced through seven thin lines tethering the yachts to the mother ships that had assembled and serviced them. Until this moment, all had been circling Earth together in a rigidly held formation, but now the yachts would begin to disperse, like dandelion seeds drifting before the breeze. And the winner would be the one that first drifted past the Moon.
Aboard Diana, nothing seemed to be happening. But Merton knew better. Though his body could feel no thrust, the instrument board told him that he was now accelerating at almost one thousandth of a gravity. For a rocket, that figure would have been ludicrous—but this was the first time any solar yacht had ever attained it. Diana’s design was sound; the vast sail was living up to his calculations. At this rate, two circuits of the Earth would build up his speed to escape velocity, and then he could head out for the Moon, with the full force of the Sun behind him.
The full force of the Sun . . . He smiled wryly, remembering all his attempts to explain solar sailing to those lecture audiences back on Earth. That had been the only way he could raise money, in those early days. He might be Chief Designer of Cosmodyne Corporation, with a whole string of successful spaceships to his credit, but his firm had not been exactly enthusiastic about his hobby.
“Hold your hands out to the Sun,” he’d said. “What do you feel? Heat, of course. But there’s pressure as well—though you’ve never noticed it, because it’s so tiny. Over the area of your hands, it comes to only about a millionth of an ounce.
“But out in space, even a pressure as small as that can be important, for it’s acting all the time, hour after hour, day after day. Unlike rocket fuel, it’s free and unlimited. If we want to, we can use it. We can build sails to catch the radiation blowing from the Sun.”
At that point, he would pull out a few square yards of sail material and toss it toward the audience. The silvery film would coil and twist like smoke, then drift slowly to the ceiling in the hot-air currents.
“You can see how light it is,” he’d continue. “A square mile weighs only a ton, and can collect five pounds of radiation pressure. So it will start moving—and we can let it tow us along, if we attach rigging to it.
“Of course, its acceleration will be tiny—about a thousandth of a g. That doesn’t seem much, but let’s see what it means.
“It means that in the first second, we’ll move about a fifth of an inch. I suppose a healthy snail could do better than that. But after a minute, we’ve covered sixty feet, and will be doing just over a mile an hour. That’s not bad, for something driven by pure sunlight! After an hour, we’re forty miles from our starting point, and will be moving at eighty miles an hour. Please remember that in space there’s no friction; so once you start anything moving, it will keep going forever. You’ll be surprised when I tell you what our thousandth-of-a-g sailboat will be doing at the end of a day’s run: almost two thousand miles an hour! If it starts from orbit—as it has to, of course—it can reach escape velocity in a couple of days. And all without burning a single drop of fuell”
Well, he’d convinced them, and in the end he’d even convinced Cosmodyne. Over the last twenty years, a new sport had come into being. It had been called the sport of billionaires, and that was true. But it was beginning to