Launch Pad (4 page)

He was slowing down as he rose toward the edge, and the toolpack was speeding up as it fell. He stretched toward it, spread-eagled across the mirror, but the toolpack slid past well outside the reach of his outstretched fingers.

But he had no time to cry out over missed chances. In another moment the edge of the mirror approached, and he clambered across the mirror’s surface on all fours, stroking like a swimmer. If he could just gain even a single meter of altitude.…

To no effect. The edge hovered ahead of him, tantalizingly close, tantalizingly out of range. All his effort hadn’t gotten him a millimeter closer.

The rim disappeared in the distance, as he gained speed back downward.

Why hadn’t the pack come back to him? It was that elliptical motion, he realized. The toolpack was orbiting the center of the mirror, just as he was, sliding in an ellipse that didn’t intersect his trajectory.

He was sliding back down now. Six more minutes to the bottom, twelve to the other side. And then another twelve minutes down again, and back, and back … until his battery died and he froze and suffocated. And after that, how long would his body continue oscillating? Days? Years? The mirror couldn’t be perfectly frictionless; nothing in the universe was perfect. If it was perfect, the rubble wouldn’t be there in the center; the rocks that fell in would still be oscillating.

He was the bob on a pendulum, he thought, with a frictionless surface instead of a rope. For a moment his thoughts took him back to his childhood, growing up on Vesta. He and his brother had competed with each other on the swings, seeing who could go higher. They must have tried a hundred times to swing so hard as to go all the way around, over the bar. They never succeeded, even with Vesta’s low gravity making it easy; when they barely got higher than the pivot point, the rope would go slack, and the swing would fall with a jerk.

Thinking about the past wasn’t going to help him, and he forced his thinking back to his present situation. In a few minutes he would be back to his starting point. What about the safety rope? If it was still dangling down—but it wouldn’t be. He replayed his fall in his mind. The safety rope had snapped back like an elastic band when the clip broke, and disappeared over the edge. He would try to grab it, if it was in reach, but he wouldn’t count on it.

It wasn’t. He slid up, frustratingly close to the rim, and for a moment he seemed to hover with the rim just out of reach, and then slid away. The tool pack hadn’t come any closer to him this time than it had on the opposite rim, and the rope was nowhere in sight.

But here was something else to think about. Sedna rotated once every ten hours. In—he checked the time—two hours, the sun would be overhead. In the cold dark a hundred astronomical units from Earth, the intensity of the sun was dim, but what would happen when it was focused by a mirror twenty kilometers in diameter? In fact, that was very likely have been the purpose of the mirror, he realized. It wasn’t a telescope; it was an enormous solar furnace.

But he wasn’t thinking. The mirror might focus sunlight to a high concentration indeed, but that would be miles overhead, at the focal point of the mirror. On the surface of the mirror itself, the sunlight would be no brighter, and no less bright, than any other time. It was freezing he had to worry about, not frying.

Passing the bottom of the mirror. Lee clicked his image intensifier on again, watching the rubble in the center, trying to think of a way to make use of it. But it was still fifty meters away. Nothing useful there.

He clicked it off, and he was surrounded again by a world of stars and darkness.

Should he go back to reflecting on his life? Swinging with his brother, that was a good time, even if they never did make it over the bar. He could spend the remaining few hours remembering good times. The thing about being a prospector, he thought, is that you see a lot of places, but you only see the backsides, the seedy sides, the places in town near the dockyards. And they all look the same. He knew miners with a girl on each rock-town they visited, but no matter whether the deal was explicit or implicit, one way or another they were strictly pay propositions. He made good money, when he was employed, but somehow he never really managed to save any of it. It wasn’t that he was wasting his life, not exactly, he thought, but there had been enough of it already. It was time for him to move on. He needed to study, finish a degree, make something of himself.

Well, he had plenty of time to study, if that was what he wanted to do. Not that it would do him much good—he was trapped in a bowl. But that reminded him, he did have one resource that he hadn’t though of. His personal databot had a load of study materials, and one of his subjects was physics. What if his problem had a solution somewhere in the physics texts? It was a long shot, but why not try?

He booted up his study material, and put in search text: “PROBLEM, SLIDING ACROSS AN ENORMOUS MIRROR.” He had no real hope that anything would come out, but the search gave him one hit.

Astonishingly, the hit was in literature, not physics. The link was to the twentieth century, an ancient science-fiction story that had two men sliding on the surface of a frictionless mirror. He’d always hated classic science fiction. He’d read enough of it in school, before he’d dropped out. The teachers all seemed to love it. But the old authors had always gotten everything so wrong. The characters did amazingly dangerous things, with no safety backups; they were uniformly too stupid to live.

Things like stealing a snowcat to drive across an alien planet, without telling anybody where they were going? Well, it has seemed like a good idea at the time.

The databot didn’t have the text of the story, only a brief summary in a survey on 20th century literature. He scanned through it. It wasn’t quite his situation, he realized with mounting disappointment: the characters in the story had far more resources at their disposal. In the story, the two characters were roped together, and they used that fact to pump up rotational speed to allow them to fly apart. The discussion went on to say how the solution in the story wouldn’t work; the author had ignored conservation of angular momentum. No help! Lee would have thrown the book away in disgust, if it had been a physical book, and not just a glow in his heads-up display.

If only he had a book to throw away! Or anything at all. He could have used the momentum. It was exactly like being adrift in space without a pack. He had no control over his motion.

See related terms, the summary said. Simple harmonic oscillator, Frictionless motion.

He queried simple harmonic oscillator, saw that it seemed to be a tutorial about sines and cosines with no obvious application to him, and then flicked over to frictionless motion and scanned the tutorial. Superfluid helium, it said, was the only substance known to support frictionless motion. Well, that was interesting. Could the aliens have found some way to solidify superfluid helium? No, that was ridiculous. But, still, the surface of the mirror was desperately cold, cold enough to make even God shiver. Maybe the mirror was made of some substance that had a thin film of superfluid helium on the surface? Could he possibly heat the mirror, and destroy the effect?

But no, that was a dead end. Even if it weren’t frictionless, the surface would still be far too smooth for him to be able to climb the slope to the rim. He’d have to carve steps into the slope, and he had no tools to do that. Did the material have any give at all? He kicked at it as hard as he could, but it was like kicking solid granite. His toe hurt, even through the boot, but there had been not the slightest give to the surface. Whatever material it was made of, it was hard.

A frictionless surface probably had commercial value, even if it only worked when it was cooled nearly to absolute zero. If that bastard Kellerman just knew that one of his workers was slipping along the surface of a material more valuable than any ammonia on the planetoid, rescue would be here soon enough.

That line of thought didn’t bring him any closer to rescue.

The rim approached, or rather, he approached the rim. He slid toward it, slowed, hovered frustratingly short of the edge, and then dropped away. Lee checked that his radio was still broadcasting the useless call for help; verified that the toolpack was still out of reach, checked his battery status. No help, no help, no help.

He was sliding down the slope on his stomach, like riding a sled. He twisted around and then carefully pushed himself up onto his hands and knees. He pushed upright, balancing on his knees, with one hand on the slippery mirror for balance. Wobbly, but after a while he could keep his balance. That wasn’t too hard. He tried getting up onto to his feet, and made it for a moment, his arms windmilling desperately to keep his balance before his feet shot out from under him.

It was like trying to stand on ice. He worked at it, and eventually found his balance. It was a lot like snow-boarding on the hills of Callisto, he realized, or skiing the polar caps of Mars, something he’d tried once on shore leave. The carbon dioxide snow of Mars was nearly frictionless, too, but if you stayed loose and alert, you could stay vertical. The trick was to keep his center of gravity above his feet. It was a matter of holding his arms out, keeping his knees bent, and making continuous sliding adjustments. The low gravity worked in his favor, giving him time to correct.

He stood, surfing down the slope. If only his brother could see him now!

It did nothing to help his situation, but just being able to stand gave him a tremendous feeling of accomplishment, as if he were now in control of his environment. He imagined himself an Olympic ski champion, gliding down the run of artificial-snow on the slopes of Olympus Mons. He checked his display: almost to the bottom and heading uphill again, he was racing at 150 meters per second. That must certainly be breaking all ski records! He raised his hands in triumph to the imagined cheers of thousands—and skittered backwards, landing on his butt.

In a tenth gee, falling down was no big deal. Lee twisted around and tried again, and with practice found he could stand almost without conscious effort.

As if being able to stand up would do him any good.

Or would it? Wait, if he could stand, couldn’t he jump? In a tenth gee, he ought to be able to jump pretty high. Wouldn’t there be some way he could just jump that tiny distance from the top of his trajectory to the rim?

With a little practice, he discovered that indeed, he could push himself off the ice hard enough to get momentarily airborne. It took concentration and a lot of coordination to actually jump, instead of just having his limbs all flail out in all directions across the ice. (Not ice, he thought. Mirror. It’s not really ice.)

But as quickly as his elation rose in him at the sudden hope, it drained away. Being able to jump didn’t do him any good, because he could only jump straight up. No, not even straight up—he had no traction at all, so he could only jump in a direction exactly perpendicular to the surface of the mirror. He called up the picture of his trajectory across the mirror in the heads up display, and stared at it, trying to see a flaw in his reasoning. Suppose he jumped right at the moment he reached his highest point. But the slope of the mirror was the wrong direction; he’d actually be jumping away from the rim. No help. If he jumped a little early? No, still no good; he’d always be jumping the wrong direction.

He drew himself a little diagram in the heads-up display, and put an icon of a man in a space-suit on it. Any way he studied it, though, he couldn’t see a way that jumping was going to help him. In fact, it even hurt him—if he could add just a little bit to his velocity toward the rim, he could make it, but his jumping added velocity away from it.

Or, wait, was that right? His jumping would actually be perpendicular to the way he was moving. So it wouldn’t change his velocity along the mirror. Or would it? He wished he understood the physics a little more. The mirror was curved. It sure looked like there ought to be a way to make this work. His jump was a vector, and there had to be some way to make that vector work in his favor. But he couldn’t see it. It was too complicated for him

Appraise resources available, and apply them to solving your problem. His resources were himself, the child on the world’s biggest swingset … and a databot tutorial about physics.

He flicked back to the tutorial, searching through screen after screen explaining simple harmonic motion. That was his situation, he saw; sliding in a parabolic potential well. But nothing in the tutorial discussed pushing off in the third dimension. It explained that his motion followed a perfect sinusoidal curve—he knew that already—and that the period of oscillation was constant, a fact which didn’t help him any. Then the tutorial went on to cover the case of driven oscillators, when there was an external force pushing in time with the oscillation. Even a very small force, if he could apply it in phase with his motion, would quickly increase the amplitude of his motion. Even a small force—he wanted to scream at it. That was the problem! He didn’t have a small force, and the tutorial wasn’t giving him any clues. Instead, it wanted to tell him about kinetic and potential energy.

When in doubt RTFM, he thought. Read the fancy manual. A hundred times he’d gotten that advice, although sometimes the adjective used was something other than “fancy.” And the tutorial on simple harmonic motion was the only manual he had. If the answer was anywhere, it had to be there.

He started in on the chapter on harmonic motion, reading from the beginning, working the problems, single minded in his approach. Once he looked up, checked the heads-up display, and realized with a shock that over an hour had gone by, three full oscillations, while he hadn’t been paying attention. With his attention fully engaged, the material was interesting, he thought, worth studying just for its own sake. He could suddenly see why physicists were so passionate about their work. The solution had to be there, it had to be hiding somewhere in the mystery of kinetic and potential energy.

And it was.