The Clockwork Rocket

by Greg Egan

  “I’m not interested in spreading panic,” she said. “But we’re going to need as many people thinking about this as possible.”

  “I’ve already set up every experiment you could wish for,” Lavinio insisted. “I’m looking at every combination of factors: light, soil, air, neighboring plants… what is there left to test?”

  “And nothing appears to be working?”

  “Not so far,” Lavinio admitted.

  “Then we both know what’s needed,” Yalda said. “The wheat’s been fine until now—and only one thing has changed.”

  Lavinio buzzed humorlessly. “So what are we going to do? Fire the engines again, until the next crop is established? And the next one, and the next?”

  “Hardly. We’d run out of sunstone in a generation, and then just starve to death a few years later.”

  “Then what?” Lavinio demanded. “If only gravity will make the wheat grow—?”

  Yalda held up a hand and twirled a finger around. “Spinning creates gravity too. We could put the seeds in a rotating machine—a centrifuge—until they germinate.”

  Lavinio considered this. “It’s an idea,” he said. “But what if germination’s not enough? What if it takes half a season under gravity to establish the plant’s growth axis?”

  Yalda was reluctant to answer that. The crew was still struggling to adapt to the last change: refitting every apartment, every workshop, every corridor; relearning every daily routine. How much discontent would it foster, to announce that all their efforts had been misdirected, and that everything they’d achieved was about to become obsolete?

  Without wheat, though, they couldn’t survive. And it was no use wishing that the cure would be painless; they needed to be prepared for the worst.

  She said, “If germination isn’t enough, we’ll have to set the whole mountain spinning.”

  The meeting hall continued to fill slowly long after the scheduled time had passed, but Yalda had no intention of starting until everyone had arrived. People were coming from every corner of the mountain, many of them making a journey they had never attempted before under weightlessness.

  Yalda stayed close to the entrance, greeting people and marking off their names on a list. Frido had offered to do the job for her, but she’d insisted on making the most of this chance to come face-to-face with every member of the crew again, however briefly.

  Now Frido waited in the front tier, clinging to the ropes beside Babila and half a dozen of the old feed chamber machinists. Yalda hadn’t been able to bring herself to confront him, to accuse him of acting in bad faith. She suspected that he’d been keeping the problem with the wheat to himself as a way to strengthen his position, hoping to make himself a hero to the crew by announcing a simple, biological remedy that would save them all from starvation—courtesy of Lavinio, but still created under his patronage and Yalda’s neglect. No doubt he’d also been prepared to claim the rotational cure as his own, if it had come to that. In fact, Yalda remembered Frido as being part of a group who’d discussed the possibility of spinning the Peerless, when the first real plans were being made for the mountain. The consensus they’d reached was that it would have made navigation and course corrections far too complex, for the sake of some very uneven gains in comfort. It had never crossed their minds that gravity could be a matter of life and death.

  Half a bell later, the list of non-arrivals was down to one unavoidable entry. Yalda gave a few quick words of thanks then introduced Lavinio, who explained what he’d seen, and the experiments he’d tried.

  “There must be something within a wheat seed that’s sensitive to gravity,” he concluded reluctantly. “Three days in a centrifuge will make the seed sprout, but then it stops growing when the signal is taken away. The established crop didn’t die in the fields when the engines were switched off, so we’re going to keep trying longer periods in the centrifuge in the hope that we’ll find a point where the seedlings can be taken out and planted. But there is no guarantee that such a point exists, short of maturity.”

  He moved aside, and Yalda dragged herself back on stage. She clung with four hands to the ropes behind her, surveying the anxious crowd, wondering what would happen if someone took this opportunity to lambast her over her leniency toward the saboteur. But these people had just learned that they risked starvation; Nino was a long-vanquished enemy, rotting away out of sight.

  “Sometime in the next dozen stints,” she began, “we might discover that a few more centrifuges and a bigger workforce in the farms are all we’re going to need to fix this problem. But if that turns out to be a false hope, the only alternative will be to spin the Peerless itself, which is not going to be quick and easy. So we need to begin work to prepare for that immediately, doing all we can to make it possible in time for the next harvest—even as we hope that we won’t need to do it at all.

  “It might seem tempting to try to spin the Peerless around a horizontal axis, in the hope of making the gravity in the fields as close as possible to the old direction—but I’m afraid the mountain’s center of mass is so low that it wouldn’t work out that way. There’s also a question of stability: if you try to spin a cone around anything other than its axis of symmetry, the slightest disturbance can set it wobbling. So we really have no choice: the mountain needs to spin around a vertical axis, running from the summit to the base.”

  She glanced down at Frido. Should she have had him stand beside her, backing her up, confirming these technical claims? Everyone understood centrifugal force, but half the crew would still have to take the finer points on faith.

  Frido gazed back at her with a neutral expression. They both knew that he’d been preparing to move against her. It was too late to try to bring him on side.

  “We’ll need to install two dozen small engines,” Yalda continued, “spread out down the slope of the mountain, along two lines on opposite sides of the axis. These will be very gentle devices compared to the ones we’ve used to accelerate, but we’ll still need to put them in deep pits so their thrust doesn’t merely tear them loose—or peel away parts of the surface of the mountain.

  “That means digging into the rock out there, with no gravity to hold us down. It also means working in an air-filled cooling bag, to avoid hyperthermia. No one has ever done anything like this before. And however optimistic we are about it, it’s more work than the usual construction crews could hope to complete in time for us to sow the crops. Everyone who isn’t working in the farms will have to help. Once the construction crews have worked out the protocols, they’ll start training other people to join in. I’ll be among the first of their students, myself—because nothing could be more important than this.”

  “Stints of dangerous work in the void, possibly for nothing?” Delfina interjected. She was in the front tier, a few strides left of Frido. “That’s your solution to an agricultural problem?”

  “What do you suggest instead?” Yalda asked her.

  “Find another food source that isn’t so dependent on gravity,” Delfina replied. “What are the arborines living on, in their forest?”

  “Lizards, mostly. Which are living on mites—which in turn feed on bark and petals.”

  “We could get used to lizard meat,” Delfina declared. “If it’s good enough for our cousins, why not eat it ourselves?”

  “I’m sure we could,” Yalda conceded, “but the whole forest only supports about six arborines.”

  “We can’t farm the lizards more intensively?”

  “That’s… worth considering,” Yalda said. “But it would be another gamble, and even if we could make it work the payoff would come too late. The only thing we know for sure is that we can raise a wheat crop under gravity. Once we spin the Peerless, all we’ll have to do is prepare new fields and plant the seeds.”

  “Where, exactly?” Delfina pressed her. “Which chambers were built with their floors pointing away from the mountain’s axis?”

  “We’ll have to improvise for the first crop,”
Yalda admitted. “We’ll have to lay down fields on surfaces that used to be walls—we won’t have time to carve out new chambers with the ideal geometry.”

  “And what happens if we need to fire the engines? To avoid some unanticipated obstacle?” Delfina was enjoying this; someone had prepared her well.

  Yalda did her best not to grow flustered. “As things stand, we’d need to get rid of the spin first. But there’s no reason in principle why we couldn’t redesign the attitude controls and the engine feeds to work while the Peerless was rotating.”

  Delfina hesitated, as if she’d finally reached the end of a list of objections that she’d committed to memory. But her contribution wasn’t over.

  “I’m sorry,” she said, “but I’m not convinced. On balance, I don’t think your plan is worth the risk. I won’t be joining any work team for this purpose.”

  Yalda said, “There is no coercion here. You’re free to make your own decision on this.”

  “And free to persuade my friends to make the same decision, I hope,” Delfina added cheerfully.

  “Of course.” Yalda was angry now, but she was not going to change her stance and start making threats. Help spin the mountain, or you can go without food next harvest.

  Far better, she decided, to call the spoilers’ bluff.

  “But we’ll need to start drawing up the rosters,” she said, “so I’d like to get the numbers clear right now. How many people are prepared to work to make this happen—either in the farms, or out on the slopes? Please raise a hand if you’re willing to do that.”

  About a third of the crew responded immediately. For a long, painful moment it looked to Yalda as if that burst of enthusiastic support was all she would get, but then the numbers began to grow.

  In the end, only about two dozen people chose to side with Delfina. Most were from the feed chambers, sending her a message about Nino. No doubt there were many more who wanted the saboteur dead, but they weren’t going to risk the crops—or even risk being seen as risking the crops—just to express their anger over something else entirely.

  Frido was not among the dissenters. At some point he had counted the numbers around him and decided to raise his hand.

  17

  As they waited to use the airlock, Yalda helped Fatima into her helmet and cooling bag. No one’s flesh was flexible enough to conform to the shape of the fabric perfectly—and the whole point was to ensure that there was air moving freely over your skin—but if you let the bag hang too loosely anywhere it just blew out into a rigid tent, leaving you fighting it with every move. The trick was to come close to filling the bag but to wrinkle your skin as much as possible, creating a series of small air channels between skin and fabric.

  Yalda finished checking the fit. “I think you’re right now,” she said.

  “Thanks.” Fatima reached into the hold beside them and took out two canisters of compressed air, passing one to Yalda. Yalda attached it to the inlet at the side of her own bag.

  “Someone should find a better way to keep cool,” Fatima suggested.

  “In time for the next shift?” Yalda joked.

  Ausilio had finished pumping down the airlock pressure; he slid the external door open, took hold of the guide rail just outside the exit, then pulled himself through. As soon as he’d reached back to slam the door closed, Fatima opened the equaliser and air hissed slowly back into the lock.

  Yalda was growing tired of these laborious preparations, shift after shift, but she kept her frustration to herself. Three more stints, and she’d never have to go through this rigamarole again.

  Fatima entered the airlock and began working the pump energetically, bracing herself with three hands against the clearstone walls.

  By the time Yalda was through onto the slope, Fatima and the rest of the team were already out of sight. Yalda swung herself between the guide rails and set off down the mountain, moving briskly but always keeping at least two hands on the rails. In the absence of gravity she ought to have been oblivious to the gradient of the slope, but the rim of the inverted bowl of garish color trails above her matched the old horizon perfectly, making it impossible to think of the ground as level.

  The new horizon was a dazzling, multicolored circle where the fastest ultraviolet light from the old stars was shifted to visible frequencies before giving way abruptly to blackness. Straight ahead of her—“downhill”—the more modest trails of the orthogonal cluster shone sedately. Away from the guide rails, silhouetted in the starlight, dead trees sprawled at odd angles. Notwithstanding the high altitudes to which they’d been accustomed, their roots had not been enough to keep them cool in the complete absence of air. Patches of red moss had colonized the deadwood, but its faint light suggested that it was struggling.

  A few saunters from the airlock, Yalda reached the pit. Lamplight from deep within the tunnel shimmered off the dust emerging from its mouth. At first glance it was easy for a planet-trained eye to see these motes as being borne on some kind of breeze, but then the thumb-sized fragments of rock scattered among the specks—moving more slowly, but just as freely—put an end to that illusion. Nothing was propelling the dust; it was flowing out of the tunnel for no other reason than its own chance collisions, inexorably driving it to occupy more space.

  The guide rails, dating from before the launch, ran right past the tunnel’s entrance but couldn’t take her in. Yalda shifted her grip to a pair of ropes anchored to a series of wooden posts that veered off into the light. The floor of the tunnel sloped gently down into the rock; it was another half saunter before the roof was above her.

  The haze of dust and grit thickened. When Yalda gripped the rope close to the posts, she could feel the vibration of the jackhammers. When she raised her hand, backlit motes of rock swirled away from it, driven by the air slowly escaping through the fabric. Fatima was right to be dissatisfied; it was a crude business when the only way they could cool themselves was to throw warm air away.

  Gradually the rock face came into view, ringed by blazing sunstone lamps. Seven members of the team were working it with jackhammers, braced against the rock within their cages. Three taut guy ropes ran from the top of each cage to the tunnel wall, holding worker and cage in place against the tool’s relentless kick. Yalda had done that bone-shaking job for two stints, and then finally conceded that she was past it.

  Four other workers were moving between the cages, clinging to the guy ropes and dragging the open mouths of their rubble sacks over the fragments of broken rock that were bouncing away from the hammers. It was impossible to scoop up all the debris, but their efforts kept the workspace more or less navigable.

  Fatima spotted Yalda and waved to her, then turned her attention back to the rubble she was chasing. With the cooling bags covering everyone’s skin, communication was reduced to glances and hand gestures. If you brushed against someone you could exchange a few muffled words, but mostly the shifts were spent in a kind of tacit camaraderie, where the rhythms of the work itself—shifting the hammer cages, re-pinning the guy ropes—had to take the place of friendly banter.

  There were already two full sacks waiting to be removed, the drawstrings at the top pulled closed and used to tie them to hooks on a pulley line that ran the full height of the tunnel. Yalda dragged the line around to bring the sacks within reach, slipped their drawstrings over her shoulders, then set off back to the mouth of the tunnel.

  The catapult sat on the other side of the guide rails. Yalda put the rubble sacks on holding hooks at the side of the machine, grasped a nearby support post with her two left hands, then started turning the crank that ratcheted the catapult’s launching plate back along its rails, stretching a set of springs below. As the crank began stiffening its resistance, she could feel the support post working itself loose from the ground. Cursing, she shifted her lower hands to the catapult, dug a mallet out of the tool hold, and bashed the support post half a dozen times.

  Yalda checked the post; it felt secure now. But as she bent to
put the mallet back in the hold, she could feel a tiny rocking motion in the catapult itself: she’d managed to loosen some of the tapered wooden pegs that held its base against the ground.

  Never mind; she’d deal with that later. She swung the first sack onto the launching plate, checked that it was properly closed and sitting squarely on the plate, then reached down and released the catch. The plate shot up a full stride before the springs stopped it, leaving the whole machine reverberating. The sack continued on, gliding away smoothly into the void. Yalda had had her qualms about disposing of the rock this way; who knew what demands their descendants might have for even the most mundane materials? But the effort that would have been needed to secure the rubble on the slopes—let alone cycle it all through the airlocks and stash it somewhere inside the mountain—was more than they could spare.

  She launched the second sack into oblivion, then headed back down the tunnel.

  The haze was growing thicker. Two of the hammers had hit a lode of powderstone, which left no solid pieces to collect and just wafted out like smoke, coating everyone’s faceplates with gray dust.

  Four more sacks were waiting on the pulley line. Yalda brought down two of them, then paused to wipe her helmet clean and squint up at the rock face. The crumbling powderstone was a nuisance, but it would speed progress. Once the main excavation was completed, half a dozen small feed chambers would be constructed behind the rock face, accessible through a separate tunnel leading straight up to the surface. Apart from Benedetta’s probes, this would be their first real test of an engine that wasn’t gravity-fed, with the liberator pushed through the fuel by compressed air. Yalda was already feeling anxious about that, but in some ways the test would be forgiving. The geometry of the engine placement would be the most important thing; small variations in the thrust wouldn’t be critical.

  She slogged her way back out to the catapult. As she cranked it, the support post she was holding came loose again. She fumbled for the mallet—the simple task of retrieving it made harder by the streaks of gray powder still stubbornly clinging to her faceplate—then she realized that one of the sacks was actually blocking the front of the tool hold, so she shifted it onto the launching plate. Then she gripped the base of the catapult with her lower pair of hands to brace herself, and started bashing the support post.