The Clockwork Rocket by Greg Egan
“Wonderful.”
It was not the outcome they’d been hoping for, but Lavinio couldn’t hide his fascination. “It’s as if the maturation process is triggered directly by the cessation of growth, so long as the plants are larger than some critical size. If we really understood the mechanism, perhaps we could intervene further. But for now—”
“For now, we have the option of growing six crops a year—each with extremely low yields.” Yalda prodded one of the seed cases with a fingertip. “And these actually germinate?”
Lavinio said, “Yes—if we put them in a centrifuge, like their parents. The seedlings start out extremely stunted, but they catch up in size by about the fourth stint.”
Yalda had been expecting a clear-cut verdict, one way or the other, to force her hand. The utter failure of the centrifuged seedlings would have left her with no choice but to spin the Peerless, while a perfect fix that let them grow the old-style crops would have allowed her to declare that building the engines had been a worthwhile precaution, but actually firing them had mercifully proved to be unnecessary. “So where does this leave us?” she asked.
“It would be much more labor-intensive than ordinary farming,” Lavinio said. “And we’d need at least ten dozen centrifuges to yield the same total volume of grain as we were harvesting in a year, when we had gravity.”
Ten dozen centrifuges, running around the clock. Burning fuel, demanding maintenance. Spinning the whole mountain would eat into their sunstone reserves—but they would only need to do it once.
“It would be survivable,” Lavinio added. “Not ideal, but not completely impractical.”
Yalda thanked him, and promised a decision within the next few days.
She headed back to the summit, skimming along the stairwell’s ropes. With ordinary wheat in ordinary fields, it would be a simple matter to increase the size of the crop to feed a larger population. Having to build and run a dozen more centrifuges just to increase the yield by one tenth would change everything.
But if they went ahead and spun the Peerless, and then some wayward pebble set the slopes on fire, how much harder would it be to douse the flames when the mountain was flinging everything off into the void?
Yalda left the stairwell in the academic precinct and dragged herself down the corridor toward her office, trying not to betray her anxiety as she returned the warm greetings of passersby. Now that the tunnels were finished, the completion of the spin engines was in the hands of skilled machinists—but everyone here had been out on the slopes in the dust and danger, everyone had earned the right to think of the project as their own.
Some people flashed her looks of excitement and anticipation; some called out “Three stints to go!” If she turned around and announced that all of their work had been for nothing—and that they would now have to live on meager supplies of machine-raised, stunted wheat—she was going to need a spectacularly compelling argument to back up her decision.
Marzia was waiting outside her office. “The test rig’s ready,” she said. “Just give the word, and we’ll launch it.”
“Are you sure this is safe?”
“It will be five strolls from us when it ignites, and still moving away,” Marzia reminded her. “I don’t see how we could make it any safer without giving up the chance to observe it at all.”
Yalda accepted this, but it was hard to be relaxed about the experiment. The engines of the Peerless had failed to set the world on fire, but that had never been their purpose. Marzia’s rig was designed to ignite a mineral that had never been seen burning, except perhaps on the surface of a star.
“What if a spark comes back and hits the mountain?”
“Any debris that would be hot enough to harm us will be hot enough to burn up long before it reaches us.”
“Unless you ignite the Eternal Flame,” Yalda joked weakly.
Marzia gave an exasperated buzz. “If you’re going to start invoking those kinds of fantasies, why not throw in another twist and let us survive anyway? Then we can all head home to see our families.”
Yalda said, “Go ahead and launch the rig. Just make sure that the fire lookouts know what to expect.”
Three bells later, Yalda met Marzia in the precinct’s observation chamber. Marzia had set up two small telescopes and trained them on the rig, which from their point of view appeared almost fixed now as it drifted away from the mountain. By starlight the device was just a slender silhouette, but after Yalda had taken a peek to confirm that the instrument was aimed correctly, Marzia handed her a filter to slip into the optics. The image was about to brighten considerably.
As Yalda checked the wall clock with her rear gaze, a globe of light erupted at one end of the rig’s calmstone beam, spraying luminous shards into the void. The beam had been slotted straight through the middle of a spherical charge of pure sunstone, encased in a solid hardstone shell; on the timer’s cue, the fuel had been saturated with liberator and the heat and pressure had risen until the casing was blown apart. A slight equatorial thinning of the shell had directed the explosion outward from the beam, sparing the other equipment attached to it and leaving almost no net force or torque; the beam had acquired a barely perceptible rotation, and had remained squarely in view.
And it was burning. The sunstone had scattered, and the calmstone itself was ablaze.
Marzia let out a chirp of triumph at this unprecedented feat. Yalda would have been far happier to learn that calmstone was impossible to ignite—and that the stars, and Gemma, must have simply lacked the mineral that covered most of the surface of the world. Calmstone sand could douse burning fuel. Calmstone had contained the Great Fire of Zeugma. Calmstone had borne the launch of the Peerless without succumbing to the flames. But now—
“Air does make a difference,” Marzia muttered happily. Similar experiments had been attempted back home, but with air always present to carry away some of the heat, the calmstone had never reached its flashpoint.
They’d soon know if the same effect was enough to put out the flame once it was already burning. A few strides along the beam from the ignition trigger, four tanks of compressed air were fitted with clockwork ready to discharge their contents onto the flame. There was no missing this when it happened: as the air rushed down the beam the whole rig accelerated sideways, and Yalda had to start turning the scope to keep the apparatus in view. Once she managed to track it closely enough to steady the image she could see the artificial wind distorting the incandescent halo around the beam—but the calmstone itself grew no dimmer. The fire remained self-sustaining: the creation of light by each tiny patch of the disintegrating mineral was accompanied by enough heat to guarantee the same fate for its neighbors, with enough to spare to make up for whatever the surrounding gases were carrying away.
Yalda was dismayed, but there was one more stage to the rig, one more trick to test. A pause or two after the first four tanks emptied, a second set opened up—but now the air, though much gentler, was being routed through pipes half-filled with powdered hardstone. This was the ultimate bucketful of sand: a dose of the most inert mineral of all to draw the heat into itself and try to disrupt the cascade of energy.
The hardstone sand was poured radially, with four symmetrical flows directed straight down onto the beam to cancel out any rocket effects and allow the material to accumulate as much as possible in the absence of gravity. It was a model for the best-case scenario: the equivalent of dousing the mountain’s slopes in the absence of any confounding spin.
The timing of the release had been guesswork, chosen on the basis that earlier was better, and the portion of the beam subject to this treatment had not yet caught alight. Some sand was drifting away, but there was more than enough being added to make up for that; Yalda could see the mound growing by the light of the encroaching flames.
As the fire hit the mound, the view faded to black; with the filter in place even the stars were invisible. Yalda restrained herself; anything could still be happening beneath the
A light flickered and brightened, illuminating the remains of the rig. The fire had continued to consume the beam; it had merely been hidden. There was no “dousing effect” to be saved.
Yalda turned to Marzia. “What now?” she asked numbly.
“We could vary some parameters,” Marzia suggested. “Tweak the flow rate, or the quantity of the hardstone powder.”
“I thought this was already the best setup you could think of.”
“It was,” Marzia said. “But my guesses aren’t infallible; some small change might still improve it.”
“Enough to make a difference?” Yalda pressed her.
“It’s not impossible.”
Yalda said, “Then it’s worth trying.”
There had to be a solution. She could not accept a life for the travelers as hazardous as the life they’d left behind. The flashes of light on the surface had been harmless enough so far—but they wouldn’t get a second Gemma moment out here. The proof that the worst could happen would only come when the Peerless itself burst into flames.
Marzia said, “You know I studied chemistry in Zeugma?”
“Of course. I think we met once, after I visited Cornelio.”
“We always worked with a knife beside us,” Marzia said. “We protected our bodies as much as we could… but when something went wrong, you couldn’t really hope to find an effective extinguisher in time.”
Yalda was horrified. “And you think that’s the best we can do? Prepare ourselves for an amputation?”
“I had to cut off my own hand twice,” Marzia replied. “It was either that, or lose everything.”
“I admire your resolve,” Yalda said, “but hands can be reformed. Flesh can be replenished. Any rock we discard is gone forever.”
Marzia thought for a while. “Our ‘empty corridor’ has turned out not to be as empty of ordinary matter as we hoped,” she said. “Could we have missed some orthogonal matter as well?”
“That’s possible.” The orthogonal star cluster was more than a dozen blue light-years away, but the dust and pebbles of the Hurtlers themselves were all around them, and there could be larger non-luminous bodies as well.
“Whittling the mountain down to nothing over the generations is an alarming prospect,” Marzia said, “but if tossing the occasional fire-afflicted portion off into the void is the only way to protect ourselves… maybe we can take comfort in the possibility that what we’re losing isn’t really irreplaceable.”
Yalda said, “Comfort isn’t quite the word I’d use.”
Marzia persisted. “The idea of crossing the void to try to mine another body of rock might seem daunting to us now, but who knows what our descendants will be capable of?”
“How much more are we going to load onto them?” Yalda asked wearily. “It’s bad enough that we expect them to invent their way home with whatever fuel they have left. Now they’re meant to find mines in the void in time to patch up the mountain before fire damage shrinks it to an uninhabitable core.”
“What choice do we have?” Marzia replied. She gestured toward the dying embers of the rig. “I’m happy to try more experiments, but I can’t see our luck changing there. Whatever the solution is, we have to trust the people who come after us to play a part in finding it. If we’d had all the answers ourselves, we would never have needed to make this journey at all.”
Three times a day, the fire lookouts climbed down their rope ladders for the change of shift. The number of impact flashes they reported rose and fell, but no more than Yalda would have expected for random collisions.
If the dust had comprised some kind of well-defined obstacle with known borders, they could have planned a route around it, or at least done the calculations and decided whether it was worth the cost in fuel. But they had not seen any hint of this in advance, before their velocity blinded them to all the ordinary matter ahead, and now any maneuver that sought to escape the problem would amount to no more than trying out random detours one by one and then seeing if they’d made things better or worse. They did not have that much sunstone to burn.
Marzia’s follow-up experiments came to nothing. If burning calmstone could be extinguished at all, they were as far as ever from discovering how to do it.
Yalda sought out Palladia, the most experienced of the construction engineers, and asked her to consider the possibilities for discarding parts of the mountain. After a couple of days pondering the matter, she returned to Yalda’s office to sketch out her preliminary ideas.
“The two simplest options,” Palladia said, “would be to install a kind of sacrificial cladding—expendable tiles covering the surface that could be detached easily if they caught alight—or leaving the exterior as it is, and being prepared to blast an outer wall away, if necessary.”
“Blast an outer wall away?” Yalda was no longer prepared to rule out anything. “So we lose pressure, then spend a couple of years with everyone in cooling bags trying to make repairs?”
“Hardly,” Palladia replied, amused. “We’d divide the outer precincts into individual sections. We’d put pressure doors in all the access corridors, and pre-install a set of charges in each section. Once the lookouts identified the precise location of the fire, there’d be a procedure to follow: start the timers on the charges, evacuate everyone, seal the section… then the wall is blown into the void, taking the fire with it.”
“Tell me about the first option.” Yalda resisted adding: the sane one. “The tiles, the cladding.”
“There are two issues there,” Palladia said. “Can we mine enough material from the interior to put an effective layer of cladding on the surface, without causing structural problems? We need to be able to guarantee the integrity of every chamber under the loads arising from centrifugal force, not to mention the eventual re-use of the main engines. But even if we have enough raw material, the next question is whether we’d have time to clad the whole exterior before our luck runs out and the surface catches fire. That would be a massive task under any conditions—but with the mountain spinning it would be the hardest thing we’ve ever attempted.”
“We could delay the spin-up, if it was worth it,” Yalda suggested reluctantly. They could live off stunted wheat while they completed this shield, if it was actually going to be capable of protecting them.
Palladia said, “Let’s try to get some solid numbers.”
They worked together for ten days. Thanks to Marzia’s experiments they knew the rate at which calmstone burned, and though no one had yet been able to find one of the tiny impact sites on the surface, Yalda could estimate the depth to which dust particles of various masses would penetrate the cladding when they struck with infinite velocity. Palladia had surveyed the whole mountain during the construction phase, compiling the first detailed records of its composition, and she’d witnessed firsthand how various chambers had stood up to the stresses of the launch.
The numbers were not in their favor. To cover the mountain with a worthwhile protective layer would leave it gutted and weakened inside, to the point where its spin alone could start breaking it apart. But giving up on spin wouldn’t save them; the next time they fired the engines, to decelerate, the Peerless would turn to rubble.
“I want you to draw up plans for… our other option,” Yalda said.
Palladia regarded her with something close to panic.
“I’m not asking you to rush anything,” Yalda assured her. “You should take as long as you need to get this right. But you should make all your choices on the basis of structural considerations alone. We’ll address the other practicalities separately—if we have to move some pieces of equipment to safer locations, or duplicate some facilities, so be it.”
Palladia was still not
Yalda said, “I’m speaking to you, because I know you can do the job. You can have as many assistants as you need—just pick whoever you want. You might have to wait until the spin engines are finished for some people to become available, but once that’s done this will be our highest priority.”
Palladia replied carefully, “I’m honored to be given this responsibility—but with respect, I think Frido and Babila should be involved. Assistants can follow instructions and check my calculations, but they won’t have the confidence to argue with me if I head down a wrong path. This is too important to be left to one person.”
Yalda could see the logic in that. “Why Frido and Babila?”
“They’re the most experienced engineers we have,” Palladia said. “Who else should I consult?”
She was afraid, Yalda realized. If something went wrong with the scheme and the Peerless ended up crippled and airless, the architects of the plan would be held accountable. Though Yalda would take most of the blame, anyone who had been too close to her on this would share the opprobrium. But if the most powerful members of the only other viable faction were equally enmeshed in the project, Palladia would have some protection in the aftermath.
Was that so unreasonable? And regardless of the politics, Yalda didn’t doubt that Frido and Babila would scrutinize the plans diligently. Whatever their disagreements, they were not going to jeopardize the Peerless itself just to undermine her.
“All right,” she said. “Let’s talk to Frido.”
They found Frido in his office. He listened patiently to their summary of the problem and the results of their calculations.
“Of course I’m happy to help,” he said. “But before we go any further, I think we should put this to a crew meeting—just as we did with the spin engines.”