Greg Egan - The Clockwork Rocket

Yalda bent down from the ropes that crossed the test field and examined the plants. The wheat stalks were barely two spans high.

“They’re… mature? They’re making seeds?” The tiny structures protruding from the stalks certainly resembled seed cases, but they were so small that it was hard to be sure.

“Yes, they’re mature,” Lavinio confirmed.

“But they’re a twelfth the size of normal wheat!”

“However long we keep the seedlings in the centrifuge,” Lavinio explained, “they always stop growing when we take them out—but if we raise them to this height first, they don’t die when we replant them in the fields. They don’t get any bigger, but they do form seeds of their own.”

“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.