Greg Egan - The Clockwork Rocket

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 sand. But if this worked, she thought, one more experiment would be enough. If they tried the same thing with a spinning rig and found that the centrifugal force ruined the dousing effect, then stunted wheat would be a small price to pay to retain the ability to protect themselves.

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.”