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.
Yalda was upside-down and two strides above the ground before she felt the tightness around her lower wrist; she dropped the mallet and reached down frantically toward the catapult, but it was already too late to grab any part of it. With her rear gaze she stared up at the sack’s drawstring, twisted around her hand. She must have left the drawstring protruding from the side of the launching plate, and then slipped her arm through its loop.
Her first, idiotic, impulse was simply to disentangle herself from the sack—as if it alone were the cause of all her problems, and if only she were free of it she’d drift gently back to the ground. Her next thought was to pull it closer to her body, which she did. Then she freed her wrist from the string and clutched the coarse fabric of the sack against her chest, but she managed to stop herself from completing the plan: tossing the sack upward in order to propel herself back toward the mountain. Her instinctive sense that this tactic ought to work was almost overpowering; had she been stranded in the middle of a chamber inside the Peerless, it would certainly have done the trick. But even if she’d pushed the sack away with all the strength in her four arms—even if she’d burst the seams of her cooling bag and extruded two more—it would not have been enough. She knew how long she’d labored to turn the crank on the catapult, how much energy she’d put into the springs. A single burst of effort couldn’t match that. And a partial victory that merely slowed her ascent would be completely useless, if in the process she lost the means to do anything more.
Yalda glanced back at the receding light from the tunnel mouth. If she panicked and acted without thinking, she was dead. Her rapidly increasing distance from the ground was terrifying, but it was not her real enemy. It didn’t matter how long it took her to reverse direction; once she was headed back to safety, the length of her trip would be irrelevant. Or very nearly so: the sole criterion was that she needed to return before her air canister ran out—and it held enough for an entire six-bell shift.
Could the canister itself help? She ran a hand over its cool surface, imagining a swift burst of air that would send her hurtling down to safety. But without any tools, she doubted she could break open the valve that limited the outflow—and even if she could, the momentum of the entire contents might not be sufficient for the task. What’s more, a marginal success would make a lie of her indifference to distance; if she ended up drifting slowly back toward the ground, without cooling she could easily die of hyperthermia on the way. There were a dozen replacement canisters in the catapult’s tool hold, but did she really want to smash this one open and gamble on reaching the others in time?
No air rocket, then. All she had for exhaust was the rubble in the sack, and all she had to propel it was her own strength. But the catapult had put her in this plight using nothing but stored muscle power; if she parceled out the rubble in a manner that allowed her to expend more energy on this task than she had on turning the crank, she should be able to reverse the consequences.
Her body’s slow spin had her facing back down toward the light from the tunnel again. Her fellow workers would certainly miss her as the rubble sacks began filling up the pulley line, but they would not be in a rush to come looking for her; she could easily have spent all this time on minor repairs to the catapult. The rock face was where serious accidents happened; what kind of fool managed to shoot herself into the void? But whenever they did start to worry about her absence, she could forget about anyone throwing her a rope; she was already too far away for that.
No matter; if she stayed calm, she could fix this. She identified the point on the star-trail horizon that, as near as she could tell, marked the direction in which she was traveling: precisely opposite the shrinking patch of light on the ground. She loosened the drawstring and opened the sack a little, fearful of spilling the contents with her jostling, then reached in and took out a handful of rubble. She waited for her rotation to bring the target in front of her again; she wasn’t going to try to reconfigure her flesh to give equal strength to a backward throw. Then she brought back her arm and flung the handful of rock away with all her strength.
The effort felt puny and ineffectual—and she suddenly realized that in her haste and agitation she’d been laboring under yet another delusion. If she threw a heavy object, like the whole sack of rubble, the energy she put into it would be limited by the maximum force her muscles could apply. If she divided the sack in two and threw each half separately, the same force would let her throw a half-sack faster than a whole one, transferring as much energy to each half as she would have used on the whole.
Two throws, twice as much energy—hooray! But two throws would still not be enough, so why not four throws, a dozen, a gross, taking her time but increasing the total energy as much as she needed? That was what she’d been thinking: matching the energy she’d put into the catapult would simply be a matter of eking out the rubble with sufficient care.
But the pattern of throwing ever smaller weights ever faster only held true up to a point—for a half-sack, yes, but not for a handful of pebbles. By that point, the limiting factor would be the speed at which her muscles could contract, not the force they could apply. And when the speed was fixed, the energy she could put into a given quantity of rubble became proportional to its mass—which meant that it would add up to the same total, regardless of how many separate throws she made.
It didn’t matter how much strength she still had in her body; it didn’t matter that she could have cranked that catapult ten dozen more times without tiring. Her fate was completely determined by the total mass of rock in the sack, and the speed at which she could throw, not the greatest load, but the smallest.