Seveneves - Страница 44

Arkies as such — people who had been selected in the Casting of Lots, who had spent up to two years in training for this mission, and who had been sent up here specifically to manage, and live in, arklets — understood it implicitly. As of Day 700, there were 1,276 of those, with about two dozen more coming up each day during the final surge of launches. New arrivals were assigned to empty arklets that awaited them at the head or the tail of the queue. These were launched on separate heavy-lift rockets about four times a day. Since an arklet consisted mostly of empty space, it weighed almost nothing compared to the lift capacity of a big rocket, and so they were always crammed from boiler room to front door with vitamins. These had to be extracted and stowed before the arklet could be occupied. Each arklet had its own unique manifest of stuff. Some of them were just full of compressed gas, such as nitrogen, which would later be used to fertilize crops. Others might be packed with enough diverse and seemingly random goods to open a space bazaar: medicines, cultural artifacts, micronutrients, tools, integrated circuits, spare parts for Stirling engines, Arkies’ personal effects, and, in one notable case, a stowaway who was found dead on arrival. With the exception of the stowaway — who was stashed in the morgue with the rest of the deceased — all of these items had to be extracted, cataloged, and stowed appropriately. Each arklet had some onboard storage space, so to some extent the storage was distributed — that being a fundamental tenet of the whole swarm-based Arkitecture. Bulk materials like gases could be pumped into external tanks or bladders: little ones dangling from arklets, big ones distributed around Izzy’s periphery where they could serve as extra shielding against radiation and micrometeoroids. So-called dry goods were likewise stashed in mesh bags that lived “outside” until such time as they were needed. Scarce and crowded “inside” space was reserved for organisms and goods that actually needed air and warmth. So, compared to the way it had looked a year ago, Izzy was spare and clean on the inside.

Anyone who had not been chosen in the Casting of Lots and trained as an Arkie was categorized as General Population. There were 172 of those. The number grew only slowly, since most of the people who were qualified, and who were needed, ought to have been sent up a long time ago. Adding new members was attended by much political controversy down on the Earth. The Crater Lake Accord had ratified the general scheme of a Cloud Ark populated by those chosen in the Casting of Lots. It had been obvious, and uncontroversial, that experienced specialists were also needed, and so no one had quibbled over sending up the Scouts and the Pioneers. The concept of the General Population had been written into the Crater Lake Accord precisely to allow for that. People like Rhys Aitken, Luisa Soter, Dubois Harris, Moira Crewe, and Markus Leuker had been sent up under the “GPop clause” because they knew how to do things. For every one of them who got sent up, however, a hundred with similar qualifications were stranded on the ground, where some of them called their congressmen, chancellors, presidents, or dictators. The politics had become so involved as to throttle the incoming flow to a trickle. The remaining available GPop slots were being hoarded by national governments. They were being filled grudgingly and with byzantine premeditation.

For Arkies and members of the GPop alike, it was easy to underestimate the “distance” separating Izzy from an arklet that was only a few kilometers ahead of or behind it in orbit.

The difficulties entailed in moving from one arklet to another could be mitigated by physically docking arklets to a common structure, forcing them to fly in a rigid formation. Or so it might seem to people who had not been steeped in the laws of orbital mechanics. But the fact was that an arklet docked to the end of a truss far off to the port or the starboard wing of Izzy was not in a proper orbit at all. Left to its own devices — free, that is, of the constraints imposed, and the forces exerted, by the truss — it would converge on Izzy, cross through Izzy’s orbit, diverge from it, turn around, and converge again, on the same ninety-three-minute cycle that clocked Izzy’s orbits around the Earth. An arklet mounted “above” Izzy on the zenith would want to go “slower” and lag behind; one mounted “below” on the nadir would want to race ahead. To the extent that the truss structure prevented those things from happening — to the extent, in other words, that it succeeded in its basic function of holding all the modules and arklets in a fixed configuration — it was undergoing stress, exerting forces on those arklets to prevent them from doing what they wanted to do. Humans in those arklets would notice themselves drifting and bumping into the walls as their natural trajectories, as ordained by Sir Isaac Newton, were perturbed by the structure of Izzy. The larger Izzy grew, and the more arklets and modules were connected to her, the greater those forces became, and the closer she came to breaking.

There was another, even more compelling reason for limiting Izzy’s sprawl. She was taking shelter behind Amalthea.

The space station’s original orbit had been carefully chosen. Any lower, and the thicker air would make the orbit decay too fast. Any higher, and the danger from micrometeoroids would increase. That was because the rocks zipping around in space were subject to the same slow orbital decay as Izzy herself. Which was a good thing, since it dragged them down into the atmosphere and destroyed them, leaving clear space for Izzy to sail through. Her orbital altitude of four hundred kilometers was a Goldilocks compromise between “too much orbital decay for Izzy” and “enough orbital decay to sweep the sky of dangerous rocks.”

The attachment of Amalthea to Izzy’s forward end a few years ago had changed all of that for the better. Orbital decay was less of a problem because of the rock’s high ballistic coefficient, and micrometeoroids tended to get stopped by the massive nickel-iron cowcatcher.

The White Sky, however, was going to put many more rocks into their path. Big ones could be detected from a distance and avoided, but little ones could do a lot of damage, and so the most important parts of Izzy needed to take shelter in the lee of Amalthea, crowding up against her aft surface. Some rocks might still come in from unexpected directions, but in general there would be a “prevailing wind” in the drift of lunar debris. Amalthea was aimed into it.

But Amalthea couldn’t protect any parts of Izzy that projected beyond its silhouette. Dinah and the rest of the Arjuna Expeditions crew had made some progress in “embiggening” the asteroid, carving out slabs of metal and then elevating them like flaps on an airplane wing to extend the sheltered envelope, but it could only get so big. At some point it had been necessary to draw a line under the expansion and “fix the envelope,” meaning that Izzy took on a definite shape and size. This had occurred on A+1.233. Since then they had found ways to jam more modules inside that envelope, or, where that wasn’t possible, to pack bags and bladders of stored material into gaps. And they had tacked on additional storage in the unprotected volume outside of that envelope. But nothing had been added to her before or since. She couldn’t grow in the aft direction because Amalthea’s protective shadow only extended back so far — bolides could “wrap around” in any direction, since they weren’t in perfectly parallel trajectories. Anyway, boost engines were needed back there, and being in the path of rocket exhaust made standing in hellfire seem like a pleasant summer’s day by comparison.

Amalthea was now enveloped in scaffolding, anchored directly into the nickel-iron by connection points welded on, or drilled in, by Dinah’s robots. A proboscis extended forward from that cloud of trusswork and supported a little cluster of radar and communication antennas. Forward of that, the closest arklets — seven of them, docked to a hexagonal framework — kept station about a kilometer away, far enough that the firings of their thrusters would not blast those antennas with jets of hot gas. Other heptads, as the seven-arklet clusters were called, were spaced ahead of that one at the same interval. Beyond a certain point these petered out and were replaced by triads — three arklets on a triangular frame — and beyond that were singletons.

A similar tapering could be observed aft of Izzy, though the distance to the first heptad was greater, respecting the danger posed by Izzy’s boost engines. These heptads and triads were a bit like Lego or Tinkertoy parts, making it possible to cluster arklets together without much ado; hamster tubes were laced through their trusses so that, once an arklet was docked, persons and material could be easily moved to other arklets on the same frame. Adapters were also floating around that would facilitate nose-to-nose coupling, but these had been found to be not as useful as the hep and tri frames.

Farther out toward the ends of the train, it was not uncommon to see bolos. Each of these spun with its center of gravity — the grapple joining the two cables — tracking along the shared orbital path of Izzy and the other arklets. For now, though, almost all such coupling was for training purposes. Only about three weeks remained before the White Sky. The Arkies could survive that long in zero gravity. Formation of bolos and simulation of Earth-normal gravity was a practice intended for the long haul, when people might live their entire lives in arklets and would need gravity to build and preserve their bones, their eyesight, and other body parts that went bad in its absence.