Seveneves - Страница 60

When the Bolide Fragmentation Rate shot up through a certain level on Day 701, marking the formal beginning of the White Sky, a number of cultural organizations launched programs that they had been planning since around the time of the Crater Lake announcement. Many of these were broadcast on shortwave radio, and so Ivy had her pick of programs from Notre Dame, Westminster Abbey, St. Patrick’s Cathedral, the Imperial Palace in Tokyo, Tiananmen Square, the Potala Palace, the Great Pyramids, the Wailing Wall. After sampling all of them she locked her radio dial on Notre Dame, where they were holding the Vigil for the End of the World and would continue doing so until the cathedral fell down in ruins upon the performers’ heads and extinguished all life in the remains of the building. She couldn’t watch it, since video bandwidth was scarce, but she could imagine it well: the Orchestre Philharmonique de Radio France, its ranks swollen by the most prestigious musicians of the Francophone world, all dressed in white tie and tails, ball gowns and tiaras, performing in shifts around the clock, playing a few secular classics but emphasizing the sacred repertoire: masses and requiems. The music was marred by the occasional thud, which she took to be the sonic booms of incoming bolides. In most cases the musicians played right through. Sometimes a singer would skip a beat. An especially big boom produced screams and howls of dismay from the audience, blended with the clank and clatter of shattered stained glass raining to the cathedral’s stone floor. But for the most part the music played sweetly, until it didn’t. Then there was nothing.

Paris is gone, she texted. Through the military systems, which were patched in with NASA’s, she could still communicate with Cal.

Dive bbs, he answered. Which by itself was pretty enigmatic, but she knew its meaning: the submarine had to dive below the surface for a little while, to avoid some danger, but he expected he’d be back soon.

But he might be wrong about that. She might never hear from him again. She decided it was long past time. She texted him a message that he would find waiting when and if his boat returned to the surface: I release you from your vow.

Then she felt a strange wave pass through her body, almost as if she were in a submarine in the Atlantic when a pressure wave rolled through from some distant meteor strike. She assumed it was an emotional reaction to what she had just done. But then she noticed that every loose floating object in her workspace was drifting in the same direction, toward the wall against which she had braced her back. Pops and creaks and groans propagated through Izzy. The space station was accelerating gently, at just a fraction of a gee. The thrusters must be firing.

The lights had turned red. The PA speaker in her module emitted a slight pop as it came on. “Alert,” said a synthesized voice. “All personnel should now be awake and at stations for urgent swarm maneuver. This is not a drill.”

So it had happened. They had been practicing this for months. But this was the first real Streaker Alert. It meant that a bolide had been detected by SI — the Sensor Integration team — on an unusual trajectory that might pose a danger to Izzy unless the course was corrected slightly.

Her first, nervous impulse was to look out the window toward Amalthea. The big rock was still there. The maneuver hadn’t caused it to snap off.

But this was Ship thinking: placing top priority on Izzy. She, and everyone else, needed to get in the mental groove of Cloud thinking. The majority of the population lived on arklets. Izzy’s purpose was to help the arklets survive.

So she wrenched her gaze away from the window — an antiquated thing, that — and brought up a display on her tablet showing the disposition of every vessel in the Cloud Ark. It was an app called Parambulator. It was not a literal rendering of what the cloud looked like, though you could make it show you that if you clicked the right menus. Parambulator was a tour de force of data visualization that would only make sense to people like Ivy, Doob, and most of the Arkies, who had spent a lot of time learning about orbital mechanics. Starting with empirical observations from Lina Ferreira and other mathematically sophisticated biologists, mathematicians like Zhong Hu had extrapolated swarm algorithms from three to six dimensions and physicists like Ivy had figured out how to make these algorithms work under the special constraints of orbital mechanics. In general, every vessel in the cloud was shown as a dot on a three-dimensional scatter plot showing information about its orbit. Six numbers — the orbital parameters, or, as everyone up here had begun to call them, the params — were required to convey everything about an orbit. Only three could be visualized in any given plot. So that was where the user-interface legerdemain came into play, and where someone like Ivy had to pay attention and engage all available brain cells. But the gist of it was that each arklet was a projectile that could strike Izzy, or another arklet, if its params were wrong. In a hypothetical, extremely simple Cloud Ark consisting of only two arklets, only one calculation needed to be performed: namely, the calculation that answered the question “Will Arklet 1 bang into Arklet 2 if both stay on their current courses?” In a three-arklet cloud, it was also necessary to figure out whether Arklet 1 would collide with Arklet 3, and whether 2 and 3 were going to collide. So, that was a total of three calculations. If the cloud expanded to four arklets, six calculations were needed, and so on. In mathematical terms these were known as triangular numbers, a kind of binomial coefficient, but the bottom line was that the number of calculations went up rapidly with the number of arklets in the cloud. For a hundred-arklet cloud it was 4,950 calculations, for a thousand-arklet cloud, about half a million. It would have flummoxed the simple computers of Apollo days but was nothing by modern standards — provided that accurate information could be had about each arklet’s orbit. An old-school, centralized approach would have been for all the arklets to report their params to a computer on Izzy, which would then do all the calculations and report the results. The reliability of that process could be improved if Izzy’s radars, observing the arklets and plotting their movements, filled in gaps in the data. And indeed something like that was happening all the time, not just on one computer on Izzy but on several. But this, again, was Ship thinking. Cloud thinking dictated that each arklet make those observations and do those calculations separately. The computer on a single arklet — call it Arklet X— might not have all the information needed to track every single one of the other arklets in the cloud, but it could identify the ones most likely to be a danger and focus on those. Others, as well as the central processors on Izzy, could assist it by sending messages to the effect of “You might not be aware of it, but you are possibly in danger from Arklet Y and might want to move it to the top of your list of things to keep an eye on.” To which it might reply “Thank you, but I’m not getting good params for Arklet Y because Izzy is blocking my view on the radar.” The cloud would then respond by in some sense becoming aware that Arklets X and Y needed to know more about each other’s params and giving a higher priority to making that happen.

The cloud, in other words, became not just a physical cloud of flying objects in space but a computational cloud as well, a free-floating, self-regulating Internet. The function of Parambulator was to give its users an Olympian perspective on all that was happening in that network, and at some level all you really needed to know about it was that scary things were shown in red. Ivy looked at it now, more in curiosity than in alarm, since they had been practicing maneuvers for weeks and she thought she knew what to expect. Whenever Izzy fired her thrusters and changed her params, red propagated through the scatter plots like a drop of blood in a glass of water. All the free arklets, and all the ones connected to bolos or to heptads or triads, now needed to evaluate their params and see whether they were in danger of colliding with Izzy. Or — almost as bad — of drifting away so far that they could never get back to the swarm, a condition shown by a yellow dot in the display. It was a simple matter for any given arklet to plot a new course that would avoid both of those fates. Much more complicated was for three hundred arklets to do it at the same time without banging into each other. So a kind of negotiation had to take place, based not on awaiting commands from Izzy but on observing what “nearby” arklets were doing and coordinating the firing of thrusters with them to minimize the amount of red showing up on the plot.

It was necessary to place the word “nearby” in scare quotes because it had a different meaning in this swarm than it did to a bird in a flock. To a bird, nearby meant just that. To things maneuvering in the six-dimensional parameter space of orbital mechanics, “nearby” meant “any set of params that is potentially interesting to me in the next few minutes,” and it could apply to objects that were currently too far away to be noticed. Once that was accounted for, however, the arklets could do as birds did when flying in flocks. In the simulations that they had seen shortly after the concept had been proposed, it had looked astonishingly like the behavior of schooling fish. And the reality of it, which had only been implemented in the last few months of round-the-clock launches from Kourou, Baikonur, Canaveral, et al., answered well to those simulations. It just happened more slowly in real time.