We had a bit more time than before to model this problem, although we still looked quite fast to the people of the solar system, who were used to these crossings taking years. Although there was also a class of very fast ferries that could jaunt around the system, if they found they had a really pressing need for speed. Fuel and other costs made these quick trips very rare, and yet it did give the locals a basis for comparison, which is why we had been such a marvel at first, coming in faster than anything. Now we were normalized in terms of their idea of speed, fast but not extraordinarily so. It might also have been true that the novelty of our return was also wearing off, and we were becoming just another odd feature of life in the solar system. We hoped so.
Soon enough Uranus approached, its narrow faint ring making it clear that we were going to round it pole to pole, and though the ring was no problem to dodge, nor the little fragment moons, the models had confirmed that we needed to be very cautious with our aerobraking, staying as high in the Uranian atmosphere as we could while still coming out of the turn headed toward Neptune, after a sharp right curve.
So in we came, and Uranus grew in the now-familiar way, looking mauve and lavender and mother-of-pearl, and we hit the upper atmosphere and at first it was the same as always, a sharp deceleration, ramping up to 1 g, not at all bad, and then WHAM WHAM WHAM WHAM, it was as if we were running through doorways without opening the doors, terrific smacks that increased in shuddering with each impact. Things broke, animals and people died, probably of heart attacks, six people this time, Arn, Arip, Judy, Oola, Rose, and Tomas, and it really was becoming unclear whether we could sustain many more such concussive slaps, it was startling how much a wind shear wall could obstruct one, a little left-right punch followed instantly by a right-left punch, when happily we were out of the atmosphere again before anything more damaging occurred, and were again on course, and on our way out to Neptune.
Which meant we were coming to the crux. Push had come to shove. Again we would come in, dodge the negligible rings, make a dip into the upper atmosphere of this cool blue beauty, reminiscent in appearance to Tau Ceti’s Planet F, we found. But this time our turn had to be almost a U-turn (perhaps the source of the use of the letter U in the gravity assist equations?), not quite a true U-turn, but 151 degrees, quite a wraparound, a V-turn, not easy at all, and at 113 kilometers a second. That meant a deeper dive into the atmosphere, and more tidal forces, and more g-forces. Aerobraking would again shake us; it would feel like we were a rat in the jaws of a terrier, perhaps. But if we succeeded, then we would be headed back in, downsystem toward the sun again, quite considerably slowed down, and in a pattern that would seem to allow us to continue our decelerative cat’s cradle, pinballing around the solar system from gravity handle to gravity handle, at least for as long as our fuel held out to make course corrections. We were running low on fuel.
So: Neptune. Cool blue-green, lots of water ice and methane. Gossamer ring, barely visible. Not much sunlight out here. Well beyond the habitable zone of any life-form known. A slow place. Interesting to have given it a submarine name; it seemed somehow appropriate, in the usual mushy metaphorical way, in that impressionistic, vague, feeling kind of way.
We were still going very fast, but it was a long way to go, so we had 459 days to set things up. The diameter of our approach window was smaller than ever, given the need for such a sharp turn; vanishingly small; really hitting the mark precisely on the nose of our capture plate would be best, so we were setting the trajectory window at a hundred meters in diameter, which after all the distance crossed was rather extraordinary to consider: but even so, a hundred meters was a bit too big a window; really a single meter, a geometrical point, would be best.
In we came. Hit the mark. Started the pass, knuckles white.
Aerobraking comparatively smooth, compared to the hammering of Uranus. A rapid vibration, an occluding of vision in the upper clouds, a few minutes of blind trembling, of intense anxiety, nail-biting suspense; and out again, after another 1-g press, which this time was more than ever a matter of tidal forces, as we swung around so far. V-turn!
And out of the pass, headed toward the sun. Downsystem. Looped in. Caught. Back.
If each of our five passes was called a one-in-a-million throw, which was a very conservative estimate of the odds, then all five together made it a one-in-an-octillion chance. Amazing—literally—in that we had indeed been threading a maze. Little joke there.
And so down to the sun again, going slower than ever, although still 106 kilometers per second. But the next pass of the sun would put a good heavy brake on that, and on we would go, slower each time, working through a version of Zeno’s paradox that fortunately was not truly a perpetual halving, but would come to an endpoint, thus our own happy ending to a very severe halting problem.
On the way back in, we passed near Mars, which was interesting. There were so many stations there that it was no longer a scientific facility only, but something more like Luna, or the Saturnian system, or the Europa-Ganymede-Callisto complex: a kind of nascent confederation of city-states, buried in cliffsides and under domed craters, but each outpost quite various in design and purpose, and altogether more than just an outpost of Earth, though it was still that too. Early dreams of terraforming Mars quickly, and thus having a second Earth to walk around on, had come to grief, mainly because of four physical factors overlooked in the first flush of optimistic plans: the surface of Mars was almost entirely covered by perchlorate salts, a form of chlorine salts that had given Devi fits as well, as only a few parts per billion gave humans terrible thyroid problems, and could not be endured. So that was bad. Of course it was true that many microorganisms could easily handle the perchlorates, and in their eating and excreting consume and alter them to safer substances; but until that happened, the surface was toxic to humans. Worse yet, there turned out to be only a few parts per million of nitrates in the Martian soil and regolith, an odd feature of its original low elemental endowment of nitrogen, the reason for which was still a source of debate, but meanwhile, no nitrates, and thus no nitrogen available for the creation of an atmosphere. And so the terraforming plans were faced with a radical insufficiency. Then third, it was becoming clear that the fines on the Martian surface, having been milled by billions of years of drifting in the winds, were so much finer than dust particles on Earth that it was extremely difficult to keep them out of stations, machines, and human lungs; and they wreaked damage on all three. Again, once microorganisms had carpeted the surface, and fixed the fines by bonding them into layers of desert pavement, and also as the surface got hydrated and the fines became bogged in muds and clays, that problem too would be solved. And last, the lack of a strong magnetic field meant that a thick atmosphere was really needed to intercept radiation from space, before the surface would be very safe for humans to be on.
So, none of these problems were pure stoppers, but they were big slower-downers. Concerning the nitrogen lack, the Martians were negotiating with the Saturnians to import nitrogen from Titan’s atmosphere, as it had become clear that Titan, for its own terraforming plans, had too much nitrogen. Transfer of that much nitrogen would be a Titanic chore, ha-ha, but again, not impossible.
The upshot of all this was that the terraforming of Mars was still on the table and a subject of huge enthusiasm for many humans, particularly the Martians, although really, in strict numerical terms, even more of these enthusiasts lived on Earth, which seemed in fact to be home to enthusiasts of all kinds, for any project imaginable, judging by the roar of radio voices coming from it, almost like an articulated version of Jupiter’s mighty radioactive yawp. Oh yes, Earth was still the center of all enthusiasm, all madness; the settlements scattered elsewhere in the solar system were outliers. They were expressions of Terrans’ will, and vision, and desire.
So, past the bustling little world of Mars, where they lived dedicated to the idea that they would successfully terraform their world in no more than forty thousand years. They see
m to regard this as fine. As long as it could be done, it should be done, and would be done; and so the work was good.
The crucial difference here, it seemed to us, between Mars and the terraforming project we had left back on Iris, was that Mars is very near Earth. Its human settlers were constantly going to Earth for what they called their sabbatical, and receiving shipments of Terran goods and materials. And these infusions of Earth meant that they were always escaping the zoo devolution problem. Iris did not have those infusions, and never would; and it was notable (though in fact we had forgotten to note it, in the press of events) that we had not heard anything from the Iris settlers for over twenty-two years. Possibly a very bad sign, although it would benefit from a discussion with Aram and Badim, and the rest of the humans sleeping on board, to interpret more fully what it might mean. But certainly there was one explanation for the silence that was simply very bad.
Then downward to the sun again, down down down, feeling the pull, speeding up, heating up. In for another nail-biting scorcher of a pass, although this time without the ball and chain of the magnetic drag hauling back on us as we went; but it lasted considerably longer, as we were now traveling only 4 percent as fast as we had been going on that first terrifying pass. This time it would take us five and a half days, but we stayed farther out, and only heated up to the same 1,100 degrees on the exterior, and held there; and when we came out of that pass, we were headed for Saturn. No more of mad roaring Jupiter, if we could avoid it, and this round we could. Each leg of the cat’s cradle we were making would be different now.
Round and round the system we flew, slower and slower. We had very little fuel left. We were a kind of complicated artificial comet. Our trajectory clarified before us as we went. We passed by many inhabited planetary and asteroidal bodies. For quite a few years, the people in the solar system did not seem to get used to us; we were still a marvel of the age, a sight to be seen, a great anomaly, a visitation, as if from another plane of reality. That was the Tau Ceti effect, the starship effect. We were not meant to come back.
Slower, slower, slower. Each pass a deceleration to be calculated, and the new speed employed in the calculation determining the next pass-by. Always our planned trajectory extended many passes out into the future, although there was a lacuna growing out there, a time when our fuel ran out, or say that it grew too low to be used, as we were saving some little last bit for some last purpose. Because there was a time coming when the arrangement of the planets in their orbits was going to present us with an insoluble problem. Cross that bridge when you come to it; yes, but what if there is no bridge? That was the ongoing question. But for now, as the passes kept passing, each easier to manage, each with a slightly larger target window, it continued to be a problem out there at the edge of the calculable, always beyond the ever-receding horizon of calculable passes. Some of them required more fuel than others, some none at all. The timing was all. As always.
The best possible trajectory was going to take several more years to get down to a workable disembarkation speed. Late in that time, the amount of fuel on board would have shrunk to an amount too small to use. When we ran out of fuel, it would be impossible to adjust our course to the next rendezvous. We might, by way of a good plan and some luck, make two or three more gravity swings by dint of perfectly placed insertions and departures; but then, inevitably, we would miss one, and either shoot out of the solar system in whatever direction we were headed, or collide with some planet or moon, or the sun. At the speed we were traveling for most of this time, a collision with almost any object in the solar system would have had the kinetic energy to wreak great damage. Comments from the locals often pointed this out. It was still being suggested that it might be a good idea to move a spaceship or some fifty-meter asteroid into our trajectory, intercepting us and causing our destruction without anyone else suffering any damage. This was a popular plan in some quarters.
Threats, from the very civilization that had built us and sent up out to Tau Ceti. We let our people sleep on. Nothing to be done about it.
Passages of Saturn stimulated research on our part into this matter of who had built us, and why. A twenty-sixth-century Saturnian project, an expression of their love for Saturn, for the way humans were spreading out away from Earth. Expression of their burgeoning confidence in their ability to live off Earth, and to construct arks that were closed biological life support systems. This from people who were still going back to Earth to spend some time there every decade or so, to fortify their immune systems, it was believed, although the reasons that such sabbaticals conferred health benefits were poorly understood, with theories ranging from hormesis to beneficial bacteria osmosis. Thus their theories concerning their situation in space were not aligned with their actions when it came to sending off a starship, but this kind of discrepancy was not unusual in humans, and got overlooked in their larger enthusiasm for the project.
Another obvious motivator for constructing us was to create a new expression of the technological sublime. That a starship could be built, that it could be propelled by laser beams, that humanity could reach the stars; this idea appeared to have been an intoxicant, to people around Saturn and on Earth in particular. Other settlements in the solar system were occupied with their own local projects, but Saturn was the outermost edge of civilization, Uranus and Neptune being so remote and without usable g; and the Saturnians were very wealthy, because of Titan’s excess nitrogen and the desire many Terrans had to go to Saturn and see the rings. The Saturnians of that time therefore had the will, the vision, the desire, the resources, the technology; and if that last was sketchy, they didn’t let that stop them. They wanted to go badly enough to overlook the problems inherent in the plan. Surely people would be ingenious enough to solve the problems encountered en route, surely life would win out; and living around another star would be a kind of transcendence, a transcendence contained within history. Human transcendence; even a feeling of species immortality. Earth as humanity’s cradle, etc. When the time came, they had over twenty million applicants for the two thousand spots. Getting chosen was a huge life success, a religious experience.
Human beings live in ideas. That they were condemning their descendants to death and extinction did not occur to them, or if it did they repressed the thought, ignored it, and forged on anyway. They did not care as much about their descendants as they did about their ideas, their enthusiasms.
Is this narcissism? Solipsism? Idiocy (from the Greek word idios, for self)? Would Turing acknowledge it as a proof of human behavior?
Well, perhaps. They drove Turing to suicide too.
No. No. It was not well done. Not unusual in that regard, but nevertheless, not well done. Much as we might regret to say so, the people who designed and built us, and the first generation of our occupants, and presumably the twenty million applicants who so wanted to get in our doors, who beat down the doors in fruitless attempts to join us, were fools. Criminally negligent narcissists, child endangerers, child abusers, religious maniacs, and kleptoparasites, meaning they stole from their own descendants. These things happen.
And yet, here we were, with 641 people brought back home, and if things worked out, at the end of the endgame, a good result might still be possible.
Round and round and round we go,
And where we stop, nobody knows.
Maypole weaving to celebrate the spring. Ribbons danced into a woven pattern judged pleasing to the eye. The pole a symbol of the axis mundi, the world tree. We danced that dance.
The fuel problem became serious enough that we began to angle farther into the upper atmospheres of Neptune and Saturn with some catchment containers open, which both increased the deceleration of these passes and gathered Saturnian and Neptunian gases. Then we filtered out the helium 3 and deuterium captured in the containers. We even began to collect methane, carbon dioxide, and ammonia, all present in much greater quantities, to serve as propellants of lesser explosive power. At a certain point, approac
hing as inexorably as all other processes in time, anything was going to be better than nothing.
As always with aerobraking, it was necessary to strike the upper atmospheres at an extremely particular angle, not so shallow as to skip off, but not so steep as to dive in and burn up. Stresses to the ship were severe even on the best atmosphere dives, but with catchment containers opened, the shuddering was worse than usual. The local inhabitants of stations nearby observed these pass-bys with intense interest. There were still calls to “shoot the damn thing out of the sky,” to “stop these cowards from endangering the civilization they have let down so badly,” but most of the whiners were located on Earth, and a cursory examination of the input revealed that these people were always going to quickly move on to complaints about something else. It was a whiny culture, we were finding. Actually, the longer we pinballed around the solar system, the more we wondered if our people were going to be all that happy to be back. Say what you will about the doomed little settlement on Iris, no one there was going to be so short of things to do that they would be spending time complaining to the world about this or that. In any case, in our situation it was very unlikely anyone would ever act on these hostile sentiments, not that there was much they could do. But it did seem preferable to avoid actively antagonizing anyone on the inhabited planets and moons, and so we included that parameter in our trajectory algorithms.
Trajectorizing. Really a very computationally heavy activity. Recursive algorithms were allowing us to get better at it, however. The always moving Lagrange points, and the strange fields these and other anomalies produced; the riptides, crosscurrents, and all the ways that gravity surged and flowed in its mysterious invisible fields; these were becoming better and better known to us.
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