Two down, three to go!

Ah, but five more hibernauts died in that pass. Dewi, Ilstir, Mokee, Phil, and Tshering. Nothing to be done about it, we were doing the necessary, as Badim would have put it, but such a shame. We knew and enjoyed those people. Had to hope they were not engaged in a dream at the time, a dream suddenly turned black: sledgehammer from the sky, an immense roaring headache, the black noise of the end come too soon. So sorry; so sorry.

Nevertheless, it was imperative to collect oneself and prepare for Saturn, there on a long beam reach, and despite the really useful and heartening decelerations achieved so far, it was still soon to come, only sixty-five days to prepare, and as we were coming in on the plane of the ecliptic, it was going to be important to miss the famous rings, which luckily are in Saturn’s equatorial plane, which is offset to Sol’s equatorial plane by several degrees, meaning we did not have to do anything but be sure to make a very tight pass of this gorgeous jewel of the system, which was our intention anyway. We were only going to turn a few degrees, and so would duck inside the innermost ring and be on our way.

And indeed, as we approached the ringed planet and the little civilization of settlements on Titan and many other moons, the civilization that had in fact built us and sent us on our way almost four centuries earlier, and also had reactivated the laser lens that had slowed us down enough to try our maneuvers now, it was a pleasure to say hello, even in passing. It was also a pleasure, not just to hear the various welcomes from the Saturnians, but also to hear nothing from the planet itself, for unlike Jupiter, Saturn has a very low amount of internal radiation. Indeed it was a quiet and cool pass-by, compared to the previous two, and the main feature of interest was the quick view of the rings, so immensely broad in reach while at the same time so thin in cross section, a great gift of gossamer gravitation, much less thick than a sheet of paper by proportionate comparison, indeed if it were reduced to a round sheet of paper in size, it would have been mere molecules thick. A natural wonder of circularities, like a physics experiment or demonstration, nicely displayed to us as we passed. And given its smaller mass, our slower speed, its coolness, and the smoothness of its upper atmosphere during our aerobraking, this was by far the calmest pass yet, maximum g-forces just 1 g, and an easy slight turn for the next leg out to Uranus. At this point we were only going 120 kilometers a second. Still fast in local terms, it was also true that we had a bit more time before our next pass would occur, which was to say ninety-six days. And no human or animal died.

On the way out to Uranus, we tried to come to grips by way of modeling with the fact that our pass-by of that lightly banded and ringed giant was going to be different, because it rotates transversely to the plane of the ecliptic; its axis of rotation is such that it rolls around the sun like a ball, a strange anomaly in the solar system, an anomaly the cause of which a cursory inspection of the literature suggested was still poorly understood. What it meant now for us was that if we did the usual aerobraking, which indeed we had to do, as it was necessary for our continuing effort at deceleration, we would be punching through several of the planet’s latitudinal bands, created by winds each rushing in the opposite direction to those above and below it, as on Jupiter; and so at each border between bands there would be a similar area of wind shear and atmospheric turbulence, well represented by the wild band borders of great Jupiter. Perhaps not a good idea!

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.