“One wave every fifteen hours?” Swan asked.

That was enough, the locals assured her, grinning crazily. She wouldn’t need more. The rides went on for hours.

“ Hours?” Swan said.

More crazy grins. Swan turned to Wahram, and as usual could not read his stone face.

“You’re going out too?” she asked.

“Yes.”

“Have you done it before?”

“No.”

She laughed. “Good. Let’s do it.”

The rings could be modeled mathematically as a fluid, and from any distance they looked like a fluid, grooved by tight concentric waves. Up close one could see that the F ring, like the others, was made of ice chunks and ice dust, layered in ribbons that thickened and thinned in masses of individual bodies, all flying at almost the same speed. Gravity: here one saw its effects in a pure state, unobstructed by wind or solar radiation or anything else—just the sling of spinning Saturn and a few small competing tugs, all creating this particular pattern.

Prometheus was a perfect put-in spot for the surfers, and the ones going out with Swan and Wahram informed them they were both going to be launched into the wave with experienced veterans going before and after, to keep tabs and give help if needed. They offered tips for how to catch the wave, but Swan nodded agreeably and forgot their advice: surfing was surfing. You needed to catch the break at its own particular speed, and off you went.

Then they were all suited up and jetting out a lock. The white jumbled wall of the F ring was right there next to them; streamers of denser clusters of rubble were braided and kinked, but the entire mass was extremely flat—no more than about ten meters north to south relative to Saturn. Those ten meters were not the height of their wave but its width—which meant one could pop out of the ice at any point and be spotted and picked up if one was having any kind of trouble. Most of the waves Swan had ridden before were not like that, and she found it reassuring.

They jetted closer and closer to the white wall, until Swan could see discrete ice chunks very clearly, ranging in size from sand grains to suitcases, with the occasional chunk of ice furniture—desk, coffin—tumbling in the midst of things. Once she saw a temporary agglomeration about the size of a small house, but it was coming apart even as she spotted it. And now a white curl of banner was detaching from the wall and flowing down toward Saturn, which though bulking hugely below them was of no interest at all.

Swan tested her jets as she flew toward the wave, pressing with fingertips like a clarinet player, jinking forward in a little sashay of her own device. Suit jets were about the same everywhere. She focused on the approaching wave, which was lifting up and over her like Hiroshige’s wave; this one was ten kilometers high, and rising fast. She needed to turn and accelerate in the direction it was going, but not so quickly that she stayed ahead of it. This was the tricky part—

Then she was in the white stuff and being struck by the bits. She jetted a bit to keep her head out of stuff, as if bodysurfing out of a spume of broken salt water, but it was chunky stuff and she felt herself being thrust forward by little hits from little bits, rather than a mass of water. Then she was at speed with the wave, her head emerging from it so she could look around—very like bodysurfing, and she had to laugh, she had to shout: she was flying in a wave of ice ten kilometers high. She hooted at the sight, she couldn’t help it. The common band was raucous with the other surfers’ yelling.

The wave was really more a slice of a wave, only as wide as a room, and it sometimes felt only a bit thicker than she was—a two-dimensional wave, so to speak, so that it seemed one could get hit sideways, or jet at a slight tangent, and accidentally shoot out the side of it. So it would not do to submerge completely back into the white stuff, dolphin style. Maybe some of the other riders were doing it, but she felt she could get lost in there. Besides, she wanted to see!

She could feel the wave lifting her and casting her along. It was not only being struck by ice chunks, but also being tugged by gravity. The feel of the ice was like getting lightly pummeled by pebbles, which together were knocking her forward. Possibly one could ride a big surfboard on the push of this mass, direct the ride with one’s feet; indeed she saw down the wave someone standing on a thing like a coracle, riding in that very manner. But most of the others were bodysurfing like she was, perhaps because you needed a suit’s jets to make the best moves. In any case she had always preferred bodysurfing to surfing on boards. To be the object of flight, to cast yourself out into the spaces you breathed, and although motionless be flying at speed, slung forward—

The wave pitched and she was knocked forward faster than ever. Most of the chunks were between tennis balls and basketballs in size, and if she emerged on her jets until only her feet were in the mass, she could hop on bigger chunks and propel herself with little jumps forward and out. The wave was still surging up, but it was like the wake of a boat, in that there was no bottom to catch the submerged half of the wave and cause the upper part to curl and break. So from now on it would lose energy, and eventually dissipate without ever breaking. Too bad in a way, but now it was time to dance!

She jumped onto larger pieces when opportunities presented themselves, and with one jump after another got just where she wanted to be, on the border between the white flock of ice and the empty black space it was rushing into; and then she was dancing on white boulders, glissading on a kind of moving scree, as if running down a mountainside that had gone liquid. She laughed briefly as she got the hang of it. There was still a lot of hooting and hollering on the common band. The figure nearest her was possibly Wahram, hopping along with remarkable agility, like the dancing hippos in Fantasia. She laughed to see it. She could feel Prometheus tugging her along; this must be what a pelican felt like, surfing the air pushed up by a water wave. A gravity wave, throwing her through the universe. The howls of the other surfers sounded like wolves.

Back under the dome on Prometheus, out of their suits, Swan gave Wahram a sweaty hug. “Thank you for that!” she said. “I needed that! It reminded me that… it reminded me… Well. It was good.”

Wahram was red-faced, puffing with exertion. He nodded once, his mouth pursed in a solemn little knot.

“Well what did you think?” she cried. “Did you enjoy it?”

“It was interesting,” he said.

Lists (9)

Boosters to get off planets, Earth especially, need high thrust

Orbit-to-orbit interplanetary rockets need high exhaust velocity to save on fuel weights.

Deuterium-helium-3 fusion spheromak engine, built on Luna, use began in 2113;

Antimatter plasma core, magnetic bottle, Martian design, 2246;

Deuterium-tritium fusion, with lithium-blanketed core to create more tritium in the burn, Luna, 2056; two have lost thrust chamber integrity and exploded with loss of all hands;

Laser thermal, mainly used within the Jupiter and Saturn leagues for local transport, 2221;

Mass drivers for the terraria, 2090; often called the workhorse;

Inertial confinement fusion, Mars, 2237;

Micro-fission Orion format, subcritical pellets of curium-245 compressed to fission by Z-pinch, magnetic thrust to the pusher plate of the rocket, Callisto, 2271;

Orion style (external pulsed plasma propulsion), Luna, 2106

Magnetoplasmadynamic engine, propellant potassium seeded helium, Callisto, 2284;