But you can’t go any deeper, Lieserl. Your design… the wormhole will implode if you try to penetrate the radiative zone…

“Maybe. Well, it’s up to you to sort that out, Kevan.”

She swooped up to the glowing roof of the cavern, and plunged down, at hundreds of miles a second, toward the plasma sea, past the slow-pulsing flanks of giant p-modes.

Like an insect circling an elephant the pod skimmed around the hull of the Great Northern.

Mark Wu, Louise Armonk, Garry Uvarov and Serena Milpitas sat and watched as their tiny pod skirted the starship. Their silence, Mark thought, was suitably deep and awe-struck, even for four who had been as close to the final stages of the project as these. And maybe that was Louise’s intention today, he thought, the subtext under what was ostensibly a simple inspection tour of the ship by her top management team.

Well, if so, she was certainly succeeding.

The lifedome of the Northern was a squat, transparent cylinder a mile wide. It was extraordinary to think that the whole of Michael Poole’s GUTship — drive section and all — would have fitted inside that sparkling box; Mark tried to imagine the Hermit Crab suspended in that great cylinder like some immense model under glass.

Mark could see clearly the multiple decks of the dome, and throughout the dome there was movement and light, and the deep, refreshing green of growing things. He was aware that the adaptation of much of the dome, and the rest of the ship, was still unfinished; most of what he saw was little more than a Virtual projection. But still he was impressed by the scale and vigor of it all. This lifedome would be a self-contained city — no, more than that: a world in itself, a biosphere suspended between the stars.

Home to five thousand people for a thousand years.

Now they wheeled to the underside of the lifedome. The pod approached the immense, tangled structure of the Northern’s main spine, and flew parallel to the spine for some three hundred yards toward the base of the dome.

The spine was a three-mile highway of metal littered with supply modules and antennae and other sensors, turned up to the distant stars like mouths. Behind them the spine led to the mysterious darkness of the drive section, where the lights of workers — human and robotic — crawled like flies. And, attached to the spine by bands of gold just before the drive section, was the huge Interface, the wormhole terminus which they would tow to the future. The tetrahedral frame looked like a gaudy, glittering toy of shining blue ribbon.

Uvarov spread his long, intelligent fingers and rested his hands against the gleaming hull of the pod. “Lethe,” he said. The pod’s lights struck highlights from his bony profile as he peered out at the spine. “It might not be real, but it’s beautiful.”

Louise laughed; beside the thin, gaunt eugenicist she looked short, compact, Mark thought. “Real enough,” she said. “The spine’s framework is a hundred percent realized. It’s just the superstructure that remains nebulous.” She thought for a moment, then called, “Configure 3-B.”

The flower-like antennae clustered along the spine melted away, dissolving into showers of pixel cubes which tumbled like snowflakes. For a few surreal seconds Virtual configurations of equipment modules blossomed over the spine; through the snowstorm of modules Mark could see the basic — and elegant structure of triangular vertebrae at the core of the spine.

At last the storm of images stilled; the spine settled into a new scattering of lenses and antennae. To Mark’s untutored eye this looked much the same as the original — perhaps rather sparser — but he became aware that Serena Milpitas was nodding, almost wistfully.

“This is the original configuration,” she said. “It’s what was planned when the ship was being designed for its oneway hop to Tau Ceti, just a century away.”

Mark studied Milpitas curiously. The project’s new chief engineer affected physical-forty, but Mark knew she was at least twice as old as that. He also knew there had been quite a bit of friction between Milpitas and Louise; so he was surprised to find, now, Milpitas praising Louise’s design. “You sound a little — nostalgic. Do you really think this is a better design?”

“Oh, yes.” Milpitas’ broad face split in a smile; she seemed surprised by the question. “Don’t you? Can’t you see it?”

Uvarov grunted. “Not particularly.”

“Inelegance was forced on us. Look — for a thousand-year flight the problems of reliability are enormous.” Her accent was broad, confident Martian. “This ship has around a thousand million distinguishable components. And all of them have to work perfectly, all of the time. Right? Now, we estimate that the chance of a significant failure of any one of those components — of a failure serious enough to knock out a ship’s system, say — is a tenth of one percent per year. Pretty good odds, you might think. But as the years go by the chances of a failure mount up, and they work cumulatively.” She fixed Mark with a direct stare. “What would you guess the chances of such a failure would be after a hundred years?”

Uvarov growled, “Oh, please, spare us games.”

Mark shrugged. “A few percent?”

“Not bad. Ten percent. Not wonderful, but liveable with.”

Uvarov clicked his tongue. “I hate your Mons Olympus grammar, engineer.”

Milpitas ignored him. “But after a thousand years, you’re looking at a failure probability of over sixty percent. You reach fifty-fifty after just seven centuries — ”

“What she’s trying to tell you,” Uvarov said heavily, his flat Lunar tones conveying his boredom, “is the obvious fact that they’ve had to perform extensive redesign to enable the ship to survive a thousand-year flight.”

“How? Louise doesn’t tell me a damn thing.”

Uvarov grinned. “Ex-wives never do. I should know. I — ”

Milpitas cut in, “With current technology, we couldn’t get the reliability rates high enough for the mechanical, electrical or semisentient components.” She waved a hand at the half-Virtual panorama beyond the hull. “Amazing, isn’t it? We think we’ve come so far. We thought that with nanobotic technology continual repair and replacement at the sub-visible level — reliability problems were a thing of the past. I mean, look at that spine out there. There’s sentience in it everywhere, right down to the nuts and bolts.”

“There are no nuts and bolts, Serena,” Louise said drily.

Milpitas ignored her. “And yet it doesn’t take much of a challenge to move us beyond the envelope of our capabilities. Strictly speaking, a thousand-year flight is still beyond our means.”

“That sounds ominous,” Mark said uneasily.

“So,” Louise said, “we had to look to the past — simple methods used to improve reliability on projects like the first off-Earth flights.” She called out, “Central configuration,” and the blizzard of virtual components swirled once more around the spine, settling at last into the pattern Mark remembered from before Louise’s change.

Milpitas pointed. “And this is what we’re going to the stars with. Look at it. Even at this gross macroscopic level you can see there are many more components.”

And, indeed, Mark realized now that there were more antennae, more sensor snouts, more maintenance pods; the spine structure looked busier, far more cluttered.

“Triple redundancy,” Milpitas said with a grimace. “Words — and a technique from the twenty-fifth century. Or further back, even, for all I know; probably from the time of those disgusting old fission reactors. Carrying three of everything — or more, for the key components — to reduce the chance of a catastrophe to the invisibly small.”

“Gripping,” Uvarov said. “But shall we move on, some time today? We do have the whole of the ship to inspect, as I recall.”