Shaft 3 was nearly finished, a yawning pit like a dead eye socket. The first group of sleep slots would be going down that way soon. A kilometer of sheltering ice would shield the sleepers from the fatal sting of cosmic rays and the sleeting solar storms.

Random gouges surrounded the shaft. Discharging mech fuel cells had pitted the crusty ice. Broken gear lay where teams had dropped it. Chem spills had condensed into powdery green and yellow splotches. Discarded girders and sonic cartridges and shockjackets lay everywhere. What mankind would study Carl thought wryly, he first messes up.

Just barely visible over the curved horizon, now slowly coming into view along the dawnline, were the black gas-suppression panels. They were an ongoing experiment, armored against the high velocity dust streams and designed to generate electricity from sunlight. Their shadows reduced the outgassing from one-eighth of Halley Core’s surface, introducing an asymmetry in the boiloff. The panels could be turned so that they trapped heat, too, increasing the outgassing on the night side of the core. The net effect was a faint, persistent push that could alter the comet’s orbit, given time.

Or so the story went. To Carl the big black panels had been one solid week of grunt labor. They were too delicate to let the mechs do more than hold them in place, while he and Lani Nguyen and Jeffers had mounted them to the robo-arms that would turn them. The astroengineers were still tinkering with the gimmicks piling up data to analyze during the long outbound voyage.

It was hard to tell what was an intentional experiment and what was yesterday’s garbage. He wondered how messy Halley Core could get. In nearly eighty years they might thoroughly trash even this much ice.

Carl could see a thin black stripe coming out of shadow at the dawnline—the polar cable. It wrapped around Halley Core, pole to pole, and joined the equatorial cable at a perfect right angle, but separated by several meters for safety. The rails provided swift ways to zip around the surface. Still, Carl seldom used them. He liked to get free of the bleak ice, swim in serene blackness above it all.

Between him and the slowly spinning, potato-shaped iceworld were the swarming mechs he supervised. He thumbed instructions into his lap console, muttering code phrases automatically, making the distant dots turn their burden—a huge orange cylinder. Its smooth sheen reflected glinting sunlight.

—Channel D to Osborn. Real pretty, uh?—Jeffers sent from below.

“Well …”

Awful color, he thought. And it’s the inner-corridor lining. We’ll have to look at it for seventy years.

The mechs dropped lower, angling the cylinder for Shaft 3, following his instructions. The potato-like shape of Halley Core revolved every fifty-two hours, just fast enough to make readjustment necessary as they approached. Subliming gas still rose from some of the active patches the scientists called “Sekanina-Larson” regions, making visibility hazy and creating a hazard of high-velocity dust. The thin fog blurred images at this distance—8.3 kilometers, his board said-and made it hard to use his automatic aligning program.

He had backup on the Edmund, in case of a malf. Fine, in theory. But by the time he got somebody online, the mechs might dutifully try to stuff the cylinder into a hill of ice. Despite Virginia ’s earnest faith, computers could do only so much. From there on you had to eyeball it.

“Bringing it in slow,” he sent.

—Looks vectored up just a hair. Two clicks too high along the local y-axis,— Jeffers replied.

Carl looked down, recalibrated, saw that Jeffers was right. “Damn.”

—You okay?—

“Yeah. Just keep those beacons going.”

The four laser aligners bracketed Shaft 3 clearly, and Carl turned the mechs into configuration using the bright markers. A touch of delta V, a compensating torque. His board approved the shift. Good. But now the irregular ice was looming fast, and—

Gravity. He’d forgotten the damn gravity. Halley Core had only a ten-thousandth of Earth’s pull…but in his half-hour decent from the solar-sail freighter the momentum had built…slow but steady…He punched in a correction, watching the equations ripple across his board.

Lights flashed red. “I’m braking;” he sent, and fired the mechs’ retros.

Damn the gravity anyway. Carl had been at Encke, worked around the rocky comet nucleus for weeks. It had been just like any deep space work—sometimes almost an elaborate waltz, smooth and sure, and a lot of grunt and sweat at crucial moments. Still, it was basically easy if you watched that your vectors matched, didn’t push anything except at its center of mass, worked steadily, kept your head.

But Encke was a runt. An old prune of a comet, broiled by its long stay in the inner solar system. Halley had a lot more mass, mostly ice. On the surface you never noticed the slight tug, but coming in like this, taking your time to aim carefully, that ten-thousandth of a G could add up.

The mechs’ blue jets fanned against the backdrop of ice, slowing the cargo. Carl saw suddenly that it wasn’t enough. The ponderous, hundred-meter-long cylinder was coming in too fast.

He ordered the lower portwise mech to turn and thrust at full bore. The unit spun, fired its reserve.

—What the hell you— Jeffers began.

“Clear the shaft!”

— What—

“Clear it!”

Standard procedure was to bring cargo to rest about fifty meters out, then nudge it in. His board said that was impossible. Instinct told him to try for something else.

He jetted forward, nearly caught up with the cylinder. A touch from the lower starboard mech, two quick torques here, a jolt sidewise to line her up—

An arrow from on high, aimed at a puckered black circle.

The orange cylinder struck the lip of Shaft 3, slowed—broke off an edge of ice—and drove on in, scattering flakes off into space.

Bull’s-eye, he rejoiced as the cylinder disappeared within the hole.

Jeffers cried out, —Hey! What’s the idea?—

“She got away from me.”

—Hell she did! You’re showin’ off, is all.—

Carl pulsed his own jets and landed easily, feet down. “Don’t I wish! Nope, I just corrected at the last minute. Figured it was better to try for a clean hit than to burn fuel decelerating. Especially since I couldn’t stop it anyway.”

Jeffers shook his head, exasperated. —Show-off,—he insisted, and went to check for rips in the material.

There weren’t any. Slick and snag proof, fiberthread could wriggle around sharp edges, which made it good for lining the snaking tunnels inside Halley Core.

The fifteen members of the Life Support Installation Group had ten days to honeycomb a fraction of the north polar region, line the shafts and tunnels with pressure-tight insulation, then flush it with air. Not long enough. And all that time the newly awakened scientists aboard the Edmund would be chafing.

Even with 112 mechs it was going to be a tight schedule. There were only so many hands to guide them. The entire expedition had only 67 “live” members at present. Nearly 300 more lay in the sleep slots, their body temperatures hovering within a degree above freezing.

Overhead, the spindly tugs waited with their human cargo. Their immense, gossamer solar sails were furled now, not needed for seventy years. Beside the whalelike Edmund, the silvery Sekanina, Delsemme, and Whipple looked like patient barracuda.

Still no word on the Newburn, Carl thought. How could it have gotten lost?

—You guys all right?— Lani Nguyen’s light, tinkling voice came from somewhere.

Carl looked around and found the speck rapidly growing as she sped along the polar cable. She had one arm clamped on the stay-carry while she waved with the other, looking remarkably like a bird skimming the ground with only one wing flapping.