Second Genesis gq-2

by Donald Moffitt

  The boy did some quick figuring in his head. “Four thou—but that would make them lighter than air!”

  “Correct. About three and a third times lighter. In fact, they have a density of only about twice that of helium, on average.”

  “But that’s impossible.”

  “I said on average.”

  Smeth bustled over. “One might posulate that they’re hollow, or honeycombed, or a gas enclosed by a membrane. Or made of a rigid, infinite-length polymer with properties we can’t imagine.”

  “What could be that light—and strong enough to maintain its shape over interplanetary distances?” the boy said.

  Jao stared out the window at the strange floating circles that had taken the place of most of the sky. His face was flushed with excitement.

  When he finally spoke, it was in Bram’s direction. “We’ll have to land on one of them to find out, won’t we, Captain?”

  Bram kissed Mim good-bye, feeling self-conscious in front of all the spectators. A crowd of about two thousand was jammed into the cavernous hangar, waiting to see the takeoff, and the rest of the population of the tree must have been watching on their holo sets. Bram could see the camera crew perched high on the spidery platform of an interbranch shuttle vehicle, where they had an overall view.

  “Be careful,” Mim said, pressing herself against the tough hide of his vacuum suit. “I wish you weren’t going this trip.”

  He embraced her one-armed, his bubble helmet tucked under the other arm. “The year-captain’s expected to lead the way,” he said. “That’s why they elect him. But don’t worry. Lydis is the best landing craft pilot we have—and it’s not going to be like landing, anyway. It’ll be more like docking with a nonrotating branch. She’s practiced it in the simulator a hundred times.”

  “But it’s spinning.”

  “So slowly at the rim that it makes practically no difference. You’re thinking in terms of a body like Yggdrasil, with a diameter only a few hundred miles across. In this case, the spin isn’t there to provide gravity. It cancels it. So when we match for it, we’ll touch down as lightly as a leaf.”

  “I’d still feel a whole lot better if I knew you were landing on the flat side.”

  A few feet away, under the skeletal arch of a landing leg, Jao left off nuzzling a clinging Ang and looked across her golden head toward them.

  “That’d be a lot trickier, Mim, even though it looks simpler,” Jao boomed past Ang’s ear, making her wince. “Your normal instincts don’t apply on a body as bizarre as that. Neither do your first mathematical assumptions about up and down. Landing anywhere between the hub and the rim on a disk-shaped body would give Lydis some complicated gravitational gradients to cope with. The vertical component and the horizontal component don’t behave the same way in relation to the center of gravity. And then there’d be the added factor of centrifugal force tending to make us slide outward, though we don’t think it’d exceed the diagonal gravitational vector tending to pin us down. To say nothing of all sorts of unpredictable edge effects to get past before we could cross to those interesting structures on the rim. No, Mim, this is the simplest way. We’ve got it all worked out.”

  Bram had felt Mim stiffen at Jao’s mention of “sliding outward” and “edge effects.” He turned it into a joke. “What Jao’s really worried about is having to hike across a ninety-million-mile plain to get to where we’re going.”

  She smiled gamely. “I guess I don’t understand physics.”

  “That’s all right, Mim, I don’t understand Bach,” Jao said.

  “Don’t worry, we’ll be very careful,” Bram told her, “and we’ll be locked in to Jun Davd and his computer the whole time.

  The third member of the exploration team, a dour geologist, named Enry, pushed his way through the well-wishers and said apologetically to Bram, “Lydis says she’s about ready. Says it’s time to get these people out of here and climb aboard.”

  Enry stood there, stolidly waiting. He was a blocky, square-jawed man who long ago had been a touch associate with a geology touch group on the Father World. Though the Father World no longer existed, Enry had never given up his speciality; he pored over the old Nar records in the library and published a monograph every quarter century or so. He was the nearest thing to an expert the tree possessed, and he handled himself well physically in the null-gravity sports at the trunk’s center. Bram had thought of him immediately when choosing the exploration team.

  “All right,” Bram said. He gave Mim a final peck that turned into something more as their lips touched again, then went with Enry to pry Jao loose from Ang.

  A warning blast came from a two-tone bass whistle. Exasperated monitors wearing headbadges rushed back and forth, trying to shoo lingering spectators out of the drop area.

  “Behind the ropes, behind the ropes! Everybody behind the ropes! Other side of the air curtain track!” The crowd moved as sluggishly as sap. “Keep it moving, keep it moving, unless you want to breathe vacuum!”

  Bram got Enry and Jao started up the landing leg ladder with their gear and was preparing to climb it himself when he became aware of a disturbance at the fringe of the retreating crowd. A small, agile figure was darting past the monitors, getting chased by them, and darting back into the forbidden area. The interloper evaded a pursuer and made a beeline for the base of the ladder.

  Bram saw corn-yellow hair flying and green eyes on either side of an upturned nose and recognized his great-great-great-granddaughter. “Ame!” he exclaimed. “What are you doing here?”

  “I’m going with you,” she announced. “Here, take this.”

  She unslung a lumpy shoulder bag and thrust it at him. The clinking sound of some kind of equipment came from within.

  “You can’t,” he said. “We don’t know what we may run into. Anyway, it’s only a scouting trip. You’ll have plenty of opportunities to go along on the later landings, like everybody else.”

  “That’s the point, Bram-tsu. You ought to have a palentogist along on your first survey, and I’m the only authentic specimen you’ve got.” She grinned engagingly at him. “Besides, I’ve turned myself into a pretty fair geologist, so I’ll carry my weight.”

  “We’ve got a geologist, a good one.”

  “Oh, Enry knows his subject, I’ll give him that. But his subject’s the Father World. Those disks out there are something nobody’s an expert on. But my group’s been doing theoretical studies for twenty years now—you’d be surprised at some of the computer simulations we’ve come up with!” She wrinkled her nose. “We really ought to have an archeologist with us, too.”

  “An archaeologist, is it? Spare me! A theoretical paleontologist’s farfetched enough on a preliminary scouting expedition like this.”

  “Does that mean you’ll—”

  A monitor came puffing up, a man with a broad, law-abiding face and a long-suffering expression.

  “Sorry, Captain. She slipped past us. I’ll get her out of here.”

  Ame turned on him. “I’m not going with you. I’m going aboard, isn’t that right, Bram-tsu Captain?”

  The monitor looked doubtfully at the lightweight knee-lengths and slipover she was wearing. “If you want, I can get one of the other safety marshals and we can escort her forcibly.”

  “No, it’s all right. I’ll talk to her,” Bram said. “Go on, Marshal, I’ll take responsibility for sending her back.”

  The monitor raised a quizzical eyebrow and withdrew. Bram turned to Ame. “You haven’t rehearsed with us. There’s the question of equipment—”

  “Oh, that! There are spare space suits in the ship, and one of them is bound to fit me—it isn’t as if they had to be custom fitted. I’ve ridden with Lydis lots of times before—on trips to other branches and even to the probe. And when it comes to that, I’ve spent as much time in vacuum as anybody. If I can climb around the branches under spin, I ought to be able to manage on one of those nice flat things out there.”

  Bram refrained
from bringing up Jao’s speculations on the nature of disk gravity gradients. “Are you sure you want to leave the twins alone for that long?”

  “Smeth will take care of them. They adore him. He spoils them like mad. They’re two years old now—they don’t need to have me around constantly.”

  Bram sighed. “Everybody and their gene sibling wanted to be included on this trip. I almost had a riot. I had to promise that if there are no problems, everyone who wants to will get a turn while we’re parked in this orbit. And here I am, giving preference to a descendant. They’ll have my hide for nepotism.”

  “I can go, then?”

  He gave in. “Your great-great-grandmother is the pilot. It’s her decision. If she says you can go, then you’re on. Otherwise you promise to leave quietly, all right?”

  “I promise.”

  Above, Jao stuck his head out of the hatch. “What’s holding you up? Lydis’s already lost a turn while you’ve been palavering.”

  Ame scrambled up the landing leg ladder, with Bram behind her carrying the sack of equipment. It was bulky; he felt the handle of a digging tool through the fabric as it swung against his hip.

  At the top, Bram twisted around and caught sight of Mim waving to him from the other side of the barrier. He waved back and squeezed through the hatch after Ame.

  Jao filled the air lock, huge and grinning. “Stay here a minute with her,” Bram said, “while I—”

  “Lydis says it’s okay,” Jao said. “Let’s get going.”

  A great rumbling sound filled the bay as the curtain rolled around its track and sealed off the cylindrical launch chamber. The crowd on the other side would be streaming toward holo monitors to watch the drop as relayed by the exterior pickups.

  Bram turned sternly to Ame. “You had it all arranged with her in advance, didn’t you?”

  She wrinkled her nose at him. “She said you’d only be stuffy about it, and she was right.”

  Bram shrugged and sealed the outside hatch, then, after herding Jao and Ame through the air lock, screwed the inner lid into place.

  He looked around the dome-shaped cabin. The landing vehicle was basically a squat hemisphere supported on five arched legs. It had started out as a Nar design with the pilot’s seat in the middle, but like the rest of the considerable fleet the tree had been stocked with, its interior had been rearranged during the intergalactic crossing to give it something resembling front-back orientation, and the controls had been shifted to conform to human morphology. Lydis and her copilot sat facing one of the five bulging ports—the one that had been designated “forward.” The rear of the cabin contained passenger couches—more than the current mission profile called for—storage, equipment, and minimum amenities.

  “You have exactly ten minutes to tie yourselves down,” Lydis said. “I don’t intend to sit here for another go-round.”

  “Sorry,” Bram said.

  He nodded to his daughter’s co-pilot, a wiry, nonchalant fellow named Zef, then helped Enry and Jao stow their gear. Ame went to a locker and helped herself to a spare vacuum suit. While she struggled to get into it, Bram hefted the clanking sack she had given him and, after a moment’s reflection, shoved it into a padded locker. “I hope there’s nothing breakable in there,” he said.

  “Nothing very breakable,” she said.

  They climbed onto their couches and fastened the armpits-to-hips webbing in place. Jao cranked his couch to a sitting position.

  “I want all you treelubbers to lie prone for the drop,” Lydis said. “And while you’re at it, put your helmets on.”

  She herself was sitting upright, as was Zef. Jao pointed that out.

  “You do everything by the list when you ride with me,” Lydis said. “Otherwise, you can get out and walk.”

  Grumbling, Jao complied.

  “It’s surprising, the number of things that can go wrong,” Zef said cheerfully. “Why, I saw a fellow explode once because he forgot to screw his helmet on all the way and nobody’d told him the cabin wasn’t going to be pressurized that trip.”

  “Oh, stow it,” Jao said. “I’m not falling for any more of your stories.”

  Zef laughed. “It’s not that we care about the safety of our passengers. We just don’t want a lot of helmets floating around and bumping into things.”

  Jao started to reply, but his voice was cut off as Lydis watched the passengers off the Talk circuit. Abruptly Zef dropped his smile and became all business. Bram found himself gripping the armrests of his couch. Drop must be imminent.

  He was still plugged into the Listen circuit, though. He could hear Lydis talking to Jun Davd back in the observatory.

  “I have your readout,” she said. “Please confirm.”

  “Three minutes more and you’ll be in optimum drop position. As tangent as you can get. Do you want the computer to open the trapdoor for you?”

  “No, I’d rather do it by feel. The computer doesn’t have nerves in its bottom, and it has too much faith in the invariance of mechanical systems. I’m going to have to make a lot of small burn corrections, anyway, once we’re out there. Just keep feeding me the figures.”

  It was a point of pride with Lydis to be in fingertip control. She believed piloting was an art, not a science.

  “A computer with nerves in its bottom!” Jun Davd chuckled. “My goodness. We’ll work on it.”

  By craning his neck, Bram could see one of the duplicate screens left over from the original Nar installation, next to the observation blister closest to him. In a simplified computer cartoon it showed a great dull-red disk, slightly angled to give a sense of perspective, and a jolly little green representation of Yggdrasil, much out of scale, floating above and to one side of it. Discreetly flashing and dotted lines showed the direction of rotation of both bodies and their intersecting orbits around the rice-grain sun shining through a cluster of red lobes at the center of the system.

  It obviously hadn’t been very practical to put Yggdrasil into orbit around the rim of a disk-shaped body with a circumference of two hundred seventy million miles. And parking Yggdrasil sixty degrees ahead of the disk—at the stable point which in this crazy system neatly coincided with the point of equilibrium with the disk ahead of it in orbit—would still have placed them an inconvenient forty-five million miles away from the forward edge of the disk and all of one hundred million miles away from the present “top” of the disk, which they had chosen as their likeliest base of operations.

  So instead, with Jun Davd’s help, Bram had put Yggdrasil into a solar orbit that intersected the disk’s orbit at a tilted angle. It started above and behind the disk at a distance of only a few million miles, slanted down at a tangent that almost grazed their target point on the rim, and continued on past to a point ahead of the disk in orbit that would place Yggdrasil directly “above” the spot where the disk’s own slow rotation would have brought the explorers’ base of operations by that time.

  Thus, for at least the first half year, travel time between Yggdrasil and the main landing site would be measured in days rather than months. At that point, Yggdrasil’s solar orbit could be converted into a powered orbit around the rim, which would take it back to its starting point for another such orbital stern chase.

  Bram kept his eye on the pulsing orange line that emanated from the tiny cartoon Yggdrasil on the screen and ended tangent to the disk. It represented a vector of the momentum that would be imparted by Yggdrasil’s own orbital motion plus the added kick from Yggdrasil’s rotation at the moment of release.

  Lydis would add her own increment of momentum by firing the spacecraft’s engines once she was in a position to judge how well lined up she was. Then she would have to cut it fine at the other end, killing all her pseudoorbital velocity and matching the speed of her target on the rotating edge of the disk—so that the net cancellation of both would come out even at the precise moment of touchdown.

  No wonder she didn’t trust the computer.

  Once launched, the comp
lex orbital mechanics boiled down to an eyeball-and-seat-of-the-pants job, and Bram himself trusted Lydis’s instincts more than he trusted the unreeling chains of glowing figures superimposed on the computer cartoon that kept changing their final decimal places.

  “Hold on to your valuables,” Zef warned through the helmet circuit.

  The trapdoor beneath the spacecraft sprang open, and they fell through. Sudden weightlessness was a faint thrill along Bram’s spine till his body adjusted. He made an incautious movement and floated an inch off the couch, held down by the webbing pressing against his chest.

  He lost interest immediately in the computer display and applied himself to the view outside the blister. Yggdrasil’s great gnarled branches floated by, pierced by random points of light from people’s living quarters.

  The tree rose until it was a green cloud above them. It began to dwindle and in minutes was far enough away that its shape could be seen against a sprinkling of stars: a double-ended mushroom divided by darkness.

  He turned his head to see how Enry was taking it and saw that the man was sweating inside his helmet. Of the four passengers, Enry was the only one who had never been away from the tree; Ame had gone on jaunts with Lydis, and Jao had gone with Bram on comet-chasing expeditions. Bram could understand how Enry felt. It was a wrenching experience to part from the entity that nutured you in blind universe.

  From this angle, line of sight was out of the system, and nothing could be seen except the stars. Now, with Yggdrasil shrinking overhead, Lydis rotated the ship to point toward their destination.

  An uncanny collection of glowing circles rose to fill the viewport. Here, above the equatorial plane of the system, one could look down past their scalloped fence into the inner heart where the polar disks orbited. Their tininess was an illusion of distance; they still dwarfed the enclosed sun. One of them was skewed; Jao had been right about that. A collision with a leftover planetoid or a solar flare some time in the past had altered its carefully timed spin. The sun spilled its light through like a glowing egg in a nest.