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One of the biggest faults with the concept of a one-shot slower-than-light colony mission was the proportion of the time spent accelerating and slowing down. Take Barnard's star, for example. At 5.9 light-years away, with a ship capable of 0.3 lights, a plausible speed for a ramscoop . . . you'd be there in 19.7 years, right?

Wrong. It all depends on acceleration. High-speed acceleration is expensive and creates engineering stresses, to say nothing of the stresses on the biological matter. A slow steady push is best. You accelerate slowly for at least a third of your trip. And then you have to slow down again. If you're going to visit a number of systems, this adds hugely to travel time. What's more, the momentum you've lost has to be built again.

Momentum is expensive. It is energy. Energy, whether taken from solar-pumped lasers or A-bombs is a consumable. Even if it is "free" solar power, it still costs to get it into a usable form, and once it has been used, it is gone. A metal space habitat has a finite lifespan—but it is an enormous one. The depreciating cost, amortized over its space-life, divided by its carrying capacity, makes it the cheapest vehicle humanity ever built.

However: Building the momentum needed to travel between the stars is too expensive to waste on one stop journeys, or even on leapfrogging between stars. Once the colony ship accelerates, it must never slow down again. Never. It will drop space habitat modules at each sun. But it must itself just keep cruising along, a slow train to the stars.


From: Slowtrain: The Stars Within Our Grasp,
Conquist, A., Mordaunt
Scientific Press, NY. 2090.


 
 . . . More than any other space-used technique, the blowing of nickel-iron bubbles changed engineering. From ship hulls to habitats, it was the death of the 'plate-and-rivet' technology that had dominated since the nineteenth century. Bubbles blown from space-melted m-type asteroids altered nearly all the dynamics, both economically and in engineering terms.


From: An Introduction to Space Engineering,
Vol. 1. 2202, Braun, W.J. and Casern, D. (ed.)
SoCalTech Press (pub.)


 


In the Miran spacecraft now rapidly approaching the enormous alien starship, Kretz swam up from the drug induced trance-hibernation. He opened his eyes and looked at the cramped room, and up at Selna, the ship-physician, leaning over him.


"We're on the final intercept approach," said Selna, beaming down at him. From the transit-massage couch, Kretz smiled back, a little wary, a little confused.


That was to be expected. It would take his livers time to clear the drugs out of his system. Selna was much closer to sexual changeover than he was, and was therefore bigger and had more body, and more liver, available to deal with the trance-drugs. It was a reason to be wary with him. Moods were even less stable than sexuality, at this stage. Selna would only get worse until he became fully female, and settled down.


Well, thought Kretz, eventually he'd get there himself. It was odd to think of being sedentary and child-rearing. Selna had better watch his hormone supplements, though. There was no space on the intercept ship for a nesting territory, let alone a creche. Anyway, it would all smell wrong.


Kretz sat up. He was still giddy, but the excitement was beginning to push aside the drugs that had allowed them to make the six-year journey.


Selna lent him a hand, helping him to his feet. The physician-communications specialist's eyes were alive with excitement. "And have I got news for you, my xenobiologist-engineering friend! It looks like both of your specialties may just be needed."


Incredulously, Kretz turned on him. "There is something alive on the alien craft? It is not just a probe?"


Selna laughed. "To hear Leader Zawn, you'd think it will be full of aliens."


Kretz had to laugh too. "Probably fluffy and pink with tentacles."


"Well, he has detected beamed laser signals coming from one of the spheres. The sixth. I've started computer analysis of the signal."


"It's just an automated signal system. Look, when they started checking the back-record from Astronomy, they found signs of the alien ship as far back as two hundred years ago. It'll be a treasure trove, all right, but Zawn's archaeology will have more of a role to play than my xenobiology."


By this time they'd walked forward down the narrow passage to the science deck. Kretz was glad to flop into a chair. Leader Zawn was peering intently at some instruments, so absorbed that he didn't even look up. He just waved a hand in greeting. His mouth was stretched into a beam of pure delight.


Kretz stared at the forward viewscreens as Selna handed him a high-energy drink, designed to stimulate the mind, flush the body of trance-drug metabolites and, naturally, taste vile. The alien ship filled the entire viewscreen, although they must be at least seven light-seconds away from it. It looked even more like a string of white beads—beads moving at nearly a third of the speed of light, but beads none-the-less. Of course there was not much light out here to reflect, but the infrared view confirmed that the thing was, by comparison to space, quite warm. The machinery inside must still function, somehow. No matter how well you insulated anything it would—eventually—leak heat.


"Behind the ramscoop is a fusion plant," said Zawn, looking up from his instruments and not bothering with niceties like asking how his xenobiologist felt after trance-sleep. The answer was always the same anyway: awful.


"And behind that the spectroscope confirms the next object is water-ice. Probably a whole comet. Now what do you think they'd want that for, Kretz?"


Kretz hid his smile. "Fuel?" he said just for the sheer joy of watching Zawn's face. The poor fellow almost showed his teeth before realizing that he was being teased.


"Someone will kill you in a mating fight, Kretz. Don't be more obstructive than you have to be. Replenishment, that's what. Replenishment of lost materials. There will be some leakage, but this gives the lie to Melka's ideas. Of course there could still be life, even if his calculation of the effectiveness of seals is correct. They just brought replenishments along. A lot of replenishments. The third object is nitrogen ice and carbon dioxide."


"Well, they're transporting water, nitrogen and CO2 along does suggest that they're not the sort of alien life-forms Melka and Ferni proposed," said Kretz. Zawn had a habit of leaping to conclusions. Archeologists had to, he supposed. Often there wasn't that much to go on. But the combination was indeed promising for life as they knew it on Miran. Perhaps the theories of what the basic conditions for the formation of life were, were about to be proved. The theories of evolutionary convergence were another matter entirely. Yes, they worked within a planetary sphere, but out here . . . 


Why should two legs and two eyes be a norm? He already knew the answer: because function shapes form. But even if there was a remnant of life on the alien ship, it was going to be very different. Excitingly different, beyond his wildest dreams.


Zawn leaned in, beamed, and came up with his clincher. "And it is very plain that they're using energy. Quite a lot of energy for a ship full of machinery or even sleepers. Each of those beads is rotating. There are small ion-jets on the equatorial ridge of each bead to keep them spinning."


Spin. Centrifugal force would provide the effect of gravity. And why should gravity matter to machinery, or, as had been postulated by the excitable fringe media on Miran, to a spacecraft full of frozen aliens?


There might be a huge cargo of trance-state aliens on that ship . . . but if so, where were they heading for? The ship showed no signs of slowing. The initial theory had been that the vessel's purpose was to deploy probes, and that that had caused the flash that had originally caught astronomers' attention. Objects moving at considerably higher fractions of C had been detected relatively soon after that.


But this was a different prospect altogether. A vastly different prospect. There could even be live "minders" on the alien string of pearl-like beads. The idea frightened and excited Kretz, as the rest of the Miran expedition crew were brought out of trance and the distance to the alien ship closed, hour after hour. Laser streams of data hurtled back toward Miran. Kretz could imagine the newscasts getting it all wrong, and a whole generation of young males wishing that they were on this grand adventure themselves, and the nest-mothers being terribly glad that their young males weren't out here.


The amount of information going back now was nothing to what they'd send when they actually made physical contact. That would take the greater proportion of their reaction mass . . . and was giving both the steersman and navigator sleepless rest-periods, and relentless computing.


"It'll have to be the distal pole of the last bead," said Steersman Kastr firmly. "I'm sorry, Leader Zawn. The spin means we have to land on a pole—and the link between the beads means only the last pole is an option. Besides, deep-radar suggests that the surface at the pole is exposed metal, whereas we think most of the rest is covered by some form of film—possibly a coating on an inner regolith layer. The sixth from last bead may be transmitting laser signals, but we can't land the intercept there."


"The lifecraft?" said Zawn desperately.


"Possibly. Once we've matched velocity . . . well, all things are relative," said Kastr, in his this is another one of your stupid ideas, archeologist voice.


Kretz knew Zawn well enough to suspect that, stupid idea or not, the lifecraft, intended to provide their final stage home, would be attempting the journey to the sixth bead. It had been a possibility in the design phase, Kretz knew. There was a crawler in the hold too. It had seemed like a waste of space to Kretz, but then it had been difficult to guess what they'd need to explore an alien artifact moving at 0.3 lights. The only obvious answer seemed to be: You need whatever you haven't thought of. Kretz was cynically sure that that was as certain to be true as Selna suggesting a little recreational sex next rest period. It was one of those thing about approaching change. Selna's hormones were in a riot, just like his moods and his temper. And the ship had three of its crew heading that way . . . full of hormone supplements to avoid sex-change.


 


"It's an airlock," Kretz said, looking at the shape of the alien structure that Zawn had projected up onto the screen. "That much is obvious, Leader Zawn. Engineering convergence is as inevitable as biological convergence. A bridge looks like and works like a bridge—within certain limits—no matter where on our world it was built, by whatever linguistic group or culture."


Zawn looked thoughtful. "And tetrahedronous religious building and tomb-structure are more of a sign of structural and material dictates than historical contact. True. But the question remains. Do we attempt to open this airlock?"


"It's what we came for," said Selna, caressing Kretz's back.


"Not strictly speaking," said Kretz. "We came to investigate an alien artifact, assumed long dead, or to be a probe. Yes, I'd love to see an alien life-form. But it is also true that whatever is in there may not care to be disturbed. And we are the interlopers."


Selna snorted, stopping his distracting activity. "Look," he said, "what are we going to do? Come nearly 1.8 light-years and then go home wringing our hands and grimacing, just in case the occupant might be showing their teeth, and not welcoming visitors to their nest? We are males. Some of you are even quite attractive." His hand trailed down Kretz's back again.


The physician didn't see things quite the way a behavioral biologist did. "They might not have two sexes," said Kretz. "Maybe three. Or only one."


Selna laughed. "No. Convergent evolution dictates that they'll have at least two. Females to tell the males what to do. Males to ignore them."


"And get killed," said Kretz.


Selna laughed again. "Well, we'd have overpopulation problems if males were as nest-minded as females."


"I think they're going to be very small and very different, or else in cyronic preservation," Kretz said firmly. "Look at the size of the each of those beads. They're not really big enough to be bio-viable."


"I thought that the consensus was that they'd have to be at least of roughly equal cranial capacity to us to allow for the evolution of sentience," said Selna, betraying that he'd read far more than he admitted to. After the existence of the alien artifact had been confirmed, theories had proliferated like bacteria. The cranial capacity one had quite caught the public eye. Of course it assumed that aliens would have a cranium . . . 


"Only assuming that their biology is close to ours. If the brain is not convoluted, for example, they'd need about three times the cranial capacity—assuming their nervous system works even remotely like ours," said Zawn, showing that he'd read the same speculation.


"I personally hope that they're going to be dead sexy," said Selna, getting up and walking off in search of new prey, with one of his sudden mood-swings. "You're all too boring."


Selna's absence did make rational conversation easier. "So," said Kretz to Leader Zawn. "I suppose what you are really trying to ask me is how many people we should send in, and what dangers they can expect to face? I know you well enough to know you are going to go yourself."


Zawn smiled. "Yes," he said. "So long as you accept that the number will include me."


"Both of us," said Kretz. "We're relatively expendable."


Zawn was amused. "What a shocking thing to say to your leader."


"True enough, though. And as for the dangers . . . well, it is relatively unlikely that we're going to find any life in there, or that any contamination will survive contact with hard vacuum."


Zawn's lips stretched and narrowed in a smile. "And that pink furry tentacled aliens will come out and run off with Selna."


"He's being exhausting right now," admitted Kretz. The attention was flattering, but still . . . 


"We'll all get there," said Zawn tolerantly.


"If we live that long. I'm quite looking forward to him changing and settling down in a nest-territory and never moving again," said Kretz.


"At the moment his promiscuity is a little tiring," said Zawn. "But spare me a territorial female to deal with as well. So: You and me, and maybe Abret. There is not much call for a deep-space radiation scientist. We have a spare pilot, besides him. And Selna can do his life-support work in a pinch."


There was more to Leader Zawn, thought Kretz, than mere boundless enthusiasm and a capacity to think the best of everyone. More than an encyclopedic knowledge of the historical artifacts of seventeen cultures, too. It must have been difficult for the expedition committee to chose a male to lead, but he was as good a candidate as you were likely to find this side of changeover. "My choice, exactly," he admitted. "So when do we go?"


"Now," said Zawn calmly. "Abret is just off getting some adjustments done to his suit. His growth has been slower than predicted while he was under the trance-drugs."


"In other words, you'd already made up your mind before you asked me," Kretz said.


"Well, not quite," admitted Zawn. "I wanted your opinion, and I wanted you along, of course. But I wasn't sure how expendable to engineering you considered yourself." Zawn showed the tact that had led to him being chosen to lead the alien artifact interception mission, over the heads of the obvious candidates in Navigation or Steering. He took Kretz by the arm and the two of them walked toward the passage to the outer airlock. "The decisions on risk profiles were actually taken back on Miran, before we left, you see. But a willing participant is always best." He looked mischievously at Kretz. "And if we go now, well, what Selna doesn't know he can't fuss over. He is not to be considered for any high-risk operations."


"A very good point," admitted Kretz.


 


The team had set up the laser-video links, before retreating on the Miran spacecraft. Kretz had had the frisson of knowing they would forever be the first Miran males who had finally penetrated an alien spacecraft. That laser relays would have those pictures on datafiles back home.


He'd also had the fear of walking into an alien airlock, and the knowledge that Selna was furious with him.


Abret painstakingly checked the atmosphere being pumped into the airlock. "We'd breathe this and live, you know," he said, looking at the readouts again. "More nitrogen and less carbon dioxide than we're used to. Traces of methane. And sulphur compounds . . .  But the oxygen level is tolerable."


"Sorpon's prediction on the environmental requirement for intelligent life comes true," Kretz said regretfully, pausing in the setup of the radio repeater. "I'd have preferred you to prove him wrong, as I always thought his premises for the evolution of intelligence were simply too narrow. What's the temperature like?"


"Chilly," said the scientist. "Enough to make you sprout cilia, but not to kill you."


The inner airlock door beckoned. Aside from bridges and religious tetrahedrons . . . function demanded that a door look like a door. It was lower and wider than Miran would have made it, but it was still a door.


"Well?" asked Kretz. "Do we open it? Or do we examine this area carefully first?"


"Caution and good archeology suggests the latter," said Leader Zawn. "But I am still a young enough male to be foolish and reckless," he said, smiling. "Besides, our time is limited. If we follow good archeological principles we'll still be looking at the edge of the launchpad when the artifact heads on for the next star, and we'll have to go along for a one-way ride. I suggest we have laser pistols at the ready, but don't hold them obtrusively."


He began pulling on the wheel-device on the door. It responded. External sound pick-ups on the suit recorded a faint creak. But Kretz had not even had time to draw the laser pistol, when the door slid open. Inside . . . 


Inside the alien ship was not, as some had suggested, a huge hollow space. They were in a large open area, true, but it was not high-roofed. An elderly female Miran would have had to duck her head. Before them, open entryways gaped. One passage was wide enough to take a lander, and had, Kretz noticed, a roof-rail. But most of them were narrow. Some were lit, as this area was, with a light that seemed a little too yellow and too bright. And they could see spindly green things there.


The truth dawned on Kretz then. "It's not a probe. Or a spaceship. It's a habitat. A space habitat. They've got away from the space-constraint issue with layering."


His engineering side was doing some hasty recalculation as to the surface area in the habitat. This would increase area by several thousand percent. True, it would be more than a little claustrophobic in the passages—walking closer they could see the walls were covered in growing things.


"I think it is both a habitat and a spaceship. Those inside have a small world to live in," said Zawn, slowly. "They must be a species far more adapted to life in space than us. Better able to tolerate enclosed spaces, for starters."


"But why?" asked Abret, peering around. "I mean, why build a ship that appears to do nothing but transport their habitat across maybe a hundred light-years? The ship isn't slowing. It hasn't slowed—according to examination of back data—for at least a hundred years. And yet . . . a species content to dwell in space habitats could make their home around any star. And there is more room around any one star than they could ever use."


It was quite a question, thought Kretz. "Maybe they like to travel or to explore, and this is just to provide them with a home while they do?"


"Could be, I suppose," said Zawn, staring around. "We make the arctic observatories as homelike as possible. Or maybe this is a failed colony ship. Do you think anything is still alive in here? Besides the plant-life that you're peering at, Kretz?"


"Could be too," said Kretz, peering at the divided leaves. The convergence was amazing! He clipped a tiny piece off with a monomolecular-edged sampling blade and dropped it into a sample holder on his belt. Of course it would have to be examined under the strictest quarantine conditions, even if the risks of biocontamination were minuscule. But he could hardly wait to get a microscope to it, and to begin investigating its chemical makeup.


"Then why aren't they here?" asked Abret, moving back nervously from the leafy passage-mouth.


"Maybe they're not expecting visitors in deep space," said Zawn, flippantly. "I don't think you should be damaging the flora, Kretz. It's their property. They might take offense—"


And then something moved, darting forward towards them.


Abret must have been nearer to the thin edge of panic than he'd let on, because he fired.


A piece of alien greenery was cut and fell, and something exploded and burst into flames briefly.


A stripe-faced creature, clad in green and brown mottling that had made it difficult to see, dropped something and raised its hands. So did two others that had been so perfectly hidden that none of the Miranese explorers had seen them.


Three Miran had faced three aliens for a long moment before Zawn said "Raise your hands too. It must be a greeting. See, empty palms, a gesture of friendship and peace."


The aliens stood like statues as Zawn and Kretz echoed the two-handed greeting, while Abret, obviously almost paralyzed with fear, stood with his laser pistol at the ready.


"Abret. Greet them," said Zawn, firmly. The frightened deep-space physicist responded slowly, raising just the one hand above his head, keeping his laser pointed at the aliens. They all stood like that for a very long time, looking at each other. They were disturbingly Miran-shaped, and yet alien. Wrong. Yes, they were bipeds, and had the normal arrangement of arms and a head. Two eyes, a mouth and a nose. But the hands were wrong. Five digits instead of the normal three and opposable. It looked as if one of their digits—the inner one—might be opposable. And the head and face were even more wrong. The heads had filaments on them, as if the aliens were suffering from extreme cold. And the face pigment-stripes were all different. The position of the eyes, the shape of the nares, the angle of the mouth were all slightly different, and the external part of what was probably an ear was too low. At least they were not showing their teeth. Eventually, Kretz said in whisper—ridiculous, because the aliens couldn't hear their radio transmissions and certainly couldn't understand them: "Can we stop greeting now? My arms are getting very tired."


Zawn slowly lowered his arms. The aliens looked at each other and slowly did the same. And the external mikes picked up the sound of alien speech.


Transcomp cut in. "Unknown but sequential pattern," the computer supplied. "Analyzing."


"So what do we do now?" asked Abret.


"Hope like hell that they're not too mad at the damage you did shooting at them. Apologize," said Zawn.


"How do we do that?" asked Kretz.


"We repeat their words back them from Transcomp. And then we do some miming," said Zawn. "It appears as if we have similar meanings in our hand-gestures, anyway."


What the expedition leader lacked in animal-behavior knowledge he made up for in decisiveness. Personally, Kretz thought that the miming could have meant nearly anything from "sorry" to "if you move we'll shoot at you." But the repeat-back of the Transcomp recorded words had produced a flurry of more alienese. When this was repeated back to them, one of the aliens had grasped the situation and began pointing to objects and naming them. They plainly were quick on the uptake. But that was what you'd expect from the builders of such a magnificent artifact.


 


What followed was the most exhausting and thrilling time period of Kretz's life. Transcomp got the names of objects quickly enough. Once they got the idea the aliens had even contrived to show actions and provide words. Kretz wasn't sure how much of the translation was getting through the other way. The aliens called all of them "Zawn." And they appeared willing to help, even if Abret had kept his distance, nervously, most of the time. Another thing had been noting the appearance of small 'bots of alien design which had eventually appeared and begun repairing the damage from Abret's shot. Obviously the alien ship's internal machinery still functioned well, if slowly.


It had been a triumphant and excited group that had returned to the ship.


The aliens were . . . alien.


And yet, less so than some of the scientists and the general public had expected. If they'd been blobs of slime they might have been more wary. If Transcomp, designed to provide interface between nests from any island or culture on Miran had proved less adaptable and successful, things might have been different too, admitted Kretz.


 


Everyone had wanted to be part of the next group, but Leader Zawn had taken that cautiously too. "We'll take four people next time. They seem friendly. I'm afraid, Kretz and Abret, I won't be able to take you two, this time."


Abret, in the nervous-moody stage before change, certainly didn't mind. Kretz too hadn't regretted it in the slightest. The systematic examination of the plant sample he'd taken took up most of that time. The others would merely have been part of the second contact. He'd been part of the first, and his monograph on the alien plants would ensure that his fame continued long after he'd mothered his sons and become a vast matriarch, too big to move without help. The structure of the plant had been like looking at a young student's first badly understood research of Miran vegetation. It was . . . similar in function, but obviously had arrived there from a different direction. The chemists would have fun with some of the long-chain organic molecules too, but they were carbon compounds. Evolution had a myriad possible paths to follow in theory, but perhaps in practice there were certain constraints. Kretz found himself intensely curious as to how these alien plants would taste. He resisted the crazy urge. Miran digestion was robust, but who knew what alien toxins would do to one's livers?


The second expedition came back bubbling with excitement at the friendliness of the aliens. "They want to meet all of us. It . . . seems they are rather vague on 'outside,' " said Zawn. "We're making huge strides with the language. I've decided: Except for Abret and Derfel, who will be taking the lander to the source of the laser pulses, and Leter and Guun, who will remain onboard the ship, we're all going in after next rest period. It's a veritable treasure house of alien life-forms and equipment, Kretz. And . . . you know what? We think it was supposed to be a colony ship. A whole series of them, rather. They say their bead was supposed to take them to a new sun. Obviously their astronomy must be far ahead of ours, to predict what suns would have habitable planets."


Kretz had been just as excited about the idea of more material to add to his biological firsts and keen on engineering discovery. He'd quietly taken along the better part of an engineering repairman toolkit.


He was expecting great things.


 


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