Donald Moffitt - Genesis 02

the distant fusion flame. “ We came back here in a multiple of thirty-seven million years—just as fast as we could after the Message reached the Father World, not counting the few insignificant millennia that fell through the cracks while the Nar remade us, and so forth. They got here in a rough multiple of twenty-six million years after the Message stopped.” He pursed his lips. “They seem to have arrived about four million years early. That’s within the limits of your timetable, isn’t it, Ame?”
    “Divided by three, yes,” she said.
    Around them on the booty-littered plain, people were gathering into groups, pointing excitedly at the sky. Bram knew that if he switched to the general frequency he would hear a babble of voices. A delegation of about a dozen people, spotting Jun Davd’s tall space-suited figure and his own well-worn tabard, were bouncing across the flat ribbonscape toward them.
    “Who?” Bram said. “Relatives of the Cuddlies? The collateral branch you postulated that might have evolved from the same root stock after the longfoots carried the Cuddlies here?”
    “No,” Ame said. “That would have been the last cycle— twenty-six million years ago. The proto-Cuddlies missed their chance. They never traveled to the stars.”
    Bram stared at the blue spark that was heading toward them. “Who then?” he said.
    “We’ll know very soon,” Jun Davd said.
     
    CHAPTER 9
     
    The alien ship resembled a long jointed stick studded with budlike structures and a cluster of bubbles like white foam at one end. It was very large, as starships must be. It was not worldlike in Yggdrasil’s sense, but the segmented shaft was many miles long, and each individual bubble was easily a half mile in diameter.
    “It’s a fusion vessel, all right, but not a ramjet,” said Jun Davd’s deep, composed voice from the screen. “They carried their fuel with them. They’re using a deuterium-helium three reaction. But there are traces of tritium from previous burns.”
    Bram saw the implications immediately. “They started their trip with a deuterium-tritium reaction. And they’ve been at it long enough to have to switch fuels because of the decay of their tritium.”
    He turned his eyes from the sticklike image on the portable viewscreen long enough to exchange glances with Jao. Jun Davd had returned to the tree in order to have the full resources of the observatory at his disposal, but the burly physicist had left Trist to hold the fort and returned to the diskworld, where, he said, “the action’s going to be.”
    The strangers’ starship had been decelerating steadily for six days now at half a g. It had covered more than two hundred million miles since it had first been spotted approaching from the outer system. It would rendezvous with the diskworld in only a few hours—still with too much velocity, according to Trist.
    Bram, waiting with Jao, had set up shop in the great sports arena, which was mostly cleared out now. A few people in casual dress moved through the empty spaces, picking over the remaining exhibits. Ame was among them, a distant figure working with a male associate to pack and label pods. Bram had sent all the junketing tourists—and everybody else who could be spared—back to the tree. He didn’t want half the population milling around where they could not easily be rounded up. Not with this new development unfolding. But Ame had refused to go. “Not on your life,” she’d said. “I wouldn’t miss this for anything. Besides, you’re going to need me, and Jorv, and all the other experts on terrestrial life.” She was right, Bram knew. Only a few hundred people remained on the diskworld, but he had seen to it that a sprinkling of specialists in the once-abstract disciplines was included.
    “Yes,” Jun Davd’s voice agreed. “If they came from Sol, they’ve been traveling at nonrelativistic speeds. Tritium’s half-life is only twelve years and a bit. At the end of their first fifty or sixty years, most of it would have turned into helium three, their secondary fuel. And what does that suggest?”
    Jao’s eyes glinted. “Deuterium-tritium fusion is easy. But tritium’s hard to come by. They would’ve made it back home as a by-product of their fusion reactors. Deuterium-helium three fusion’s easy, too—but first you have to accumulate enough helium three. Deuterium’s more plentiful. But I guess they’re not capable of deuterium-deuterium fusion yet. Nor