He put down the interphone set and faced the circle of suddenly quiet people. “That was Smeth,” he said. “Our sensors have detected the firing of launch vehicles. It appears that the dragonflies have decided that Yggdrasil is a likely-looking piece of real estate.”
Bram watched through the scope as a pattern of orange sparks rose above the brown curve of the atmosphere and died out one at a time.
“End of boost phase,” Jun Davd said from his console a few feet away. “I make that eighty-four vehicles, launched from twelve separate locations.”
“Eighty-four!” Bram exclaimed, remembering the colony-size environmental bubbles that had tried to settle in Yggdrasil’s branches in the diskworld system. “So many for a target our size?”
“These are relatively small multistage vehicles,” Jun Davd said. He put a computer-enhanced image on the big screen so that everybody could see it. Bram saw a flecked bottle shape with a pinched waist jiggling at the approximate center of the field. Glowing green lines showed where the computer had used its imagination to fill in the outline.
“Designed to come up through atmosphere, with a final stage carrying no more than fifty or a hundred passengers, from its size. Probably their regular Earth-Moon bus. Their numbers, I assume, reflect those they happened to have standing by in a state of near-launch readiness. Yggdrasil is a target of opportunity. A new world that appeared suddenly out of the miraculous plenum.”
Somebody said, “Don’t they have shuttles?”
“No, these are throwaway vehicles,” Jun Davd said. “Typical of them.”
On the screen, the bottle shape divided in two at its pinched waist. Bram looked through his scope again and saw a fresh shower of sparks.
“Their parking orbit didn’t last very long,” Jun Davd said. “Not long enough, really, to qualify as a parking orbit at all. They hardly bother to calculate, do they—just eyeball it.”
The minutes crawled by as the blanket of sparks moved perceptibly against the murky face of the planet, then slowed, then stopped moving and seemed to hover there. Jun Davd had removed the isolated ship from the big screen and replaced it with the wide view for the benefit of his visitors. What they were seeing was not strictly an honest telescopic image but one enriched by infrared, gravitational sensors, and synthetic aperture radar.
Then the sparks went out.
“Final velocity of somewhat over a hundred thousand miles an hour,” Jun Davd said. “They’ve done very well on their hydrocarbons and oxygen. They don’t appear to have injected themselves into Yggdrasil orbit. They’re going to try for a direct landing.”
The visitors waited in silence, trying to make sense out of the dancing dots on the screen. But there was really nothing to see except the background planet.
A voice on the edge of hysteria finally said, “Aren’t we going to do something?”
“We’re going to have weight very soon,” Jun Davd said soothingly. “I suggest that everyone orient themselves toward the floor.”
The floaters drifted to upright positions. People used walls and handholds to nudge themselves into foot contact as best as possible.
Bram felt returning weight: a few ounces at first, then a steadily increasing poundage. Smeth had gotten the fusion engine going in record time.
Yggdrasil groaned and creaked with the stresses of acceleration. The tree didn’t like this at all. It had come into this system under its own power—the ramjet having been shut down at about one hundred astronomical units—and finished the last seven percent of braking with its lightsails. It had broken out of its hyperbola and taken up its present orbit under the hormonal and mechanical inveigling of its human passengers, and it was just settling down to enjoy the sunlight only to be subjected to the rude yank of the tether again.
Slowly, the tree began to outdistance the gnats that were pursuing it. The one-hundred-thousand-mile orbit straightened out into a larger curve. The pursuing craft were in no danger from the photon exhaust yet, but they would be when their interception trajectory intersected the line where Yggdrasil had been.
After an hour, when the tree had built up a velocity of twenty miles a second and it became obvious that the gap would continue to widen, radar showed that the dragonfly landing stages had simultaneously flip-flopped.
“Now, why would they do that?” Bram asked.
“I’m afraid I know,” Jun Davd said.
The answer came a moment later. Once again, a cloud of orange sparks twinkled into life. The burn lasted for several minutes, then extinguished.
“They used their retrorockets to give themselves an extra boost!” Bram said unbelievingly. “There’s no way they can come to a soft landing on the Moon, now! All they can hope to do is—”
“Crash into Yggdrasil,” Jun Davd finished for him. “Project our delta-vee and gamble that by the time they intersect our path, the angle will be acute enough and the relative velocity close enough to zero to enable them to survive the crash.” His face was somber. “They don’t care about being able to get back, of course.”
Bram scrambled for a console and punched out figures, while Mim watched him, biting her lip in apprehension. After a bad couple of minutes, he gave her a reassuring smile and turned to Jun Davd.
“They can’t catch up to us,” he said.
A general sigh of relief went through the observatory, though anxiety still showed on many faces.
Jun Davd said, “No, an eye—even a wondrous thing like a dragonfly eye—isn’t a computer. Orbital interceptions can be misleading. But they had to try. It seems to be an imperative with them. Spread their wings, figuratively speaking—the wings they haven’t got—and set out for new worlds. Nature can be profligate. It doesn’t matter if most don’t survive.”
Something like pity appeared on Mim’s face. “Can they be rescued, Jun Davd?”
“I doubt that the lunar dragonflies would care to make the effort,” Jun Davd said. “Their territory’s overcrowded as it is. In any case, the question is immaterial.”
It took another hour to demonstrate that. Jun Davd slid back the cover of the observation well in the floor. It gave a good view backward along their line of flight, between the twin puffs of foliage and foliated root. The people in the observatory crowded around the safety rail and stared downward.
Jun Davd fiddled with dials, and the tough, transparent membrane became a magnifying lens. The expanse of tree crown fled past in a blur as the focus came to rest somewhere beyond. Filters masked the glare of the caged sun, spitted on the slender shaft of the probe; the darkened circle of eclipse also made bearable the beam of virtual photons, briefly swollen with abnormal energy by a factor of ten billion before it satisfied quantum theory by decaying into pions.
The swarm of dragonfly vehicles peppered the view. They were harshly lit on the side facing the hadronic beam, and their shape could be clearly seen as squat bells, with the spent cone of the descent engine for a clapper.
“No way they can stop,” Jun Davd said. “Nor can we.”
The beam was very tight, but there was a certain amount of scattering. To the watching humans, it seemed that each bell instantly evaporated while still some distance away. One by one, they flicked out of existence, soaked up by the terrible light.
In minutes, space was swept clean of the glittering cloud.
“We’re safe,” Dal said. “Let’s get out of this cursed system.”
He spoke too soon. Yggdrasil’s straightening course was taking it past the Moon. It lay before them, huge and yellow through the grand observation blister that formed one wall, Through sulfurous wisps of clouds could be seen a landscape of round lakes, patches of sparse unhealthy vegetation, pocked scars softened by weather, oily seas dotted with ring islands that had once been craters.