At a hundred gees acceleration you head out of the Solar System on a trajectory that’s very close to a straight line. The gravitational accelerations produced by the Sun and planets are negligible by comparison, even in the Inner System. We were bee-lining for a point in the constellation Lupus, the Wolf, where Vandell lay close in apparent position to an ancient supernova fragment. That explosion had lit up the skies of Earth more than a millennium ago; an interesting object, but we wouldn’t be going even a thousandth of the way out to it. Wicklund was right; Vandell’s rogueworld sat in Sol’s backyard.
Without a complicated trajectory to worry about, I went round and round with a different problem. When the drives were on, both the Merganser and the Hoatzin were blind to incoming messages, and drowned out any of their own transmissions. Thus we had a chance to get a message to Sven Wicklund and Jan only when their drive was turned off, while they were coasting free to rubberneck or study the starscape scenery from a slightly different point of view. Even though they might not be listening for an incoming signal when the drive was off, their computer would, and should notify them of anything important.
But now see my problem: to send a message, we had to switch our drive off, and that would delay our arrival a little bit every time we did it. Our signal would then take days or weeks to reach the Merganser — and to receive it, their ship had to have its drive off at just the right time. DON’T LAND was all I wanted to say. But how would I know when to switch off our drive and send an urgent message, so it would get to them just when their drive was not operating?
I wrestled with that until my brains began to boil, then handed it over to McAndrew. He pointed out that we had knowledge of the occasions when their drive had been switched off, from the gaps in their drive wake. So making a best prediction was a straightforward problem in stochastic optimization. He solved it, too, before we had been on our way for a week. But the solution predicted such a low probability of successful contact that I didn’t even try it — better to leave our drive on full blast, and try to make up some of their lead.
With the shields on to protect us from the sleet of particles and hard radiation induced by our light-chasing velocity, we had no sense of motion at all. But we were really moving. At turnover point we were within one part in ten thousand of light speed.
If I haven’t said it already, I’ll say it now: the 100-gee balanced drive is nice to have, but it’s a son of a bitch — you travel a light-year in just over a month of shipboard time. Two months, and you’ve gone fifty light-years. Four shipboard months, and you’re outside the Galaxy and well on your way to Andromeda.
I calculated that two hundred days would put you at the edge of the Universe, 18 billion light-years out. Of course, by the time you got there, the Universe would have had 18 billion more years to expand, so you wouldn’t be at the new edge. In fact, since the “edge” is defined as the place where the velocity of recession of the galaxies is light-speed, you’d still be 18 billion light-years away from it — and that would remain true, no matter how long you journeyed. Worse still, if you arranged a trajectory that brought you to rest relative to the Earth, when you switched off the drive the Galaxies near you would be rushing away almost at light speed…
An hour or two of those thoughts, and I felt a new sympathy for Achilles in Zeno’s old paradox, trying to catch the tortoise and never quite getting there.
Travel for a year, according to McAndrew, and you’d begin to have effects on the large-scale structure of space-time. The vacuum zero-point energy tapped by the drive isn’t inexhaustible; but as to what would happen if you kept on going…
An academic question, of course, as Mac pointed out. Long before that the massplate would be inadequate to protect the drive, and the whole structure would disintegrate through ablative collision with intergalactic gas and dust. Very reassuring; but Mac’s intrigued and speculative tone when he discussed the possibility was enough to send shivers up my spine.
The position fixes we needed to refine Wicklund’s original position and velocity for Vandell rendezvous were made by our computer during the final three days of flight. Those observations and calibrations were performed in microsecond flashes while the drive was turned off, and at the same time we sent out burst mode messages, prepared and compressed in advance, to the Merganser’s projected position. We told them when to send a return signal to us, but no counter-message came in. There was nothing but the automatic “Signal received” from their shipboard computer.
One day before rendezvous we were close enough to throttle back the drive. We couldn’t see Vandell or Merganser yet, but the ships’ computers could begin talking to each other. It took them only a few seconds to collect the information I was interested in, and spit out a display summary.
No human presence now on board. Transfer pod in use for planetary descent trajectory. No incoming signals from pod.
I keyed in the only query that mattered: When descent?
Seven hours shipboard time.
That was it. We had arrived just too late. By now Jan and Sven Wicklund would be down on the surface of Vandell. Then another part of the first message hit me. No incoming signals from pod.
“Mac!” I said. “No pod signal.”
He nodded grimly. He had caught it too. Even when they were down on the surface, there should be an automatic beacon signal to fix the pod’s position and allow compensation for Doppler shift of communication frequency.
“No pod signal,” I said again. “That means they’re—”
“Aye.” His voice was husky, as though there was no air in his lungs. “Let’s not jump to conclusions, Jeanie. For all we know…”
But he didn’t finish the sentence. The pod antenna was robust. Only something major (such as impact with a solid surface at a few hundred meters a second) would put it out of action. I had never known a case where the pod’s com-link died and the persons within it lived.
We sat side by side in a frozen, empty silence as the Hoatzin brought us closer to the rogue planet. Soon it was visible to our highest resolution telescopes. Without making a decision at any conscious level, I automatically set up a command sequence that would free our own landing pod as soon as the drive went off completely. Then I simply sat there, staring ahead at Vandell.
For much of our trip out I had tried to visualize what a planet would be like that had known no warming sun for millions or billions of years. It had floated free — for how long? We didn’t know. Perhaps since our kind had descended from the trees, perhaps as long as any life had existed on Earth. For all that time, the planet had moved on through the quiet void, responsive only to the gentle, persistent tug of galactic gravitational and magnetic fields, drifting along where the stars were no more than distant pinpricks against the black sky. With no sunlight to breathe life onto its surface, Vandell would be cold, airless, the frozen innermost circle of hell. It chilled me to think of it.
The planet grew steadily in the forward screens. As the definition of the display improved, I suddenly realized why I couldn’t relate the picture in front of me to my mental images. Vandell was visible, at optical wavelengths. It sat there at the center of the screen, a small sphere that glowed a soft, living pink against the stellar backdrop. As I watched the surface seemed to shimmer, with an evanescent pattern of fine lines running across it.