Hidden Variables

by Charles Sheffield

  "Give me a Doppler read-out," I said. "Let's find out what sort of orbit he's in. Damn it, what's he doing there, sight-seeing?"

  Now that it looked as though we had found them, I was irrationally angry with McAndrew. He had brought us haring out beyond the limits of the System, and he was sitting there waiting when we arrived. Waiting, and that was all.

  Wenig had called up a display and was sitting there staring at it in perplexity. "No motion relative to HC-183," he said. "He's not in an orbit around it, he's got the ship just hanging there, with the drive balancing the gravitational attraction. Want me to take us alongside, so we can use a radar signal? That's the only way he'll hear us through the drive interference."

  "I guess we'll have to. Take us up close to them." I stared at the screen, random thoughts spinning around my head. "No, wait a minute. Damn it, once we set up the computer to take us in there, it will do automatic drive control. Before we go in, let's find out what we're in for. Can you estimate the strength of HC-183's gravitational attraction at the distance that Merganser is at? Got enough data for it?"

  "Give me a second." Wenig's fingers flew over the console again. If he ever decided that he didn't want to work at the Penrose Institute, he'd make the best space-racer in the System.

  He looked at the output for a second, frowned, and said, "I think I must have made an error."

  "Why?"

  "I'm coming up with a distance from the surface of about nine thousand kilometers. That means the Merganser would be feeling a pull of fifty gee—their drive would be full on, as high as it's designed to go. It wouldn't make sense for them to hang there like that, on full drive. Want to go on down to them?"

  "No. Hold it where we are." I leaned back and closed my eyes. "There has to be a pattern to what Mac's been doing. He went right through the System back there with the drive full on, now he's hanging close in to a high-density object with the drive still full on. What the hell's he up to?"

  "You won't find out unless we can get in touch with him." Wenig was sounding impatient again. "I say we should go on down there. Now we know where he is it's easiest to just go and ask him."

  It was hard to argue with him, but I couldn't get an uneasy feeling out of the back of my head. Mac was holding a constant position, fifty gee of thrust balancing the fifty gee pull of HC-183. We couldn't get alongside him unless we were willing to increase Dotterel's drive to a matching fifty gee.

  "Give me five more minutes. Remember why I'm here. It's to keep you from doing anything too brave. Look, if we were to hang on our drive with a twenty gee thrust, how close could we get to the Dotterel?"

  "We'd have to make sure we didn't fry them with our drive," said Wenig. He was busy for a couple of minutes at the computer, while I tried again to make sense of the pieces.

  "We can get so we're about sixty thousand kilometers from them," said Wenig at last. "If we want to talk to them through the microwave radar link, the best geometry would be one where we're seeing them side-on. We'd have decent clearance from both drives there. Ready to do it?"

  "One minute more." I was getting a feeling, a sense that everything that McAndrew had done had been guided by a single logic. "Look, I asked you what would happen if the drive failed when the life-capsule was up close to the mass disk, and you said the system would move the capsule back out again. But look at it the other way round now. Suppose the drive works fine—and suppose it was the system that's supposed to move the life-capsule up and down the column that wouldn't work? What would that do?"

  Wenig stroked at his luxuriant mustache. "I don't think it could happen, the design looked good. If it did, everything would depend where the capsule stuck."

  "Suppose it stuck up near the disk, when the ship was on a high-thrust drive."

  "Well, that would mean there was a big gravitational acceleration. You'd have to cancel it out with the drive, or the passengers would be flattened." He paused. "It would be a bugger. You wouldn't dare to turn the drive off—you'd need it on all the time, so that your acceleration compensated for the gravity of the disk."

  "Damn right. If you couldn't get yourself farther from the disk, you'd be forced to keep on accelerating. That's what happened to the Merganser, I'll bet my pension on it. Get the designs of the capsule movement-train up on the screen, and let's see if we can spot anything wrong with it."

  "You're an optimist, Captain Roker." He shrugged. "We can do it, but those designs have been looked at twenty times. Look, I see what you're saying, but I find it hard to swallow. What was McAndrew doing when he came back through the system and then out again?"

  "The only thing he could do. He couldn't switch the drive off, even though he could turn the ship around. He could fly off to God knows where in a straight line—that way we'd never have found him. Or he could fly in bloody great circles, and we'd have been able to see him but never get near to him for more than a couple of minutes at a time—there's no other manned ship that could match that fifty gee thrust. Or he could do what he did do. He flew back through the System to tell us the direction he was heading, out to HC-183. And he balanced here on his drive tail, and sat and waited for us to get smart enough to figure out what he was doing."

  I paused for breath, highly pleased with myself. Out of a sphere of trillions of cubic miles, we had tracked the Merganser to its destination. Wenig was shaking his head and looking very unhappy.

  "What's wrong," I said cockily. "Find the logic hard to follow?"

  "Not at all. A rather trivial exercise." He looked down his nose at me. "But you don't seem able to follow your own ideas to a conclusion. McAndrew knows all about this ship. He knows it can accelerate at the same rate as Merganser. So your idea that he couldn't fly around in big circles and wait for us to match his position can't be right—the Dotterel could do that."

  He was right.

  "So why didn't Mac do that? Why did he come out all this way?"

  "I can only think of one answer. He's had the chance to look at the reason the life capsule can't be moved back along the axis, so the drive mustn't be switched off. And he thinks that this ship has the same problem."

  I nodded. "See now why I wouldn't let you take the Dotterel all the way up to fifty gee?"

  "I do. You were right, and I would have taken us into trouble if you hadn't been along. Now then"—Wenig looked gloomier than ever at some new thought—"let's take the logic a step farther. McAndrew is hanging down there near HC-183 in a fifty gee gravity field. We can't get there to help him unless we do the same, and we're agreed that we dare not do that, or we'll end up with the same difficulty that he has, and we won't be able to turn off the drive."

  I looked out of the port, toward the dark bulk of HC-183 and the Merganser, hovering on its plume of high-temperature plasma. Wenig was right. We daren't go down there.

  "So how are we going to get them out?"

  Wenig shrugged, "I wish I could tell you. Maybe McAndrew has an answer. If not, they're as inaccessible as if they were halfway to Alpha Centauri and still accelerating. We've got to get into communication with them."

  * * *

  When I was about eleven years old, just before puberty, I had a disturbing series of dreams. Night after night, for maybe three months, I seemed to wake on the steep face of a cliff. It was dark, and I could barely see handholds and toeholds in the rock.

  I had to get to the top—something was hidden below, invisible behind the curve of the black cliff face. I didn't know what it was, but it was awful.

  Every night I would climb, as carefully as I could; and every night there would come a time when I missed a handhold, and began to slide downwards, down into the pit and the waiting monster.

  I woke just as I reached the bottom, just as I was waiting for the first sight of my pit beast.

  I never saw it. Puberty arrived, sex dreams replaced my fantasy. I forgot all about the cliff face, the terror, the feeling of force that could not be resisted. Forgot it totally—except that dream memories never disappea
r completely, they lie at some deep submerged level of the mind, until something pulls them out again.

  And here I was again, back on the same cliff face, sliding steadily to my fate, powerless to prevent it. I woke up with my heart rate higher by thirty beats a minute, with cold perspiration on my forehead and neck. It took me a long time to return to the present, to banish the bygone fall into the pit.

  I finally forced myself up to full consciousness and looked at the screen above me. The purple blaze of a plasma drive danced against the black backdrop of HC-183 and its surrounding star field. It hung there, falling forever but suspended on the feathery stalk of the drive exhaust. I lay there for about ten minutes, just watching, then looked across at Wenig. He was staring at me, his eyes unblinking.

  "Awake at last," He made a sort of coughing noise, something that I think was intended to be a laugh. "You're a cool one, Captain Roker. I couldn't sleep with that hanging there"—he jerked his thumb at the screen—"even if you doped me up with everything in the robodoc."

  "How long did I sleep?"

  "About three hours. Ready to give up now?"

  I was. It had been my idea, an insistence that we ought to try and get some sleep before we did the next phase of our maneuver around HC-183. Wenig had opposed it, had wanted to go on at once, but I thought we'd benefit from the rest. So I was wrong.

  "I'm ready." My eyes felt as though they'd been filled with grit, and my throat was dry and sore, but talking about that to Wenig wouldn't do much for McAndrew or Nina Velez. "Let's get into position and try the radar."

  While Wenig juggled us over to the best position, sixty thousand kilometers from HC-183 and about the same distance from the Merganser, I wondered again about my companion. They had drawn lots to come with me, and he had won. The other four scientists back at the Institute seemed a little naive and unworldly, but not Wenig. He was tough and shrewd, and I had seen the speed of those hands, dancing over the keyboard. Had he done a bit of juggling when they drew lots, a touch of hand-faster-than-the-eye?

  I thought of his look when he spoke about Nina. If McAndrew was infatuated, perhaps Wenig shared the spell. Something strong was driving him along, some force that could keep him awake and alert for days on end. I wouldn't know if I was right or not unless we could find a way to haul Merganser back out of the field. The ship still hovered over its pendant of blue ionized gases, motionless as ever.

  "How about this?" Wenig interrupted my thoughts. "I don't think I can get the geometry any better than it is now."

  We were hanging there too, farther out from the proto-planet than the Merganser but close enough to see the black disk occulting the star field. We could beam short bursts of microwaves at our sister ship and hope there was enough signal strength to bore through the sheaths of plasma emitted by the drives. It would be touch and go—I had never tried to send a signal to an unmanned ship on high-drive, but our signal-to-noise ratio stood right on the borderline of system acceptance. As it was, we'd have to settle for voice-links only.

  I nodded, and Wenig sent out our first pulses, the simple ship ID codes. We sent it for a couple of minutes, then waited with our attention fixed on the screen.

  After a while Wenig shook his head. "We're not getting through. It wouldn't take that long to respond to our signal."

  "Send it with reduced information rate and more redundancy. We have to give McAndrew enough to filter out the noise."

  He was still in send mode when the display screen began to crawl with green patterns of light. Something was coming in. The computer was performing a frequency analysis to pick out the signal content from the background, smoothing it, and speeding it up to standard communication rate. We were looking at the Fourier analysis that preceded signal presentation.

  "Voice mode," said Wenig quietly.

  "Merganser." The computer reconstruction of McAndrew's voice was slow and hollow. "This is McAndrew from the Merganser. We're certainly glad to hear from you, Dotterel. Well, Jeanie, what kept you?"

  "Roker speaking." I leaned forward and spoke into the vocal input system—too fast, but the computer would take care of that at the other end. "Mac, we're hanging about sixty kay out from you. Is everything all right in Merganser?"

  "Yes."

  "No," broke in another voice. "Get us out of here. We've been stuck in this damned metal box for sixteen days now."

  "Nina," said Wenig. "We'd love to get you out—but we don't know how. Didn't Dr. McAndrew tell you the problem?"

  "He said we couldn't leave here until the ship you are on came for us."

  Wenig grimaced at me and turned away from the input link. "I ought to have realized that. McAndrew hasn't told her the problem with the drives—not all of it."

  "Maybe he knows an answer." I faced back to the microphone. "Mac, as we see it we shouldn't put the Dotterel up as high as fifty gee thrust. Correct?"

  "Of course." McAndrew sounded faintly surprised at my question. "Why do you think I went to such lengths to get to this holding position out here? When you go to maximum setting for the drive, the electromechanical coupling for moving the life-capsule gets distorted, too."

  "How did we miss it on the design?" Wenig sounded unconvinced.

  "Remember the last-minute increase in stabilizing fields for the mass plate?"

  "It was my recommendation—I'm not likely to forget it."

  "We recalculated the effects on the drive and on the exhaust region, but not the magnetostrictive effects on the life-support column. We thought they were second-order changes."

  "And they're not? I ought to be drawn and quartered—that was my job!" Wenig was sitting there, fists clenched and face red.

  "Was it now? Och, your job, eh? And I've been sitting here thinking all this time it was my job." For someone in a hopeless position thirty billion miles from home, McAndrew sounded amazingly cool. "Come on now, we can sort out whose doing it was when we're all back at the Institute."

  Wenig looked startled, then turned to me again. "Go along with him on this—I'm sure he's doing it for Nina's sake. He doesn't want her worried."

  I nodded—but this time I was unconvinced. Mac must have something hidden away inside his head, or not even Nina Velez would justify his optimistic tone.

  "What should we do, Mac?" I said. "We'd get the same effects if we were to accelerate too hard. We can't get down to you, and you can't get up to us without accelerating out past us. How are we going to get you out of there?"

  "Right." The laugh that came over the com-link sounded forced and hollow, but that may have been just the tone that the computer filters gave it. "You might guess that's been on my mind too. The problem's in the mechanical coupling that moves the life-capsule along the column. It's easy enough to see, once you imagine that you've had a two millimeter decrease in column diameter—that's the effects of the added field on the mass plate."

  Wenig was already calling the schematics out onto a second display. "I'll check that. Keep talking."

  "You'll see that when the drive's up to maximum, the capsule catches on the side of the column. It's a simple ratchet effect. I've tried varying the drive thrust up and down a couple of gee, but that won't free it."

  "I see where you mean." Wenig had a light-pen out and was circling parts of the column for larger scale displays. "I don't see how we can do anything about it. It would take a lateral impact to free it—you'll not do it by varying your drive."

  "Agreed. We need some lateral force on us. That's what I'm hoping you'll provide."

  "What is all this?" It was Nina's voice again, and she sounded angry. "Why do you just keep on talking like that? Anybody who knew what he was doing would have us out by now—would never have got us into it in the first place if he had any sense."

  I raised an eyebrow at Wenig. "The voice of infatuation? I think the bloom's off the rose down there."

  He looked startled, then pleased, then excited—and then tried to appear nonchalant. "I don't know what McAndrew is getting at. How could
we provide any help?" He turned to the input system. "Dr. McAndrew, how's that possible? We can't provide a lateral force on Merganser from here, and we can't come down safely."

  "Of course you can." McAndrew's voice sounded pleased, and I was sure he was enjoying making the rest of us try and work out his idea. "It's very easy for you to come down here."

  "How, Mac?"

  "In a free-fall trajectory. We're in a fifty gee gravity field because we're in a stationary position relative to HC-183. But if you were to let yourself fall in a free orbit, you'd be able to swing in right past us, and away again, and never feel anything but free fall. Agreed?"

  "Right. We'd feel tidal effects, but they'd be small." Wenig was calling out displays as he talked, fingers a blur over the computer console. "We can fly right past you, but we'd be there and away in a split second. What could we do in so short a time?"

  "Why, what we need." McAndrew sounded surprised by the question. "Just give us a good bang on the side as you go by."

  * * *

  It sounded easy, as McAndrew so glibly and casually suggested it. When we went into details, there were three problem areas. If we went too close, we'd be fried in the Merganser's drive. Too far off, and we'd never get a strong enough interaction. If all that was worked out correctly, we still had one big obstacle. For the capsule to be freed as Dotterel applied sideways pressure, the drive on the other ship would have to cut off completely. Only for a split second, but during that time McAndrew and Nina would feel a full fifty gee on them.

  That's not quite as bad as it sounds—people have survived instantaneous accelerations of more than a hundred gee in short pulses. But it's not a picnic, either. Mac continued to sound cheerful and casual, mainly for Nina Velez's benefit. But when he listed the preparations that he was taking inside Merganser, I knew he was dealing with a touch-and-go situation.

  After all the calculations (performed independently on the two ships, cross-checked and double-checked) we had started our free-fall orbit. It was designed to take us skimming past the Merganser, with a closest separation of less than two hundred meters. We dared nit go nearer without risking crippling effects from their drive. We would be flying right through its region of turbulence.