So the fusion plants don’t sit in one place. They’re big caterpillars, crawling endlessly outward from the equator. Their computer programs make them seek the surest footing over the outcroppings of rock—only they run on tracks, not feet. We saw one about midday, creeping over a ridgeline in the distance, making about a hundred meters in an hour, sucking in ice and spewing an ammonia-water creek out the tail. It carried a bright orange balloon on top. If it melts its surroundings too fast and gets caught in a lake, it will float until a team can come to fish it out.
Given half a century, they’ll give us a thick atmosphere and burn away the toxic gases. Another twenty years and there will be Earth-style air and crops and people on Ganymede. I might live to see that—or maybe by that time I’ll be in a Walker on Titan. Saturn’s huge moon.
Not that Ganymede was all that cozy now. Our cabin heater ran constantly to fight off the chill that seeped in. Halfway through Monday morning we stopped in a narrow valley and I suited up; the sensor package I had to check out was a klick away, halfway up the side of a hill. The path was too dangerous for the Walker.
I was glad to get the exercise. Ammonia fog boiled up from the valley and wreathed the peaks ahead. I got so interested in the view I almost missed the package. It was a metal box with scoops and nozzles sticking out in all directions. I opened it up and took out the set of test tube samples I was to carry back. The map had carried a red tag at this one, so I looked it over.
The water collector had a pebble caught in the middle. Probably it had lodged there during one of the pint-sized quakes Ganymede has: tidal strains keep the rock and ice sheets butting each other. I replaced a defective bleeder valve in the oxygen sampler and hiked back to the Walker.
After I unsuited I made the mandatory hourly radio call back to the base. A familiar voice answered.
“Zak!” I said. “Don’t tell me you’re holding up your literary career to stand radio watch.”
“Funny man. There isn’t anything else to do, with a bum ankle. How are you and Yuri making out?”
“Okay. Say, would you monitor that package I just fixed?”
“Sure, just a minute. Yes, she’s sending an all clear now.”
We talked for several minutes. There wasn’t any important news from the Can and Zak seemed a little bored.
Yuri nudged me. “You guys going to talk forever?”
“Signing off, Zak.” I said, and replaced the mike. “What’s bugging you, Yuri?”
“Nothing. I just don’t think you guys should jam up the airwaves with idle chatter,” he said, not looking at me.
It seemed to me he was put out because Zak didn’t ask to speak to him. Even Yuri wanted to have some friends; there’s nothing like a few days out in the Ganymede wastelands to make you feel lonely.
We stopped several times that day to check out sensor packages. Most of them were at least a few hundred meters from any spot a Walker could reach. They’re set up high to keep them out of the gully-washers that sometimes come pouring down the valleys from some distant fusion caterpillar. Yuri and I took turns going out to them; somebody has to stay with the Walker at all times.
I found one package that had been the victim of a quake. The soil under one of its legs had dropped two feet and the package was teetering on the edge of a hole. All its sample tubes had broken.
The third time Yuri went out he came back empty-handed. He couldn’t find his package. I violated regs a little—the site was only a city block away from the Walker—and walked out to it with him.
“You know, I remember this spot,” I said. “We came by here a few years ago. The package is right around this ledge.”
“Well, it’s not here now,” We were standing by a shelf of yellow rock with boulders scattered around.
“What did the map say was wrong with it?”
Yuri looked around impatiently. “It stopped transmitting a few months ago. That’s all they know.”
I turned to go. “Well, there’s—wait a minute! Isn’t that a Faraday cup?”
I bent down and picked up a little bell-like scrap of metal that was lying in the dust. “One of these is usually attached to the top of a sensor package.”
I looked at the nearest boulder. It must have weighed a ton, even on Ganymede. “I bet I know where our package is.”
We found one other piece of metal wedged under the edge of boulder. I hiked back and got a replacement package. It took a while to set up and this time we put it away from any overhang.
Getting the package’s radio zeroed in on the base was a little tricky since we were down in a low trough and had to relay the signals from base through the Walker’s radio at first. It took a big chunk out of the day. The next package to be checked was a mile walk from our planned way station for the night. We elected to leave it for morning, but then I got restless and said I would walk out to the site myself.
Jupiter’s eclipse of the sun was just ending as I set out. I took a break to watch the sun slip out from behind Jupiter. Suddenly the planet had a rosy halo; we were looking through the outer fringes of the atmosphere. The Can was a distant twinkle of white. I walked along a stream bed and in a way it was like early morning on Earth—as the sun broke out from behind Jupiter things brightened, and the light changed from dull red to a deep yellow. Everything had a clean, sharp look to it. The sun was just a fierce, burning point and there were none of the fuzzy half-shadows you’re used to on Earth. Ganymede’s man-made atmosphere is still so thin it doesn’t blur things.
I felt a pop. I stopped dead. I stood still and quickly checked my suit. Nothing on my inboard monitors. My lightpipe scan showed nothing wrong on my back. Suit pressure was normal. I decided it must have been a low-energy micrometeoroid striking my helmet; they make a noise but no real damage.
The micrometeoroid was probably some uncharged speck of dust, falling into Ganymede’s gravity well. If it had been charged, the superconductor threads woven into my suit would have deflected it. Superconductors are a marvel. Once you run a current through them, they keep producing a magnetic field—forever. The field doesn’t decay because there’s no electrical resistance to the field-producing currents. So even a one-man suit can carry enough magnetic shield to fend off the ferocious Van Allen sleet. And inside the suit there’s no magnetic field at all to disturb your instrumentation, if the threads are woven in right. The vector integrals involved in showing that can get messy, especially if you don’t know Maxwell’s equations from a mud puddle. But the stuff works, and that’s all I needed to know.
When I found the sensor package it needed a new circuit module in its radio; the base had guessed the trouble and told me to carry one along on the walk out. That wasn’t what interested me, though. This particular package was sitting in the middle of a seeded area. Two years ago a team of biologists planted an acre of microorganisms around it. The organisms were specially tailored in the Lab to live under Ganymede conditions and—we hoped—start producing oxygen, using sunlight and ice and a wisp of atmosphere.
I was a little disappointed when I didn’t find a sprawling green swath. Here and there were patches of gray in the soil, so light you couldn’t really be sure they were there at all. Over most of the area there was nothing; the organisms had died.
The trouble with being an optimist is that you get to expect too much. The fact that anything could live out here was a miracle of bioengineering. I shrugged and turned back the way I had come.
I was almost halfway back to the Cat when I felt an itching in the back of my throat. My eyes flicked down at the dials mounted beneath my transparent viewscreen. The humidity indicator read zero. I frowned.
Every suit has automatic humidity control. You breathe out water vapor and the sublimator subsystem extracts some of it before passing the revived air back to you. The extra water is vented out the back of the suit. You’d think that if the microprocessor running the subsystem failed, you’d get high humidity.
But I had too little. In fact, none.
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I flipped down my rear lightpipe and squinted at my backpack. Water dripped from the lower vent. I checked my—
Dripped? I looked at it again.
That shouldn’t happen. The suit should have been venting water slowly, so it vaporized instantly when it reached the extremely thin atmosphere outside. Dripping meant the relief valve was open and all my water had been purged.
I called up a systems review on my side viewplate, just below eye level inside my helmet. From the data train I guessed the humidity control crapout had been running for over half an hour. That was what had made the popping noise. And I had written it off as a micrometeoroid. Wishful thinking.
I stepped up my pace. The tickle at the back of my throat meant I might have suit throat. That’s the coverall name for anything related to breathing processed air. If you get contaminants in the mix, or just lose water vapor, your throat and nose soon dry out, or get irritated. A dry throat is a feasting ground for any bacteria hanging around. If you’re lucky, the outcome is just a sore throat that hangs around for a while.
I hustled. Off in the distance I could see the faint aura of orange from a fusion caterpillar. The rising mist from its roaring fusion exhaust diffused the light for tens of klicks. Blue-green shadows in the eroded hillsides contrasted with the gentle orange glow. Suddenly Ganymede felt strange and more than a little threatening.
I was glad when the Cat came within sight. It was backed up to the way station. I clumped up the ladder and wedged through the narrow lock into the cabin.
“You’re in time for the feast.” Yuri said.
“Hope I can taste it.”
“Why?”
I opened my mouth and pointed. Yuri looked in, turned my head toward the light, looked again. “It is a little red. You should look after it.”
I got out the first-aid kit and found the anesthetic throat spray. It tasted metallic but it did the job; after a moment it didn’t hurt to swallow.
I broke down the humidity control unit in my suit. Sure enough, the microprocessor had a fault. I look a replacement chip slab out of storage and made the change. Everything worked fine.
I was surprised at how much Yuri could do with our rations. We had thin slices of chicken in a thick mushroom sauce, lima beans that still had some snap in them, and fried rice. We topped it off with strawberry cream cake and a mug of hot tea. Pretty damned elegant, considering.
“My compliments,” I said. “That was undoubtedly the best meal within a million miles.” I felt giddy.
“Some compliment,” Yuri said. “That means I’m better than the base cafeteria.”
I got up from the pullout shelf that we used for a table. The room began to revolve. I put out my hand to steady myself.
“Say!” Yuri shouted. He jumped up and grabbed my arm. The room settled down again.
“I—I’m okay. A little dizzy.”
“You’re pale.”
“The light is poor in ultraviolet here. I’m losing my suntan.” I said woozily.
“It must be more than that.”
“You’re right. Think I’ll go to bed early.”
“Take some medicine. I think you have suit throat.”
I grinned weakly. “Maybe it’s something I ate.” I jerked on the pull ring and my foldout bunk came down. Yuri brought the first-aid kit over. I sat on the bunk taking off my clothes and wondered vaguely where second aid would come from if the first aid failed. I shook my head: the thinking factory had shut down for the night. Yuri handed me a pill and I swallowed it. Then a tablet, which I sucked on. Finally I got between the covers and found myself studying some numbers and instructions that were stenciled on the ceiling of the cabin. Before I could figure out what they meant I fell asleep.
The morning was better, much better. Yuri woke me and gave me a bowl of warm broth. He sat in a deck chair and watched me eat it.
“I must call the base soon,” he said.
“Um.”
“I have been thinking about what to say.”
“Um… Oh. You mean about me?”
“Yes.”
“Listen, if Captain Vandez thinks I’m really sick he’ll scrub the rest of the trip. We’ll have to go back.”
“So I thought.”
“Do me a favor, will you? Don’t mention this when you call in. I’m feeling better. I’ll be okay.”
“Well—”
“Please?”
“All right. I don’t want this journey ruined just because you are careless.” He slapped his knees and got up. “I will make the call.”
“Mighty nice of you,” I mumbled. I dozed for a while. I was feeling better, but I was a little weak. I heard Yuri talking to Zak briefly. I ran over the route we would follow that day. The next way station was a respectable distance away and there was only one sensor package to visit. We would have to spend our time making tracks for the next station—which was just as well, with one crew member on the woozy side.
“Yuri,” I said, “check and be sure we got our tanks filled with air and water. It’s a long way to the next—”
“Bohles, you may be sick but that doesn’t mean you can start ordering me around. I will get us there.”
I rolled over and tried to go to sleep. I heard Yuri suit up and go out. A little later there were two faint thunks as the hoses disconnected from the way station. Then Yuri came back in, unsuited and sat down in the driver’s chair.
The Cat lurched forward and then settled down to a steady pace. I decided to stop worrying and let Yuri handle things for a while. I was feeling better every minute, but another forty winks wouldn’t do any harm. I let the gentle swaying of the Walker rock me to sleep.
I woke around noon; I must have been more tired than I thought. Yuri tossed me a self-heating can of corned beef; I opened it and devoured the contents immediately.
I passed the next hour or so reading a novel. Or rather, I tried. I dozed off and woke up in mid-afternoon. There was a lot of sedative in that medicine.
I got up, pulled on my coveralls and walked over to the control board. “Walked” isn’t quite the right word—with my bunk and the table down, the Cat resembled a roomy telephone booth.
I sat down next to Yuri. We were making good time across a flat, black plain. There was an inch or so of topsoil—dust, really—that puffed up around the Cat’s feet as they stepped. The dust comes from the cycle of freezing and thawing of ammonia ice caught in the boulders. The process gradually fractures the Ganymede rock, breaking it down from pebbles to shards to BB shot to dust. In a century or so somebody will grow wheat in the stuff.
Some of the soil is really specks of interplanetary debris that has fallen on Ganymede for the last three billion years. All over the plain were little pits and gouges. The bigger meteors had left ray craters, splashing white across the reddish-black crust. The dark ice is the oldest stuff on Ganymede. A big meteor can crack through it, throwing out bright, fresh ice. The whole history of the solar system is scratched out on Ganymede’s ancient scowling face, but we still don’t know quite how to read all the scribblings. After the fusion bugs have finished, a lot of the intricate, grooved terrain will be gone. A little sad, maybe—the terraced ridges are beautiful in the slanting yellow rays of sunset—but there are others like them, on other moons. The solar system has a whole lot more snowball moons like Ganymede than it has habitable spots for people. Just like every other age in human history, there are some sad choices to make.
Yuri sidestepped a thick-lipped crater, making the servos negotiate the slope without losing speed. He had caught the knack pretty fast. The bigger craters had glassy rims, where the heat of impact had melted away the roughness. Yuri could pick his way through that stuff with ease. I leaned back and admired the view. Io’s shadow was a tiny dot on Jupiter’s eternal dancing bands. The thin little ring made a faint line in the sky, too near Jupiter to really see clearly. You had to look away from it, so your side vision could pick it out. There was a small moon there, I knew, slowly breaki
ng up under tidal stresses and feeding stuff into the ring. It’s too small to see from Ganymede, though. You get the feeling, watching all these dots of light swinging through the sky, that Jupiter’s system is a giant clockwork, each wheel and cog moving according to intricate laws. Our job was to fit into this huge cosmic machine, without getting mashed in the gears.
I yawned, letting all these musings drop away, and glanced at the control board. “You do a full readout this morning?”
Yuri shrugged. “Everything was in order last night.”
“Huh. Here—” I punched in for a systems inventory. Numbers and graphs rolled by on the liquid display. Then something went red.
“Hey. Hey. B and C tanks aren’t filled,” I said tensely.
“What? I put the system into filling mode last night. The meter read all right this morning.”
“Because you’ve got it set on A tank. You have to fill each independently, and check them. For Chrissakes—!”
“Why is that? Was that your idea? It’s stupid to not combine the entire system. I—”
“Look.” I said rapidly, “the Cat sometimes carries other gasses, for mining or farming. If the computer control automatically switched from A to B to C, you could end up breathing carbon dioxide, or whatever else you were carrying.”
“Oh.”
“I showed you that a couple days back.”
“I suppose I forgot. Still—”
“Quiet.” I did a quick calculation. With only a third of our oxy capacity filled—correction, we’d used some already—and on our present course—
“We won’t make it to our next station,” I announced.
Yuri kept his eyes on his driving. He scowled. “What about our suits?” he asked slowly. “They might have some air left.”
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