Titan

by Stephen Baxter

  Now, Voyager One was racing across space at a million miles per day, heading for the stars.

  But in the year 2014, an expected command from Earth did not arrive.

  Voyager had been designed to operate during an extended lifetime and at a great distance from Earth, with an hours-long downlink-uplink communications round-trip time. Since contact with the ground would not be continuous, the spacecraft could know if it had lost contact with Earth only if it missed an expected command. So the software embedded in its engineering flight computer contained a command loss subroutine.

  When the command did not arrive on schedule, an internal alarm went off.

  The computer went into an algorithm designed to protect the spacecraft and its mission.

  First Voyager was placed in a stable, passive state. Then, for two weeks, Voyager waited for the ground control to solve whatever problem had arisen on Earth, and to send the spacecraft a new command sequence. The basic design assumption was that the control centers would be sending a stream of commands, frantically trying to get the spacecraft’s attention.

  When no command sequence was received Voyager assumed the fault was with itself. It went through an emergency routine, in a bid to reestablish contact with the Deep Space Network stations.

  The procedure worked in a loop. First the computer tried to figure out whether the craft’s radio antenna was still pointing at Earth. Voyager had sensors to detect the sun, and fixed, bright stars like Canopus; it knew where it was in three-dimensional space. The craft was smart enough to know where Earth should be, relative to the fixed stars, at any moment during the extended mission.

  So the software checked the angles, and the antenna was pointed at Earth.

  Still no commands were detected.

  Voyager’s next assumption was that its radio receiver was dead. So it shut down its primary radio and turned on its backup receiver. It broadcast telemetry to Earth, indicating what it thought might have happened.

  There was no response from Earth.

  Voyager went back to the beginning of the loop, and began the reacquisition process once more…

  It could not know there was nobody on Earth who was listening, any more, to voices from the sky.

  The Space Shuttle orbiter Discovery sailed over the equator of Titan, five hundred miles above rust-brown cloud tops. It was flying with its payload bay facing the clouds, and its instruments, battered by their billion-mile flight, peered down at the hidden surface. The blunt heatshields of two Apollo capsules, facing Titan, glowed in the light of the world they had come so far to challenge.

  Nicola Mott sat in the flight deck commander’s seat, loosely strapped in.

  Titan hung above the flight deck windows, above her head.

  From pole to pole, she could see no differences, no details in the drab burnt-brown clouds, no breaks, no structure. There was perhaps a subtle shading, the south hemisphere a little lighter than the north. But the light was so uncertain that Mott couldn’t be sure. And Titan was dark, darker than the enhanced Voyager and Cassini images had led her to expect, a deep dull brown rather than orange.

  It was almost like the flybys of Venus again, Mott thought. Here was the same perfect sphere, the billiard-ball-smooth sheen of haze and cloud, hiding any glimpse of the ground. But the light of the sun was less than a hundredth its strength at Venus; the clouds of Venus had been dazzling white, almost blinding, like sheets of sunlight. Titan looked almost spectral, somber, the ochre hue of its clouds drawn from the palette of some obsessive, gloomy painter.

  And Titan was a small world. Its curve was evident, much more so than Earth from low orbit, and its orange-brown belly protruded at Mott, shaded, obviously three-dimensional.

  Discovery rolled into another two-hour sunrise.

  Mott watched the sun lift through the cloud layers. The thin light, occluded by the air, gave her glimpses of structure: onion-skin layers deep in the clouds, perhaps the glimmerings of faint outer shells, beyond the bulk of the atmosphere.

  And Saturn rise was … remarkable.

  The planet was like a sculpture of glass, two or three feet across, held at arms’s length. Saturn itself was a fat ball of milky yellow crystal, at the heart of a plate of shining rings. The rings—contained well within the orbit of Titan—were tipped up, from Mott’s perspective; they emerged from darkness on the face of the planet, and formed a thin, banded ellipse. Looking along the rings, Mott could see other moons, a string of glowing crescent-beads.

  Under the clouds of Titan the sky would be hidden. It was going to be hell to know that Saturn itself was suspended above the clouds, as motionless as Earth in the black sky of the Moon, and yet forever invisible.

  The hatch opened. Benacerraf and Rosenberg came bustling onto the flight deck, up the tunnel from the orbiter’s mid deck. Through the open access-way to the mid deck—through the airlock and the connecting tunnel to the hab module—Mott could hear the aimless crooning of Bill Angel, blind and alone. His gull-like cries were diminished by distance; sound didn’t carry well in the reduced pressure of the hab module.

  Mott said, “What do you want?”

  “We have to talk,” Rosenberg said.

  Benacerraf looked at Mott and shrugged.

  Mott, reluctantly, released her restraints and pulled herself across the cabin.

  Rosenberg said, “We have to discuss Bill. How in hell are we going to get him to the surface?”

  Benacerraf sighed. “Damn your logical mind, Rosenberg.”

  But it’s a non-question, Mott thought. She avoided the eyes of the others; she stared at the dull ochre Titan highlights on the instrument panels. She said, “Logical, maybe, but he’s starting from an assumption.”

  “What assumption?”

  “That we take Bill down at all.”

  There was a long silence.

  The three of them drew closer together like conspirators, Mott thought, their hair drifting in the sluggish currents of the air. They were gaunt, withered by years of microgravity and a lousy diet and canned air; they must look like three witches, gathered around some spell-book, plotting the fate of another human being.

  Benacerraf said at last, “There is nowhere to leave him. We’re taking Discovery down too, remember.”

  “I know,” Mott said. “That doesn’t alter the suggestion.”

  Rosenberg raised graying eyebrows. “Right. And you’ll be the one who will shove him out the airlock.”

  Mott opened her mouth to reply.

  Benacerraf said, “This isn’t doing us any good. Niki, Bill Angel didn’t ask to finish up as he has. He’s just turned out to be the weakest of us, is all. It could have been any of us. And now, he’s a billion miles from the nearest person who can help him. Save for us. So we take him down.”

  “Anyhow,” Rosenberg said, “you know what Houston says. Maybe being returned to a stable gravity environment will help bring Bill out of this. He’s always going to be disabled, of course. But he was a competent astronaut. Maybe he can still be useful.”

  “And you believe that?” Mott said mildly.

  “Enough,” Benacerraf snapped.

  Mott thought about pushing it.

  After six years, she was sick of Benacerraf’s peevish bossiness. One day, perhaps, she was going to have to challenge the authority that Benacerraf assumed so easily. But now wasn’t the time.

  “Which returns me to my original question,” Rosenberg said. “How do we get him to the surface?”

  Benacerraf frowned. “Each Apollo can hold one, two, three—even all four of us if it has to. Logically, we ought to split evenly between the capsules: two and two.”

  Rosenberg shook his head. “I got to advise against that. We know little enough about this Titan entry as it is, and we’re not sure how the Apollos will behave, after a couple of decades in store and six years of space soak. Anything could happen. Who would want to be alone in a failing Command Module with Bill Angel?”

  “Even if he was sedated?”<
br />
  “Even so. Paula, the entry is going to take hours, remember.”

  Mott said, “We could all four of us ride down in the one capsule. It wouldn’t be comfortable, but with a couch installed in the lower equipment bay—”

  “Again, bad idea,” Rosenberg said. “We ought to go down separately. If one Apollo has a bad landing, we only hurt half the crew; the rest are on hand to help.”

  “But,” Benacerraf said, evidently irritated, “that logic leaves us with only one combination. One and three: one person alone, and two of us sandwiching Angel. Hardly an ideal.”

  “Well,” Mott said angrily, “it might not be what we planned. But it’s what we’re left with. We never planned for Siobhan to get herself killed—”

  “Nicola. The one alone. It has to be you.”

  That hadn’t occurred to Mott. “Tell me why,” she said.

  “You’re the nearest thing to a pilot we have left. I could trust you to fly that Apollo down alone, but not myself or Rosenberg.”

  To fly down to the surface of Titan, a new world, alone… She felt an odd mixture of exhilaration and sheer, unadulterated fear.

  It would be the first time the crew had been separated, since the launch day.

  The three of them gathered a little closer, watching each other, as if in awe of how far they had traveled together, of what they were planning now.

  “All right,” Mott said. “I’ll do it.”

  Both Rosenberg and Benacerraf, simultaneously and apparently on impulse, reached out towards her. Physical contact had become a major taboo for them all; but now they held onto each other’s arms, feebly hugging.

  Benacerraf said, “We don’t have anything to fear. We can do this. We’ll be there for you when you land.”

  “Sure,” said Mott. “See you in the mud.”

  Rosenberg tugged at his wispy beard. “We need another name. A call-sign for the base camp, the landing site of the orbiter… You know, in Greek mythology the Titans were a family of giants, the children of Uranus and Gaia, the sky and the Earth. Before the gods, they sought to rule the heavens. You’ll know some of their names: Rhea, Tethys, Iapetus, Hyperion, Phoebe. And others—Cronos, the leader, Oceanus, Coeus, Crius, Mnemosyne. Their stronghold was Mount Othrys, a counterpart of Mount Olympus.”

  “Oh,” Benacerraf said. “Hence the Geological Survey name for our friendly ice mountain down there. So what happened to the Titans?”

  “Cronos overthrew Uranus, his father. But then there was a ten-year battle, between the Titans and the gods. Zeus beat out Cronos by bringing in Hundred-armed Giants—the Hecaton-cheires—as his allies. Then the Titans were imprisoned, for eternity, in Tartarus. They were locked behind huge bronze doors, and the Hundred-armed Giants were appointed jailers—”

  “Tartarus? Where’s that?”

  Rosenberg pulled a face. “You don’t want to know. A place as far below Hades as Hades is below Heaven.”

  Mott stabbed a finger at Titan. “Then that’s the name for our colony. Where we’re going to have to live out the rest of our lives. Underneath all that orange shit. Tartarus.”

  Nobody disagreed.

  The rusty light of Titan, washing from the hab module’s multiple monitors, made their skin look old, pallid.

  Mott lay on her back in the center couch of Apollo Command Module CM-115, now known as Jitterbug.

  She was alone in here. She was wearing her orange pressure suit. Cool air washed over her face, inside her helmet, bringing with it a smell of plastic and metal; all around her the fans and pumps of the Command Module clicked and whirred. It was a mundane, comforting noise, louder than a Shuttle orbiter or the hab module, somehow more obviously mechanical; it was like being inside some huge, elaborate clock.

  She looked ahead, through the small docking windows set in Jitterbug’s nose.

  She was sailing backward over the orange-brown cloud-sea of Titan. She was in Titan’s shadow, but some light was diffused forward by the thick atmosphere, so that the clouds before Jitterbug were a blanket of rusty oranges and browns, fading into curved darkness far ahead of her.

  And now, in her side windows, the sun rose, a spot of light like a helicopter searchlight, rising up from the blurred haze, the multiple layers of atmosphere she would, today, traverse.

  It was probably the last dawn she would ever witness.

  “Hey there, Jitterbug.”

  It was Benacerraf. Mott flicked the switch on her microphone wire. “I hear you, Bifrost.”

  “I can see you, fat as a goose.”

  She twisted in her couch. And there, framed by the small window to her right, was Bifrost. The familiar cone profile of the second Apollo, illuminated by Titan light, was unmistakable.

  In space, the various upgrades were obvious. No attempt had been made to refurbish the Apollos’ old ablative heat-shields. The base of Bifrost, which would take the brunt of the entry heating, was coated by black silica-based tiles, the same material used on the undersurface of the Shuttle orbiters, bonded to an aluminum honeycomb beneath. And the upper conical surface, which would reach much lower temperatures, was coated with white Nomex felt tiles. The black and white finish, punctured by windows and the gaping mouths of reaction control nozzles, gave Bifrost an oddly modern look, Mott thought, compared to the baroque silver hulls of the old Moon-mission designs.

  Strapped to Bifrost’s base there was another novelty. The classic fat silver cylinder of the Apollo Service Module was replaced by a squat tube six feet long—about half the length of the Command Module—with a fat, flaring nozzle. This was a PAM-D-II, a payload assist module. It was a Thiokol solid rocket booster which had been used as an upper stage for launching satellites from Shuttle and Earth-orbit flights. It was strapped to the center of Bifrost’s heatshield by metal straps, which would be severed by pyrotechnic bolts. The PAM would be used to knock Bifrost out of orbit…

  Discovery had already been flown down, under automatics, to the surface. So here were two Apollo Command Modules, flying in formation around a moon of Saturn.

  “Okay, Niki,” Benacerraf called over now. “You ready for your preburn checklist?”

  “I got it.” The checklist was Velcroed to the instrument panel in front of Mott.

  “Thrust switches to normal.”

  Mott closed her switches. “Thrust switches normal.”

  “Inject prevalves on.”

  “Okay. Prevalves on.”

  “One minute to the burn, Niki. Arm the translational controller.”

  “Armed…”

  The crews had agreed that Mott, alone in Jitterbug, would be walked through her entry burn first, with the aid of Rosenberg and Benacerraf Bifrost would descend an orbit later, two hours after Mott.

  Thus, Mott would be the first human to land on Titan.

  She had been given the mission’s remaining flag to set up, a plastic-coated Stars and Stripes, neatly wrapped in a little cellophane bundle. And on her chest was stitched a tiny Union Jack.

  “Thirty seconds,” Benacerraf said. “Thrust-on enable, Niki.”

  Mott unlocked the control and gave it a half-turn.

  “Fifteen seconds. That’s it. You’ve done it, Niki. Sit tight, now.”

  Sit tight. Sure. And what if the PAM-D doesn’t fire, after six years of space soak? The PAM-Ds were pretty reliable, but had been known to fail, even in Earth orbit, a couple of hours after leaving the KSC pad. And nobody was sure what would happen if those straps failed to sever, and a Command Module finished up carrying a PAM-D, partially expended, through the fires of entry.

  She braced herself for the kick in the back.

  “Two, one.”

  There was a bang, a rattly thrust which pushed her into her couch. It had the crisp, crude sharpness characteristic of solid rocket burns. The push felt enormous, but she knew it was no more than a half-G.

  There was a green light before her.

  “Retrofire,” she said.

  “Copy the retrofire, Niki. See you on
the ground. Don’t mess up the place before we get there.”

  “I won’t.”

  The burn lasted thirty seconds, yellow rocket light flaring from the PAM-D nozzle ahead of Jitterbug.

  The thrust died.

  She heard a thump of pyrotechnics, a clatter against the hull, like birds hopping over a tin roof. It was the straps holding the PAM-D against the heatshield; they had burned through, and the PAM-D was discarded. After a few seconds she could see it through her window, a squat cylinder spinning away over the orange clouds, shiny straps dangling, abandoned after being hauled across two billion miles for its half-minute of service.

  Jitterbug was still in orbit around Titan. But Mott’s orbit now would take her dipping deep into the outer layers of Titan’s thick atmosphere. And there, she would lose so much energy that she would not be able to climb out again.

  She was, she knew, committed.

  “Godspeed, Niki,” Benacerraf called distantly.

  Six hundred miles above the surface of Titan, on the fringe of the deep, massive atmosphere, Mott felt the first brushes of deceleration. The couch frame dug into her microgravity-softened flesh.

  In her window, she could still see Saturn, like a gigantic, gaudy toy.

  There was a rattle of solenoids. Outside the windows, to her left and right, there were little flashes of light. That was the gas of the RCS clusters, flaring against the air of Titan. The onboard computer was trying to keep Jitterbug in its forty-mile-wide reentry corridor, before the air thickened so much that the reaction control system was disabled.

  A light came on before her. It was the oh-five-G light, the measure of the first feeble tugs of deceleration.

  Five hundred miles high, Mott passed through the first haze layer. It was a shell of faint rusty light, which seemed to coalesce above her, blurring Saturn’s image.

  It ought to be a gentle entry. CM-115 was entering the atmosphere from low circular orbit around Titan. It would have to shed a mile per second against atmospheric friction. That compared to the Earth-orbital velocity of five miles per second survived by the Shuttle, Gemini and Mercury, and with the even greater seven miles per second survived by Apollo capsules returning from the Moon. The peak deceleration, in the next few minutes, ought to be no more than one and a half G. That was eminently survivable by an Apollo—even a Command Module that had been in storage for most of Mott’s lifetime…