Titan n-2

by Stephen Baxter

  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…

  The pressure mounted, climbing fast, impossibly quickly, slamming her into the couch. Titan’s thin, cold upper atmosphere was hauling at Jitterbug in earnest.

  …Assuming, of course, the theoretical models of Titan’s atmosphere were right. And Mott, after six years in microgravity, for all her exercising, wasn’t as robust as she used to be.

  A pale, grey-white glow began to gather at the base of the window. It was plasma, the atoms of Titan’s air smashed to pieces by the passage of this intruder from Earth, gathering in a thickening shock layer beneath the Command Module. The air of Earth produced a pinkish, almost welcoming glow on reentry. But the light of Titan’s plasma, a thin mix of ionized nitrogen, methane and argon, was a cold pearl-grey glow.

  Even the plasma was alien here.

  Benacerraf was still speaking to her, she realized belatedly. She tried to call back, to acknowledge; but Benacerraf’s voice was breaking up in static as the plasma shell engulfed Jitterbug.

  A hundred and eighty miles above the surface, the deceleration peaked. Mott lay on her back, buffeted, compressed, while the cabin equipment rattled around her. She was deep in the atmosphere, moving at Mach twenty. The weight on her was huge, crushing, worse than anything she had imagined in six years of anticipation of this ordeal. The surges in deceleration seemed astonishingly abrupt, violent. She could feel her internal organs sliding over each other, flattening against her spinal column. Her limbs felt as brittle as twigs, her muscles as limp as wet string; she didn’t dare move a limb. She didn’t seem to have the strength to draw in a breath, and she felt panic creeping over her as the oxygen in her lungs grew depleted.

  The colors leached out of the big clunky control panel in front of her, and walls of darkness closed in around her vision. It was hard even to blink, to relieve the dryness of her eyes. Her mouthpiece felt like an iron bar being forced against her jaw. Unable to see a chronometer, she tried to count, to reduce this experience to a finite time that must pass. A thousand and one. A thousand and two…

  She couldn’t concentrate. She lost count. She wasn’t even able to maintain the rhythm of the count.

  Starved of blood and oxygen, her brain was closing down. The darkness at the fringe of her vision closed in, like sweeping curtains.

  Then, as suddenly as it had mounted, the pressure faded. The weight on her chest was lifted off. She sucked in air, her chest expanding against emptiness.

  The glow of the plasma was fading. Beyond Jitterbug’s window there was a rusty orange glow. Already she was deep within the air-ocean of this drowned moon; above her was a hundred miles of murky aerosol haze, a hundred miles of cigarette smoke.

  For the first time in six years, Mott’s sky was no longer black.

  The fiery entry phase was already over. The G meter read nought point one four — Titan gravity, one-seventh of a G. Three minutes after leaving orbit she was falling, alone, towards a hidden landscape, at nine hundred miles an hour.

  Now, the first drogue parachute should deploy. It would burst from the parachute compartment in Jitterbug’s nose with a pyrotechnic bang, blowing away the apex cover of the compartment, and then open with a snap…

  Nothing happened.

  She checked her mission timer and G-meter against the checklist, still fixed to the control panel before her.

  The drogue should have opened by now. If the drogue didn’t open, neither would the main chutes.
/>
  Shit, she thought. What did I miss?

  She punched the manual drogue deploy button.

  After a few seconds she heard the bang of the drogue’s pyrotechnics. The drogue chute hauled at the capsule, jolting her hard into her couch.

  Jitterbug’s velocity slowed — in thirty seconds and five miles — to three hundred feet per second, well below the speed of sound.

  A hundred miles up, the air temperature outside was minus 120 degrees C.

  Another bang. That had to be the mains, the three eighty-footer ringsails which would lower Jitterbug gently to the surface of Titan. Through the little docking windows above her Mott could see the main chutes as they unfolded, streaming upwards lazily in the thickening air. The chutes were unbleached, to save weight; they were yellow, like three big dirty jellyfish.

  Jitterbug became a huge pendulum, swinging on a wide, slow path, suspended beneath the mains, in Titan’s feeble gravity taking all of forty-five seconds to complete a cycle; it was a slow, comforting rocking.

  She felt her heartbeat slow, the moment of panic over.

  What did I miss?

  The Command Module was supposed to be controlling its own sequence of operations, now, as it went through its cycle of pyrotechnic explosions and parachute deployment. The main Arming Timer fired the pyrotechnics in a hard-wired sequence keyed to deceleration measured by a G-switch. The idea was to improve reliability, to provide a hardware-managed timelining that was independent of the Command Module’s computer processor and software.

  That was the idea, anyhow. She scanned back up her checklist.

  …Oh.

  She had been supposed to enable the whole system by throwing a couple of switches, to start the Titan landing system and disable the reaction control shutdown. She should have done that just after emerging from the heavy deceleration of the entry phase.

  She hadn’t. Maybe if she hadn’t been alone, she wouldn’t have missed it.

  So far it all seemed to be working, however. Except for her human error. Everything — her life — depended on how robust the reworked systems now proved to be, in the face of that mistake.

  She heard a rattle of solenoids; the capsule jerked about, startling her.

  It was the reaction control thrusters. They were still firing, trying to damp oscillations in the vehicle’s attitude, their action futile so deep in the atmosphere. It shouldn’t be happening. The RCS should have been disabled, at the start of the auto sequence that she’d missed.

  She snapped the RCS switch to OFF. The solenoid rattle died immediately.

  The fact was, she was off the nominal program, now.

  By failing to enter that command to start the new customized automated sequence, she was having Jitterbug follow fallback paths.

  Fifty-year-old logic paths, designed, originally, for entry into Earth’s comparatively benign atmosphere. And although those logic paths had been tested out, there was no way they could have been made as safe as the primary path…

  She felt a flicker of unease.

  For fifteen minutes Jitterbug drifted under its main chutes, its speed gradually dropping. It was as if she was suspended above the surface of Titan in the metallic gondola of some balloon.

  She monitored the Command Module’s clunky systems, waiting for the next glitch, the next anomaly.

  She tried the periscope display. This was an oval piece of glass about a foot across set in the middle of the instrument panel before her. The periscope gave her a fish-eye view of the surface, looking down past the scorched white tiles of the hull:

  A layer of thin white cloud, like cirrus, came ballooning up around her. Methane ice. Once through that, she looked down on a rolling, unbroken layer of thick, dark methane-nitrogen clouds, hiding the murky ground below. The clouds were almost Earthlike: fat, fluffy cumuli…

  She could turn the periscope this way and that, with a little joystick in front of her. She imagined the tiny lens poking out of the hull and swivelling, above her head. The periscope had actually been cannibalized from an antique Mercury capsule, one of the original production run, which had been designed without windows; the periscope had been installed after protests from the astronauts to give them a view.

  Even the effort of twisting the joystick seemed to deplete the muscles of her hand. It was going to take her a good while after landing before she had acclimatized enough to clamber out of her couch and try cracking the hatch.

  After fifteen minutes the Command Module’s velocity was reduced to a hundred and twenty feet per second, and she was ninety miles above the surface. Now, with a crack of pyrotechnics above her, the main chute was jettisoned.

  For an instant she was falling freely.

  And then the final chute, the paraglider, opened up; and she was joked back into her couch once more.

  She let out her breath. She was through another command sequence which hadn’t gone wrong. Maybe she would live through this yet.

  The paraglider was just a shaped canopy, marginally steerable. It was another old idea, that had been tried out for Gemini. Thus, a Gemini paraglider and a Mercury periscope should let Mott fly an Apollo capsule, like Dumbo, down to the wreck of a Shuttle orbiter, a billion miles from home…

  Fifty miles above the ground, Jitterbug was immersed in thickening orange petrochemical haze. But the sun was still plainly visible as a brilliant disc, surrounded by an aureole, a yellow-brown halo. Mott swivelled her periscope until Saturn was fixed at the center of her oval window. But already the water-color yellow wash of Saturn’s surface was becoming fainter, obscured by the uniform brown smear of the smog. She stared into the periscope until at last the planet’s fat, elliptical outline was lost, as if fading out on a poorly tuned TV screen, and the cloud closed over.

  The sun, she saw, had vanished too. She had watched her last dawn, her last sunset. She was stuck down here, for good or ill.

  Forty miles high, Jitterbug fell out of the condensate haze, into a layer of clearer air. Then, at thirty miles, it penetrated the fat methane clouds. The temperature was close to its minimum here, at minus two hundred degrees Centigrade. The clouds were dark, brooding, as if stormy. Deep within the clouds, the cabin grew dark, and the lights of the instruments on the panel before her seemed to glow brighter.

  Suddenly the altimeter kicked in. She was at a hundred and fifty thousand feet, it said. Feet, not miles: the measure of an aircraft, ballooning down through Titan’s atmosphere.

  Jitterbug emerged from the base of the clouds, which now hid the orange sky.

  Gradually, through mist and scattered cloud, for the first time, Titan’s surface became visible to human eyes.

  …Fluffy clouds of ethane vapor lay draped over glimmering circular lakes, which were cupped in continents of water ice. The liquid in those lakes was black to her vision, the round ponds puncturing the red-brown carcass of Titan like neat bullet-holes. It might have been a high-altitude view of Earth’s surface, though rendered in sombre, reds and browns, a twilit panorama…

  She reached out and took hold of a handset on the panel in front. of her. The handset controlled the paraglider, by tweaking at its cables. Using this she ought to be able to fly the Command Module right in to the orbiter, with an accuracy of — the designers had told her — a hundred yards or so. And in the limited VR sims they’d set up, she’d consistently scored better than that, getting down to within thirty or forty feet of the target.

  But first she had to spot her target, the orbiter on the surface. She peered anxiously into the periscope. The surface of Titan — in the fish-eye view, bulging towards her — was resolving into a landscape of mud and crater lakes. The smaller lakes, a couple of miles across, were simple circles. But she could see central peaks protruding from the centers of some of the larger lakes, their shores washed clean of muddy slush.

  And now Jitterbug drifted over a pair of giant craters, each perhaps fifty miles across. In one of these the central peak seemed to have broadened into a dome, so that the ethan
e pool was contained in a thin ring around a central island. But she could see a pit at the center of the dome, itself containing a small pool, so the whole structure had a bull’s-eye shape, with the solid circle and band of dark fluid contained by the circular crater rim. And in the second of the big craters, the outer annulus of fluid seemed to be heaped up against one wall of the crater — perhaps by some tidal effect — so that the lake was in the form of a semicircular horseshoe. The landscape was strange, even the shape of the lakes bizarre. This is Titan, she reminded herself with a shiver. You are a billion miles from home. And there’s nothing in human experience to guide you as to what you’ll find here. The Command Module shuddered, the hull groaning. She gripped her seat, hard. She could feel the hard metal frame through the thickness of her pressure suit gloves. The Command Module felt fragile around her; it was like being inside some flimsy aluminum bathysphere, descending into this murky orange ocean. Now she was suspended over a mountain range, wrinkles in the glimmering surface. The peaks were exposed, dark grey water ice bedrock, and the uniform orange coating of the lower ground lay in streaks that followed the contours of the mountain, like snow runs. The area looked familiar from Rosenberg’s Cassini maps. She turned the periscope, jerking it from one side of the ship to the other.

  There.A little way away from the range was a crater lake, the muddy liquid pooled in the shape of a cashew nut.

  It was Clear Lake: just like the radar images. And Mount Othrys must be somewhere in that range below her.

  …She caught a glimpse of white, embedded on the dried-blood surface like a splinter of bone protruding from a wound.

  It was a delta-shape. Discovery.

  She grinned fiercely, her spirits rising for the first time since Saturn had disappeared. She wouldn’t even have to steer the paraglider much; now all she had to do was glide her way down this last ten thousand feet and—