24
Traci’s final task before their encounter was to retract the ship’s micrometeor umbrella, minimizing any drag it might create in the planet’s upper atmosphere. At a relative velocity approaching three hundred kilometers per second, their closest approach would only last a few minutes. If they had been slow enough to enter orbit, the impact of stray hydrogen atoms against their spacecraft would have been imperceptible. With the electromagnetic net deployed beneath them she could feel the drag slowing them down ever slightly, a perceptible change in the press of acceleration against her. “One minute to interface,” she said for her own sake more than anything else. Bob would be innately aware of every detail.
As the parasol panels folded back at acute angles, Neptune filled her forward windows. The control deck was awash in shades of blue, the planet ahead an ocean of azure clouds stippled with whitecaps of condensed ammonia and methane rolling past at a dizzying rate as they drew closer. The sensation of speed was a malleable thing in deep space; the background stars were so distant as to seem permanently fixed. But when drawing close to a massive planet like this, their dizzying speed became immediately apparent. While not the behemoth that was Jupiter, Neptune was easily five times larger than Earth and they would be leaving it in their wake in a matter of minutes.
As it had been at Jupiter years earlier, she wished they could linger to study it. Back then they had bypassed every other planet in the outer system on their mad dash to Pluto, once again reacting to Russian audacity. Perhaps it was best to blaze the trail as far as possible, giving others time to follow in their footsteps at a more leisurely pace. Someday.
Taking her focus off the planet and onto the heads-up display projected on the window before her, she was reminded there was nothing leisurely at all about their current condition. Pitch and roll angles remained on target, but relative velocity was at two-ninety-eight kps, down nearly two meters per second. That was enough velocity change to throw their trim angles all to hell if the stabilizing gyros suddenly went screwy. The reaction control jets would compensate at the cost of burning fuel she needed to keep in reserve. She glanced down at the multifunction display and tapped the RCS menu, then caught herself before going any deeper. Not a second of attention could be spared if she could avoid it. “Bob,” she called. “Can you tell me how attitude control is holding up?”
“Stabilizing gyros are at nominal function, forty-six percent of maximum load. Are you concerned about them compensating for the increased atmospheric drag?”
“I am. Let me know if they get inside”—she had to think for a second—“twenty percent of max. I want to keep the RCS jets in reserve.”
“Roger that,” Bob replied crisply, as if he were a copilot in the empty seat beside her.
It was one more adjustment she had to make in her thinking. It was too easy to imagine the AI occupying some space deep inside Columbus, shepherding their untested intake manifolds as they screamed across Neptune’s tenuous exosphere. In reality, Bob could be—was—everywhere. He could at once be shepherding their hydrogen intakes, monitoring the ship’s stability and recalculating trajectories while she piloted them around the planet, all with a speed and accuracy she couldn’t hope to achieve. It was enough to make her question if Cheever and her ilk had a point all along.
That was for later. Right now there was work to do, and it was a little unnerving having this much machinery at her fingertips. Flying F-16s and F-35s had been a different matter—they were designed for one pilot. This felt more like driving a battleship solo through the eye of a hurricane. The altitude on her HUD turned an urgent amber as they passed the first critical point. “We just crossed atmospheric interface. Talk to me, Bob.”
“I thought we were observing sterile cockpit rules. What would you like me to say?”
“I meant tell me how the ship’s doing. Reassure me that we’re not about to fry the exhaust nozzles or lock up the gimbals. Or melt the intake grids.”
“At present there is nothing for you to be concerned with. All systems are operating within acceptable parameters. Would you prefer continuous callouts?”
She stole a glance down at the master panel. The inlet temperatures climbed as they dove deeper into the exosphere, its rarified atoms of hydrogen and helium becoming less so with each passing second. Nothing to worry about yet, but that could change quickly. “That would be nice,” she finally answered, deciding he deserved a better explanation. “It’s for my own reassurance,” she said. “I’m what we call ‘task saturated’ right now.”
“That must be a disconcerting sensation. I have not experienced it yet.”
That drew a laugh. “For my sake, I hope you never have to.”
“As do I. You have geometric altitude, relative velocity and trim angles on your heads-up display. What values would you like to have called out?”
“Delta-v, inlet temps and sink rate.”
Bob immediately began reciting them in his precisely modulated voice. “Minus twelve meters per second . . . minus 12.2 . . . minus 12.25 . . .”
“Whole numbers are fine,” she interrupted. “My brain can’t process any more right now.”
“Roger that,” he said, adopting pilot lingo once more. “Inlet temperatures are within nominal range. Descent rate two meters per second.”
At this speed above the cloud tops, their sink rate was gentle enough to not be worth mentioning. Keep it there and they’d only lose about three and half kilometers. That was good enough. “Drag effect’s about as predicted,” she said, more for herself than Bob.
“It appears so. The intake manifold is beginning to register hydrogen accumulation.”
“I’ll need the rate for that too.” She began to notice a subtle vibration coursing through the hull as hydrogen atoms impacted the collection grid to be ionized and drawn through the intakes, not unlike a spaceplane kissing the first tendrils of atmosphere on reentry. She began to notice a disconcerting glow around the lower edges of the micrometeor panels ahead of them. “What’s the story on structural heating?”
“Hull temperatures approaching one thousand Kelvin. The umbrella shield is steady at twelve hundred.”
“We’ll need to keep it that way,” she said. “Warn me if we’re getting near its upper limit.”
The vibrations became more pronounced, coalescing into a disconcerting rattle. Icons in her display began to jump against the background of Neptune’s cloud tops. Reaction jets began firing automatically, adjusting the ship’s attitude as its center of mass shifted from its rapidly filling tanks. “Pitch trim’s compensating for the CG changes. We must be taking in a lot of propellant.”
“We are,” the AI said. “Surge tanks are almost full. Preparing for transfer to the main tanks.”
“Do it.”
As the freshly collected hydrogen was vented into the cryo tanks, the ship’s balance point moved farther aft. The ship pitched up gently before its attitude jets fired again. Traci kept a light grip on the control column, feeling its automated movements through each pulse of thrusters and ready to take over herself if she felt it getting out of hand. While not exactly bucking like a bronco, she couldn’t let a ship this big lurch into un-commanded pitch oscillations.
As she watched the attitude indicator superimposed on the planet’s limb, she compared it to the rattling sensation she felt through her seat. The control stick shook ever so slightly beneath her fingertips, as if the entire ship was humming to a new rhythm. She checked the event timer: three minutes into their flyby, less than two to go. “Bob, I’m getting concerned about resonance vibration—”
As she said it, seat restraints dug into her waist and shoulders. She was slammed forward to be just as quickly slapped back hard into her seat, biting her tongue. Before she could react, it happened again. Then again. She reached up over her shoulders to cinch down the straps as tight as she could bear. Now it was like riding a bucking bronco. “Pogo!” She vaguely realized Bob might not pick up the lingo.
“Vibrations are approaching vehicle resonance frequency,” he said all too calmly for the situation. The ship was now alternately lurching forward and backward as it raced above the cloud tops.
“No shit!” Her voice rattled along with the spacecraft. The atmospheric drag, however slight, had combined with the changing center of gravity and the engine’s thrust to induce vibrations that matched the ship’s natural resonance. Taken to its extreme, it was the same effect that caused certain notes to shatter crystal if sustained long enough. “Any suggestions?”
“Recommend reduce thrust of the outboard engines,” Bob said. “Alter the vibration frequency.”
Her vision became a blur, the rapidly alternating positive and negative g’s threatening to thrash her like a rag doll against her straps. “That loses too much velocity. Shut down the intake grid instead!”
“Not recommended. Collection manifolds are at full capacity. The catalyzation process is almost complete.”
She cursed under her breath. Bob could be right at the most annoying times. They could eventually compensate for a loss of thrust; losing propellant was another matter despite her private plans to the contrary. The less time in hibernation the better.
Traci reached for the engine controls, then pulled her hand back sharply as the keypad jerked in and out of her reach. This wouldn’t be as simple as hauling back the throttle levers; those were for fine adjustments and this would be anything but. She glanced back up at the event timer, its digits dancing about with the rest of the instruments. A minute and forty to go. It was tempting to see if they could ride it out.
No. If the vibration reached full resonance, it could tear them to pieces in a matter of seconds. She gritted her teeth and reached down for the control pad again, matching her hand’s movement to the ship’s violent back-and-forth lurching. Engine one, engine four. You can do this. She extended her thumb and forefinger and depressed keys labeled MODE SELECT for one and four simultaneously.
She was rewarded with a command query on screen: SELECT MODE. It took all of her concentration to page through the menu prompts while the touchscreen commands were jumping all over the place. Her fingertips hovered over the bouncing screen as she tried to time her movements. Time.
The lurching seemed to be getting worse, and time was something she had precious little of. This chaotic dance with the flight management computer had already eaten twenty seconds.
Computer. Yes. Engine controls had been locked down until she’d opened up the mode-select menu, which meant any crew member could change the thrust settings. “Bob!” she called, her voice quavering. “Controls on one and four are unlocked! Roll them back to fifty percent!”
She felt their forward acceleration tapering off. The AI’s soothing voice narrated their progress. “Ninety percent . . . eighty . . . seventy . . .”
The frenzied lurching began to subside, settling back into a steady vibration. “Oscillation has receded,” Bob reported dutifully. “Engines one and four are at sixty-seven percent thrust. Shall I continue?”
The event timer passed fifty seconds. “No,” Traci said shakily. “I think we’re safe now.” She heaved out a sigh and was tempted to close her eyes, but there was still too much to do. She picked up her instrument scan, falling back into the time-worn habits that had kept her alive when everything else seemed like it was trying to kill her. After a quick assessment of each system to ensure nothing important had just shaken itself to pieces, she focused on the nav display. The pitch cues in her HUD would be useless if they weren’t still targeting the correct orbit.
She shook her head angrily; it was far too much to digest at once. When everything goes to hell, fly the ship and let the controllers do the rest. Aviate, navigate, communicate. That had been the mantra she’d learned from the first day of training. Pilots who forgot that lesson tended to get themselves killed. But in this case, all of her ground support was almost four hours away. If she screwed the pooch, they wouldn’t know about it until it was all over with.
A soothing voice sliced through the frenzied thoughts threatening to consume her. “I have corrected our trajectory to compensate for the new acceleration profile. Attitude cues have been updated in your heads-up display.”
She blinked, clearing the mental clutter to see their situation with fresh eyes. “Yeah . . . yeah. Got it.” The event timer was passing twenty seconds and the chaotic jumble of icons in the HUD had settled back down into something that made sense. “Thanks, Bob. Forgot you were there for a minute.”
“One minute and twelve seconds, to be precise.”
If he was trying to be funny, she needed it. Had it really taken her that long? “Save that for the debrief. How’s the intake grid holding up?”
“Structural integrity appears sound. We did approach the design load limits, but carbon fiber is exceedingly strong. I am still evaluating the effect on the collection field.”
Ten seconds. “Little late for that. What was our uplift?”
“Seventy-eight percent of targeted volume.”
Better than expected, she thought, but maybe not good enough. They could sort that out later.
Five seconds. Neptune’s ocean of azure clouds began to slip beneath them as they pitched up gently in their climb away from the planet.
Two . . . one . . . zero. She snapped open a covered switch on the control pedestal. “Collection grid off.” With the ship no longer bucking wildly, she could confidently tap out commands to the fusion engines once more. “Rolling back to cruise thrust.”
“Grid power off,” Bob confirmed. “Hydrogen uplift now at eighty-one percent of optimum. There is still a considerable amount in the surge tanks to be processed through the catalyst beds.” Before they could be fed into the main tanks, stray helium and methane would have to be separated. “Estimate final uplift at eighty-six percent.”
“Not bad.” She craned her neck forward, stealing one last glance at Neptune as it receded beneath them. Yes, it would be nice to actually spend some time at one of these giants someday.