Acid Sky (8 page)

The room was dominated by a large illuminated table in the centre, which showed the ship at its centre and a radar view of the weather around them, overlaid with a navigation grid. Directly in front of the table was the elevated command seat, which was unoccupied at present; the duty commander was leaning over the chart table. He nodded briefly at Coombes’s request to show Clare around, and bent back to the table.

‘We spend half of our time flying through cloud,’ Coombes explained in a low voice, ‘and even during the day, we’ve got to watch the weather radar constantly, to avoid any significant turbulence.’ He pointed out the thin green line of their forward flight path on the chart table, and the coloured masses of rising and descending air that lay ahead of the ship.

‘Is that the helm position?’ Clare asked. She nodded at two seats set side-by-side, facing forward in a cockpit arrangement, with the main flying displays set in front. A crewman sat in one of the seats, his hands off the controls, monitoring the
Langley’s
flight.

‘Sure is. And to the left of it, that’s the trim and ballast console. We move ballast – mainly water, but also the stored propellants for the aircraft – between tanks to maintain our trim in the air. It reduces the control forces and helps keep us stable during takeoffs and landings.’

The duty commander stood up from the table and beckoned them over.

‘Lieutenant Colonel Conway, first officer. Sorry I missed you last night.’ He extended a hand to Clare. Conway was tall and thin, with a narrow face to match, and didn’t smile. He looked tired, as if he had been up all night.

‘Sec— First Lieutenant Foster, sir.’

‘Congratulations on your promotion, lieutenant.’

‘Thank you sir.’

‘Come and see what we do here.’ They clustered round the chart table, and he zoomed out the display until the globe of Venus was visible, with its latitude and longitude lines overlaid. ‘Right now, we’re flying a course along the line of fifty-five degrees north latitude. Our airspeed’s just under seven hundred kilometres per hour, and we’re flying with the prevailing winds, so our ground speed is about nine hundred. You can see us here, on the ground track view—’

He switched modes on the display, and the small arrowhead of the ship could be seen moving rapidly across the hidden landscape below. ‘If we zoom in again and go back to airspeed mode, you can see the various components of our velocity, and our attitude to the relative wind.’

‘You reduce airspeed for recoveries though, sir?’

‘Yes we do; we come down to about four hundred and sixty kilometres an hour. It’s a bit of a balancing act – we’d prefer to fly faster as it gives us more lift, but then aircraft making landings would be flying too fast to lower their landing gear into the slipstream. We increase our speed after recovery so that we can maintain our circuit of the planet every twenty-four hours. It’s not a precise thing; sometimes we have to circle back, or reposition ourselves for takeoffs and recoveries, and that changes the sunset and sunrise times, but it averages out overall. We can always increase engine power and do a catch-up if we need to.’

‘Is it true that we can fly on just one engine?’ Clare asked cautiously.

‘More or less,’ Conway nodded. ‘We can stay flying and maintain altitude with one engine on maximum continuous power. Two engines, and we can climb and move where we like on the planet, and the other two engines are for safety. But the ship’s more stable and controllable if we keep all four engines running all the time. The reactors and engines last longer at lower power settings, too. Number three engine can’t be run at a hundred percent thrust any more, as it’s showing early signs of a problem in one of the shaft bearings, but it doesn’t cause us any issues.’

‘Are the engines controlled from here as well?’

‘Yes, we can adjust reactor power, bypass ratio and the inlet configurations if we want to –’ he indicated a set of controls in front of the helmsman ‘– but most of the time we don’t touch them; all the engine parameters are managed through the autopilot. We do have manual controls if we need them, though.’

Clare looked at the helmsman’s position and saw the sidestick and rudder pedals. ‘Do you ever have to fly manually?’

‘Only for practice. You have to be very careful with control inputs to avoid overstressing the airframe and shortening its life. Normally, we fly on the autopilot, and just dial in any course or altitude changes; the autopilot looks after the rest.’

Conway turned back to the chart table and changed the display again. ‘This is the weather radar view, with us at the centre. We’re taking a course round this line of thunderheads here.’ He tapped the display about fifty kilometres ahead of the ship. ‘We’re actually turning now, although you can’t feel it.’

Clare stood still and tried to feel any motion, but Conway was right; the ship felt rock-stable beneath her. She looked back at the illuminated chart table, and the red splotches of storm clouds ahead of the ship.

‘Can you see lightning in the clouds, like on Earth?’

‘Sure. You can sometimes see flashes in the clouds at night if we’re flying directly over a storm, but the lightning is mostly deep in the clouds.’ He straightened up from the table. ‘I need to get back to my duties, but you can stay and watch as long as you want.’

Coombes looked at Clare, but she smiled and shook her head.

‘Thanks very much sir, we’ll move on.’

‘Thank you, sir,’ Clare added.

‘You’re welcome, lieutenant.’ Conway nodded and bent back to his task, the light welling up from the chart table showing up the lines on his face.

Coombes and Clare walked along the corridor that led away from the control room, past the captain’s and senior officers’ staterooms. They put their heads round the door of the communications room (‘just a load of blinky lights in racks,’ Coombes remarked), and continued to the end of the accommodation area, and went up the aft stairs. At the top, Coombes opened a red airlock door into an access way, and they stepped through, leaving the accommodation decks behind them.

Clare had been this way before, yesterday when they had arrived. It was cold in the corridor, and very basic, with bare metal walls; they had left the living areas behind.

‘We’re walking over the main liquid oxygen tanks; that’s why it’s so cold,’ Coombes explained, his voice echoing along the walls. ‘Deck elevator pit’s on our right.’

They stepped through another airlock door, and continued down a long corridor that ran right to the back of the ship. Stairwells led down at intervals to the lower deck, and about halfway along, a branch to their left ran out through the wing structure to the control tower, where Clare had been first thing that morning.

They went down the next stairwell to the lower deck, and along an identical corridor that ran beneath the upper one. A noise of hammering and machinery came through the walls as they came up to a red-painted airlock door. They stepped inside, and Coombes closed the door and pressed the two buttons to start the airlock sequence. The status display stayed green, and he pressed the button to release the outer door, which was marked with a prominent sign in large white letters:

DANGER

OPEN TO ATMOSPHERE

‘Don’t worry, this hangar’s pressurised at the moment.’ Coombes indicated the sign. ‘But if that indicator light isn’t green when you come in here, you’ll need a facemask to go in.’

The inner door slid aside, and the noise of the maintenance hangar opened around them, along with the familiar smells of oil and hydraulic fluid.

The hangar was at the very end of the carrier, located behind the unpressurised main hangar, and occupied a large space about forty metres across each way and seven high. A closed set of large pressure doors sealed off the entrance to the main hangar, and the two end corners were cut off by curving walls where Clare guessed the refineries lay. The entire space was filled with Frigate aircraft in various stages of repair and overhaul. Hoses and cables snaked across the floor to where technicians worked on the aircraft, and the intermittent sound of an impact wrench punctuated the banging and crashing noises of a busy maintenance operation.

With a whine of electric motors, an access platform lowered from above them, and the maintenance chief leaned over the side.

‘Mind if we take a look around?’ Coombes shouted up.

‘Go ahead. Just stay clear of anything that moves, we’re about to power up the hydraulics.’ The chief leaped off the descending platform and walked off towards the nose of the nearest aircraft, which was raised off the deck on support frames, its landing gear hanging in the air.

‘Major maintenance check,’ Coombes commented. ‘They’re up against the clock because we've always got to keep a minimum of eight aircraft in serviceable condition.’

Clare nodded. She was still taking in the scale of the operation, and she had to keep reminding herself that this hangar wasn’t on the ground, but flying along in the skies of Venus.

Red warning lights started flashing, and there was a sharp hiss of compressed air. A loud whine of electrically-powered hydraulics broke out close by, and Coombes and Clare stepped backwards instinctively as the folded wingtip of the aircraft started to move. It swung up and over in a graceful arc until it stopped in its flight position, and there was a clunk of metal pins sliding home to lock the wing in place.

Underneath the aircraft, the nose and main landing gear lifted up into their bays, and the doors closed over them. Then the sequence reversed, and the doors opened and the landing gear lowered again and locked in place. The chief stood off to one side with his arms folded, watching the test with a group of technicians, and finally signalled for the systems to be powered down.

The red lights stopped flashing, and Coombes and Clare walked under the right wing and round to the rear of the craft. The painted finish on the underside of the Frigate was dirty and worn in places from countless landings. She stopped, and ran her finger over the exposed metal.

‘What do you do about corrosion?’

‘Huh?’

‘Corrosion – from the acid in the air.’

‘Oh – well the metal's a special alloy to resist corrosion, but it’s not really a problem at this altitude in any case, as the concentration’s so low. They get regular checks for corrosion on critical components, and a wash down every so many flying hours. The biggest corrosion problem is the carrier structure itself, as it has to go deep into the clouds every night to mine the air.’

‘So what do you do? About the carrier I mean – you can’t go outside to inspect it.’

‘No, but it’s so big that most of the critical parts of the airframe – the wing spars and so on – can be inspected from the inside. The outside skin though, well that’s just got a service life. It’s supposed to last longer than the reactors will, at least in theory, so it shouldn’t matter. It’s too early to tell, really.’

Coombes paused, and looked round the maintenance hangar, then back at Clare. ‘You seen enough?’

‘Sure.’

They walked back to the airlock, raising a hand to the chief as they left the hangar.

‘Where next?’ Clare asked as they stepped out into the lower main corridor again.

‘The refinery. Don’t look like that, you’ll love it. It’s my favourite place.’

Clare smiled and shook her head as they walked along the corridor towards the rear of the aircraft, a steady roar growing on their left. Coombes stopped at a featureless point in the corridor. ‘This is as near as you’ll ever get to a working nuclear reactor.’ He patted the outer wall.

‘The engines, right?’

Coombes nodded. Right inner engine, just the other side of this wall. And a hundred-megawatt through-flow nuclear reactor, although there’s plenty of shielding between it and us.’

Clare swallowed. It was incredible to think that less than three metres from where they stood, a working nuclear reactor was heating highly compressed atmosphere, and expelling it to provide thrust and power. And there were three other engines besides this one.

‘What power’s it running at?’ she asked.

‘Well, we’re in cruise at the moment, so maybe a third power. We only use full power if we need to get somewhere in a hurry.’

‘And the refinery, that’s on the other side of this corridor?’

‘Yup. The intake ducts from the engine compressors go under where we are now. Come on, let me show you.’

They walked to the end of the corridor and took a door on their right. The noise assailed them as they entered a large space, as high as the hangar they had come from, filled with machinery, pipes, pressure vessels, and the noise of a working chemical extraction plant.

‘The air comes in over there,’ Coombes shouted above the din, pointing to a wide duct at the end of the room. ‘First step is the pressure swing adsorbers – these four big columns, which extract the useful gases from all the carbon dioxide. We have to process a million tonnes of atmosphere to get just forty tonnes of condensate – that’s dilute sulphuric acid to you and me, although there’s other stuff mixed in with it. The nitrogen from the adsorbers is used for our breathing air mix, and the condensate goes to the electrolysis plant –’ he waved to two vertical cylinders ‘– where we extract hydrogen and oxygen, then the hydrogen’s purified further over here before it goes off to the Fischer-Tropsch reactor, and we get propane, water and – well, you know how it works.’

‘Sort of.’ Clare made a wry smile. ‘Chemistry was never my strong point.’

‘It wasn’t for me either, until I came here. Then I saw this place, and I was just blown away by how it made all this stuff, just from the air. So I read up about it. You see over there?’ He pointed out some frost-covered pipes. ‘That’s the output from the Fischer-Tropsch reactor. It takes carbon monoxide and hydrogen in, and – makes fuel. Those pipes take the liquefied fuel to the holding tanks in the middle of the ship, ready for our aircraft.’

Clare stared upwards at the refinery plant and its intricate pipework. A million tonnes of air, just to get forty tonnes of condensate. And from that, this plant could make oxygen, water, nitrogen, fuel – everything they needed. The sheer volume of atmosphere passing through this plant every day beggared belief.