Free Acid Sky by Mark Anson Page A

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.
    ‘What happens if it breaks down?’
    ‘What?’ Coombes shouted above the noise.
    ‘I said, what happens if this breaks down? It makes our air, yes?’
    Coombes started to answer, then gestured that they should leave the refinery. ‘Let’s go somewhere quieter.’
    It was a relief to close the door behind them and return to the relative peace of the corridor, where Coombes could continue. ‘There’s another identical refinery on the other side of the ship. We can manage fine on one, although we wouldn’t be able to do as many spaceplane launches – it takes several days’ production for each one of those.’
    He turned and led the way to the very end of the corridor, and up another stairwell. Clare was finding the climbing tiring by now, and she was breathing heavily by the time they emerged in the upper corridor, by another security door.
    ‘Engineering control room,’ Coombes announced as he tapped in the code. The door opened into a large room directly underneath the flight deck ramp, with curved windows looking out to the rear of the ship. Here