Below Mercury (12 page)

Clare adjusted the polarization of the windows, and the glare from the sunlight lessened. Her hands moved occasionally, making small adjustments to the autopilot to take them towards the tanker, ready with its load of liquid oxygen.

The spaceplane’s nose lowered gently, and the roar of the turbojets lessened, as the autopilot completed the climb and levelled out at 9,000 metres.

‘I have the LO2 tanker on radar, five kilometres ahead,’ Wilson reported, ‘they’re rolling out of their hold onto our course.’

‘Okay. Report to Andersen when we have them on visual.’ Clare turned her attention to the passengers. ‘Guys, we’re going to be taking on LO2 in a few minutes. You’ll hear some noise when we hook up and the lines are purged, but this is normal, there’s nothing to worry about. Once we’ve tanked up on LO2, there’s just a quick top up on fuel, and we’ll be ready for the orbital climb. Is anyone not okay?’

Nobody spoke, and Clare turned back to the instruments, then looked out and forward, scanning the sky for the tanker.

Two minutes passed before Wilson announced: ‘I’ve got it. Eleven o’clock. Can you see it?’

‘Yup.’ Clare flicked switches, and banked the spaceplane to the left, adjusting thrust to bring them up behind the tanker, a grey airliner-shape streaming faint contrails in the sky ahead. The Sun glinted along the tanker’s wings as the spaceplane moved onto a closing course.

‘Open LO2 fuelling port. Let them know we’re coming in.’ Clare’s eyes didn’t leave the tanker as the spaceplane closed on it from below and behind.

Halfway back on the spaceplane’s upper hull, a section of the smooth metal surface lowered slightly, to reveal the waiting mouth of the liquid oxygen filling port.

Clare increased thrust a fraction, and the spaceplane moved towards the waiting aircraft. The tanker loomed above them as they drew closer, its grey-painted wings filling the sky.

The spaceplane heaved and bucked as it encountered the tanker’s wake. Clare corrected for each unexpected motion, until the spaceplane steadied out in the relatively clear air closer in below the tanker. The contrails from the tanker’s engines streamed out to either side of the spaceplane, racing away into the sky behind them.

Clare lined up with the yellow-and-black fluorescent strip on the tanker’s belly as she closed in. Coloured lights on the underside of the tanker helped direct her into the ‘box’, the cube of air behind the tanker where the refuelling would take place.

The spaceplane shuddered as it flew through a patch of light chop, and Clare compensated. Too much – the spaceplane drifted downwards, and she caught it and brought it back.

The tanker’s copilot directed them to move in closer.

‘Mercury Two Zero Seven, you are four metres behind the box and two metres low, keep it coming.’

Clare adjusted the thrust fractionally; the lightest of touches on the four levers to bring them forward and up. The spaceplane crept closer, and the lights on the tanker flicked to amber, then to green. She was in the box.

‘Two Zero Seven, hold it just there. Extending boom.’

Under the belly of the tanker, the refuelling boom disengaged, and lowered until it trailed below and behind the tanker. The boom extended in sections towards the spaceplane, the small vee-shaped wings at its tip guiding it towards and over the spaceplane, until the probe at its end floated in mid-air, just ahead of the spaceplane’s open fuelling port. It hovered there for a moment, and then slid into the waiting fuelling port with a gentle thud.

The boom contracted slightly, absorbing the energy of the contact, then lengthened again, taking up the gap between the tanker and the spaceplane.

‘Contact.’

‘Roger contact. Purging.’

A sudden roar echoed through the ship’s structure as cold helium gas surged at high pressure down the length of the boom and through the spaceplane’s internal piping. The purge not only cooled the pipework, but also cleared it of any contaminants that could get into the tanks and damage the spaceplane’s rocket engines.

‘LO2 flowing.’

The roar of purge gas cut off abruptly, and was replaced by a steady rushing noise as the super-cold liquid flowed into the spaceplane’s enormous oxygen tank.

‘Okay, that’s it, slaving autopilot now.’ Clare waited until the tanker took over control of the spaceplane, and carefully released her grip on the controls.

She watched the primary flight display intently, her hand resting on the sidestick, ready to break contact at the first sign of trouble, while Wilson monitored the rising levels of liquid oxygen in the main tank.

Minutes passed. Creaks rang through the spaceplane’s structure as the tank adjusted to the sudden chill of tonnes of cryogenic liquid flowing into it. Boiling liquid oxygen streamed away in a long plume behind the spaceplane through the open vent lines. The spaceplane rocked back and forwards slightly, the noise of the engines rising as the autopilot compensated for the increase in mass.

‘Nine zero tonnes,’ Wilson said, ‘still venting.’

‘Keep it coming,’ Clare murmured.

A shower of white ice broke off from the refuelling boom, and was snatched away instantly by the spaceplane’s slipstream. The boom was so cold now that water vapour from the air was freezing onto its outer surface.

‘One hundred tonnes. Nearly there,’ Wilson said. ‘Stand by to break contact.’

A few seconds later, a fountain of pure liquid oxygen gushed out from the venting tubes, leaving a spectacular vapour trail of boiling oxygen behind the spaceplane.

‘Tank full,’ Wilson confirmed, ‘break contact.’

Clare disengaged the autopilot and reduced thrust, and the spaceplane detached from the refuelling boom in a shower of ice and vapour. Clare let the spaceplane fall behind the tanker, and then banked away to the right.

‘Mercury Two Zero Seven, contact broken, moving away. Thanks for the fill, guys.’ Wilson bent back to the navigation display, looking for the rendezvous with the waiting propane tanker.

‘Tanker Eight One. Have a good day.’

Thirty minutes later, over the empty expanses of the western Pacific Ocean, the Olympus-240 spaceplane followed close behind a second tanker.

The transfer of the last few tonnes of super-cold liquid propane fuel was complete. Clare continued to hold contact with the tanker, keeping the fuel tanks topped up while they waited for their orbital climb clearance from Guam Centre, far behind them in the ocean.

High above them, the invisible plane of the Sun and planets crept higher in the sky, until it was almost directly overhead. They hung there for what seemed like an age, floating in the clear blue skies behind the tanker, waiting for the moment when their launch window would open, the narrow sliver of time where the spaceplane’s projected climb path would neatly intersect the orbital plane of the space tug. Finally the clearance came through, the voice faint with distance:

‘Mercury Two Zero Seven, Guam Centre. Clear to launch, left turn onto zero six seven, clear through flight level one one four and orbital climb to three two zero kilometres. Orbit inclination plus two three decimal five, insertion point Sierra One at zero one zero two Zulu.’

‘Okay, let’s get moving,’ Clare said. ‘Breaking contact.’ The spaceplane shuddered slightly as she detached from the tanker and banked away onto their new course, lining the spaceplane up with their orbital path. She nudged the thrust levers forward slightly to give them more airspeed.

‘Clear launch, heading zero six seven, clear climb through one one four to three two zero kilometres, inclination plus two three decimal five, Sierra One insertion at zero one zero two Zulu, Mercury Two Zero Seven.’ Wilson released the transmit and watched the tanker slide away into the distance, propane vapour trailing from its refuelling boom.

‘Visor up,’ Clare commanded, and the heat-resistant visor moved slowly up to cover the windows, smoothing the airflow over the nose and shielding the main cockpit windows from the heat of the hypersonic climb. The interior of the cockpit darkened as the visor closed over them; its small windows gave only the minimum necessary view forward. The roar of air over the spaceplane lessened as the airflow smoothed out.

‘Cockpit lighting.’ Clare’s voice seemed louder in the muffled quietness of the cockpit as she turned to the passengers. ‘Okay, gentlemen, it’s time to prepare for the climb. I want you to check your seat straps, close and lock your faceplate, and cross-check with your neighbour.’

Matt’s pulse quickened as he pulled his seat straps tight over his shoulders and closed his faceplate; the climb was seconds away now. The sound of his breathing was loud inside his helmet as he gave a thumbs-up sign to Rick and received one in return.

Wilson’s voice came over their headsets.

‘Tanker reports clear of launch area. Orbital climb checklist complete.’ His eyes scanned the instruments in an unbroken sequence from behind his faceplate, checking fuel temperatures, engine readiness, and the navigation display for any stray aircraft in the launch area.

They were the only human beings in a five-kilometre radius of the launch. The spaceplane held nearly 160 tonnes of cryogenic propellants and was now a flying bomb; if those propellants were to mix and suddenly ignite, the resulting explosion would obliterate the spaceplane, its crew, and any aircraft that happened to be nearby.

Clare took one last look round the instruments, put her hand on the sidestick, and took a deep breath.

‘Everyone ready? Okay. Set mode to orbital climb. Tanks up to full pressure.’

On the engine displays in the centre of the cockpit, pressure readings swung into the green part of their arcs. The spaceplane’s structure creaked again as the fuel tanks were pressurised with helium, ready to force the propellants into the turbopumps.

‘Full pressure. Ready for ignition,’ Wilson confirmed.

‘Roger. Starting climb.’ Clare eased the thrust levers all the way forward to their maximum thrust setting. The engines’ roar increased, and the spaceplane started to accelerate, climbing into the sky.

Clare watched the thrust and airspeed build up, making small adjustments to the spaceplane’s pitch.

‘Afterburners.’

Wilson pressed the four switches below the thrust levers, and the afterburners lit up in a thunder of blue flame, pushing the crew into their seats. Clare raised the nose further, until they were climbing at thirty degrees, arrowing up into the sky.

The spaceplane shook as its speed built up to Mach one. They were passing through the supersonic transition region, where the aerodynamic forces on the craft’s structure changed rapidly, and shock fronts formed, streaming out behind the spaceplane in invisible compression waves. The engine intakes moved, becoming narrower, slowing the air so that it could flow safely into the whirling blur of the engines.

Suddenly, they were through; the buffeting faded as the supersonic flow stabilised around the craft, and the roar around the cockpit grew strangely quiet. Far behind them, and unheard in the cockpit, a dull, rolling
boom
echoed across the empty skies.

‘Mach one. Engine management to auto.’ The spaceplane’s flight smoothed out now. Behind them, the roar of the engines could be heard through the structure of the craft, but there was no sound coming from outside; just the faint hiss of the boundary layer, where the supersonic flow dragged over the spaceplane’s skin. Clare watched the airspeed rise until they were at Mach two. Her right hand hovered over the autopilot engage button.

‘You’re in the launch box. Vee three.’ Wilson confirmed, watching the figures in his primary flight display change from magenta to white.

‘Commit.’ Clare pressed the autopilot button, and gently released her grip on the sidestick.

Under the control of the autopilot, the spaceplane accelerated towards three times the speed of sound. The climb sequence and engine management from here was entirely automatic, the flight computer adjusting constantly to get the optimum flight trajectory and engine configuration. As speed increased, the air entering the engine intakes was compressed by the sheer speed of the spaceplane through the air, and the hot, compressed air was diverted directly to the afterburners, turning the engines into giant ramjets.

‘Mach three point five. Skin temperature two hundred and climbing,’ Wilson’s voice informed them.

‘Ejection seats safed,’ Clare said, turning and locking the ejection control switch. The display panel changed to show six green LEDs. The seats could not be used from now on; anyone attempting to eject at hypersonic velocities would be smashed instantly to a pulp by the roasting, sledgehammer blow of the airstream.

As the spaceplane’s speed climbed higher still, cold fuel coursed through cooling channels in the nose, and the leading edges of the wing and fins, carrying away the intense heat of air friction. More cold fuel, passing through a dense mass of cooling pipes in the engine intakes, soaked up the scorching heat of the incoming air, followed by a deluge of liquid oxygen to cool the air further and boost thrust from the engines.

‘Mach six. Engines at maximum temperature.’

The autopilot raised the nose slightly, taking the spaceplane into thinner air, trading off ram air pressure, speed, propellant consumption, aerodynamic loads and engine temperature to optimise the spaceplane’s trajectory. It was a delicate balancing act; if the craft stayed too long in denser air, the engines would get too hot and melt, but if the craft climbed too fast, the air would be too thin to provide sufficient thrust.