Below Mercury

by Mark Anson

  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.’

  CHAPTER FOURTEEN

  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.�
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  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.

  It was a battle between two forces: the thrust of the ramjets, pushing the spaceplane forward, and the searing blast of the air, its very molecules torn apart by the hypersonic speed of the craft.

  Through the slit-like windows of the visor, the colour of the sky, already a deep midnight blue, darkened towards black. They were passing into the highest reaches of the atmosphere. Occasional streaks of brilliant light zipped up and over the visor, as tiny flecks of heat resistant paint came off the spaceplane’s nose and flashed instantly to glowing vapour in the airstream.

  ‘Mach ten, reducing thrust,’ Wilson announced. The push in their backs dropped fractionally. The incoming air was so hot now that, even with precooling, the engines could not run at full power. The ramjet combustors and nozzles glowed red-hot as the craft tore upwards into the thinning air, guzzling liquid oxygen to maintain combustion. The roar of the engines altered, rising in pitch to a distant falsetto screech, as the air faded towards vacuum.

  ‘Mach eleven. Ramjet shutdown. Main engine ignition in five.’

  The thrust and noise of the ramjets faded, and for a few seconds, the crew could breathe again. The spaceplane coasted upwards, rising out of the scorching hypersonic air. The glowing nozzles of the ramjets were cooling down, their job done, as the main rocket engines pressurised, ready for firing.

  ‘Ignition.’

  For a moment, nothing seemed to happen, then the main valves to the four engines opened wide, and the whirling blades of the turbopumps forced 32 tonnes a minute of cryogenic propellants into the engines’ combustion chambers.

  The crew were slammed back into their seats by the sudden onslaught of two million newtons of rocket thrust, and the spaceplane surged forward, accelerating into the fringes of the atmosphere on the edge of space. A deep-throated bass rumble came through the spaceplane’s structure, as the huge aerospike engines accelerated the spaceplane past Mach eleven, to Mach twelve, Mach thirteen and beyond; pushing it faster and faster as it climbed towards its orbital speed of nearly eight kilometres per second.

  The navigation displays in front of Clare and Wilson changed, to show the spaceplane’s climb and acceleration against the curving magenta line of its planned orbital trajectory. The control surfaces had no effect, now that the craft was flying in vacuum, and the flight computer steered the spaceplane by tiny nudges to the engines, adjusting the angle of thrust to keep the craft in the correct attitude.

  The spaceplane’s flight angle flattened out as it climbed, so that it was moving almost parallel to the ground far below, adding forward velocity to accelerate the craft into orbit.

  The acceleration mounted as the propellant tanks emptied, rising through two gees, to three gees, and still it climbed. Matt could hardly raise his arm off the armrest of his seat, and it was an effort to breathe; his ribcage was being squeezed in by the mounting acceleration.

  The noise of the engines was changing, sounding hollower as the huge tanks emptied. The last few tonnes of fuel and liquid oxygen quivered over the mouths of the feed lines.

  The engines blasted on, the thrust unrelenting, forcing the rapidly lightening craft to dizzying speeds. The final few seconds of the climb carried the greatest acceleration of all, crushing them into their seats, turning the spaceplane from an earthbound object doomed to fall, into an orbiting spacecraft that would fall round the Earth and never land.

  The navigation display showed the white path of their trajectory moving closer and closer to the magenta line, until the little arrowhead of the spaceplane grazed it, and the two lines became one.

  The thunder of the engines stopped.

  ‘Main engine cutoff.’

  Wilson’s voice sounded strange in the sudden quiet. A long, declining wail came faintly through the craft as the turbopumps ran down, followed by the brief roar of helium gas in the purge cycle.

  The superb engines had done their job flawlessly, taking the spaceplane all the way from the runway on Guam, up to an altitude of 320 kilometres and an orbital speed of nearly eight kilometres per second. Clare locked the thrust levers in their cutoff position and disarmed the firing controls, and gave the console a short pat of appreciation.

  The purging roar ceased, but nobody spoke; it felt as if they were falling forward, as indeed they were; falling round the curving surface of the world below. Matt gripped the arms of his seat, waiting for the feeling to pass, and hoped that the anti-nausea pills he had taken several hours previous would do their job.

  Matt’s arm drifted up, and he realised he was weightless, floating in his seat, only held there by the pressure of his seat straps. As always, he grinned helplessly at the sensation; it truly had to be experienced. The vestibular disturbance was passing, and h
e looked around. Bergman was smiling as well, watching the ends of his seat straps float out in front of him.

  Wilson inspected the navigation display, which had changed to show their orbital situation, and the location of the waiting tug, 200 kilometres above them in its higher orbit.

  ‘Confirm orbit established. We’re here to stay. Tug beacon locked on, MMS is ready for orbital transfer update. We’ll make rendezvous in – seventy-four minutes.’ He nodded in satisfaction; they were right on target with their orbit insertion.

  ‘Okay everyone, welcome to orbit. Hope you enjoyed the ride.’ Clare’s voice came over their headsets. ‘Very smooth climb up, no problems at all. We just need to run through some checks, and then we’ll start preparing for the rendezvous. You can take off your helmets now, but make sure you stow them properly – I don’t want any of them floating around while I’m docking.’

  There was a brief hiss as Clare unsealed her faceplate and swung it upwards, then removed her helmet. The rest of them followed suit, and Matt sighed with relief as he struggled free of the confines of his helmet and stretched his aching neck muscles.

  ‘Right, let’s take a look at the view.’ Clare reached out to the centre console, and the protective visor, which had covered the windows throughout the orbital climb, unlocked and lowered slowly out of sight, opening up the view ahead.

  The black sky of space expanded around them, and then the brilliant blue-and-white curve of the Earth flooded into the cockpit. The wide expanse of the Central American coastline straddled the centre windows, a mass of browns and greens against the blue of the Pacific.

  The thin shell of the atmosphere could be seen clearly, a deep blue band along the curved horizon. Scattered clouds floated above the landmass as another day drew to its close; a band of deep shadow in the distance marked the terminator, the line of oncoming night.