Mark Anson - Below Mercury

After so long in low-gravity and weightless conditions, the deceleration was hard on their bodies; Matt found it an effort to breathe as his chest was squeezed in by the tremendous thrust.

By turning his head, he could see the planetary approach display on Clare’s navigation display. The white line of the tug’s track was changing, curving closer to the globe of Mercury with each passing minute, the ship’s headlong rush braked by the mighty thrust of the nuclear engine. The magenta line of the target orbit seemed to curve impossibly close to the planet – surely there was no way the ship could slow down enough?

The tug’s structure quivered with the tremendous thrust of the engine. Behind the passenger seats, something escaped from its fastenings and fell onto the floor with a clang.

On the forward view monitors, a wavering, glowing nimbus hovered ahead of the ship, all that could be seen of the engine flame and the enormous energies being expended to slow them down.

Wilson watched the fuel displays sink as the nuclear engine drank its way through their fuel reserves at nearly fifty tonnes a minute, slowly bringing the tug’s colossal speed down so that Mercury’s gravity could take hold.

The ship slid down through the darkness, its engine flame a bright star in the night sky.

Beyond the black curve of Mercury’s horizon, the Sun’s corona flared above the hills as the Baltimore slid back towards the day. There was a silent explosion of brilliant light, and the Sun lifted its huge arc above the dark hills and rose above the horizon, the day side of Mercury growing above them.

‘One hundred seconds to run,’ Clare announced.

Crater rims stood out in sharp relief in the oblique light as they flew into the day. They were following the planet’s surface round now, instead of flying past it and off into space.

The deceleration pressing them into their seats continued to increase as the tug’s fuel dwindled. The ship had shed nearly seven hundred tonnes – over a quarter of its mass – during the burn, and still the engine blasted on. Matt closed his eyes and tried to shut out the noise and the increasing vibration.

‘Reducing thrust to ninety percent,’ Clare said, watching the autopilot controls. There was a slight reduction in the engine’s rumble, and the deceleration eased fractionally.

Matt’s breathing was laboured now, as he waited for the burn to end. It seemed to have been going on forever. How much longer could—

The vibration and noise faded, and the weight lifted from Matt’s chest as the engine fell into silence. Below them, on the external monitors, Mercury’s cratered surface moved slowly past.

Clare conferred briefly with Wilson, and then turned round to face them all.

‘Well, I’m pleased to inform you that the burn was successful and – we are in a stable orbit round Mercury.’

She allowed herself a smile as the four passengers burst into a round of spontaneous clapping, and for an instant, Matt saw her face transformed. The lines and cares on her face disappeared as the smile lingered, and her eyes shone.

‘Spot on target – stable orbit, two hundred by two zero one kilometres. Nice piece of navigation, captain.’ Wilson congratulated her, smiling broadly.

Matt heaved a sigh, and he lay back in his seat, relishing the ease of free-fall, watching the surface roll by below them on the display. They were rising up the sunlit side of the terminator; in about forty-five minutes, they would cross over the North Pole again.

He tried to relax, telling himself that this would be the last chance he would have to rest for some time, but he couldn’t; he was too keyed-up with the thought of what lay ahead. They would be abandoning the space tug, that had been their home and their world for the last three months, and exchanging it for the uncertainties of what awaited them on the surface.

After all the years of legal battles, the investigation boards, the preparations and the planning, the long voyage, and the orbit insertion manoeuvre, the final stages of Matt Crawford’s personal odyssey were within reach. In a few short hours, he would be back at the doors of Erebus Mine, deep in the darkness of a crater floor on the South Pole of Mercury.

CHAO MENG-FU:

88.3°S 150.0°W, 167km diameter. Large impact crater at South Pole of Mercury (pole is on NE crater rim).

Morphology:

C4-class crater with central peak and terraced inner walls; relatively little degradation to rim walls or ejecta blankets. Crater mountains range up to 4km above crater floor.

Crater floor:

Relatively smooth crater floor formed from impact melt and subsequent volcanism. Entire crater floor in permanent shadow due to location and low axial tilt of planet. Extensive ice field covering c.80% of crater floor, depth variable up to 500 m in places; layered and banded structure of mixed ices and regolith in several layers of variable thickness from successive cometary events in Bach region. Significant concentrations of ammonia, alkane clathrates and helium-3 in varying proportions in each layer.

Subsurface structure:

Impact event penetrated flood basalts and excavated into underlying anorthosite and gabbro layers. Crater floor mainly impact melt overlying large breccia lens. Significant metal orebodies in differentiated deposits in outer rim of impact melt, likely to be of meteoric origin. Inner crater walls and central peak complex are impact breccias of basalt and anorthosite, with minor gabbro inclusions.

Mining in area:

Erebus Mine, 86.6°S, 167.0°W, operated by Planetary Mining Inc. Mining for helium-3 and liquid fuels in ice deposits on crater floor, also deep mining of precious metal deposits (gold and platinum group metals) under crater floor. Extraction, processing and refining facilities for LO2, LH2, mixed alkanes, ammonia and water. Refuelling and resupply base. Space tug orbital refuelling base.

Excerpt from Engineering Geology of Mercury (USAC Geological Survey, 2nd edn, 2129).

Matt watched from his seat in the spaceplane as the enormous structure of the Baltimore dwindled upwards into the sky over Mercury. They had left the tug in the care of its autopilot, and the huge silver flower of the sunshield rippled in the backwash from the thrusters, as the tug moved round to face away from the Sun once more.

The spaceplane was falling away from the tug; Clare had fired the engines briefly to change their circular orbit to a long ellipse that would come within a few kilometres of the surface. Once they were close to the South Pole, she would fire the engines again in the main burn to brake their orbital speed and bring them in for a landing.

There wasn’t much to see during the long minutes as the spaceplane fell backwards towards Mercury. The view out of the spaceplane’s forward windows was obscured by the large drop tank, latched onto the nose that supplemented the spaceplane’s own tanks with extra fuel for the descent.

Instead, Matt watched their trajectory on the navigation display, and the small icon of the spaceplane as it followed the long curving line downwards.

The mission team were wearing the same crew escape suits and spacesuit helmets that they had worn on the ascent through Earth’s atmosphere; their faceplates were raised for now, but would need to be lowered for landing.

‘Tanks are at full pressure,’ Wilson reported, ‘ready for de-orbit burn.’