Acid Sky (30 page)

‘One Six Three, clear for takeoff. Right turn after takeoff, heading two eight five, clear orbital climb to three four zero kilometres. Orbit inclination plus one five, insertion point Tango One at one eight five one Zulu and rendezvous with Space Tug Three Five Cleveland.’

Gray read the clearance back, then glanced across at Clare. ‘Ready?’

‘Ready.’

‘Right. Let’s go.’ Gray lowered the wing spoilers as Clare pushed the thrust levers forward to their full takeoff setting. The spaceplane trembled now on the deck, straining to get into the sky.

‘Thrust set.’

‘Afterburners,’ Clare called, and Gray pressed the four switches below the thrust levers. The engines’ noise rose to a deep-throated thunder.

‘Full thrust.’

‘Go!’ Clare yelled exultantly.

Gray switched the landing lights on as the signal for launch, and a moment later, they felt the sudden swoop of the stomach as the carrier dumped lift. Then the hold down clamps released with a
bang
of pent-up tension, and the spaceplane leaped into the air. Clare steered the heavy craft up and away from the falling carrier, lifting into the sky.

For a moment, she had a strange sense of déjà vu, until she realised that she was reliving seeing Hartigan’s spaceplane climb into the dawn sky, on her first morning on the
Langley
. Then, she had felt as if her old life was departing. Now, she was looking ahead to the rest of her life, coming towards her. She smiled.

Clare banked the spaceplane to the right and started to climb into the dusk, away from the
Wright
, away from Venus, and into her future.

Behind them on the
Wright
, Coombes stood at a darkened window and stared after the receding shape of the spaceplane. The four tongues of blue flame from its engines reflected in his eyes as he watched it climb and diminish into the western sky. He remained there, gazing into the distance, his hands held besides him, long after it had gone from sight.

His eyes, bloodshot from lack of sleep, stared sightlessly ahead, and the knuckles of his hands whitened as they clenched into fists, released, then formed again, in an unbroken cycle.

BACKGROUND NOTES

Venus

Venus is a planet that occupies a closer orbit to the Sun than Earth. It can be seen as a brilliant object, far brighter than any star, in the morning sky before the Sun rises, or in the evenings after the Sun has gone down, depending on the time of year and its position with respect to the Sun. For this reason, it was familiar to ancient civilisations as a ‘morning star’ and ‘evening star’, although it is generally held that the Babylonians had realised that it was one object, from the
Venus tablet of Ammisaduqa
of 1581 BC.

Because Venus is closer to the Sun that Earth, it shows phases (waxing and waning like the Moon) when observed through the telescope. It was this behaviour that inspired Galileo Galilei (1564–1642) to realise that Venus orbited the Sun and not Earth; a violation of the geocentric model (and religious dogma) that held Earth at the centre of the universe.

Galileo was forced to recant his heretical beliefs and scientific principles by the Inquisition in Rome, but the idea would not go away, and the work of Johannes Kepler (1571–1630) on planetary orbits further reinforced the concept that Venus orbited the Sun. By 1687, when Isaac Newton used the theory of universal gravitation to provide an explanation of Kepler’s laws, the idea had gained widespread scientific acceptance, although it would take the Catholic Church considerably longer to integrate these developments into its ideology. Kepler’s influential book propounding a heliocentric model of the Solar System was not removed from the Church’s list of prohibited books (the infamous
Index Librorum Prohibitorum
) until 1758.

In 1761, Mikhail Lomonosov (1711–1765) observed the transit of Venus across the Sun and saw the signs of an atmosphere around Venus. This was further confirmed in 1790. Improved telescopic observations of Venus provided little more detail; the planet appeared to be covered in a featureless layer of cloud that prevented any view of the surface. It was not until the twentieth century, and the advent of radar-based observations of the planet’s surface, that the rotation period could be measured. This provided another revelation – the planet’s axis of rotation had tilted over so much that it was completely inverted, so that Venus rotated ‘backwards’ compared to the other planets. In addition, the planet rotated very slowly; it took 243 days to turn once about its axis, about 18 days longer than its year. The combined effect of this makes the Venusian solar day last nearly 118 Earth days, with the Sun rising in the West and setting in the East.

Beginning in 1962, many unmanned probes have been launched to Venus, including ten Soviet landings. The first successful landing was by
Venera 7
in 1970, which managed to send back faint signals for twenty-three minutes from the surface, indicating a surface temperature of 475
°
C. In 1981,
Venera 13
sent back the first colour images of the surface, analysed a small surface sample, and survived for over two hours. Two years later,
Venera 15
and
16
made radar-based surveys of the surface, and in 1985,
Vega 1
and
Vega 2
dropped floating balloon probes into the atmosphere to investigate the Venusian clouds. In 1990, the US
Magellan
probe conducted high-resolution radar mapping of the surface. The European Space Agency’s
Venus Express
is still in orbit at the time of writing, and continues to make long-term observation of the Venusian atmosphere and surface temperatures.

No manned missions to Venus have ever been made, although a 1967 mission study investigated using a Saturn V to launch an Apollo-based manned spacecraft on a year-long Venus flyby mission, utilising the empty S-IVB upper stage for additional living space.

The atmosphere of Venus

The atmosphere of Venus is mainly carbon dioxide – 96.5% of it is composed of this relatively unreactive gas. The remainder is nitrogen (3.5%), and tiny amounts of sulphuric acid, water and other gases. Due to its thickness, Venus’s atmospheric pressure at the surface is stupendously high – over ninety-two atmospheres. This is the equivalent pressure at over nine hundred metres depth in Earth’s oceans, or three times the operating depth of a typical military submarine. The mean temperature at the surface is a searing 464
°
C; it is the hottest surface in the Solar System, exceeding that of Mercury. The high temperature is in part due to the runaway greenhouse effect caused by the dense carbon dioxide atmosphere.

At higher altitudes, however, it is a different story. The crushing pressure and the temperature fall with increasing altitude; at fifty kilometres, the air pressure is the same as that on Earth and the temperature 75
°
C. The average wind speed increases, however, until at sixty kilometres altitude, the equatorial winds blow at three hundred and sixty kilometres per hour, circling the globe in just four days. This is much faster than the planet’s slow rotation, a phenomenon called
super rotation.

The few probes that have survived to the Venusian surface have shown that the sky there is a dark orange, and the lighting conditions similar to a dark, overcast day on Earth. Higher up in the atmosphere, however, the colour is less certain. It is thought that below about sixty kilometres altitude the sky would appear a pale green due to preferential absorption at the blue end of the spectrum. Above this altitude, however, where the clouds thin out, it is likely to be a pale blue similar to Earth’s sky, and this is reflected in the descriptions in the story.

The clouds that block the surface of Venus from view are composed of aqueous sulphuric acid droplets. The clouds exist in three broadly distinct layers from about forty to sixty-three kilometres, with the lowest two layers being more turbulent than the upper layers, which are flattened off by the change in conditions at the tropopause. The atmospheric conditions at the cloud tops are very similar to those encountered in stratospheric flight on Earth, hence the positioning of the
Langley
at this altitude.

Venusian clouds are extremely thin, as measured by their particle size and density; even from within a cloud, their appearance would be like a faint mist that extended in all directions. The depth of the clouds is so great, however, that despite their tenuous nature, they completely obscure the surface of the planet. Viewed from above, the cloud deck would likely appear as a featureless sea of mist blanketing the planet, and it would not show the sort of structure that we are familiar with on Earth. For dramatic effect in the story, however, the clouds are described with more structure than would be apparent in reality.

Although there is a lot of sulphuric acid in the atmosphere on Venus, there is an
enormous
amount of air, and the bulk concentration of the sulphuric acid is very low. If a human were to breathe Venus’s air at one atmosphere pressure, the carbon dioxide content would quickly induce hyperventilation and death, long before any ill effects due to the acid in the air.

Similarly, aircraft flying in Venus’s atmosphere would be unlikely to suffer significant corrosion effects from the acid, unless they were spending a great deal of their time in the deeper cloud layers, and this issue is mentioned in the story.

Mining the air

The atmosphere of Venus can be converted into useful products through a complex series of chemical reactions, starting from sulphuric acid. Sulphuric acid can be extracted from the air by condensation, but very large volumes of air would need to be processed, hence why the
Langley
dives into thicker air for its mining operations.

The acid would be extracted as an aqueous solution (the sulphuric acid in Venus’s sky is bound up with water), and this is electrolysed to yield oxygen and hydrogen. The oxygen is used for life support on board and the hydrogen is reacted with atmospheric carbon dioxide in a
reverse water gas shift
reaction to yield carbon monoxide and water, which is further electrolysed into oxygen and hydrogen. The carbon monoxide is reacted in the Fischer-Tropsch process to yield a variety of alkanes, specifically propane (C
3
H
8)
. The energy demands for the process are supplied by the nuclear-powered generators on board. The overall reaction can be summarised as:

12CO
2
+ 16H
2
O → 4C
3
H
8
+ 20O
2

Water is present in the atmosphere in concentrations of only twenty parts per million, so this requires extraordinary amounts of air to be processed. Fifty thousand tonnes of air would need to be processed to yield just one tonne of water. To put this into perspective, a large turbofan engine ingests approximately one tonne of air per second, so would have to run for fourteen hours to ingest enough air to make one tonne of water. The turbofans and turboexpanders on the
Langley
are much larger, but a typical night’s run would only yield twenty-five tonnes of water.

The
Langley

The
Langley
is a flying aircraft carrier, cruising in the lower mesosphere of Venus. The idea of a floating aerostat in the atmosphere of Venus was suggested by Geoffrey A. Landis in a 2003 paper (for this and other references, see Bibliography). While Landis envisaged a floating city sustained by an envelope of breathable flotation gas, there are some practical issues with the stability of smaller aerostats. Any aircraft attempting to land would cause the aerostat to sink unless an equivalent amount of ballast was jettisoned, and any aircraft leaving would require lifting gas to be vented to stop the aerostat rising. For an object as large as a floating city, this issue might be insignificant, but for smaller objects, the loss of mass and lifting gas would be a serious problem.

The dynamic trim and buoyancy control for a floating carrier also present additional challenges, and for these reasons the
Langley
is described as a heavier-than-air winged vehicle. Ballast is still used for trim, but the masses involved are considerably less than those needed for an airship.

As described in the story, the
Langley
is constructed in orbit and piloted down into Venus’s atmosphere. The craft re-enters ‘upside down’ compared to its flight configuration; this presents the toughened upper surfaces to the heat of re-entry and protects the complex structures behind it. Once reduced to flight speed, the entire ship is rolled over and the superstructure components (tower, radomes, antennas etc.) are raised from their protective covers.

A flying vehicle as vast as the
Langley
presents formidable engineering challenges in design and construction, but once assembled and flying, it has numerous advantages. The chief benefit is its large size and mass; unlike smaller vehicles, it possesses considerable inertia, making it highly stable even in gusting conditions. The same inertia is of benefit when landing heavy aircraft on its flight deck; a feat that would be difficult and dangerous on a lighter structure, or an aerostat.

The
Langley
remains flying for its entire design life; it cannot land, or climb back to orbit. Its four nuclear-powered turbofan engines are fuelled for its lifetime and run continuously. If this seems stretching belief, it is not unusual for contemporary turbofan aircraft engines to remain on the wing of an aircraft without removal for upwards of 25,000 hours, and the current record is held by an RB211-535E4 turbofan with an on-wing life without removal of over 40,000 operating hours or over 4.5 years. The
Langley’s
engines operate continuously, using the heat from a nuclear fission core instead of burning a conventional fuel. This concept was first explored in the 1950s, using a B-36 bomber modified to carry a 1 MW reactor for feasibility tests.