by Mark Anson
Once the aircraft has come to a halt on the deck, however, it is part of the carrier, and will experience the headwind of the carrier’s forward motion relative to the air. This will tend the blow the aircraft backward along the flight deck unless the motion is counteracted by brakes, forward thrust or being clamped to the deck.
For takeoff, the relative headwind is an advantage, as it provides an initial airspeed that is sufficiently high to generate lift. An aircraft waiting to takeoff must disrupt the lift over its wings with spoilers or risk an inadvertent takeoff. For takeoff, all that is required is for the spoilers to be withdrawn and sufficient thrust applied, and the aircraft will take off and climb away.
Flying in Venus’s atmosphere
At first sight, using a gas turbine engine in an atmosphere of carbon dioxide (CO2) would seem impossible; there is no oxygen to support combustion of the fuel. Only a small proportion of the air entering a turbojet engine, however, is actually used for combustion, the remainder serves as a working fluid that is compressed, heated in its compressed state, and then allowed to expand and do useful work by rotating the turbine. In a turbofan engine, an even greater proportion of air is accelerated by a large fan around the central turbojet core, and this bypass air takes no part in the combustion cycle.
The only requirement for oxygen for combustion comes from the (relatively) small amount of air needed for fuel combustion, which heats the compressed air in the very core of the engine. Only about 20% of the air on Earth is oxygen in any case – the remainder is nitrogen, which takes only a small part in the combustion process.
The aircraft (and spaceplane) described in the story carry liquid oxygen as well as fuel, and their engines have combustors that are fed directly by a mixture of fuel and oxygen, and can operate even when surrounded by carbon dioxide. A similar principle allows an oxy-acetylene cutting torch to operate underwater.
A practical implementation of such an engine would be far more involved than this explanation might suggest. The basic principles of subsonic flight, however, would be the same in a CO2 atmosphere at the same temperature and pressure as on Earth.
The green flash
A green flash is seen on Earth under certain conditions when the Sun just disappears below the horizon; it is caused by green light being preferentially refracted over the horizon and into the observer’s line of sight. In the story, the flash is depicted as being more pronounced, due to the greater apparent size of the Sun.
The spaceplane
The Olympus spaceplane used on Venus is a specialised variant of the spaceplane first depicted in Below Mercury, and is optimised for operations in the atmosphere of Venus. There are no landing jets, as they are unnecessary in the dense atmosphere. An arresting hook is fitted, and the landing gear is strengthened to cope with the greater stresses of carrier landings.
Internally, the passenger seating is increased from six to eight, as there are no ejection seats installed; there are no survivable escape scenarios in the Venusian atmosphere. The liquid oxygen tank is also enlarged (and the liquid propane tank reduced correspondingly) to cope with the different proportions of propellants needed during the ascent through the Venusian atmosphere.
The engine intakes utilise diverterless, variable-geometry intakes. These close completely for spaceflight and re-entry, open progressively for supersonic flight, and open wide for subsonic flight. Inside the inlets, movable internal ramps slow down the entering hypersonic air to subsonic speeds, with precoolers and liquid oxygen injection to control the enormous temperature rise.
The spaceplane can carry up to five tonnes of freight down from Venusian orbit to the carriers. The ‘down’ direction is most important for freight, as this is the resupply direction. For ascents, the spaceplane has almost no freight capacity when carrying a full complement of passengers, as the ascent direction is the most prohibitive in terms of load carried.
The materials from which the spaceplane is made are also different due to the need for enhanced corrosion resistance; no magnesium alloys are used, and other alloys are chosen carefully to ensure resistance to the atmosphere while retaining adequate strength and heat resistance.
Orbital mechanics
The most efficient trajectory between two planets orbiting the Sun (or, two moons orbiting a primary) lies on a half-ellipse between the two bodies, referred to as a Hohmann transfer trajectory. While other routes are possible, they always involve more fuel, more time, or both. Whatever type of transfer trajectory is used, it is important that these transfer trajectories are started when the two bodies are in the correct relative positions, i.e. that the target planet has moved in its orbit so that it coincides with the arrival of the ship by the time it gets there. There is a range of dates either side of the optimum transfer opportunity when a less efficient transfer may be made, but the fuel penalty rises prohibitively the further away the transfer is from the ideal date. Outside of a certain range – the launch window – the transfer simply cannot be achieved within the limits of the launch vehicle. For Earth and Mars, these launch windows are centred 780 days apart and this is too restrictive for a regular transfer operation, which would be needed to support permanent bases on other planets.
Venus is an inferior planet to Earth, meaning that it orbits closer to the Sun. Mars is a superior planet and orbits further away. It is counter-intuitive that voyages between Mars and Earth can go past Venus, but the explanation lies in the slow movement of Mars compared to the inferior planets.
Because Venus orbits closer to the Sun, its orbital period is shorter than Earth’s, and launch windows between Venus and Mars occur more frequently, every 334 days. Depending on the situation of the planets, it can be faster to travel from Earth to Venus, then on to Mars, than to wait for a direct transfer window to Mars. The same is true in reverse, for voyages from Mars back to Earth.
In the story, the orientation of the planets, the journey times, and the rising and setting of the Sun, Earth and Mercury are as they would be in December 2141. The orbital transfer trajectories, journey times and other astronomical events described in the story are consistent with the technologies described, and the performance data as shown in the drawings.
Units and conventions
The nautical mile (NM) and the knot (kt) are used commonly in aviation as the units of distance and speed, respectively. The NM is convenient for navigation as it represents one second of arc on Earth’s surface. On other planets, however, the terrestrial NM would be less appropriate, and the kilometre (km or ‘klick’), metre per second (m/s) and kilometre per hour (kph) are used instead, as a consistent system of measurement that would work in all situations. One metre per second is approximately two knots.
I have described the US Astronautics Corps as loosely following US Air Force customs and practices when dealing with aviation, and the US Marine Corps and Navy when on board the carrier. The carrier has a forward, an aft, and port and starboard quarters. It is steered by a helmsman, but from a control room, as the carrier does not have a bridge in the conventional sense.
There are inconsistencies, however, as Lieutenant Gray notes in the story. The carrier has a left wing (aviation) on its port quarter (nautical).
MANNED DEEP SPACE VESSELS
IN USAC INVENTORY, 2141
Deep Space Tug (STN) – Chicago-, Boston-, San Diego- and Omaha-class space tugs. The Chicago-class was the first tug type to be constructed. Chicago (STN-01) and Detroit (STN-02) were decommissioned in 2138 and 2140 respectively.
Deep Space Explorer (DXN) – Columbus- and Magellan-class science exploration vessels based on the Chicago- and Philadelphia-class space tug designs.
Deep Space Interceptor (DIN) – Philadelphia-class dedicated asteroid movers based on the San Diego-class space tug designs, with increased propellant and thrust capability.
Venusian Carrier (VCN) – Wright-class airborne carriers, designed to operate in the lower atmosphere of Venus.
GLOSSARY
Albedo (Bond a
lbedo) – in astronomy, the fraction of solar radiation reflected back into space. Venus, for instance, has a very high albedo compared to Earth due to its reflective clouds.
Alkane – a family of hydrocarbon compounds where each of the constituent atoms are linked together by single bonds. Methane, propane and butane are all alkanes.
Aphelion – in astronomy, furthest distance of an orbiting body from the Sun.
Arresting hook – a long hook that hangs from under the tail of an aircraft, designed to catch the arresting wire.
Callisto – fourth Galilean moon of Jupiter.
Comlink – cell-based, handheld telecommunications device.
Cryogenic – super-cold; generally any temperature below about –100 °C or 173 K.
EGT – Exhaust Gas Temperature, an important operational parameter for jet engines.
EICAS – Engine Indicating and Crew Alert System. A dedicated display that shows key engine parameters and alerts the crew to the situation of other key systems.
Elevon – a single control surface combining the functions of an elevator (for pitch control) and an aileron (for roll).
EVA – Extra-Vehicular Activity. Any activity conducted outside the shelter of a pressurised vehicle or habitation.
Fischer-Tropsch (process) – a series of chemical reactions that convert carbon monoxide and hydrogen into various liquid hydrocarbons.
FSAA – Federal Space and Aviation Administration, a twenty-second century evolution of the FAA.
Gee (g) – an acceleration equal to that exerted by gravity at Earth’s surface, approximately 9.8 m/s2.
Glideslope – a radio-based navigation aid that establishes an accurate vertical course to a runway or landing pad.
Hydrosphere – the combined mass of all the water (including water vapour in the atmosphere) on a planet.
Klystron – a vacuum tube-based high power amplifier for high-frequency radio signals such as radar.
LO2 – common abbreviation for liquid oxygen.
Localiser – a radio-based navigation aid that establishes an accurate horizontal course to a runway or landing pad threshold.
Mesosphere – the upper regions of Venus’s atmosphere, where the temperature increases with altitude, eventually transitioning into the thermosphere and space.
Navigation Display (ND) – information from external navigation aids and geographical databases are combined to create a display of the craft’s position and course.
Obliquity (to orbit) – in astronomy, the tilt of a body’s equator relative to the body’s orbital plane.
Orbital inclination – for a planet, the inclination of its orbital plane round the Sun relative to that of Earth’s. All the planets orbit within a few degrees of this plane.
Perihelion – closest approach of an orbiting body to the Sun.
Phobos – larger of Mars’s two moons, believed to be a captured asteroid.
Primary Flight Display (PFD) – situated in front of each pilot, the PFD provides all the relevant flight information needed by the pilot for each phase of the mission, e.g. re-entry, atmospheric flight, and landing.
Propane – gaseous hydrocarbon of the alkane family, chemical formula C3H8. Can be liquefied at cryogenic temperatures.
Sidereal orbit period – the time for a body to make one revolution about the Sun relative to the fixed stars.
Sidereal rotation period – the time for a body to make one rotation on its axis relative to the fixed stars. This is different to the length of day, especially for planets that rotate slowly (or backwards) compared to their orbital motion around the Sun.
Sidestick – evolution of the more traditional control yoke, for controlling an aircraft in pitch and roll. A sidestick is controlled by small wrist and arm movements, and can be operated even under high-g conditions.
Solar irradiance – in astronomy, incident solar power per unit area on a body.
Stall – in aerodynamics, a sudden reduction of lift over a wing caused by the wing’s angle of attack increasing to a point where the stable airflow over the wing breaks down and becomes turbulent, drastically reducing lift.
Tropopause – the transition region of Venus’s atmosphere between the troposphere and the mesosphere.
Troposphere – the hot and dense lower regions of Venus’s atmosphere, where most of the weather and clouds are contained. The temperature in the troposphere decreases rapidly with altitude until the tropopause, when it reverses and starts to increase again in the mesosphere.
VHF – Very High Frequency, typically applied to radio communication.
X band – a region of the electromagnetic spectrum between about 7.0–12.5 GHz, used for voice and data radio communications between spacecraft and planetary bases and Earth.
Zulu – Zulu Time, a standard aviation term for UTC.
SELECT BIBLIOGRAPHY AND FURTHER READING
Beatty, J. Kelly (ed.), Carolyn Petersen (ed.) and Andrew Chaikin (ed.) The New Solar System. 4th edn. Cambridge University Press, 1999.
Coonts, Stephen P. Flight of the Intruder. Simon and Schuster, 1986.
Greeley, Ronald, and Raymond Batson. The Compact NASA Atlas of the Solar System. Cambridge University Press, 2001.
Gunston, Bill. The Development of Jet and Turbine Aero Engines. 4th edn. Patrick Stephens Ltd, 2006.
Jenkins, Dennis R. Magnesium Overcast: The Story of the Convair B-36. Specialty Press, 2002.
Jenkins, Dennis R. and Tony R. Landis. Valkyrie: North American’s Mach 3 superbomber. Specialty Press, 2004.
Krasnopolsky, V.A. and Parshev, V.A., ‘Chemical composition of the atmosphere of Venus’. Nature 292 (1981): 610-613.
Landis, Geoffrey A., et al. ‘Atmospheric Flight on Venus’. 40th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, 14–17 Jan. 2002.
Landis, Geoffrey A. ‘Colonization of Venus’. STAIF Conference on Human Space Exploration, Albuquerque NM, 2-6 Feb. 2003.
Landis, Geoffrey A. ‘Exploring Venus by Solar Airplane’. STAIF Conference on Space Exploration Technology, Albuquerque NM, 11-15 Feb. 2001.
Lewis, John S. Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Basic Books, 1997.
National Aeronautics and Space Administration. ‘Preliminary mission study of single-launch manned Venus flyby with extended Apollo hardware’. NASA MSC Internal Note 67-FM-25, 13 Feb. 1967.
Oates, Gordon C. (ed.) Aircraft Propulsion Systems Technology and Design. American Institute of Aeronautics and Astronautics, 1989.
Sellers, David. The Transit of Venus. Magavelda Press, 2001.
Sobel, Dava. The Planets. Fourth Estate, 2005.
Sutton, George P. Rocket Propulsion Elements. 5th edn. John Wiley & Sons, 1986.
United States Department of the Navy. CVN Flight/Hangar Deck NATOPS Manual. NAVAIR 00-80T-120. Department of the Navy, 2010.
COMPARATIVE ASTRONOMICAL DATA
For explanations of terms, see Glossary
Ten years later …
IN THE DARKNESS BELOW MERCURY, THE DEAD LIE WAITING …
Mercury – closest planet to the Sun. In the permanent darkness of Chao Meng-fu crater lie vast fields of ice that that have never seen the Sun, and the ruins of Erebus Mine, abandoned and forgotten after a devastating explosion that claimed the lives of 257 people. After an eight-year legal battle, the relatives of the victims have finally succeeded in forcing the Space Accidents Board to reopen its investigation. Matt Crawford, a mine engineer who escaped the disaster, joins a team sent back to the mine to discover the true cause of the accident. The team is led by Clare Foster, a pilot in the U.S. Astronautics Corps, who has taken on the mission in the hope of rebuilding her career after a near-miss incident.
But powerful forces are determined that what lies hidden in the mine will never be uncovered, and have taken steps to ensure that the mission team will never return. Stranded on Mercury, the team are divided by internal conflict, and a growing realisation of what really happened in the mine. Soon Matt and Cl
are are thrown together in a desperate race for survival against an implacable enemy that will not rest until it has killed them all …
