Below Mercury

by Anson, Mark

  It is designed for simplicity and reliability of operation within its limited role, and is fuelled by liquid propane and liquid oxygen.

  The fuel tankers, although not described in any detail in the story, are large, unmanned vehicles that carry propellants and other refinery products into orbit. A tanker can refuel a space tug’s tanks directly, or can be transported in a fully loaded state on the nose of the space tug to another destination.

  The fuel tanker is composed of two main modules: a large spherical fuel tank; and an ascent/descent stage that is a larger version of the one used for the crew shuttle. Tankers are dedicated to particular payloads due to tank size and safety issues, liquid oxygen being a key example.

  Maximum payload (for a fully loaded Mercury ascent and an empty return) is over 400 tonnes. Even with this huge payload, it would still take six full tankers to refuel completely a space tug’s liquid ammonia tanks.

  The Mining Robots

  There are no drawings of the robots; these are left to the reader’s imagination. The robots’ power source is a fuel cell powered by liquid propane. The ‘power pack’ described in the story is the fuel cell itself; this replaceable module contains the fuel cell and the batteries required to start it up. The cell is eventually exhausted (its reactor cell becomes poisoned by impurities in the fuel) and has to be replaced.

  The fuel cell requires oxygen from the air to function and generate electrical power, so when the robots venture out into the open, they run on the charge contained in their main batteries, and recharge as soon as they are back in atmosphere again. In the story, Bob Five received a new cell shortly after the mission team reactivated him, so he was able to recharge his batteries and make it up the mountainside to the peak with Abrams and Elliott.

  Orbital mechanics

  The positions of the Earth, Sun, Mercury and other planets are described as they would appear in May to August 2151. The orbital transfer trajectories, journey times and spacecraft manoeuvres described in the story are consistent with the technologies described for the space vehicles and their performance data as shown in the drawings.

  There is only one place where accuracy has been sacrificed intentionally, for dramatic effect.

  Units of measurement

  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 the Earth’s surface. On other planets, however, the terrestrial NM would be less appropriate, and the kilometre (km) and metre per second (m/s) are used instead, as a consistent system of measurement that would work in all situations. One metre per second is approximately two knots.

  Flight levels used during ATC and DSC dialogue are metric: Flight Level 90, for instance, is 9,000 metres above mean sea level.

  GLOSSARY

  Aerospike:

  in rocket engine design, a type of engine nozzle that maintains its aerodynamic efficiency across a wide range of altitudes.

  Airway:

  in mining, any passage which conveys a substantial airflow to or from more remote parts of the mine.

  Alkane:

  a family of hydrocarbon compounds where each of the constituent atoms are linked together exclusively by single bonds. Methane, propane and butane are all alkanes.

  Anorthosite:

  an igneous rock characterized by a very high concentration of plagioclase feldspar, and a low concentration of heavier elements. The ancient lunar crust is composed of anorthosite, formed by crystallisation from a magma ocean.

  Aphelion:

  furthest distance of an orbiting body from the Sun.

  Basalt:

  dark, fine-grained extrusive igneous rock, formed when molten magma erupts and cools on the surface of a planet.

  Baseband:

  in telecommunications, a signal with low-frequency components (e.g. speech, or a digital bitstream) used to modulate a higher frequency carrier wave, so that the signal can be transmitted by radio.

  Breccia:

  a rock composed of fragments of rocks or minerals in a cementing matrix. A common rock type in impact craters.

  Callisto:

  fourth Galilean moon of Jupiter.

  Clathrate:

  a substance in which a lattice of one type of molecule traps a second type of molecule. A methane clathrate hydrate, for instance, is an ice-like substance consisting of methane gas molecules trapped inside a crystalline lattice of water molecules. Clathrate hydrates tend to be stable only at very low temperatures or high pressures.

  Comlink:

  cell-based, handheld telecommunications device.

  Cryogenic:

  super-cold; generally any temperature below about –100 °C or 173 K. Commonly applied to gases that need to be held at these very low temperatures to remain liquid.

  Delta-v (delta-vee):

  in astrodynamics, the amount of velocity change needed to carry out an orbital manoeuvre. A space vehicle’s mission capability can be quoted in terms of its delta-v – the maximum change in velocity that the fully loaded and fuelled vehicle can provide.

  DSNB:

  Deep Space Navigation Beacon. Part of the network of radio-based navigation aids located on Solar System bodies, which allows precision navigation across interplanetary distances.

  DSTC:

  Deep Space Traffic Control.

  EGT:

  Exhaust Gas Temperature, an important operational parameter for jet engines.

  Ejecta:

  the debris ejected during the formation of an impact crater.

  Ephemeris:

  in astronomy, a table giving the positions of astronomical objects in the sky.

  EPR:

  Engine Pressure Ratio, an important operational parameter for jet engines.

  Europa:

  second Galilean moon of Jupiter.

  EVA:

  Extra Vehicular Activity. A spacewalk, or surface excursion.

  Gabbro:

  dark, coarse-grained, intrusive igneous rock, formed when molten magma is trapped beneath the surface of a planet and cools into a solid mass.

  Gas core nuclear engine:

  a rocket engine powered by a fission reactor, where the fissile material is an incandescent gas (as opposed to a solid core).

  Gee (g):

  an acceleration equal to that exerted by gravity at the Earth’s surface, approximately 9.8 m/s2.

  Hoist:

  in mining, the system of electric motors, guide wheels (sheaves) and wire rope used for lifting or lowering a load up or down a shaft.

  ILS:

  Instrument Landing System. A system of radio-based navigation aids that allow a precision landing.

  Intake shaft:

  in deep mining, the shaft through which fresh air enters a mine.

  Ka-band:

  a region of the electromagnetic spectrum between about 20–30 GHz, used for high data rate radio transmissions to and from Earth. See X-band.

  Level:

  in mining, a horizontal or near-horizontal passage.

  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.

  Mission Management System (MMS):

  a computerised avionics system to assist pilots in navigating and managing a spacecraft. The MMS works with the autopilot to guide the craft through the series of speed, course and altitude changes in the planned route.

  Mode Control Panel (MCP):

  situated between the pilots, below the forward windows, the MCP is used to select and activate autopilot and autothrottle modes and establish altitudes, speeds and climb/descent profiles.

  Navigation Display (ND):

  information from the MMS, external navigation aids and geographical databases are combined to create a display of the craft’s position and course.

  Orebody:r />
  region of rock that contains economically significant concentrations of a mineral.

  Perihelion:

  closest approach of an orbiting body to the Sun.

  Primary Flight Display (PFD):

  situated in front of each pilot, the PFD provides all the flight information needed by the pilot for each phase of the mission. The PFD shows relevant information for each mode of flight, e.g. takeoff, atmospheric flight, suborbital climb, and planetary approach and landing.

  Propane:

  gaseous hydrocarbon of the alkane family, chemical formula C3H8. Can be liquefied at cryogenic temperatures.

  Radionuclide:

  an atom with an unstable nucleus, which can undergo radioactive decay, and emit gamma rays and/or subatomic particles.

  Raise:

  in mining, a shaft that is begun from a level and is excavated upwards, as opposed to being sunk downwards. Once completed, there is no real difference between a shaft and a raise, other than the method of its construction.

  Regolith:

  the layer of loose, soil-like material covering solid rock on the terrestrial planets. On airless bodies such as Mercury and the Moon, the regolith is formed by the action of micrometeoroids breaking down surface rocks into a powder, and can be many metres thick.

  Return shaft:

  in deep mining, the shaft through which spent air leaves a mine.

  Rock bolt:

  a long anchor bolt, for stabilizing openings or passages in rock.

  Shaft station:

  in mining, any location in a shaft where the cage can be halted, and men, materials or ore loaded or unloaded.

  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.

  Stope(s):

  in mining, rooms supported by surrounding areas of standing rock.

  Terminator:

  the line separating night and day on a planetary surface.

  UTC:

  Coordinated Universal Time. A high-precision time standard used in aviation and space navigation, broadly equivalent to Greenwich Mean Time (GMT).

  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.)

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  Blyth, F.G.H. and M.H. De Freitas.

  A Geology for Engineers. 7th edn. Butterworth-Heinemann 1984.

  Cummins, A.B. (ed.), I.A. Given, and H.L. Hartman (ed.)

  SME Mining Engineering Handbook. 2nd edn. Society for Mining Metallurgy & Exploration, 1992.

  Davies, Merton, et al.

  Atlas of Mercury. SP-423. NASA, 1978.

  Dunne, James, and Eric Burgess.

  The Voyage of Mariner 10. SP-424. NASA, 1978.

  Harmon, J.K., et al.

  ‘Radar mapping of Mercury’s polar anomalies’. Nature 369 (1994): 213-215.

  Heppenheimer, T.A.

  Facing the Heat Barrier: A History of Hypersonics. SP-2007-4232. NASA, 2007.

  Heppenheimer, T.A.

  The Space Shuttle Decision. NASA’s Search for a Reusable Space Vehicle. SP-4221. NASA, 1999.

  Huzel, Dieter, and David Huang.

  Modern Engineering for Design of Liquid Propellant Rocket Engines. Revised edition. American Institute of Aeronautics and Astronautics, 1992.

  Jenkins, Dennis R. and Tony R. Landis.

  Hypersonic: The Story of the North American X-15. Specialty Press, 2008.

  Jenkins, Dennis R.

  Space Shuttle: The History of the National Space Transportation System. 3rd edn. Specialty Press, 2001.

  Lewis, John S.

  Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Basic Books, 1997.

  Li, Chu-Tsing.

  The Autumn Colours on the Ch’iao and Hua Mountains. A Landscape by Chao Meng-fu. Artibus Asiae, 1965.

  Miller, R., and Frederick C. Durant III.

  The art of Chesley Bonestell. Paper Tiger, 2001.

  Oates, Gordon C. (ed.)

  Aircraft Propulsion Systems Technology and Design. American Institute of Aeronautics and Astronautics, 1989.

  Strom, Robert, and Anne Sprague.

  Exploring Mercury: The Iron Planet. Springer-Praxis, 2003.

  Strom, Robert, Michael Malin, and Martha Leake.

  Geologic Map of the Bach (H-15) Quadrangle of Mercury. USGS Map I-2015. US Geological Survey, 1990.

  Sutton, George P.

  Rocket Propulsion Elements. 5th edn. John Wiley & Sons, 1986.

  Thomson, William.

  Introduction to Space Dynamics. Dover Publications, 1986.

  Woods, W. David.

  How Apollo Flew to the Moon. Springer-Praxis, 2007.