Colonization of Venus

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Venus

The colonization of Venus, Earth's nearest planetary neighbour, has been a subject of much speculation and many works of science fiction since before and after the dawn of spaceflight. With the discovery of Venus' hostile surface environment, attention has largely shifted towards the colonization of the Moon and the colonization of Mars. Recently however, papers have surfaced on the feasibility of colonizing Venus beginning from the less hostile cloud-tops, making surface exploration in the beginning unnecessary. This two-part approach to the exploration and colonization of the planet has refocused interest on Venus.

[edit] Reasons for colonization

Space colonization is a step beyond space exploration, and implies the permanent or long-term presence of humans in an environment outside Earth. Stephen Hawking has stated that colonization of space would be the best way to ensure the survival of humans as a species. ^[1] Other reasons for colonizing space include economic interests, long-term scientific research best carried out by humans, and sheer curiosity. With current technology, the only areas of space that could realistically be colonized are Earth's nearby environment, the Moon, near-Earth asteroids, Mars, and Venus.

[edit] Advantages

Venus and the Earth shown to next to each other. Venus is only slightly smaller.

Air pressure on Venus, beginning at a pressure on the surface 90 times that of Earth and reaching a single bar by 50 kilometres.

Venus has certain similarities to Earth which might make colonization easier in many respects in comparison with other possible destinations. These similarities, and its proximity, have led Venus to be called Earth's "sister planet".

• At present it has not been established whether the gravity of Mars, about one-third that of the Earth, would be sufficient to avoid bone decalcification and loss of muscle tone experienced by astronauts living in an environment of microgravity (the probe Mars Gravity Biosatellite will be the first probe to investigate this). In contrast, Venus is close in size and mass to the Earth, resulting in an almost identical surface gravity (0.904 g). Most other space exploration and colonization plans face concerns about the damaging effect of long-term exposure to fractional g or zero gravity on the human musculoskeletal system. Humans born on Venus would have almost no difficulty adapting to Earth gravity should there be a reason to visit or return.
• In Venus's upper atmosphere, at an altitude of approximately 50 kilometers, the pressure and temperature is Earth-like (1 bar and 0-50 degrees Celsius). In addition, in this region, solar energy is abundant. The solar constant at the top of Venus's atmosphere is 2610 watts per square metre, 1.9 times that of Earth, and the clouds are reflective enough that solar panels pointing downward towards them would be nearly as effective as those pointing upwards towards the sun. The atmospheric winds at this altitude would drive a floating station around the planet once every 100 hours or so. At higher latitudes this would take even less time, resulting in a 'day' much closer to the 24-hour day experienced on Earth than on the surface of Venus with the 243 days it takes to make a single rotation.
• Venus is also the closest major body to the Earth other than the Moon, making transportation and communications easier than for most other locations in the solar system. With current propulsion systems, launch windows to Venus occur every 584 days, compared to the 780 days for Mars. Flight time is also somewhat shorter; the probe Venus Express which recently arrived at Venus spent slightly over five months en route, compared to nearly six months for Mars Express. At closest approach, Venus is 45 million km from Earth compared to 56 million km for Mars.

[edit] Obstacles

Venus also presents several significant challenges to human colonization:

• Hostile surface conditions: the surface of the planet is extremely hot, with temperatures at the equator of around 500 °C (932 °F), higher than the melting point of lead. The atmospheric pressure on the surface is also at least ninety times greater than on Earth, which is equivalent to the pressure experienced under a kilometer of water. These conditions have caused missions to the surface to be extremely brief: the probes Venera 5 and Venera 6 for example were crushed by high pressure 18 km above the surface. Following landers such as Venera 7 and Venera 8 succeeded in transmitting data after reaching the surface, but these missions were brief as well, surviving no more than a single hour on the surface. Obtaining materials from the surface for use by an upper-atmosphere colony would be a problem.
• Water, in any form, is almost entirely absent. The atmosphere is devoid of oxygen and is primarily carbon dioxide in poisonously high concentrations. In addition, the visible clouds are comprised in part of sulfuric acid and sulfur dioxide vapor.

[edit] Methods of colonization and exploration

Given the hostile conditions of Venus, a colony on the Venusian surface in its present form is far beyond current technological capabilities. Some authors suggest overcoming this by terraforming Venus - making the planet more earthlike. The energy requirements for all terraforming plans are daunting when compared with our current technology, and the time required could possibly span tens of thousands of years, if not millions. In spite of this seemingly pessimistic time frame, terraforming in this matter offers the potential for exponential growth to remake the industrial base of the human race if humans are to set about the task of settling space en masse. If a large portion or the entire planet could be shaded, Venus would cool to a useful temperatures in mere decades. Such methods would include placing sails between Venus and the sun at Lagrange points between the two, controlled dust clouds in space, and a large number of other ideas. Others suggest a different approach, however, arguing instead for colonization not of the surface of the planet but of its upper atmosphere, the most habitable part of any planet outside Earth.

[edit] Exploration and research before colonization

As Venus has not been studied as much as objects such as the moon and Mars have, further research would have to be conducted on the planet before a human-powered mission could be approved. The probe Venus Express is currently in orbit around the planet, but other low-cost missions have been proposed to further explore the planet's atmosphere, as the area 50 kilometres above the surface where air pressure is at the same level as Earth has not yet been explored.

One such proposed mission is a solar-powered flyer. Though wind speeds in the upper atmosphere of Venus can reach up to 95 m/s at the cloud top level, the slightly lower gravity (8.87 m/s²) and the higher air pressure alleviate this somewhat, and flying an aircraft on Venus would be easier than one on Mars with its extremely low air pressure. The proposed flyer would base itself at an altitude of about 72 kilometres where the pressure is low enough and solar energy abundant enough that it could recharge itself for temporary incursions lower into the atmosphere for a number of hours. As daytime on Venus persists for over 100 days due to its extremely slow rotation, a flying craft could remain in perpetual sunlight, and would only need to move at a speed of 13.4 km/h at the equator to keep up with the planet's rotation. Exploring the other side of the planet however, would not be possible until sunlight reaches the area, as a solar-powered craft would not have the power to traverse the entire night side without recharging.^[2]

[edit] Aerostat habitats and floating cities

Geoffrey A. Landis has summarized the perceived difficulties in colonizing Venus as being merely from the assumption that a colony would need to be based on the surface of a planet:

"However, viewed in a different way, the problem with Venus is merely that the ground level is too far below the one atmosphere level. At cloud-top level, Venus is the paradise planet."

He has proposed aerostat habitats followed by floating cities, based on the concept that breathable air (21:79 Oxygen-Nitrogen mixture) is a lifting gas in the Venusian atmosphere, with about half the lifting power that helium has on Earth.^[3] This would allow breathable air domes to lift a colony in addition to their own weight. Alternatively two-part domes could contain a lifting gas like hydrogen or helium (extractable from the atmosphere) to allow a higher mass density^[4].

[edit] Terraforming

Main article: Terraforming of Venus

Artist's conception of a terraformed Venus. (credit: Daein Ballard)

Terraforming (literally, "Earth-shaping") is the theoretical process of modifying a planet, moon, or other body to a more habitable atmosphere, temperature, or ecology. Venus has been the subject of a number of terraforming proposals. Amongst such proposals are the following:

Carl Sagan in 1961^[5] suggested terraforming Venus by seeding its atmosphere with algae in order to convert some of the planet's carbon dioxide to oxygen. However, it is known today that water is so rare on Venus that even the best efforts of photosynthesis would add a negligible amount of oxygen while consuming what little water vapor there is.

Robert Zubrin, following the 1991 study^[4] by Paul Birch, has proposed^[6] a large solar shield, designed to protect Venus from the Sun and cool it down sufficiently to permit liquefaction, from a temperature less than 304.18 K and partial pressures of CO₂ down to 73.8 bar (carbon dioxide's critical point) and then down to 5.185 bar and 216.85 K (carbon dioxide's triple point.) Below that sublimation of atmospheric carbon dioxide into dry ice will cause it to accrete via deposition onto the surface, after which it would somehow be buried or shipped off-world perhaps to Mars, which has the opposite of Venus' problem from a human perspective -- insufficient atmospheric pressure and greenhouse gases, as opposed to too much. With the sun shielded and excess greenhouse gases removed, the problems of atmospheric pressure and heat would be solved. However, Zubrin concedes that the lack of water would remain a serious problem, and even the bombardment of the surface with comets or asteroids containing ice would take a long time and accomplish little to solve it. Birch suggests disrupting an ice-moon of Saturn and bombarding Venus with its fragments to provide perhaps 100 metres/sq. metre of water. Thus the terraformed Venus would have very shallow, salty seas, helpful in reducing the greenhouse effect from water vapour. Speeding up the planetary rotation would seem to be a project for the far-distant future, neglecting exponential growth. ^[7]

Landis has suggested that as more of his floating cities were built, they could form a solar shield around the planet, and could simultaneously be used to process the atmosphere into a more desirable form, thus combining the solar shield theory and the atmospheric processing theory with a scalable technology that would immediately provide living space in the Venusian atmosphere. If made from carbon nanotubes, recently fabricated into sheet form, then the major structural materials can be produced using carbon dioxide gathered in situ from the atmosphere. The recently synthesised amorphous carbonia might prove a useful structural material if it can be quenched to STP conditions. According to Birch's analysis such colonies and materials would provide an immediate economic return from colonizing Venus, funding further terraforming efforts.

[edit] Present exploration of Venus

The ESA space probe Venus Express arrived at the planet in May of 2006 and is currently undergoing an approximately 500-day mission to study the atmosphere and clouds in detail.

Future missions include JAXA's Planet-C. The MESSENGER mission to Mercury will have flybys of Venus in October 2006 and June 2007, and the BepiColombo mission also plans a flyby of the planet.

[edit] See also

• Mars Society

[edit] References