Colonization of Venus

Space colonization is a step beyond space exploration, and implies the permanent or long-term presence of humans in an environment outside Earth. Colonization of space is claimed to 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. Venus is the second largest terrestrial planet and Earth's closest neighbour, which makes it a potential target.

Venus has certain similarities to Earth which, were it not for the hostile conditions, 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, 0.38 times 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 was going to be the first probe to investigate this, however it has since been canceled due to lack of funding). In contrast, Venus is close in size and mass to the Earth, resulting in a similar 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 probably have little difficulty adapting to Earth gravity should there be a reason to visit or return; contrasted to return trips from Mars where humans would likely need rehabilitation or the use of an exoskeleton.^{[citation needed]}

Venus's relative proximity makes 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 that arrived at Venus in April 2006 spent slightly over five months en route, compared to nearly six months for Mars Express. This is because at closest approach, Venus is 45 million km from Earth compared to 56 million km for Mars, making Venus the closest planet to the Earth.

Venus also presents several significant challenges to human colonization. Surface conditions on Venus are practically impossible to deal with: the temperature at the equator averages around 450 °C (842 °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 whilst still 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.

Furthermore, water, in any form, is almost entirely absent from Venus. The atmosphere is devoid of molecular oxygen and is primarily carbon dioxide in poisonously high concentrations. In addition, the visible clouds are composed partly of corrosive sulfuric acid and sulfur dioxide vapor.

Given the hostile conditions on Venus, a colony on the Venusian surface is far beyond current technological capabilities.

This has not prevented some science fiction authors from speculating on ways of overcoming this by, for example, terraforming Venus – making the planet more earth-like. Outside of fiction, the energy requirements for all terraforming plans are daunting in the context of our current technology, and the time required could possibly span hundreds of years. Other authors speculate that, if a large portion or the entire planet could be shaded, Venus would cool to a useful temperature in mere decades. Such authors postulate cooling methods such as placing sails (Solar shades) between Venus and the Sun at the Lagrange point between the two, controlled dust clouds in space, and a large number of other ideas.

Others suggest a different approach, however, claiming that rather than attempting to colonize Venus' hostile surface, humans might attempt to colonize the Venusian atmosphere (the most habitable known part of any planet outside Earth). This is because at an altitude of approximately 50 kilometers (in Venus's upper atmosphere), the pressure and temperature are Earth-like (1 bar and 0-50 degrees Celsius).

Exploration and research

Due to the planet's hostile environment, Venus has not been studied as much as objects such as the Moon and Mars have, and it is extremely unlikely that research would be conducted with a view to a human mission to the planet. 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.

It is possible to land a robot on the surface, as the Soviet Venera program succeeded in doing so. Several of the Veneral landers survived on the surface for some time; the Venera 13 lander survived for 127 minutes, and the Venera 14 lander for 57 minutes. Improved materials and technology designed to work at the high temperatures and pressures would be necessary to increase probe survival time. As the survival times of the robotic probes grow longer, enhanced missions might be feasible, including the establishment of a robotic base at locations where important (perhaps fissionable) compounds might be found. The technology for operating under such conditions is at the current time so exotic as to be difficult to conceive, and funding is likely to go elsewhere.

Aerostat habitats and floating cities

Geoffrey A. Landis of NASA's Glenn Research Center 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.”

Landis 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 dense carbon dioxide atmosphere, with over 60% of the lifting power that helium has on Earth.^[2] In effect, a balloon full of human-breathable air would sustain itself and extra weight (such as a colony) in midair. At an altitude of 50 km above Venusian surface, the environment is the most Earth-like in the solar system – a pressure of approximately 1 bar and temperatures in the 0°C–50°C range.^[3] Because there is not a significant pressure difference between the inside and the outside of the breathable-air balloon, any rips or tears would cause gases to diffuse at normal atmospheric mixing rates, giving time to repair any such damages. In addition, humans would not require pressurized suits when outside, merely air to breathe, a protection from the acidic rain; and on some occasions low level protection against heat. Alternatively, two-part domes could contain a lifting gas like hydrogen or helium (extractable from the atmosphere) to allow a higher mass density.^[4]

At the top of the clouds the wind speed on Venus reaches up to 95 m/s (approximately 212 mph), circling the planet approximately every four Earth days in a phenomenon known as "super-rotation".^[5] Colonies floating in this region could therefore have a much shorter day length by remaining untethered to the ground and moving with the atmosphere. Allowing a colony to move freely would also reduce structural stress from the wind.

Terraforming

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.^[6][7] The proposals seek to remove or convert the dense carbon dioxide atmosphere, reduce Venus's 450 °C (770 K) surface temperature, and establish a day/night light cycle closer to that of Earth.

Many proposals involve deployment of a solar shade and/or a system of orbital mirrors, for the purpose of reducing insolation and providing light to the dark side of Venus. Another common thread in most proposals involves some introduction of large quantities of hydrogen or water. Proposals also involve either freezing most of Venus's atmospheric CO₂, or converting it to carbonates, urea or other forms.

• A Floating City on Venus - article from The Space Monitor