Venus is a horrific hellhole of a planet. The surface temperature averages 450 degrees Celsius, easily enough to melt lead. It has an atmosphere 90 times denser than Earth's, composed mostly of carbon dioxide with sulphuric acid clouds. It is one of the most inhospitable places to human life in the whole solar system. It will take a far more sophisticated and robust technology to set foot on the surface of Venus that it will Mars or most moons of the gas giants.
However, that does not mean that Venus is completely off limits to a possible human presence. As pointed out in detail by NASA researcher and science fiction author Geoffrey A. Landis, Venus' lower atmosphere is so dense, a sealed habitat with a gas mixture breathable to humans would actually float. In fact, it would settle out at a stable altitude of about 50 kilometers above the surface, where the atmospheric density and temperature would be similar to conditions on Earth. Given the atmospheric pressure, standard human breathing mixture at sea-level pressure would have as much lifting power on Venus as half that of helium on Earth.
Temperatures at that altitude would also be human-amenable, averaging between zero and fifty degrees Celsius. However, even though the atmosphere at 50 kilometers up would be at the right pressure and temperature, there would still be too little oxygen for it to be breathable. The gas mixture at those heights would be mostly nitrogen and carbon dioxide.
This phenomenon opens up a very intriguing method for exploring and perhaps some day colonizing Venus: by floating among its cloud tops.
Venus is the easiest major terrestrial body in the Solar System for humans to reach besides the Moon. Launch windows to Venus occur every 584 days, compared to the 780 days for Mars. Its gravity, even 50 kilometers up, is very similar to Earth's, meaning humans living and working on the planet would not suffer the potential bone loss and other complications lesser gravity environments may incur. With so much carbon dioxide in the atmosphere, it can be mined for its oxygen and mixed with trace nitrogen for an abundant air supply. That much closer to the sun, solar cells on Venus could provide up to almost twice that of similar cells on Earth.
But why go to Venus at all? What benefits could be culled from such an infernal world?
While Venus no doubt has plenty of potentially valuable mineral resources, extracting them in the midst of the planet's surface conditions would likely be more expensive and trouble than they would be worth, even with automatons. Very advanced technology (at least Tech Level 17 or higher) may change this equation, but until then economic compensation for mining efforts there may be negligible.
Venus still offers a treasure trove of scientific discoveries that could be of great potential value. A manned presence could be justified in order to pursue research there. Farther in the future, Venus' convenient closeness to Earth may also make it a target for colonization by groups and interests who want to establish a substantial presence away from the Earth-Moon system for various reasons but may not have the means or resources to range farther afield. Its assumed that setting up a manned base or colony in the clouds of Venus, with its semi-friendly environment, would be less expensive and troublesome than, say, setting up a surface base on Mars or an asteroid with their much more hostile vacuum conditions.
Farther in the future, Venus could also act as an 'incubator' for anaerobic extremophile microbes among its sulphuric clouds, and a manned presence setup on Venus could be used to help harvest them for commercial use. If Venus ever becomes a target for terraforming, a manned presence in its cloud tops may be set up to oversee the early stages of such a many-centuries-long project.
Interestingly, Venus is also a better staging area for accessing the asteroid belt than Earth or Mars, being able to take better advantage of it greater orbital velocity to launch spacecraft. For example, a minimum-energy trajectory to the largest main-belt asteroid, Ceres, takes 0.95 years from Venus, and 1.05 years from Earth. Though common perception (fueled in part by Hollywood scifi) paints the asteroid belt as a crowded floating rubble pile, in fact bodies in the belt are spread very far apart, many thousands or millions of miles of distant form one another. Being actually in the Belt would not necessarily make one any closer to many desirable asteroids. In fact, with lower average orbital velocity that far out, they may sometimes actually be more difficult to reach than from points in the inner system, such as Venus.
While the flight time difference quoted above may not at first seem significant, in terms of fuel and habitat resources it could add up to substantial savings. A human infrastructure built up on Venus could be dedicated to launching mining probes and manned expeditions to targeted asteroids in the outer solar system. Once the infrastructure is in place, it would be theoretically cheaper to run in terms of resources consumed than a similar operation based on Earth or Mars or even the asteroid belt itself.
Any initial manned presence on Venus would likely take the form of exploratory airships. These would at first be used mostly for research, exploration, and testing techniques and equipment. Later, if numerous bases and colonies are established in the Venusian cloud tops, they could also be used for transport and commerce.
A Venusian airship would in many ways resemble those found on Earth, in terms of general design and operation. However, there would be many differences as well. An airship's primary lifting gas would be an oxygen/nitrogen mix breathable by humans, which means that the crew could actually inhabit the ship's gas cells instead of being confined to a relatively small gondola or cabin. While most aerostats would have multiple cells and airlocks between the cells, it would still dramatically open up the available space in these vehicles to human crews. Compared to most other off-Earth habitats of comparable tech level, Venusian airships and bases would be practically luxurious in terms of sheer available room.
However, the breathing gas mixture would only have about 60% of the lifting capacity of helium on Earth, meaning the airships would have to be built considerably larger with more lifting gas volume for about the same amount of payload mass. This could be supplemented with secondary lifting cells filled with a lighter gas, such as helium or hydrogen in order to offset extra mass. Very advanced airships could also use vacuum cells for additional lift.
The airship would also have to be built more robustly than on Earth. At the heights they are designed to operate, Venus has constant hurricane force winds that circle the planet every four days in a phenomenon called 'super rotation.' While this is not as devastating as it may at first seem, as everything at that altitude would be moving at the same speed, localized turbulence and cross currents could pose a substantial problem. Advanced but lightweight materials that can stand up to such potential punishment would be required. Because of the abundance of carbon in the form of carbon dioxide in the atmosphere, and given the future timeframe of these vehicles, its possible that carbon nanotubes or graphene materials could be manufactured on-site in order to build tough enough airships to take on such weather conditions.
The phenomenon of super rotation would also make insertion of spacecraft and probes into the Sweet Zone a difficult venture. Previous probes that landed on the surface did not have to worry overly much about matching wind speeds and direction so far up, since they would zip right past the super rotation band on the way down. Our hypothetical airships would have to slow down to just the right speed at just the right angle fifty kilometers above the surface to slip into the Sweet Zone. And worse, the local weather conditions wouldn't necessarily be the same every time; the guidance systems or the pilot would have to adjust to local wind conditions as needed.
This may be complicated even more by the need to inflate the airship once in the Sweet Zone. Doing so in space would probably not be practical, and during atmospheric entry would be all but impossible. The craft may have to employ large but disposable drag chutes or an inflatable aerobrake shield. These would arrest the airshipÃ¢â‚¬â„¢s plunge through the Sweet Zone long enough for the vehicle to inflate its lifting cells.
A orbital skyhook or rotovator could help circumvent this problem, but such devices for worlds such as Venus would be considerably further in the future than the first airships sent there
Another environmental hazard in the clouds of Venus is sulphuric acid rain. Anything exposed to the Venusian atmosphere would have to be armored against this, or composed of an acid-resistant material such as ceramics, to avoid slowly corroding away. The skin of the airship, as well as any exposed equipment and excursion suits, may also need to be coated in a layer of polyethene or polypropylene for protection.
Propulsion for these dirigibles need be nothing more complicated than what blimps use today, usually electric or fuel cell propeller motors. Their topsides would be covered over lightweight thin solar cells in order to provide vehicle power and to supplement any fuel-dependent engine. Given how large these vehicles can be and the greater concentration of sunlight that Venus enjoys, the power they could generate would be substantial.
In order to better handle potential high winds, they would also have aerodynamic shapes, with cross sections reminiscent of an airplane's wing. They would also take advantage of dynamic buoyancy systems, which would alter the volume of the lifting gas cells, changing the vehicle's overall density and allowing it to rise or fall much more smoothly.
With so much wind available, the airships may also take advantage of advanced sail designs, which would allow propulsion and maneuvering with a minimal use of power. Combining these with the more conventional engines and advanced computer control, venusian airships may prove to be quite adept at moving around in their environment, perhaps more so than their Earth equivalents.
Life aboard these airships for their human crews would take some adjustment. It would probably be akin in some ways to sailing on Earth's oceans, as the airship would be in constant motion thanks to Venus' winds. Some days would be calm and routine, perhaps even with sunshine and blue skies, while others would be marked by constant turbulence and being tossed about by dark storm clouds for hours on end.
A step up from pure transportation is a larger permanent floating structure. These bases would be designed to be continuously manned, with crews rotating on and off in watches of week, months, or even years.
These bases would be much larger than the more mobile airships, in order to give them greater stability and resistance to being battered about by wind turbulence. This would be important to more easily receiving supply and personnel transfers to and from orbit on a regular basis. Their greater stability would also allow them to service and maintain smaller airships, functioning as a harbor and drydock for them.
An actual permanent floating base on Venus could take many forms. It may just end up being a large collection of individual airships, perhaps permanently moored to one another into a kit-bashed base. It could end up very reminiscent of the ISS, with many interconnected hard shell habitat modules. Or they could be made up of an interconnection assembly of inflatable, spherical, blimp-sized modules, much larger than any individual airship.
One design proposal posited creating a large habitable ring supported by an even more enormous torus of hydrogen lifting cells. The facility was designed in such a way that crew gondola could be retracted up into its lifting gas torus, the latter to act as a 'storm cellar' against high solar activity. At that altitude, personnel ships and bases would get a larger dose of radiation from space, and greater precautions against it would be
A colony is differentiated from a base in that a colony by definition must be fully self-sufficient. That means it must supply its own air, consumables, and raw materials without depending on resupply from Earth. Without easy access to the surface of the planet, obtaining some of these could be a major obstacle, especially for one very scarce resource on Venus: water.
Venus is a very dry world, more so than Mars, with only trace amounts of water vapor in its atmosphere. Even hydrogen to make water is fairly rare, what there is of it tied up in trace methane or acidic compounds.
Its assumed that any manned craft floating in the Venusian atmosphere would have extremely efficient recycling systems, just out of sheer necessity. But even so, such systems would still need to be replenished with outside sources from time to time. Importing their water all the way from Earth could also prove to be expensive and time consuming.
One solution would be to set up a much closer source for water as well as other consumables in the form of orbiting asteroids. Carefully-chosen planetoids rich in water and other vital materials could be redirected to eventually settle into Venus orbit. Bases could be set up on these new minor moons, dedicated to extracting needed resources for the floating colonies below. A symbiotic relationship could form between the two sets of colonies, with an economy of traded resources going back and forth.
Floating Habitats on Venushttp://spacemonitor.blogspot.com/2007/05/floating-city-on-venus.html http://www.universetoday.com/15570/colonizing-venus-with-floating-cities/ http://en.wikipedia.org/wiki/Colonization_of_Venus#Aerostat_habitats_and_floating_cities
Advanced Airship Designshttp://orbitalvector.com/Aircraft/Airships/ADVANCED%20AIRSHIPS.htm
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