At about 50 kilometers (30 mies) altitude, the atmospheric density on Venus is close to “sea level” density on Earth, and temperatures are basically Mediterranean, you get plenty of sunlight, and the CO2 atmosphere is sufficiently denser than air on earth that a breathable air mix provides about half the buoyancy on Venus as Helium does on Earth. Basically, at 50km you could build multiple-km-scale flying cities that would be extremely roomy since more air space means you can support more mass. Or in other words, Lando Calrissian, eat your heart out.
Sure you can make a super large city like that float in the Venusian atmosphere, how do you get it there in the first place? There’s also the question of why you’d want to, but I want to focus this series on how you might build your castles in the sky. What I’d like to suggest in this blog post series is that the Venusian atmosphere may provide most of the raw materials needed to build such flying cities using in-situ resources, and many of those resources may be readily extractable.
For Mars, Venus, and other planetary environments that have atmospheres, the atmosphere itself can provide a feedstock for in-situ resource utilization (ISRU). Both atmospheres have a mix of gases and condenseable vapors that can be processed in the gas-phase.
A hypothetical floating outpost 30 miles above the surface of Venus. (Wikimedia Commons/Anynobody)
Venus Has lots of Carbon, Oxygen, Nitrogen, and Sulfur, decent amounts of Argon, Helium, Neon, and Hydrogen, and trace amounts of Chlorine and Fluorine. What can you do with these building blocks, assuming you can make the chemical engineering work to take these feedstocks and convert them to the outputs you want?
* Breathable air
* Drinkable water (from the water vapor and chemically extracted from the sulphuric acid)
* Chemical rocket propellants (LOX, Methane, Hydrogen, and with a lot more work maybe some storables like N2O, N2O4, Hydrazines, H2O2, and storable hydrocarbons and alcohols)
* Most plastics including PE, PP, PC, PET, PVC, Epoxies, Teflon and other flouropolymers (in modest quantities–the Florine’s pretty rare). Just no silicones unless you bring your own Si
* Carbon and aramid fibers
* Graphite, Graphene, and Carbon Nanotubes
* Sulfur “Concrete” (likely using graphite whiskers as the reinforcement)
Anything metal would likely need to be imported, but if the ISRU equipment to get to simple polymers and carbon fibers isn’t prohibitively large, you might actually be able to build most of the structures, the sulfuric-acid resistant outer skin, and the breathable atmosphere, and drinking water all from local materials
How do you actually send vehicles to/from a floating cloud colony?
Geoffrey Landis had a paper on low-altitude Venus balloons [Low-altitude Exploration of the Venus Atmosphere by Balloon]. One of the mind-blowing conclusions from this paper was that you could make a 1mm thick titanium spherical pressure vessel about 3.8 meters in diameter that could both survive reentry, and function as a “balloon” that would hover at around 5-10km altitude.
Rocket stages are relatively low density when empty… Could you get a rocket stage post-burnout to float in the Venusian atmosphere? If so, could you do it at an altitude high enough that the temperature wouldn’t destroy the stage?
A sphere with titanium skin 0.04″ thick would be able to survive reentry and float a couple of miles above the surface.
* All of the stages could float at altitudes over 5km
* LOX/LH2 stages tend to float higher than LOX – Kerosene stages (fluffier tanks)
* More mass efficient stages (higher pmf stages) tended to float higher
* The pressures at this altitude are in the 30-40bar range, so you’d want to keep the tanks themselves pressurized enough that the tank was always a little bit higher pressure than the outside atmosphere. This could be done by letting the residual cryogens boil, and using a relief valve set to some nominal say 15-20psid setting.
* The temperatures are all still a bit on the high side. No metal parts would likely fail, but this is hot enough that unless cooled (either via active refrigeration or by boiling-off a coolant), any electronics or plastic components would fail.
After the chemical processes involved with producing life-supporting materials are demonstrated and perfected, the Selenian Boondocks team suggest small robotic labs could be sent to Venus, where they would bob in the atmosphere, extracting life-sustaining materials, gradually inflating great bladder-like structures (perhaps a Bigelow Aerospace module made of Kevlar). Years into the project, it might look like a gargantuan bunch of grapes. Permanent settlers could tether these floating blobs together, extending walkways and building platforms, creating something that might eventually look like a massive floating oil rig, complete with tubes dangling dozens of miles below to gather materials from the surface.