Friday 21 October 2016

How to live on Other Planets: Venus

Venus is our closest neighbour and Earth's 'sister planet', and yet it is very different from our cool blue marble.
We have a look at some of the challenges and advantages of colonizing this planet.

Venus is a very interesting choice for colonisation. At first look, it is hell.

Picture taken by Venera
Surface temperature is a constant 735 K (462 degrees Celsius), which is hotter than Mercury in direct sunlight. Its atmosphere is nearly entirely composed of carbon dioxide, and is generates pressures 92 times greater than earth. It is like diving a kilometre under the sea. An acidic, boiling sea. 

The cloud cover makes it oppressively dark. The winds are slow, but can knock over buildings. Lighting strikes light up the barren landscape, littered with broken rocks. 

So what's in it for colonists?


It's on second inspection that Venus shines as a candidate for colonisation.

Gravity is 0.9G, meaning that the difference would be barely noticeable from Earth. The surface is not practical to live on, but at an altitude of 50 to 55 kilometres, atmospheric density and temperatures are quite terrestrial.

Since Venus's atmosphere is mainly dense carbon dioxide, lighter gasses such as oxygen and nitrogen will float in it. A ball containing a breathable mixture can suspend a colony with no additional pressurisation or heating.
In other words, the perfect Venus colony is a large transparent balloon containing living spaces and a 21% oxygen, 79% nitrogen gas. Because the difference in pressure between the inside and outside are nil, structural requirements are lax. Gasses won't tend to move in or out, just mix slowly if the canopy is pierced. 

This is probably the only environment in the Solar System where you can walk around in normal clothing, without fear of sudden depressurisation, meteorite strikes, radiation sickness, microgravity bone loss and so on. With a thin suit and an oxygen mask, you could even walk outside!

There are some challenges to living high above Venus, but both can be turned to the colonists' advantage. 

Sulphuric acid clouds roam the 50 to 75km altitude band. They would eat through metallic structures and cause nasty chemical burns if they leaked into the colony. However, they are a great source of water, if they are broken down and the sulphur is removed.

Winds reach hurricane speeds at 300 to 400km/h. The clouds they drag along circle the planet every four days! A colony would be pulled along similarly... which is great for transport. By following the jetstreams the same way intercontinental flights do on Earth, large colonies can travel at a rapid pace to where they need to be.


What does Venus have compared to other colonizable bodies?

Venus surface in infrared.
Venus is a poor candidate for mining. The surface is dotted with ancient volcanoes constantly spewing lava. Protecting mining equipment against uneven terrain, incredible pressure and heavy winds will make operations expensive. Overheating is even more of an issue than on Mercury, as there are no shadows to radiate heat into, and touching lava can raise temperatures to 1000K or more.

The lava, in the cooler regions, becomes igneous rock. It should be rich in metals such as aluminium, nickel and iron. However, these are also commonly found in metallic asteroids, and the latter are easier to exploit.

Overall, any mining operation on Venus will be wastefully expensive and much less performant than other options around the Solar system. The fact that you can float up payloads from the surface to high altitudes is negated by the existence of strong, unpredictable winds.

The real benefit in Venus is the atmosphere's composition and conditions. 

Far from the surface, Venus enjoys nearly Earth-like conditions. It is a perfect place to live in, with only minor temperature control and life support requirements. 

Composition of Venus's atmosphere
The atmosphere is also a commercial asset. The carbon dioxide is a primary resource for liquid methane/liquid oxygen rockets, meaning the high-thrust engines required to climb into orbit can be refuelled cheaply. This reduces the practical deltaV cost of a mission to Venus considerably. 

Venus lacks the hydrogen required to create water from carbon dioxide. However, it can be imported in return for the water. The energy required can be extracted from geothermal powerplants. These are much more compact and efficient than solar panels., and do not require rare metals or expensive electronics. Venus could make a profit from this trade. 

Other assets Venus enjoys include the ability to produce plastics for cheap, and having access to vast quantities of sulphur if it locates an active volcano. On Earth, most sulphur comes from the purification of fossil fuels. Once that runs out, sources of cheap new sulphur will become more difficult to find. 

The other big business would be selling places to weary spacemen in comfortable, safe and near-Earth-gravity floating habitats.

In terms of deltaV, Venus is a good destination. From Low Earth Orbit to escape velocity is 3km/s. From Earth escape to Venus is 3.5km/s. This cheaper than going to Mars. Arriving at Venus is the best part: the thick atmosphere allows for reliable aerobraking.

It is possible to send cargo to both Venus and Mars with a single booster
Going from Venus to the rest of the Solar System is slightly more complicated. It takes a lot of deltaV to reach planets such as Jupiter or Saturn, more than from Earth. However, its inner position means that there are frequent synodic 'departure windows' between Venus and other planets. Carbon Dioxide is easily captured and converted into rocket propellants. 

A solar power station high above Venus will receive double the expected amount of sunlight: one part from the Sun, another from the highly reflective cloud layer. The difficult part is transmitting this energy to colonies inside the reflective clouds. 

The Venus Colony

Three possible configurations are possible for a Venus colony.

The first is the simplest, and best adapted to smaller habitats.

It is a thin-skinned balloon taut over a solid disk. On the disk are mounted living spaces and other installations. This is where people live, walk and tend to their gardens.

Russian vision of a Venus Cloud City.
The balloon is pressurised with 1 atmosphere of breathable gasses.

The small habitat floats at an altitude of about 55km. The average temperature of the surrounding Venusian atmosphere is 20 degrees Celsius. However, the exterior pressure is about 0.5 atm, equivalent to climbing a 5km tall mountain on Earth. Most people can acclimate to 3km altitude air, but need breathing apparatus to do any work at higher altitudes. In other words, if the Venus habitat's balloon is pierced, they only need small oxygen masks to survive and perform repairs. 

Wind energy will be the primary source of electricity. Thick clouds prevent effective use of solar energy, and a small habitat is unlikely to be able to reach deep enough for geothermal energy to be effective.

The second possible configuration is better suited for larger colonies. 

Multiple, large balloons of oxygen are held at 0.5 atm. Hanging underneath them is a gondola. The gondola contains living spaces pressurized with a breathable mix to 1 atm. 

Pure oxygen balloons slightly less lifting power than a breathable mix, which is mostly nitroge but are cheaper and easier to replenish, as oxygen can be drawn directly from the surrounding carbon dioxide atmosphere. Nitrogen is better used as fertilizer for plants. Also, when pressurized at 0.5 atm, it is at the same pressure as the surrounding atmosphere. Tears, holes and punctures won't 'leak' anything, so repairs can be performed without any urgency. 

Larger colonies might need to deal with the winds taking them in unwanted directions. The oxygen balloons can be shaped into aerodynamic 'zeppelins' equipped with engines. The engines only need to be strong enough to counter wind forces.

Power can rely on a very simple geothermal system. Water can be dropped through a tube to the ground. It boils and rises up another tube, driving a turbine.  

The third version uses alternative gasses. It is best suited for automated floating platforms and other unmanned outposts. These gasses can be large balloons of heated Venusian atmosphere, or small balloons of buoyant gasses such as hydrogen. As these are not suitable for breathing, habitats cannot use the balloons as large, open spaces. 

Transport between colonies relies on electric airships. Without oxygen, chemical combustion cannot be relied upon. The airships can be quite small, however, by operating at lower altitudes. The increased pressure makes gasses more buoyant for their volume, and propellers can spin slowly for the same effect. 

HAVOC mission designed by NASA for VEnus
Low-altitude airships will position themselves under their destination, and use a system of elevators to deliver cargo.

People will need to travel much faster. Energy-intensive electrothermal jets can be used. Electricity is used to power a resistance, generating very high temperatures inside a compressor. The principle of operation is the same as a jet engine, but it can use any gas as a propellant. At high altitudes, these jets will permit supersonic travel.   

The dangers

Despite the comfortable conditions at high altitude, there are risks to living on Venus.

The first and foremost is the risk of falling. A failure of the balloons that hold up the colony will cause a drop in altitude. This increases the temperature and the force of the winds. However, it allows the colony to stay afloat with a smaller number of balloons, so a straight drop the surface is not necessarily the only outcome. Even if all balloons are destroyed, the drop will be slow. Colonists will have a lot of time to escape a falling colony.

The acid clouds that circle the planet at high altitude impose certain requirements on the materials used to build colonies. A layer of teflon has been proved to prevent any corrosion, but if it is damaged, it would expose underlying metals. Unaccounted-for corrosion can lead to the structural failure of a floating colony and its sudden collapse.

Another danger is the loss of power. Colonies designed for the 50km altitude band (for neutral pressure) must have cooling systems run permanently. The outside temperature is 50 degrees Celsius. If geothermal lines are cut, the colony must be equipped with emergency generators, as it cannot rely on sunlight. Otherwise, the colony would heat up until it escapes to a higher altitude. 

The lack of visibility and the strong winds means that mid-air collisions are more likely to happen. Colonies might have to integrate a 'bumper-net' into their design, to prevent airships from crashing into their habitats. 

A final worry for colonists is resources. They are dependent on external supplies of minerals and metals to support their life support ecosystems. Water can be extracted from sulphuric acid clouds, but it can be unreliable. It is not hard to imagine a colony trapped inside a 'dry storm' where such clouds are absent. Extracting oxygen from carbon dioxide and splitting sulphuric acid cost a lot of energy, so a colony is distress will have to add 'running out of air and water' to their list of worries. If colonies have to pay for external shipping of resources, then their expansion and proliferation depend entirely on their economic success. Markets are more volatile than the wind...


Venus is an interesting destination for colonists, but simply living in a comfortable spot does not make money.

Colonies will start out very small. Air-dropped from orbit, they will mostly be automated atmospheric extraction stations. They feed airships with dry ice, who then transport them to launch sites. The carbon dioxide is processed in orbit into rocket propellants, using solar energy. 

Venus becomes a good destination for industrial processing. When aerobraking is used, it becomes cheaper to send raw products from the Outer Solar System to Venus, then ship it to Mercury, Earth and Mars, than to stop directly at those destinations. With more sunlight than Earth and lots of carbon dioxide (and oxygen) available, it can perfectly serve the role of refining ore from rocky asteroids. Iron, zinc, nickel, copper... all can be extracted through carbon reduction. 

As the refining business creates profits, geothermal power modules are attached to ever bigger floating factories. These reduce the reliance on orbital solar power and allows Venus to send up from the clouds only the most profitable part of the ore. 

More profits and machinery means more people, which helps develop Venus as a destination for those tired in living in radiation-laden vacuum stations. Couples wanting children, elderly people and the rich expecting long lifetimes will arrive. 

Business is expanded by developing temperature-resistant mining operations on the surface. The lava flows are rich in resources, helping Venus to supply its own metals for building new colonies and ultimately becoming self-sustaining. Or, it could concentrate on using plastics to expand. 

The only thing it will forever lack is hydrogen. 


  1. If you can't mine for materials, you cannot keep producing and expanding your colony's economy. You could recycle over and over again the stuff brought in at ruinous expense from outside, but it's a massive problem.

    Also, that recycling technology - to live on Venus you need a technology where you can toss a broken component into a machine, it digests it somehow, and somehow produces a new one with near atomic level precision. It needs to be that good to make everything you need including sensors and electronics and high end bearings for the many, many pumps and fans you need to survive.

    Anyways, if you have that tech...the asteroid belt or Mercury are _much_ better places to live. As near as I can tell, you need a vast and complex system to avoid falling, dying from acid rain, dying from heat, and to deal with the winds in your colony aerostats.

    You need none of those systems living in an inflated carbon fiber balloon tethered to an asteroid. You need the same life support either way. What you need instead is a merry-go-round. My concept for the merry go round is you just make a structure out of aluminum struts and gratings similar to the floor gratings in skylab. E-mag bearings and motors are at the hub. The whole thing could be shipped in as basically a gigantic IKEA construction set, where it has to be assembled inside a hab balloon from a few rocket-loads of parts.

    Once the merry go round is assembled, it's several spinning cylinders around a central support hub. There are at least 2 cylinders spinning in opposite direction. The outer habitation balloon doesn't spin. You board it by getting inside a car with an acceleration seat that rides rails around the edge. It stops at a boarding platform from the 0 zero section, and you board the car, and it spins up to match rotation with the cylinder you're boarding.

    A small counterweight wheel is part of the system to handle weight balance shifts when people and cargo get on and off. There would probably also have to be water storage tanks around the cylinder, with water transferred from tank to tank and the tanks sometimes moved to keep the thing balanced.

    1. Venus might end up resembling the Japan of our world: does not have much national resources, but still managed to become wealthy by importing raw materials and making higher value products out of them.

      Venus will have to become profitable quickly. The 'Future history' plan I laid out is one way to do it: very little initial investment, sell low quality low extra value products that depend on how much volume you can produce. It is very scaleable and demand for simple things is unlikely to move a lot.

      If you never get to use your own cheaper materials, it never makes sense to build the precision factories to make your own tools. Venus might become a very big importer of such products, in return for vast quantities of carbon-dioxide and nitrogen-derived products. This leads back to my Japan comparison.

      Modern industries can produce items with nanometer-level precision, so all-in-one atomic assembly is not exactly a strict requirement for space travel.

      With or without that sort of tech, Venus is better to place to live on than the Moon or asteroids. Gravity comes without large, moving machines with dynamic-load-bearing parts to maintain. Radiation protection is equal to, if not better than, on Earth, which might be a major factor if we cannot cure diseases such as cancer in the future. The ability to be relatively care-free about sudden depressurisation, micrometeorite strikes and so on might be worth the risk of slower-acting, less suddenly lethal events on Venus. EVA on Venus only needs a single protective layer of clothing and an oxygen mask. In vacuum, you'd need a miniature spaceship to go outside!

    2. That's a big assumption. And I think it's flawed for the following reasons :
      1. We've already got simple versions of the technology. CNC mills and additive 3d printing can make a large pool of possible mechanical parts from raw materials. So the advantage of living somewhere where you can get raw materials is you can expand. Expand exponentially if you have a complete set of machines able to make everything including more machines. Today, we're nowhere near that point, but it does seem plausible.

      All in one atomic assembly is just an easier way to describe this, a room full of machines that can make most technological products and every component in themselves need not use atomic assembly, it just makes that room a lot smaller.

      2. If people have the ability to manufacture things locally, moving goods around the solar system is stupendously inefficient. Why send a freighter between mercury and Venus full of raw materials when you can just build whatever it is you want on Mercury and use it there? If we ever find a way to send our minds the same way, actual space travel would be rare because you could just laser beam a few petabytes of data, the neural map of an entire human brain, and get anywhere in the solar system that has a receiver at the speed of light.

      I'm not sure your miniature spaceship comparison is accurate. You can make a viable vacuum suit with just a thin suit of compression bands. It has been demonstrated - not only are there wearable modern prototypes, but this was what the early U2 spyplane pilots used.

      Either Venus or in vacuum, you need the life support backpack that controls temperature, removes CO2, controls oxygen and nitrogen, and the main mass of it is batteries. On Venus, the high gravity means that backpack will be very heavy.

      I don't see how the atmosphere of venus makes that backpack lighter in any way - 96% CO2 is deadly poison, just as deadly as vacuum. And you have the additional danger that whenever you are outside, you can fall to your death.

      Anyways, I had high hopes for your blog, Matter Beam. You have some very clever ideas. But you're not thinking very objectively. This is a clear and obvious technical comparison, and the evidence is overwhelmingly against Venus being a good place to live. Don't let your biases prevent you from seeing the reality.

    3. Addendum to the above : I see one way the Venus's atmosphere makes a life support backpack lighter. You don't need as large of a radiator to get rid of heat because you can use a fan and rely on conduction to the outside air instead of trying to radiate heat into vacuum. That does help, but the mass of the backpack hardly even matters in the microgravity of an asteroid, so...

      Also, another cognitive bias I'm accusing you of : electromagnetic bearings don't have physical contact between the rotating elements. As I specced out, they are what you'd use for your artificial gravity carousel. The only part that wears in a system like that are the FETs used by the many motor controllers and magnet controllers for the bearings. You'd use parallel control redundant boards and they would still last for years to decades on average.

      The reason this is so much better than the systems to live on Venus or elsewhere is because not only are centrifuges much simpler than airships and all the other stuff, but when the centrifuges fail you just despin them and have people work on them in shirtsleeves inside the pressurized hab balloon. You can keep them offline and work on them over a period of weeks and have the vulnerable population crowd into backup centrifuges.

      Contrast this to the emergency that you get if you have a major problem with your stability control on an aerostat city. If you don't get the problem resolved within minutes, everyone dies.

    4. The more specific advantage of having resources available is that you can use them to expand by building your own extraction, refining and machining infrastructure.

      The cost of that infrastructure must be compared to the cost of shipping the material from elsewhere.

      I think that in the short term, shipping is cheaper than infrastructure. Venus colonies can be packaged and dropped into the atmosphere in a 'ready to run' state.

      As the quantities of raw minerals required to expand increase, it becomes more and more sensible to build your own infrastructure...

      ...but I mentioned the special case where the imported goods are not completely converted into export products.

      Let's take the strongest example for this case: Jovian asteroids.

      These can be nudged into the inner solar system at little cost. A more energetic propulsion system is used at the far end to insert them into orbit. The deltaV cost for a Venus intercept is only marginally higher than for Earth or Mars, and deltaV from the nuclear-electric-powered asteroid tugs is very cheap compared to deltaV from chemical sources.

      This asteroid is majoritarily iron. Iron is too cheap to drive back up Venus's gravity well, out to Earth or Mars, and still make a profit. Venus refineries will initially concentrate on more valuable, rarer metals. This means that the 'leftover' iron will be fed into expanding the Venus colonies. It won't even be as a loss, as the asteroid companies will find themselves selling cheap iron at a premium.

      Of course, this assumes that efficient electric propulsion is prevalent by the time we set out to live on other planets.

    5. Another understanding I have of self-replicating machinery is that they cannot start out small. Simply listing all the different metals, plastics, chemicals and so forth that compose my phone reveals how much of a global product it is. And this is the venerable, efficient Earth infrastructure with errors smoothed out over decades. A private company with a limited budget trying to start a self-replicating process going on has to ensure that every single component can be built with local materials. Even on a small planet with plenty of energy, like Mercury, you will be hard pressed to gather the palladium, gold, hydrocarbons, silicates and so on in one place without a prospecting, mining and refining infrastructure spanning the whole planet already in place.

      Or maybe I am too strict with my definition of self-replicating. A milder version has simple components built out of readily available materials, complex components built off-site, and deficiencies compensated for with regular shipments.

      Interplanetary trade will always make economical sense. Getting a Martian company to provide propellant for a Terran automated miner to capture a rocky asteroid and drop it down to Venus, where it can be aerobraked safely and all the cheap materials carbon-reduced out of the way, leaving behind the thousands of tons of rare metals, and having those metals returned to Earth on a solar-electric freighter...

      will still be cheaper and quicker than opening another Mponeng Gold Mine.

      You're completely right about the spacesuit comparison. I hadn't considered the weight and bulk of the life support at all, or the savings allowed by the 'mechanical counterpressure suits'.

      I try not to follow biases, but I cannot avoid them if I am blind to them. I angered another captain of the community, William Black the other day, because I insisted on my position that current private ventures, even of the size of Virgin or SpaceX, cannot foot the bill for a full-blown colonization effort, large enough to become self-sustaining, without becoming muhc much bigger or asking help from governments. I was accused of having a political agenda! But now that I re-read my comments, he might be right for the wrong reasons. I might have been biased towards a pessimistic view of the power of corporations and their reliance on short-term returns, and seeing government cooperation as the only realistic option, it might have looked like had such an agenda.

    6. Thanks for responding and acknowledging my points. I acknowledge that the best we can do regarding "self replicating" manufacturing with today's tech is basically a halfway solution, like you said. We could pack several flavors of 3d printer and some CNC lathes into a colony ship and make maybe 50% of the needed components but the other 50% is immensely harder. Now, on the other hand, the reason trade is so prevalent today is that it's absurdly cheap. A large container ship is incredibly efficient per unit of cargo moved. (a quick google says it's ~500 miles per ton of cargo per gallon of fuel)

      Nuclear freighters...not so much. Especially when you're talking about down well transits. A freighter run between an asteroid can do the trip with just a teensy bit of thrust and a couple hundred m/s dV. Mars or Venus or Mercury are a large barrier in both directions. (aerobraking isn't free because you have to carry additional mass for the heat shield and additional structure to make your spacecraft able to handle a peak acceleration of several gravities)

      As I understand it, one problem with the asteroid belt is that very few asteroids share common orbits. Crossings are very common but since you need to live inside a larger asteroid but mine at least 3 types of asteroid to have access to all flavors of raw material, you might need to move asteroids together so they orbit each other.

      You're totally right about the corporate thing, by the way. First, you need to differentiate charity work by a billionaire with a corporation following it's mandate to make money. Corporations have to be concerned about short term gains only for several reasons, a big one is leakage.

      The reason corporations don't have an incentive to pay for a major effort to educate an employee or prospective employee is because the education pays off over the 30-40 year working lifespan of the employee, but the employee will probably work for other companies during that timespan. So only short term efforts that pay off immediately are worthwhile (OJT, short term and quick result classes). Yes, tuition reimbursement is an offered perk, but this is just a form of salary that is tax deductible and so the company offers it as a competitive benefit.

      A country has an incentive to educate a citizen because it gets to tax most workers throughout their working lifespan. Immigration is usually rare as a proportion of the population. So if paying 100k for a citizen to get a college degree, and they make a million dollars more taxed at 30% throughout their lifespan - that's a positive ROI for the country.

      So the same argument applies to space habitation. The problem is that it's a huge upfront cost with long term benefits that may get collected by other companies long after the first company that started the effort goes bankrupt. For a country that expects to continue to exist for centuries to come, it's worth the effort, but not for an individual corporation.

      SpaceX is a charity run by a billionaire and the reason it's doing so amazingly well is because NASA's main reason for existence is to redistribute wealth from taxpayers to key Congressional districts and not to do anything particularly crucial. Hence the more expensive a project that NASA wants to do, and the less actual work that must be done for the project, the more profit the key beneficiaries (mostly defence contractors) gain in the relevant Congressional districts.

    7. I think trade is possible by depreciating the fixed costs over a long time.

      If I spend 1 billion USD on my own asteroid tug today, I can set a time horizon for paying off the tug at 30 years. This means I have to make 33 million a year. If I want it to take stuff from Venus to Earth and back, I can manage a trip every 584 days. I must make 53 million per trip.

      The round trip costs 10.4km/s. With 10km/s exhaust velocity electric drives, the payload must be worth 2.72 times the propellant, plus depreciation.

      If the craft is 100 tons, and liquid hydrogen is 0.7USD/kg (like at Cape Canaveral), then we can get some numbers. In a realistic scenario, hydrogen will be 'propellant and service costs', and the craft's depreciation will have services, repairs, inspection and taxes on top. For now, we want to minimize both the payload mass and the payload worth.

      Anyways, to hit a 53 million per trip target, we need 270 tons of something worth 200USD/kg. Silver is currently worth 560USD/kg, so it could fit the profile.

      If we use a different propellant, such as methane sourced at 0.1USD/kg from Venus itself, but requiring a mass ratio of 5.2 instead, we surprisingly get similar figures, because propellant cost is very small compared to the amount you are paying back. The same goes for increasing exhaust velocity to 30km/s, the biggest factor is paying off your own spaceship.

      I think the apparent conclusion is that however expensive the trip is in deltaV, the biggest cost by far is the spaceship itself. Jumping from nuclear thermal to more advanced nuclear-electric is worthwhile in terms of deltaV, but from a costs standpoint, you are not benefiting much.

      Now that the thought experiment is over:
      -I agree with your government/private dividision.
      -SpaceX is kept afloat by more practical ventures
      -Getting electric cars into public circulation will therefore help Mars colonisation efforts.

      The upfront cost of a space station might be provide a counter-argument for artificial gravity: the government or a government-backed corporation puts into place the first modules, a spacedock and a powerplant. Private ventures then only have to burden the cost of adding extra modules. Adding module after module is how the ISS was built, and it cannot be spun. A large space station will have better and better life support margins to feed discount modules (pay your spot without paying for extra machinery to provide air, water and electricity).

    8. Quick clarification with regards to your last paragraph : there was a proposal for a spinning module on the ISS, but it was scrubbed. This is highly disappointing because in order to reasonably travel to Mars or anywhere else with humans, it needs to be determined empirically if a year+ stay in 1/3 gravity actually prevents the deleterious effects of microgravity. This has never been tested. It could be that the catastrophically bad effects of microgravity - specifically retinal detachment causing progressive blindness - aren't prevented by 1/3 g.

      Anyways, the spinning module would spin independently of the station.

      Part of the reason it hasn't been done on the ISS is because you need a very large module in radius because high RPMs cause dizziness and other unpleasant effects. Until recently, no inflatable module had been flight tested with humans, either, and there wasn't a way to launch a hard module with a large radius at all.

      Anyways my solution involves not spinning anything exposed to vacuum because the bearings between the spinning and non spinning portion would have to both spin and hold a seal against the interior pressure. Not easy to do. And the shirtsleeves carousel design is thus a lot easier and simpler. It might always make an annoying sound as the air rushes over the spinning drum, though.

  2. To TLDR it : Venus has a number of severe problems, and a comparison of Venus to asteroid/mercury/moons of Mars living has to weigh those problems versus the difficulty of artificial gravity. Since artificial gravity is straightforward, easy, and inherently safe, it's a much easier problem to solve than Venus living is. Or even non-earth planet living, really. It's safe because there are problems with launch, reentry, or falling out of the sky that can happen on planets during these very violent and short periods of time. There is nothing anyone can do if the equipment fails at the wrong moment.

    With a centrifuge, you can detect the slightest vibration or bearing misalignment and bring the thing to a safe stop. There can be backup mechanical bearings. Since the whole thing runs in air, you can just cut the power and it will gradually coast down to a stop from friction. Very few failure modes that kill everyone.

    1. I think the colonists might be offered the choice between orbiting habitats, roaming asteroid workshops and planet-side colonies such as Venus.

      They might choose one, or go to all three. I can easily imagine a young man training in a large rotating space station, getting employed by an asteroid mining mega-corporation, then staying on asteroids until he becomes worried for his health. He eventually moves to Venus as a rich man looking to start a family and retire.

    2. I think you might be overly optimistic on creating a huge centrifuge to create artificial gravity at a full city size and at contrary too pessimistic about Venus ground possibilities.
      Yes the ground is at 92 bars deep bellow but at the top of the highest mountain Maxwell Mont, it is reduced to 45 bars. That may seem like not much difference but actually it is very different. The human diving dept record in a pressure vessel equivalent is standing at 701 m breathing a special gas called Hydreliox, a mixture of Hydrogen, Helium and Oxygen. So 45 bar is much less than 70 bars. That is extremely important because it means you can go on the ground at 45 bar without a need for a pressure resistant habitat. So now that the pressure problem is solved by selection the best ground location and by using the best diving gas technology, let's look at the other ground level problem, the heat. At the lowest level the temperature is 490ºC but at Mont Maxwell it is 380ºC. That is still hot but it is already 110ºC less and for example it allows the use of special plastics instead of none at all. Then enters Buckminster Fuller, yes the one from the geodomes that wanted to put central Manhattan under a 2 mile diameter dome to save on heating energy. The project was never done but it remains that his calculations were correct. A dome has the lowest areal surface for a certain enclosed volume and therefore the heat loss is lower than that of all the fractal like contained skyscrapers. On Venus such a dome would be made of one meter thick insulating foamglass. That material is fantastic because it resist 380ºC and prevent a too high heat flux in the same time. To compensate for the remaining heat transfer a thermoacoustic heat pump can be used. That is also a fantastic system usually used to liquefy natural gas from 20ºC to -180ºC in one single step instead of the former cascade compression based systems. That is a 200ºC difference but it can do 400ºC in one step as well since the temperature difference is only set by the length of the thermoacoustic stack. So you cool the inside to 30ºC and put out heat at 430ºC in the local 380ºC atmosphere. The 30ºC inside temperature is required to compensate the increased body temperature loss due to the higher conductivity of Hydreliox. A serious problem for Comex that wanted to make dives in 4ºC water, but rater an advantage here since it further somewhat reduces the temperature difference needed to the exterior. Cooling system is tripled and domes are multiple for extra security. This is additional to the remaining possibility to go to the floating sky cities. Inside the domes, there are plants and animals and everything needed to sustain a full size colony. There are also special areas where drone robots go outside to collect ore material and bring it back for processing. V22 type vehicles are making the connection between the ground domes and the floating cities. Those V22 start their journey with a full load of liquid carbon dioxide used for dynamic coaling during the lower altitude flight time. Once at 54 km height cooling is not necessary anymore. A kind of reverse of what a boeing 777 is experimenting during its flight.

    3. I agree, Priusmaniac.
      Your solutions are workable, even if I am skeptical of the Hydreliox solution. Maybe the can be improved by instead building a tower connected to the ground, with its weight reduced by using normal-pressure human breathing-rated gas interiors? The oxygen and nitrogen will lift the structure and reduce the strain on the ground.

    4. Building a tower on Venus would have 2 big challenges. First rising to 54 km height would be very difficult, second the tower would have to resist to 300 km/h winds. I know that living under hydreliox may be unexpected but the experiments indicated no drastically adverse effect. Breathing is somewhat harder because at 45 bars the gas is denser overall but since it is made of lighter components it is not 45 times harder to breath but 5 times harder. In more it is also possible to reduce the volume you need to breath by increasing Oxygen somewhat so that you would end up with an even lower difference in breathing effort. Your body would also likely adapt to it just like it does to a higher altitude for instance. Building the domes would be a big endeavor but the reward would be equivalent. The task can be made less difficult by looking for local advantages like the presence of a natural crater on which to build the dome taking profit of the free constriction force from the surrounding rock. Perhaps local light weight lava rock could be used to create an equivalent of foamglass.
      A floating skycity would be made first and from there telebotics would allow construction from a distance using local ground materials.
      Later on the planet would be not cooled but deep frozen in order to have the carbon dioxide accumulating in two giant polar caps at the expense of the atmospheric CO2, leaving only Nitrogen in the atmosphere. This cooling would be made by Lagrange positioned screens by the millions. Each screen made in the form of a circular sail maintained in shape by centrifuge force. The photonic pressure induced dihedral would self stabilize the sails in a sun facing position, thereby occulting Venus. Later orbital reflectors would recreate an artificial 24 h day in a narrow equatorial band. That would locally increase the temperature to 20ºC and allow plants to grow starting some oxygen generation for breathable air. It would be important however to limit the plant growth to avoid a runaway Oxygen pollution above 1 bar partial pressure otherwise it would become too high in concentration and unbreathable again. Nitrogen would stabilize around 3 bars naturally since 3% is present right now. The oxygen should be somewhere between 0.6 bars and 1 bar.

    5. No, no, not to 54km altitude! I was thinking of something like a 12km tower on top of the 11km peak of Maxwell Montes. It reaches an altitude of about 25km and cooler air at a pressure of only 10atm.

      Also, I think there would be a natural progression towards towers by building on 'anchored' balloons that want to stay in one spot while ground-level machines work in infernal conditions.

      Terraforming Venus would be quite the endeavour. You can choose to freeze the poles and gradually bury frozen CO2 under reflective things like water ice.

    6. You mean you want to go to some kind of middle ground at 25 km altitude. There you will have less pressure and temperature but that is still 15 bar and 250ºC, so you still need to breath a special gas and still insulate as well. This is in addition to building the tower. Seems to be adding one difficulty without really removing the other ones. To be able to breath standard air, the pressure must be bellow 4 or 5 bars at most. That is around 40 km altitude on Venus. So starting at 11 km at Maxwell Montes, that is a 29 km tall tower. Anchored balloon seem feasible but there is still 150ºC at 40 Km, so we still need insulation but this time it must additionally be light weight. That is an extra challenge. Foamglass would be to heavy, so perhaps ETFE in multiple layers like in Cornwall Eden project greenhouses. On the plus side the cooling system would only have to bridge an half as big temperature difference and wind energy could be generated with wind turbines attached to the floating structure. The view would be awesome as well.

    7. By increasing the volume of the lifting gas, we can use denser insulation.

      The view would be nice, but I don't think colonists would be able to see very far.

  3. Venus wouldn't be very defensible in the event of a siege, what with its inability to mine materials, vulnerability to import blockades, small surface area for living and fragile cities that can't hide beneath the clouds. If its economy can't expand much, it just seems that it would end up as a pleasure ground for the super rich if that. It would never stand a chance of being a major power like Mercury or Mars.

    A pleasure ground hit by high winds? Sounds like a Caribbean Island....

    1. On a note that just occurred to me- if a reasonably aerodynamic hull with oxygen inside is all that is needed to stay up, some of those silly 'space dreadnought' designs that crop up in sf everywhere might actually make for good airship designs. Perhaps with giant bi-plane wings attached.

      Not as warships of course, unless a rich tourist starts a Miami-Vice style crime spree.
      Its probably a terrible idea, but, y'know, 'Venusian sky smugglers'!

    2. On Venus, the thick atmosphere gets in the way of the attacker and defender. Lasers won't go through, and missiles take a long time to traverse it.

      The main advantage a defender has is the lower atmosphere. Smaller, more robust balloons can be used to dive deep into the hotter bottom of the atmosphere.

      The cities won't be any less vulnerable, but they will be practically invisible to infrared and visual detection. Even radar won't be of much use, as colonies tend to be made out of non-metallic materials.

      The surface area for living is greater than on Earth. No oceans or impassable terrain in the way, just more empty sky.

      Mining materials might be more of a strategic concern. On tactical timescales, like the invasion of a planet, the amount of material you can mine will never add up to much compared to your current stockpile of weapons, and how quickly you'll go through it. No modern military estimates its survival based on how much raw minerals it can acquire, even if it does have access to a vast industrial base.

      The Space Dreadnoughts are a great design.

  4. In the short term, the primary "export" of Venus might well be carbon derived from the CO2 atmosphere. Consider how carbon fibre, nanotubes, Graphine and artificial diamond films are all considered to be important to the current and future industrial economy of Earth, and then expand that into the Solar economy.

    Sending carbon products out of the gravity well will be the biggest problem, but some sort of Skyhook arrangement or maybe a "Rotovator"will allow for economical exporting of carbon products from Venus.

    Foe a bit of mind stretching, here are some papers by Paul Birch on rapidly terraforming Venus: (look up "How to spin a planet", and "How to move a planet")

    Venus may have to wait for centuries until humanity has enough resources to contemplate really immense projects like moving Venus and spinning it up to really consider settling the planet in the long term.

    1. That's another industry I hadn't considered. Looking at the tons of high quality carbon armor I slather on top of all my warships, there sure must be a big place on the market for carbon-derivatives.

      Maybe it'll feed the construction of the tethers that should be popping up on every airless moon that can afford it.

      Around Venus, a solar electric craft can get about 275% of the irradiance on Earth, if it angles its solar panels to receive the sunlight reflected off the cloud layer. With the miraculous thin film technology, this translates to a practically free 2MW/ton power source. Paired with an efficient electric drive, it can produce decent acceleration and travel along hohmann trajectories cheaply.

      Terraforming is a rather long term view. I personally hold the opinion that it will be easier to adapt ourselves to the environment than to adapt the environment to us. I mean, spinning all of Venus just to follow a 24 hour day?!

    2. For Venus space launch, the atmosphere provides your propellants. Do *not* use methane; hydrogen is rare and better used for other things. Instead convert the carbon dioxide into carbon monoxide and combust with oxygen. Performance is unimpressive... Isp of 180 to 200 or so seconds. But probably adequate to reach a skyhook with a useful payload. Especially useful if you can make carbon fiber structures from atmospheric materials. Grind up the launch vehicles in Venus orbit and sell the carbon and oxygen and sulfur (if there's a market for that; if not, convert the sulfur into compact basketballs and distribute in high orbit to form the beginnings of a sun-shading ring system) and return to Venus materials needed below. Teflon, for example, would be terribly important on Venus. It's made from carbon and fluorine; separate out the fluorine and send back down for reprocessing, sell the carbon.

    3. Scott! I'm a big fan of your blog. Thanks for passing by.

      I forgot the chemical formula for methane, it seems. CO-O reaction does seem much simpler. With an Isp of 200, a Venus launch rocket will need a mass ratio of 77-100, assuming it launched from high altitude. That's pretty extreme. A more casual mass ratio of 10 will provide a deltaV of about 4.5km/s.

      This is an interesting problem. A secondary propulsion system will be needed to complete the remaining 4km/s. A skyhook is definitely a solution, an 8km/s exhaust velocity solar/laser thermal propulsion system using beamed energy once the spacecraft is outside of the atmosphere could be another.

      I could see such a rocket working. Payload, engines and structure 100 tons. Launch mass is 1000 tons. First stage is a CO-O chemical rocket massing 600 tons. It has 1700m/s dV and launches the vehicle out of the atmosphere. It also gives a 1000m/s initial push sideways. The second stage has 400 tons of liquid oxygen. With beamed power, it can provide up to 11km/s of deltaV!

      I think now that most structures on Venus will be made from plastics: cannot be corroded, light weight, and take most advantage of the abundance CO2.

      As for sulphur, we might run out of it on Earth. Most of it comes from refining oil. Once that runs out, our cheap source of sulphur will be gone.

      As for fluorine... that makes for interesting rockets. Chlorine-Fluorine oxidant to boost the Isp of a Carbon Monoxide rocket?

    4. Assuming sufficiently advanced manufacturing capability, there could well be unmanned floating cities that do nothing but convert carbon dioxide and sulfuric acid into standardized rocket "wooden rounds." Clusters for the first stage, smaller cluster for second, smaller cluster again for third. If it's an automated system, it begins to become irrelevant how "expensive" the process is. If it takes 10,000 tons of booster to put 1 ton in orbit... at some point you don't care and just let the robots do it over and over. So long as the spent stages don't hit floating cities on their way down, it doesn't matter much where they crash if you don't need to harvest anything from them.

      As for fluorine, I have doubts that you could get much from Venus. So as with hydrogen, that's something you'd have to carefully marshal. Venus would be a net importer of the stuff, most likely, and it'd be silly to use it as fuel. If, though, it can be processed from the Venusian atmosphere at a sufficiently cost effective rate then... sure. Most of the propellant will wind up back in the atmosphere anyway. But if you can't process it from Venus, then every gram of flourine you expend is a gram you need to import. And I expect you'll have far more important uses for it, such as coating your balloons with teflon.

      Also: You have better options for lift gases than O2/N2 (molecular weights 32 and 28, respectively, compared to CO2's 46). Sure, it's great to have a vast breathable atmosphere, but you'd likely surround *that* with other balloons filled with argon (40) water vapor (18) or straight-up hydrogen (1). If you have separate hydrogen balloons, even if struck by lightning they'll be pretty inert in the CO2 atmosphere. And a hydrogen balloon could lift a *lot* in a CO2 atmosphere.

      If your timeframes are long enough, robots could clean up the atmosphere. Turn the available materials into rockets shooting carbon and sulfur into orbit. Processing stations in orbit collect the carbon and sulfur, turning the carbon into vast quantities of graphene. These are turned into solar sails, hauling cargoes of carbon and sulfur outwards. Perhaps dropping off the sulfur in high Venus orbit as they go to create a ring system. Again, not terribly efficient, but if the work is done by robots... who cares? The Venusian colonists could spend their time building and maintaining the floating automated facilities, eventually filling the sky with 'em and incrementally shooting the atmosphere off into space.

    5. While it is true that an automated process that needs very little marginal input can create very cheap launch-to-orbit rockets, I believe the still fall under time and structural constraints.

      Time constraints because if solar electric transport becomes widespread and sufficiently powerful, and more so if beamed power is installed around Venus orbit, then payloads will be coming and going at rapid rates. The production of "wooden (?) rounds" will have to keep up with this. If it takes 10000 tons to put 1 ton into orbit, you might still make a profit on that 1 ton, but:
      -You will have a 10000:1 production ratio, or, 9999 tons or unsaleable product per ton of saleable product. This means you have to expand your non-profitable production capacity to comparable ratios before you can produce full rockets.

      Structurally, I am not sure of 10000:1 mass ratio is possible. The solid fuel might have to be braced with carbon fibre, which would further cut into the payload...

      I understand your points on fluorine now. I'll look into the availability of argon and whether it has detrimental health effects if used as a substitute for nitrogen, but isn't a molar mass of 40 much worse than that of nitrogen, and barely better than CO2 (44)?.

    6. > This means you have to expand your non-profitable production capacity to comparable ratios before you can produce full rockets.

      Sure. The obvious exaggeration was just to get the point across that you *could* perhaps make a useful launch system using little more than what can be processed out of the air.

      > The solid fuel might have to be braced with carbon fibre, which would further cut into the payload...

      If you are using a solid or hybrid rocket that uses carbon as the fuel... bracing the carbon with fibers made out of carbon doesn't seem like that'd be cutting into the payload, what with the braces being consumable fuel.

      > isn't a molar mass of 40 much worse than that of nitrogen, and barely better than CO2 (44)

      Yup. But here again, if you are processing the atmosphere on an industrial scale, you might well wind up producing and storing vast amounts of argon (*perhaps* for selling off-world as fuel for electric propulsion systems or some such). If you are, what better way to store it than as an ambient temp/pressure lift gas? Put it in it's own balloon and it'll not only support itself (unlike a dewar of cryogenic liquid argon, or a high pressure tank of the stuff), it'll also help support other structures.

    7. You raised some interesting point. I looked into solid rocket motors with no 'casing' and they're actually a thing, at least for missile propulsion.

      I think argon might be too big of a deal to use as a primary lifting gas. It can only carry 10% of its weight, so a 'mass ratio' of 10 is required for a balloon-colony to hold itself at a certain altitude.

    8. > solid rocket motors with no 'casing' and they're actually a thing

      So are solid rocket motors with no nozzles and consumable cases. United Tech fiddled with them back in the 60's and some of the employees made perfectly servicable sounding rockets using nothing more than cheap steel tubing filled with solid propellant. Performance was, of course, substantially less impressive than a well optimised design, but they were *cheap* and went to the edge of space. A Venusian colony *might* be able to slap together boosters made of woven carbon fiber, filled with solid propellant made from carbon, sulfur and some oxygen compound; these would perhaps loft better-optimised fully reusable upper stages high enough to make rendezvous with a skyhook using nothing more than CO/LOX thrusters.

      And again on the argon: the idea is *if* you are processing it out of the atmosphere for some reason, put it in it's own balloon where it'll support itself and a *little* bit more. Compress it or liquify it, you'll need to hold it up with something else. Or use it as a buffer gas: build a big bubble filled with O2/N2, put your colony within. Built another bubble around that, separated by several meters,fill with argon. Build another bubble around *that*, kilometers in expanse, filled with hydrogen. If something hot and fast - a rocket, say - comes screaming in and shoots through all the layers, the hydrogen will be separated from the air by the argon, so there shouldn't be any combustion. A nitrogen buffer would be lighter, but you might have better things to do with the nitrogen, and it's just barely possible that the hydrogen and nitrogen might be convinced to do a little chemistry.

    9. There's about 5 ppb (by volume) HF above and below the cloud layer on Venus; it should be quite present in the surface rocks (10.1016/S0019-1035(03)00212-4). So that gives another incentive to start mining the surface.

  5. The owners of Magrathea would like a word....

  6. The pressure on the surface is nothing like that needed to make a diamond, but is still substancial, twice that of the pressure a Seawolf Attack submarine can withstand. Wind speeds just under the cloud layers are lower than those above by at least 50%, but there's problem of the heat...

    Can any of these be used for industrial purposes? If one is a small colony without much industry but has access to lots of carbon-nanotube cables that can take the pressure, is it possible that they could lower products (wrapped in carbon of course for protection from sulphur) below the clouds to undergo some pressure and heat processes? Perhaps cheaply fulfilling the requirements for some niche industry?

    1. I think it is more efficient to draw upon the thermal gradient and use the energy more efficiently at altitude, by concerting it into electricity. It can melt some metals, but I don't see any of great value, and you'll have to have a power-hungry pulley system or an unreliable floating payload delivery system, plus an insulation system to keep the hot contents at the required temperature.... sounds like too great of a hassle.

    2. I've been thinking about the thermal gradient, but I'm unsure as to how well it could handle different energy demands at different times. Could you lower a conduction cable to a hotter clime at peak energy times, and then withdraw it for another less demanding time of the year? (depending on what you mean by drawing on the thermal gradient of course)

      Speaking of which, what do you know of the seasons of Venus? Might there be different seasons requiring more/less internal heating requirements for colonies?

    3. Geoffrey:
      The axial tilt of Venus is negligible & the orbit is an almost perfect circle so there are no seasons on Venus.

      The altitude where the temperature is a comfortable 20 °C has a pressure of about 0.5 atm. You would probably want to put your balloon city a bit lower to get higher pressure & need to cool it rather than heat it.

    4. @Jim:

      Thanks! Somewhat basic error of research on my part, but I've never studied Venus as much as Mars anyway.

      Having read this blog, I'm imagining a solar system with Mercury and Venus as some kind of dual-power hegemony- one has the sunlight and the metals, the other has living space and carbon. Perhaps both might depend on each other rather than being rivals? Ah, speculation...

  7. Isn't there a lot of deuterium in Venus's atmosphere? It seems like that would be an important resource following the development of commercially viable fusion reactors and rockets. The manufacture of graphene and carbon nanotubes from CO2 seems like it would be one of the main economic drivers for the colonization of Venus as well, assuming the technology matures enough.

    1. Hello Sim!

      Venus is enriched in deuterium, with deuterium/hydrogen ratio greater than on Earth by a factor 120. However, hydrogen is exceedingly rare in the Venusian atmosphere (5 to 200 times lower than on Earth), and unlike on Earth, there are no vast oceans to lock up the hydrogen in H2O. Overall, harvesting hydrogen from Venus will be very very difficult.

      A carbon industry on Venus is an interesting consequence of the atmosphere CO2, but it will be a mostly domestic industry. Other than Mercury and the asteroids, all potential customers for Venusian products (Earth, Mars, Jupiter ect) have vast reserves of carbon at home in the form of CO2 or CH4. They will find Venusian carbon products to be too expensive after being shipped over interplanetary distances, compared to home-made products.

      The only way that Venus-made carbon products become competitive is if you capitalize on something that its trade partners do no have, which is a x2.75 boost to solar power. If you use this solar power for propulsion, you can reduce the cost of transporting products over interplanetary distance, and if you use it for electricity, you will be able to process CO2 into carbon products more cheaply than on Earth. Combined, and you might have a chance!

    2. Reading through your past entries with extreme interest, especially this one on colonizing Venus, but have to chime in. I don't know where you folks are getting the idea that hydrogen is rare on Venus. Venus' atmosphere is approximately 4.8x10^20 kilograms, and 0.002% of that is water vapor. My back of the envelope quick and dirty calculations puts that at about 0.0008% of the Veneran atmosphere by mass, which works out to 4 x 10^17 kilograms of water vapor, which gives you about 4x10^17 kg or 4x10^14 metric tons of hydrogen.

      That's a lot of hydrogen. And since it's all conveniently gaseous, it's easy to harvest.

  8. In the commentary for a later post, you dismiss vaccuum balloons as beyond the scope of the blog. At risk of making more work for you, I can't help wondering if you might be wrong on that.

    A vacuum balloon built here on Earth would need to withstand the differential between outside air pressure and the vacuum inside. One being used in the upper atmosphere of Venus or one of the gas giants would probably be built in the vacuum of space, though; it would have no such need.

    Take such a balloon, reduce its speed so it gently enters the atmosphere; it should sink until it reaches an altitude of neutral buoyancy. Would currently available materials be strong enough to withstand the winds, temperatures and pressures of that altitude?

    Thank you

    1. I'll use some numbers to put things into context:
      -At sea level, the balloon has to withstand 1 atmosphere of pressure difference, while providing 1.2kg of lift per cubic meter of volume.
      -At Venus high altitude, the balloon still has to withstand 1 atm, and still provides about 1.2kg of lift per cubic meter of volume.

      So, the conditions the vacuum balloon has to withstand are very similar in either setting.

      A pressurized balloon could be filled with hydrogen. Hydrogen gas can be heated to decrease its density for the same pressure. At 600K (327C), its density is as little as 0.04kg/m^3. Subtract this density from the density of the gases outside to find that the net lift falls to 1.16kg per cubic meter of volume.

      The advantage of pressurized balloons is that they can provide most of the lift of a vacuum balloon while only needing a thin plastic sheet to keep the gases separated. A vacuum balloon would need an extremely strong and lightweight wall to actually float. No material currently in existence is strong enough to withstand a 1atm pressure difference and yet be light enough so that the balloon can float.

      You'd need a material over 3 times stronger than diamond, per kilogram, to make the walls of a vacuum balloon light enough.

      Further reading on why vacuum balloons are not currently feasible:

      So, between the supermaterials needed to build a vacuum balloon, and the tiny advantage it would provide over pressurized balloons, it can justifiably be dismissed as an option.

      On Venus, you can float using regular oxygen, so it's even more convenient.

  9. Couldn't Mercury and Venus colonies work together? Each specializing, with resource sharing symbiosis. One has the sunlight, low escape velocity and the easy access metals, the other has living space and carbon. Imagine a scenario were Mercury gets disturbed by a solar system catastrophe, pushed on a trajectory becoming Venus's moon, nabbing a meger two Mars atmospheres worth of Venus's clouds for itself as it barely misses impact. Would think a system like that would be rather interesting for human settlement.

    1. Yes, they'll definitely be part of an interplanetary economy.

      Perfect specialization is unlikely though, as it will make sense to cover certain need with local production instead of shipping it across millions of kilometers, but at a larger scale, the two planets will take advantage of their respective strengths.

      Mercury doesn't exactly have a very low escape velocity, but the deltaV needed to get into orbit becomes very very cheap to apply when abundant sunlight can be used to turn wimpy electric rocket engines into powerful thrusters.

      Moving the planets though... that's a whole other story!

      A rough calculation tells me that you need to deliver 2e18kg of oxygen to Mercury to creature a minimally breathable atmosphere at 0.2 bars of pressure. The problem would be that even if you had the energy resources to extract that much oxygen from the silicates in Mercury's rocks, the atmosphere you'd make would quickly be blown away by the nearby Sun...

  10. Hey, me again, on a different page, with a different set of nits to pick.

    You state that Oxygen is a better lifting gas than Nitrogen. It's the reverse. Nitrogen has a lower molar mass. 28 per molecule for nitrogen vs 32 per molecule for oxygen.

    1. Ah these old posts are so short!

      I'm sorry if I stated that. You are indeed correct, pure nitrogen is better than pure oxygen as a lifting gas. I can't find which sentence to edit though.

    2. It's between the picture of the double sphere habitats and the shiny zeppelins. The sentence is: "Pure oxygen balloons provide more lifting power than a breathable mix, which is mostly nitrogen."

  11. While eventually I think surface mining operations will be done for increased self-sufficiency, there are actually some volatile metal compounds that should be present as trace species in the atmosphere. FeCl3 is probably present in the upper cloud layer (10.1016/j.icarus.2016.10.003) and could be a local source of iron for cloud colonies. The book "Rethinking Our Sister Planet" by Karen Pease mentions as likely low-level constituents compounds of Zn, As, Se, In, Sb, Te, Hg, Pb, and Bi (though they are likely more present at a lower altitude, mercury should already condense out at 62 km and should be one of the more accessible ones). Unfortunately many useful metallic cations would still require going down to the surface, but this could be an intermediate step, and possibly continue to be the main one for the volatile metals even after surface mining has started.

    Could cooling systems be designed for the cloud colonies go down to about 38 km altitude (where ZnCl2 condenses out) and then back up?