Venus
More general: Colonisation of the solar system
If one does not insist to go down to the solid surface (0m 500°C 90bar)
Venus is actually a nice place for humans to colonize (52.5km 37°C 660mbar).
And it might be rather easy with nanofactories since Venus' atmosphere is is essentially an ocean of building material bathed in intense sunlight.
Venus is pretty devoid of Hydrogen (20ppm Water that amounts to about 20kg per cubic kilometer at 1bar level) which is essential for APM technology. Luckily there's this nice sulfuric acid rain which concentrates the hydrogen for us. We get a bonus of a high deuterium concentration - whatever it may be used for. Also diamond crystolecules have much less hydrogen passivated surface than the hydrocarbon chains in current day plastics. Much much less than one hydrogen atom per carbon atom.
Breathable air and nitrogen are effective lifting gasses in the dense carbon dioxide atmosphere and can be directly drawn from the atmosphere. Comparison of molecular weights: nitrogen 28, oxygen 32, carbon dioxide 44
Contents
Atmosphere
The atmosphere is not your foe its your friend. She ..
- .. provides building material in optimal standardized form
- .. makes the scarce hydrogen better available (sulfuric acid rain is a natural hydrogen concentrator process)
- .. provides radiation protection (except UV)
- .. provides protection against micrometeorites
- .. makes street infrastructure unnecessary
- .. provides an environment with nearly constant temperature
- .. to a degree protects from volcanism on the ground
- .. reduces the day night cycle to a reasonable length. (super-rotation)
The chemically neutral to reducing character of the atmosphere may allow to make use of materials that in an atmosphere containing oxygen quickly oxidize extending the range of usable base materials for higher level metamaterials. This way passivation with locally scarce hydrogen may be avoidable altogether. See: Flavors of diamondoid gem gum technology
Interesting facts
The Vega probes placed each a balloon in the atmosphere of Venus. They drifted in a height of around 53km 46 and 60 hours long. In this time they covered a distance of about a third of the circumference of Venus an measured wind speed, temperature, pressure and cloud density. Thereby more storm and air current activity was observed than anticipated. Also a sudden change in flight height of about one to three kilometer was detected. (Source: de.wikipedia)
[todo: Check the actual data - what means a sudden change in flight hight here sudden here?]
High up in the atmosphere strong wind-speed gradients like the ones on the surface of earth are probably not to expect.
How much is known about the scales of the turbulences in the venusian atmosphere?
Colonisation - (conceptual)
The objective is to create a nice place for humans to live.
Basic housing
First a nanofactory (e.g. of the size of a sugar cube) is sent to Venus. There a durable balloon is created with a semi-transparent semi-reflective diamond solar foil on top that leaves through enough light for plants to grow. The balloon further needs an atmospheric converter unit (air using micro ships) that has a number of functions. It creates among other thing breathable air. The balloon must be inflated while being built to be kept afloat at all times.
Creation of soil for plants
Creating earth like soil with humic substances such that plants can grow in a natural way takes a lot longer then the employment of such a balloon. One could start with hydroponic cultures and compose the dead plants. At that time humans may be present or may not. A small piece of earth soil may be usable to introduce a rich set of microorganisms. (Each balloon can be an experimental perfectly isolated ecosystem)
It should be rather easy to design small balloons but to create an earth like landscape a bigger free area and some soil depth is probably desired. For an average soil depth of half a meter a balloon with around one kilometer height is needed to compensate for the weight. (Put that in relation to the floating height of ~ 53km for visualization)
At this size one needs to consider the wind speed gradient in the atmosphere which is around 10m/s per 1km. One doesn't want the balloon to start rolling like a barrel. This may be a difficult problem.
Air conditioning
Although 37°C with 660mbar air pressure is endurable for most humans it's not pleasant. Can a leightweight balloon hull provide enough thermal isolation to make a more pleasurable environment of e.g. 22°C at higher pressure?
There are several options for how to handle the three parameters pressure height and temperature when the outside weather changes abruptly.
Atmospheric converter unit for Venus
- filters nitrogen from the atmosphere
- captures sulfuric acid rain which concentrates the rare hydrogen [Todo: at which heights is sulfuric acid rain present]
- sulfuric acid → hydrogen + sulfur dioxide
- carbon dioxide + hydrogen → ethyne + oxygen
Because of the reproduction hexagon it may make sense to keep it separate from the nanofactory. Related: Air using micro ships.
Possible threats
Lightning
Some kind of lightning arrester system needs to be devised.
Wing gusts (danger of toppling over)
Since there are no obstacles high up in the atmosphere on a small scale differences in relative airspeed should be negligible. On a bigger scale this might become an issue [data needed].
Fires
Building a thin walled carbon balloon filled with oxygen is basically asking for fire. (On an other note when a hole is burnt into the hull penetrating carbon dioxide will probably quickly extinquish any fire) To mend this problem one can compartmentalize bigger balloons. Only the bottom few meters get filled with breathable air. A transparent ceiling foil material separates off the majority of the balloons volume. This part gets filled with nitrogen and is uninhabited "empty" space. A nice side effect is slightly more buoyancy lift.
An other approach is to use silicon carbide as a building material which may self protect against fire by building glass. For silicon one would need to mine the surface though. Releasing excess oxygen to the atmosphere might get dangerous after a very long period colonization activity (more than centuries). A global firestorm could start making Venus rivaling/exceeding? the sun in brightness for a brief moment (this is some phantastic dystopic SciFi just for entertainment). To get rid of the excess oxygen from the silicates one can use iron as reducing agent. The place where one can get unoxidized iron for sure is the planets core. (See: deep drilling)
A closed material "cycle" can be conceived that protects against fire even if atmosphere gets really crowded.
- carbon dioxide + silicate stone → silicon carbide + oxygen
- oxygen + iron → iron oxides
- sulfur dioxide + iron → pyrite + iron oxides
- sulfuric acid + oxygen → hydrogen + sulfur dioxide
(Energy gets stored in gravity - since heavy things can't fall through (non-molten) light things there's a perfectly safe activation energy barrier)
Outlook on a very long term - Template:SciFi warning
Since with advanced nanofactories exponential growth is easy it comes naturally to think about Terraforming. We'll discuss later whether a terraforming attempt is desirable and whether it makes sense.
The main reason why the venusian atmosphere is so hot at it's bottom is not because Venus is so near to the Sun or because there is a runaway green house effect. It is so hot because it is so massive. Adiabatic compression of a gas heats it up. When a volume of gass high up in the atmosphere falls back to the ground it gets adiabatically compressed and heated.
Binding excessive elements of the atmosphere
To reduce it's mass the most part of the carbon dioxide and a good part of the nitrogen would need to be bound with some kind of Carbon dioxide collectors placed in the upper layers of the Venusian atmosphere where the conditions are benign. The carbon dioxide needs to be bound in a chemically very stable form such that in a later state of the atmosphere with free oxygen powerful ignition sources (like e.g. frequent and powerful strokes of lightning and bigger things like meteor impacts) cannot cause an epic global firestorm putting all the carbon back into the atmosphere.
To get rid of all the carbon bound in the carbon dioxide it could be combined with silicon taken from the silicon dioxide (quartz) of the planets crust. This would create the useful building material silicon carbide (moissanite) which is self protecting against fire. It forms a molten glass layer preventing further oxygen from reacting with more carbon and silicon inside.
Doing that beside the oxygen from the carbon dioxide one also gets oxygen from silicon dioxide. In sum far too much for earth like levels. Obviously it wouldn't be smart to create a super-dense (too dense for humans) oxygen atmosphere. To get rid of all that oxygen a giant amount of some reducing element is needed. Ideally the oxygen would be bound to hydrogen but there is barely any hydrogen on Venus. Most of it was blown away by the solar wind. So hydrogen would need to be delivered from space. Which sounds difficult. Gently -- not by a destructive methods like bombardment with ice meteors which has no benefits. A reducing element that is certainly present in sufficient amounts on Venus is iron. The oxygen can be bound in the useful building iron mineral materials hematite and magnetite. Big amounts of metallic non-reduced iron can be found in the planets mantle and outer core. Advanced atomically precise technology may make mining in such extreme pressure and temperature environments possible.
The iron can also be used to bind sulfur from sulfur trioxide which is another gas that needs to be bound into a solid state For the excess nitrogen there are plenty of options to bind it safely.
While setting up the process (exponential production of carbon dioxide collectors) is straightforward for this atmosphere terraforming process an incredible amount of energy is needed. As it turns out even when the complete solar energy that hits Venus is converted to chemical in the binding products this endeavor would take a very very long time - (TODO: show the math) - also just for removal for sulfuric acid and SO3 Timescales in which it is questionable whether humans will still "use" biological bodies that depend on earth like conditions. But we might just want to make a "garden" for other earth life.
Cooling by shading?
Another thing easy to set up is thin light and highly reflective floating mirrors covering the whole surface (or at least dayside) of the planet. Relative to the mass of the whole atmosphere the mass of a mirror layer is vanishing. It could be produced and employed rather quickly. The following cooling of the atmosphere might take some time (TODO: do the math). By waiting long enough all nut the nitrogen part of the atmosphere could be frozen to dry ice (assuming no chemical atmosphere conversion runs in parallel). (Maybe not so useful)
See: Josh Storrs Hall's concept of ultra-lightweight stratospheric mirror airships
(TODO: find and link video where he presents that idea (for application on earth))
Peculiarities of hypothetical terraforming result
What would a Venus with its over 100 earth day long day (that probably can't be changed) and higher solar constant look like if all the carbon where bound and most of the oxygen where trapped into the soil or water? Would there be lots of poisonous heavy metals around? Considering Venus is so flat (it lacks mountains because it has no plate tectonics.) Would there be any dry land left? How high would the waves get with the extreme winds at the day night borders? What about water vapor clouds, lack of magnetosphere ...?
Further SciFi ideas that could be investigated just for fun:
- packing a terraformed Venus in a ring of infinitesimal bearings for a 24h day night cycle
- packing Venus in a giant superconducting ring to create an artificial magnetosphere (to keep the scarce hydrogen from getting away)
- hypothetical terra-changing experiment.
Increasing the activation energy barrier for global disaster
By binding the excess oxygen from the CO2 splitting process to unoxidized iron form Venus' core one can turn the moderate chemical activation energy that prevents a global diamond oxygen firestorm into a much higher gravitative barrier where first the crust of the planet needs to be broken such that the heavy iron sinks (giant but very slow energy release due to very high viscosity) and re-releases the oxygen before the oxygen could burn with the carbon. (TODO: section is redundant - merge with corresponding parts of the article)
Comparison to the situation on earth
There is an enormous amount of energy stored in the earth atmosphere biosphere system (oxidizing agent oxygen and reducing agents hydrocarbons. (How much exactly?) This shows that even situations far from equilibrium can be quite stable and safe for geological time-scales. (Beside activation energy other factors play important roles - Extinguishing systems?) Could there be sufficient energy input (e.g. catastrophic asteroid impact) that would lead to a mostly complete reaction to carbon dioxide and water and leave the earth in a Venus like state?
Further notes
- The high gravity of Venus (almost identical to earths) is a big challenge.
- Methods for hydrogen free high thrust propulsion is are of interest.
Related
- Gas giant atmospheres
- Handling of molten iron and very high temperatures - refractory materials
