Why Colonize Venus Instead of Mars
Venus offers unique advantages and disadvantages to space colonizers, which are different from Mars.
If you ever read news on colonizing the solar system, the talk will center on Mars. This is after all where Elon Musk wants to go. Occasionally there are of detractors who will object that we ought to go to the moon instead, since it is much closer to earth.
However what we don’t hear much about is Venus. Why is that? Venus is after all considerably closer to the earth in terms of travel time. While Mars is often estimated to take 6 months or travel, you’ll get to Venus in just 3 months. Given the thicker atmosphere of Venus, one can save a lot on fuel needed to slow down and land by utilizing a principle called aerobraking. It means sending your space craft through the atmosphere and utilize the air resistance to slow down, rather than using rocket engines.
Yet there is a very good reason why Venus is left out in the cold in these discussions. Venus is unofficially labeled the hell planet of the solar system. The surface temperature of Venus is 460° Celsius, which is so hot that lead melts. The pressure is 96 bar. You got to go 1 km below water on earth to reach that sort of pressure. To put that in perspective:
High-strength alloyed steel is still the main material for submarines today, with 250–350 metres (820 to 1,148 feet) depth limit, which cannot be exceeded on a military submarine without sacrificing other characteristics
Only Soviet alfa-class subs with titanium hulls are allegedly capable of going down to 800 meters, which is still not deep enough to match the pressure on Venus.
If that wasn’t bad enough, when it rains on Venus, it rains sulfuric acid. The Venus clouds are essentially made of condensed sulfuric acid. It gets better. The surface is riddled with volcanoes. Add strong winds and lightning storms and Venus makes Mordor look like a pleasant place.
However I still intend to make the case for Venus, because there is actually a solution to all of these problems.
Venus Cloud tops
If we go about 50 km above the Venus surface, we reach the Venus cloud tops, and there the conditions change dramatically.
Temperatures drop down to a pleasant Mediterranean temperature, and pressure drops to 1 bar, just as on the surface of the earth.
Mars in contrast is significantly less pleasant with night temperatures below -70° Celsius.
So the solution to colonizing Venus is utilizing aerostat habitats. By that I mean some form of airship that keep Venus colonists above the cloud tops.
This is not new idea, several people have written extensively about this.
- Best known among Venus fans is probably Geoffrey A. Landis, who has written a paper for NASA called Colonization of Venus. He has even written a Space Opera taking place on a future Venus with thousands of cloud cities called Sultan of the Clouds.
- James McGirk makes the case for colonizing Venus.
- Ryan Whitwam describes NASAs concept for colonizing Venus referred to as HAVOC.
- Jonathan Goff on his Selenian Boondocks blog, write several posts on Venus colonization getting into details like how to utilize gasses in the Venus atmosphere.
- Peter Kokh has lots of detailed articles on suitable designs for Venus airships, resource usage in the atmosphere etc.
- Robert Walker has written a kindle book called Ideas for Colonies that Float over Venus.
The Soviets did some of the earliest work on Venus colonization, unfortunately it is hard to get hold of this writing in english online.
While I recommend reading these links to get details, in particular Geoffrey A. Landis, I would like to give a summary of the details I find most interesting from studying the subject of Venus colonization.
Air with the same composition as on earth, roughly 80% nitrogen and 20% oxygen, would be a lifting gas on Venus because CO₂ has 50% more density.
The NASA HAVOC concept details a Venus mission compromised of two separate spacecraft which will be launch from earth with a powerful launch vehicle (multi stage rocket) and made to orbit Venus.
One spacecraft will contain the crew, while the other will contain a folded up airship. The crew will transfer to this one through a docking procedure in orbit. They will then descend into the Venus atmosphere and rapidly inflate the airship.
This will give a 129 meter long airship which can carry 70 tons. In the HAVOC concept 60 tons is made up of a rocket to be used for return flight.
A sphere with diameter of 1 km can hold 700 000 tons, which adds up to two empire state buildings, giving ample lift for a small city.
First reaction is probably that is sounds really dangerous to live far up in the clouds. What happens if the balloon rips?
If you make the sphere from a rip-stop material with high-strength tension elements to carry the load then tears are not critical:
With zero pressure differential between interior and exterior, even a rather large tear in the envelope would take thousands of hours to leak significant amounts of gas, allowing ample time for repair.
An aerostat is a lot more robust than what a regular balloon will give the impression of. Zeppelins during WWI got attacked by airplanes and peppered with bullets without falling down.
Possible Raw Materials
Any colonization of course relies on being as self sufficient as possible. You don’t want to rely on massively expensive supplies from the earth being shipped on a regular basis. When you can’t have easy access to the surface, that might seem overly limiting. Landis does it in fact discuss contraptions for accessing raw materials from the surface of Venus in Colonization of Venus, but say we assume that is limited there are still more possibilities with an atmosphere than might first meet the eye.
The wonderful variety of life we see on the earth, plants, animals, trees etc is for the most part made from water and carbon dioxide. A plant is 95% water. Say we exclude the water and only look at the dry mass composition, we get these percentages for the different elements:
- Carbon — 45
- Oxygen — 45
- Hydrogen — 6
- Nitrogen — 1.5
- Potassium — 1.0
- Calcium — 0.5
- Magnesium — 0.2
- Phosphorous — 0.2
- Sulfur — 0.1
- Trace elements: Chlorine, Iron, Boron, Manganese, Zinc, Copper, Molybdenum
So 97.5% of the dry mass is made up of elements which exists in the air or water.
45 + 45 + 6 + 1.5 = 97.5
So if I wanted to make 1 ton of plant matter, for instance wood. That would only require 1.25 kg of nutrients shipped from earth. I do a more in depth discussion of growing food on Venus here.
1000 * (1 - 0.95) * (1 - 0.97.5) = 1.25
Which brings us to the next question, what can you actually obtain from the Venus atmosphere?
- 96% is CO₂
- 3.5% Nitrogen
- Venus clouds contains sulfuric acid H₂SO₄ and hydrogen sulphide H₂S
- Various gasses in trace amounts
More useful is perhaps to reformulate this as what elements we get to play with to make stuff if we can only make use of the Venus atmosphere.
Doesn’t sound like a lot, but there is a huge amount of stuff you can make with that. But it does in fact offer a lot of possibilities.
Carbon Fibre and Carbon Nanotubes
Just with carbon you can make carbon fibre, which can be woven into clothes and carbon nano tubes can be used as excellent electrical conductors, avoiding the need for metals like copper to make electrical wires.
Plastics (synthetic resin)
With carbon and hydrogen you can make all sort of hydrocarbon gasses like methane and ethylene. These are chained together in a chemical process called polymerization to create various forms of common plastics like polypropylene and polyethylene. With just carbon, you can make carbon fibre, which can be used with thermoset resins (a synthetic resin which sets when heated, e.g. epoxy).
Note, plastic, polymer and resin is often used a bit interchangeable. Usually we say resin about the plastic while it is just raw material we haven’t shaped into anything yet. While it is still just a powder, pellets or some liquid. But a resin could also come from say a tree. So strictly speaking a plastic is a synthetic resin. All plastics are polymers but not all polymers are plastics. A polymer is just a chaining of simpler molecules. That also applies to many things in our body like DNA.
Anyway plastics are very versatile as they can be used in composites, by themselves or made into threads and spun into fabrics, to make clothes, shoes, blankets, mattresses etc.
Methane (CH₄) is already being used by SpaceX for their new Raptor rocket engine, and so is Blue Origin with their BE-4 engine. Then there are rocket fuels for more specialized usage.
Hydrogen Peroxide (H₂O₂) was used in the German V2 rocket for driving the turbopump of the rocket engine. But it can also be used for more specialize needs as a monopropellant for reaction control systems (RCS). RCS are small weak rocket engines used for orienting space craft in outer space and perform docking maneuvers.
There are several other possible monopropellants which can be made from the basic elements present in the Venus atmosphere. Hydrazine (N₂H₄) is commonly used and has the added benefit that it can be used in fuel cells. Unlike Hydrogen it is liquid form at room temperature so it can easily be stored. Useful for an aerostat at night when solar cells can’t produce electric power.
Nitric Acid (HNO₃) is also a possible rocket fuel. As the others it has many other possible uses. Hydrogen Peroxide can also be used as a disinfectant. HNO₃ can be used as a cleaning agent or to make fertilizer.
How to Obtain Useful Chemical Compounds
CO₂ is easy as 96% of the Venus atmosphere is made of it, so you can pretty much just suck it in. Together with water and nutrients brought from earth, you can grow plants, which gives you food and oxygen for breathing.
The challenge then is, how to we get water? Since it doesn’t exist in pure form it has to be extracted from sulfuric acid H₂SO₄. There are several ways of doing that.
The two simplest options I can see for making this work are to react the sulfur either with hot graphite or with hot carbon monoxide. Either of those should result in Sulfur Dioxide, Water, and Carbon Dioxide
The first problem is of course how do we get hold of he sulfuric acid in the clouds?
At a NASA discussion forum it has been suggested a contraption for condensing droplets of it:
The extraction of hydrogen on Venus would actually be easier then on Mars, the idea layer for habitation is just a few km above the densest cloud layer, you would dangle a kind of ‘wind-sock’ likely composed of a thin mesh of gold, cloud droplets would condense on this as in the desert-fog wind-traps on Earth, the Venus cloud density is roughly comparable to fog, which is much less then a cloud on earth but still plenty dense enough to harvest.
The process would require very little energy as the relative wind speed differences at altitude would blow air through the collector even with a stationary dirigible, obviously supplemental intake fans would substantially increase the collection rate. For something with say a 10 m³ intake my estimates are that you would collect nearly a ton a day of raw condensate.
Water using Bateria
The bacteria take sulfuric acid (H₂SO₄) and convert it to Hydrogen Sulfide (H₂S). Basically it liberates the oxygen.
If we combine that bacteria with some rust (Fe₂O3) we get this reaction:
Fe₂O₃(s) + H₂O(l) + 3 H₂S(g) → Fe₂S₃(s) + 4 H₂O(l)
Once all the iron has been sulfited, that portion needs to be taken out of operation and reconverted.
2 Fe₂S₃(s) + 3 O₂(g) + 2 H₂O(l) → 2 Fe₂O₃(s) + H2O(l) + 6 S(s)
What we’re really doing is pumping gasses through the reaction chamber, alternatively oxygen and Hydrogen Sulfide, both created by the bacteria in sulfuric acid. This results in the creation of water and elemental sulfur, which precipitates out (insoluble in water).
Water from Heating
Although according to Karen Rei at space stackexchange it is considerably easier to create water from sulphuric acid:
No, you don’t need to do electrolysis to extract oxygen from H2SO4 — you just have to heat it. H2SO4 breaks down at high temperatures to H2O+SO3, and the SO3 reduces to SO2 + O2. So you get both H2O and O2 from a simple process.
Hydrogen has many uses. We can used with carbon dioxide to create methane gas or other hydrocarbons.
Since we have direct access to sulphuric acid on Venus, the simplest approach for making hydrogen is probably using the Sulfur–iodine cycle. It uses just high heat, no electrolysis.
We start with sulfuric acid an use high heat to create water, sulfur dioxide and oxygen.
2 H₂SO₄ → 2 SO₂ + 2 H₂O + O₂ (830 °C)
Then we add Iodine (which we can reclaim later)
I₂ + SO₂ + 2 H₂O → 2 HI + H₂SO₄ (120 °C)
After separation with condensation, we get hydrogen from the Hydroiodic acid (HI)
2 HI → I₂ + H₂ (450 °C)
2 H₂O(l) → 2 H₂(g) + O₂(g)
First step would be the same
2 H₂SO₄ → 2 SO₂ + 2 H₂O + O₂ (830 °C)
Except we won’t use iodine in the second step, but electrolysis
SO₂ + 2 H₂O(l) → H₂SO₄ + H₂(g) (electrochemical, T = 80-120 °C)
2 H₂O(l) → 2 H₂(g) + O₂(g)
Oxygen is of course needed for astronauts and oxidizer for rocket fuels. We could make it with the processes above for creating hydrogen, or get it as a byproduct of growing plants.
Robert Walker, has quite a detailed article at science 2.0, about how oxygen is currently produced at ISS today, using electrolysis of water, but how we in the future could get it from plants or algae.
Which has a lot of advantages over using machinery which may break down:
Unlike machines, plants and algae always work and don’t need to be repaired. Your dwarf wheat won’t suddenly break down and need parts shipped from Earth to keep it making wheat grains and absorbing CO2 and producing oxygen. And your green algae will never break down either, it’s as reliable as brewing beer or using yeast to raise bread. Nature, through evolution, has sorted that all out millions of years ago. All you need there is reliability of the lighting, plumbing and pumps; a rather lower level of technology, at least if we can get them to grow in space as well as they do on Earth.
So manufacturing on Venus would be quite different from Mars, in that it will be centered on chemical processing plants and processes.
There are pros and cons of this. The benefits are that chemical processing doesn’t require lots of heavy equipment for mining, crushing rocks and so on. Sucking in gasses is a lot simpler. And of course any manufacturing or processing will require lots of energy of which Venus will have 4x as much as Mars, and without need to spend energy on maintaining appropriate temperatures.
The big downside of course not having access to the same breath of resources.
But the question is how could this be done in an aerostat of limited size?
Small Chemical Processing Plants
When trying to research this, the problem is that of course most chemical processing plants on earth are huge because there is a benefit of scale. But we are of course more interested in knowing how small a versatile processing plant can be made.
However before large plants are made they make something called pilot plants, which are much smaller but still essentially does the same thing but at a smaller scale. These are also more flexible as one wants to be able to vary the process and experiment more. That is exactly what Venus colonists would need, as they can’t just build new plants whenever a new need arises. They want to be able to do as much as possible with the equipment they have.
Constructing new habitats or modules will be much harder than on Mars as there is no ground to stand on.
However there are already solutions being made on earth which involves using aerostats as cranes. Skylifter e.g. has a diameter of 150 meter and can lift 150 tons. On Venus the lifting capacity would of course be significantly higher since a CO₂ atmosphere gives more buoyancy.
Using a set of motors with cycloidal propellers, it can keep quite an accurate fixed position.
Advantages of a Venus cloud top colonization over Mars could be summed up as:
- Half the time to get there with a space craft (3 months). Less exposure to radiation for astronauts.
- Same temperature and pressure as on earth. Which means no need for complicated heating and cooling systems, or pressurized habitats and airlocks.
- Same gravity as on earth. The lower gravity on Mars has potential for a lot of long term health problems for humans.
- Same protection against solar radiation as on the Earth. No need to build extensive protective layers or burrow under ground.
- 4x as much sun, which means much better conditions for energy production and plant growth.
Of course there are some big downsides like having no easy access to a surface which could provide various useful metals and other elements. And to be fair it would be a lot less interesting to just float around in the sky rather than having the opportunity to walk around on the ground in an alien landscape.