Food: Surviving on Venus
Growing food in hydroponic systems as well as how to obtain the needed nutrients.
I’ve previously made the case for Venus colonization. I thought I’d write some more in depth articles on the different aspects of colonizing Venus, starting with how colonists would feed themselves. Next story is on manufacturing and construction.
To be honest my original interest in this was from the perspective of writing fiction. Andy Weir, wrote the amazing book, the Martian, which got turned into an almost equally great movie by Ridley Scott. In it our hero Mark Watney, who has stranded on Mars has to survive by growing potatoes in Martian soil.
This got me thinking: What would a stranded astronaut on Venus do. As in my original article, we assume the astronaut would be located above the Venus cloud tops in an airship, some 50–70 km above the surface, where temperature and pressure is earth-like.
At this location there is no access to any soil as on Mars, so we have to grow without soil. That is actually perfectly possible. It is referred to as hydroponics, which means nutrients are dissolved in water and the roots of the plants are exposed to this water. This can happen in many different ways. Either the water is run past the roots or one uses aeroponics, meaning a mist of nutrient water is sprayed on the roots at regular intervals.
There are several concerns here, what equipment do we need? What resources needs to be imported from the earth and what can be sourced locally? How much space do we need? To answer that we need to figure out what exactly what type of nutrients and how much a human need to survive and thrive.
Raw Materials and Nutrients
Let me repeat some of the details from my previous article. 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 Carbon, Oxygen, Hydrogen and Nitrogen, which we have access to in the Venus atmosphere.
45 + 45 + 6 + 1.5 = 97.5
Thus if you wanted to make 1 ton of food, in theory only 1.25 kg of nutrients needs to be shipped from earth.
1000 * (1 - 0.95) * (1 - 0.97.5) = 1.25
But things are usually more complicated than that. Most nutrients are likely bound to other elements. However the total nutrient needs can be drastically reduced through recycling. Our body doesn’t just keep on accumulating these elements indefinitely.
Nutritional Needs of a Human
To help with these calculations, completefoods was a very useful link. It helped me figure out all the nutritional needs of a human as well as what plants can provide those. It lets you look at different nutritional profiles, e.g. from the US government for a male. Which suggests how many calories in total is needed, as well as how much of that ought to come from carbohydrates, protein and fats.
Let us do some examples. You need roughly 2000 calories a day.
100 grams of Black beans gives 132 kcal, about 9 grams of protein.
1600g * 132 kcal / 100g = 2212 kcal
1600g * 9g protein / 100g = 144g protein
So 1600 grams of beans will give 2112 kcal and about 142 grams of protein, which is almost 80% of the protein needed per day, not bad.
Potatoes give about 68–90 kcal per 100 gram, Similar for sweet potato. At the site Android World, you can find quite a lot of details on how fast you can grow different kinds of vegetables in a hydroponic system.
You can grow 93 grams of edible beans per square meter per day. Or you can grow 130–140 grams of potato per square meter per day. Which means whether we grow beans or potatoes we get roughly 110–120 kcal per square meter per day, which means we need an area of roughly 20 square meters to grow 2000 kcal per day worth of food.
2000 kcal / 110 kcal/m² = 18 m²
The problem with higher order plants, which you would grow in hydroponic systems, is that they don’t offer crucial fatty acids like omega-3 found in fish. Fish gets omega-3 from krill which gets it from algae. There does seem to be a lot of debate on this. E.g. the meal replacement powder Soylent used to include omega-3 from algae oil, but switched to using rapeseed oil. It contains omega-6 and omega-3 oil. However omega-3 from plants is not the same as from the sea. It needs to be converted by the body. If this conversion is effective or not seems to be much debated.
Regardless it is possible to grow algae and use that as a basis for satisfying ones omega-3 needs. Algae has the added benefit that about 8 m² of algae is enough to produce oxygen for one human being. Although that might not be needed if you got plants.
A MacGyver stuck on Venus, should have no problems putting together a hydroponics system. All you need are some plastic tubes and some pumps.
Youtube is full of examples of people putting together pumps with just some plastic tubes and an electric motor. A mission to Venus should definitely bring a 3D printer as plastic will be the number one building material. That means you can print plastic tubes of any shape you need to build a hydroponic system.
Plastics safe for use with hydroponics include:
- PET/PETE (Polyethylene terephthalate)
- HDPE (High-density polyethylene)
- LDPE (Low-density polyethylene)
- PP (Polypropylene). Can deal with 10% concentration of sulfuric acid. Textiles, ropes.
I’ll live it to another article to talk about how one could produce various types of plastic on Venus. All the atoms need for plastics are there, but they need to somehow be arranged into the correct molecules.
For growing algae we need a bioreactor.
This isn’t too difficult for a MacGuyver to do either. At wiki How there is an example of growing Spirulina algae at home. There is not much more than a tank with water, sunlight and some nutrition needed.
For an automatic operation, what you want are temperature meters and pH measurements and heaters to maintain ideal conditions. You also need a pump to bubble air through the water to supply oxygen and carbon dioxide. Stirring the tank is also a possibility, to bring air into the water. An agitator will also stir it with an electric motor.
Closed Loop Systems, Recycling Nutrients
Wast from humans such as poop and urine can be processed into Biosolid, care has to be taken in doing this as it can pathogens if not treated properly. This can then be used to supply our hydroponics system with nutrients. Thus we create a closed loop for nutrients.
Existing Research on Growing Food in Space
While Venus colonization has not been studied extensively, there has been done a lot of research with the aim of figuring out how we can create closed eco-systems, because it is relevant for all space colonization and for long space travel.
In the space industry one refers to a system for sustaining humans as a life support system. Of interest here is both how to create oxygen for humans and food. One of the earliest projects studying this was the Russian BIOS project. More recently we got ESA’s MELiSSA project.
Soviet BIOS-1–2–3 Projects
For a long time BIOS was secret projects in the Soviet Union to test the ability of humans to survive in a closed environment like a space station.
They managed to keep a crew of 2–3 persons alive for 4–6 months with almost 100% recycling of all gasses and liquids, apart from 50% of the food being externally supplied. The reason for that was that it was not a plant only diet, but they also eat meats.
According to a detailed account of the project, it had a growing area of 63 m². They grew wheat, carrots, cucumbers and dill hydroponically. That suggests 20 m² per person for a 3 person crew. Similar to my rough estimations for black beans grown hydroponically.
The Melissa project is far more complicated than a Venus solution needs to be, because it aims to recycle almost everything. The assumption here is space travel. On Venus we can afford to waste anything made of CO₂ as it is so abundant. Water is also replenish-able as it can be obtained from sulfuric acid clouds.
Still it is an interesting project. The whole solution has been divided into multiple compartments with specific functions.
- The liquefying compartment. NH₃, H₂, CO₂, volatile fatty acids, minerals. Basically a compostation unit.
- The Photoheterotrophic Compartment. Gets rid of bad stuff from previous compartment.
- The Nitrifying Compartment. Turns waste to nitrates. Fixed Bed Reactor (cylinder with catalysts as pellets. Reactants flow through pellets).
- The Photoautotophic Compartment. Contains spirulina algae (cyanobacteria: Arthrospira) for making oxygen, and higher plants for making food.
University of Arizona
Giacomelli of University of Arizone looks into a creating a hydroponic system for Mars which requires only about 16 cubic meter to feed one person. So a room of about 8 square meters.
It recycles poop I believe so that solves problem of getting micronutrients:
Giacomelli is perfecting a closed-loop system where the plants consume the astronaut’s carbon dioxide and liquid waste and in turn the plants provide the astronauts with oxygen, fresh water and food.
It covers all oxygen and water needs but just half the calories:
Giacomelli said his high-tech hydroponic system could fit in a six-hundred-cubic-foot tube and provide a single astronaut all of his daily oxygen and water needs and about half of his daily calories.
Hydroponics vs Soil?
Since hydroponics doesn’t require any soil, it might appear as simpler solution that soil based cultivation, which is what is usually discussed for Mars based colonization. It is however not without downsides.
There is a good discussion about this on one of the many Mars forums. I’ll quote one of the more relevant quotes.
Any hydroponic system requires several highly concentrated nutrient solutions, and these bottles of liquid are heavy. The weight of those supplies is extensive, hauling that to Mars is highly questionable. You could try to make them on Mars, but extracting them from Mars soil and purifying and concentrating to what’s required for hydroponics? That would take a lot of equipment. Again weight, we need to minimize anything we send from Earth.
There are some further discussion of the pros and cons of soil and hydroponics based plant growth.
We have talked about the yields of hydroponics versus soil and it does come down to resources such as negatives hydroponic water needs are greater hydroponics also has a higher energy usage for pumps, circulating of the water positives hydroponics have a higher fruit (meaning crop) yield per acreage
What makes most sense for Venus will of course be different from Mars. Higher energy usage is less of a problem, as Venus will have 4x as much sunlight as Mars, which gives more opportunity for solar energy generation and sunlight for plant growth.
Mars colonists will struggle more with energy needs, while Venus colonists will have to focus more on recycling nutrients since they can’t obtain them from any soil.