A touch of green in space

In February 2017, the SpaceX CRS-10 mission rocket lifted off from Cape Canaveral in the United States and flew to the International Space Station. This time the rocket comes with a special mission: NASA’s first micro-observation program. The plan was designed by three agronomy students in Ravensburg, Germany, to study the cultivation of cuttings under microgravity, which is of great significance to the development of space planting technology. In other words, scientists are studying which crops can be grown outside the earth.

Agriculture is the oldest industry in human society. The idea of ​​space agriculture began in 1977. At that time, a researcher from the Chinese Academy of Agricultural Sciences studied the effects of orbital flight on plant growth and discovered that plant seeds exposed to cosmic radiation and other factors in space can undergo DNA mutations.

Between 1987 and 2005, China’s rockets launched into space carried more than 400 plant seeds. It was with these seeds returned from space that people planted giant eggplants, which were half a meter long and weighed up to 10 kilograms. cucumber. In 2006, the China National Space Administration loaded more than 2,000 kinds of grains, vegetables, fruits, flowers and other seeds with a total weight of about 215 kg on the “Shishi-8” satellite for mutagenesis experiments in the space environment, that is, the use of space The influence of environmental factors on seeds causes the seeds to produce mutations that are not available in the ground environment, and finally new crop varieties with favorable mutations are screened out. As a major agricultural country, China has never given up on exploring space agriculture technology. The “Chang’e-4” probe launched in 2018 also contained seeds and eggs to study its cultivation and hatching on the surface of the moon.

Ideas about space agriculture

Many scholars are optimistic about the development potential of space agriculture. Gerald O’Neill, a professor of physics at Princeton University in the United States, published the book “Space City” in 1977. In his book, O’Neill proposed how to use the technology available at the time to create a city in space without atmosphere, gravity and soil. The space city he designed can accommodate nearly 10 million people. To guarantee the food rations for so many people, it is necessary to establish an agricultural area and ensure sufficient light, air, water and nutrients. According to estimates, the cultivated area should reach 650 square kilometers, about 1.5 times the area of ​​Andorra.

To achieve this vision, O’Neill advocated the development of super-intensive agriculture that can grow several crops at the same time. That is to say, in a piece of land, put crop seeds with short and long growth cycles (such as corn and potatoes) at the same time, plant up to four crops at the same time each year, and control the temperature and humidity of the environment. In this way, every 21 hectares of crops produced can feed 53 people.

Obviously, planning space agriculture on paper is one thing, but realizing space cultivation is another. Otherwise, since the Soviet Union put the first space station into orbit in 1971, until 2015, the diet of astronauts has only remained at the stage of dehydrated food. Human beings can stay in space for longer and longer. Considering the high cost of transporting food materials to the space station (it costs nearly 20,000 Euros to transport one kilogram of pasta), the space planting programs that are being implemented by the space agencies of various countries are also Not surprising.

Plants suitable for space cultivation

Humanity’s exploration of space cultivation finally paid off. In August 2015, astronauts living on the International Space Station tasted the lettuce grown in space for the first time. This not only declares that humans can grow vegetables in a microgravity environment, but also has breakthrough significance for humans’ plans to continue to enter the universe. This is due to NASA’s Veggie project, which attempts to grow edible plants without soil in the greenhouse of the International Space Station with very little water and fertilizer.

The project started in 2010. On the one hand, NASA wants to ensure that astronauts can eat fresh food, and on the other hand, it is also to study which types of plants grow best in a microgravity environment. Over the years, the Veggie plant growth box has become larger and larger, and the types of plants that can be planted have become more abundant: romaine lettuce, cabbage, kale, wasabi, etc., as many as 18 kinds.

Human research on space cultivation has never stopped. In the cooperative research project “Seedling Project No. 3” of NASA and European Aerospace Agency, Francisco Medina of the Biological Research Center of the National Research Council of Spain is mainly responsible for the optimization of the cultivation method of the cruciferous Arabidopsis plants in space .

Daniel Schubert, an engineer at the German Aerospace Center, is also growing vegetables in greenhouses that simulate the environment of Mars and the Moon. He uses recycled urine as fertilizer while changing the ratio of red light, blue light and ultraviolet light. Studies have found that the higher the proportion of ultraviolet light in the light, the better the taste of the vegetables grown.

To realize space cultivation, the biggest challenge is to find suitable plant varieties. Vegetable varieties suitable for space cultivation must meet three conditions: 1. Short stems, which can save space; 2. Few inedible parts; 3. Can adapt to environments with insufficient light and have certain resistance to harmful organisms. Experts in the Seedling Project are using biotechnology to genetically identify plants such as wheat, potatoes, rice, and lettuce to find out whether these plants have genes that can survive under extreme conditions.

Preparing to explore Mars

The United States plans to implement a manned mission to Mars in 2030, and NASA’s current research projects on space agriculture are all preparing for this mission. In the ideal case, it would take at least one year for an astronaut to reach Mars. After staying on Mars for about six months, it would take another year to return to Earth. Therefore, it is unrealistic to bring enough food for all crew members at once.

The reason is simple, each astronaut needs to consume 2500 to 3000 calories per day, and in order to prevent calcium loss and other discomforts under microgravity conditions, food must contain 15% protein, 30% fat and 50% Carbohydrates, the rest are liquids such as water, coffee, and juice. Therefore, food storage has become a problem. If each astronaut needs at least two kilograms of food per day, a Mars expedition that includes four crew members requires at least seven tons of food.

Bruce Burgby, a botanist at Utah State University, said: “In order to realize the human plan to colonize Mars, the first astronauts to reach Mars must be self-sufficient in food.” To this end, NASA invested in the Space Biological Application Center. The US$5 million fund is used for a five-year research project with the goal of producing biofuels, chemical materials, medicines and food in a simulated Martian environment.

The feasibility of Mars planting

Growing vegetables on Mars is not an easy task. The earth’s soil is rich in minerals, organic matter, gas, liquid and countless microorganisms, but there is only a thin layer of volcanic rock on the surface of Mars. The volcanic rock lacks nutrients, but the more important problem is that the high concentration of chlorate in it can cause fatal harm to the human body. Maria Solsano of the Madrid Center for Astrobiology said that the solution can only be started in two directions: first, to develop plants that can clean the soil; second, to find plants that do not absorb chlorate in the soil.

In the movie “The Martian” released in 2015, astronaut Mark Watney digs pits on Mars to grow potatoes. He fertilizes potatoes with manure and uses rocket fuel to obtain liquid water. Finally, he successfully grows potatoes. Although this is only a fictional science fiction film, Burgby said that it is indeed feasible to grow potatoes on Mars, and the plants that can be grown are not limited to potatoes.

In 2016, NASA and Peru’s International Potato Center cooperated to cultivate potatoes in a Martian-like ecological laboratory on Earth. They selected 65 varieties of potatoes and observed whether they could germinate in an environment similar to Mars. Julio Silva, head of the Department of Bioengineering at Lima University of Engineering and Technology, said that in order to find a variety suitable for planting on Mars, they used nearly 300 kilograms of potatoes.

Experts tested several different planting methods, one of which proved to be effective: first put the potato seeds in a capsule filled with organic matter, and then put them in a flowerpot filled with simulated Martian soil. Surprisingly, , Three varieties of potatoes have successfully sprouted.

Potatoes are the fourth largest crop in the world. There are about 1,000 crops in human’s main food source. Although it is not possible to plant all crops in an ecological environment that simulates Mars, the successful planting of potatoes is at least a good start. What’s more, the significance of planting Mars is not just to get food. Professor Burgby said that Mars’ thin atmosphere contains a lot of carbon dioxide. Plants can absorb carbon dioxide and release oxygen, helping us transform Mars into a more suitable planet for humans.