How to grow vegetables in space?

Seeing the "Shenzhou 13" spacecraft carrying three astronauts into the Chinese space station and starting their wonderful space life, many young readers can't help but ask: What do they eat in space?

In fact, the food in the Chinese space station is still very rich, such as fish-flavored pork shreds, Kung Pao chicken, braised pork, etc., which are fast and delicious. But eating this kind of fast food all the time is not a long-term solution. As humans continue to "expand their territory" on extraterrestrial planets, "how to grow vegetables in space" becomes more and more important.

Why grow vegetables?

Since there are so many delicious foods on the space station, why do we still need to grow vegetables in space?

The biggest problem is transportation costs. Currently, each person on the International Space Station consumes 1.8 kilograms of food and packaging per day. If a team of 4 to 5 people were to explore Mars for three years (currently a one-way flight to Mars takes more than half a year), they would need nearly 10 tons of food, which would be a great burden on the flight.

The second is the shelf life of food. The hypothetical three-year Mars exploration requires that the food have a shelf life of at least three years, and as time goes by, the quality and taste of the food will deteriorate rapidly - maybe it tastes good in the first year, but it will taste wrong in the third year.

If space food is stored at 22°C for five years and its nutritional content is tested every year, it will change: in the first year, the vitamin A, vitamin C, folic acid, and thiamine in most foods will be greatly degraded. If this problem is not solved quickly, the scurvy that sailors suffered from a hundred years ago may reappear in future astronauts - scurvy in the Age of Navigation was caused by not being able to eat fruits and vegetables for a long time at sea.

In addition to food supply, growing vegetables in space is actually an important part of building an artificial ecosystem: plant cultivation can help recycle wastewater, produce oxygen, purify the air, and so on.

Growing vegetables in space is difficult

If you really want to grow vegetables in space, there are still considerable difficulties.

The most direct point is the weightless environment in space. The gravity on Mars is less than one-third of that on Earth, and the gravity on the moon and the space station is even smaller, which also causes changes in the distribution of growth hormones and the direction of plant growth.

For example, when Arabidopsis thaliana was grown in orbit and on Earth, it was found that plants in space grew more slowly and had smaller root cells. At the same time, there was a unique fluctuation in root growth, with roots being shorter and more "distorted".

At the same time, the continued presence of radiation in space may also cause DNA mutations in plants, which may affect their germination, growth or reproduction.

In addition, the sunlight, water, soil, and fertilizers needed to grow crops on Earth are also essential for growing them in space. Sunlight can be replaced by artificial light sources, water can be replaced by the water circulation system of the space capsule, and soil becomes the most critical issue.

Although the Martian soil contains most of the substances that plants need, it lacks the active nitrogen that plants need, so nitrogen-fixing bacteria need to be added to assist plant growth. Otherwise, it will be difficult for plants to bloom and bear fruit.

Scientists show off their unique skills in growing vegetables. In order to overcome the difficulties of growing vegetables in space, scientists from various countries can be said to be "eight immortals crossing the sea, each showing off their unique skills."

As early as 1971, the Soviet Union began to try to grow wheat, radishes and onions in space. After decades of attempts, scientists from the United States and Russia have achieved space cultivation of wheat, rapeseed, peas and other plants. Today, the International Space Station has grown crops such as lettuce and Chinese cabbage. Astronauts tasted these space vegetables and thought they "tasted extraordinary."

China's own space laboratories are also trying to grow vegetables. Lettuce was planted in the Tiangong-2 space laboratory launched in 2016. Through various tests, scientists found that after optimizing the irrigation method and fertilizer, the lettuce in Tiangong-2 grew even better than on Earth. In 2019, researchers planted Arabidopsis and rice on Tiangong-2 to explore the impact of the space environment on crop growth.

How to build a complete ecosystem so that future space travel can realize autonomous supply of oxygen, water and food? This is also the conception of future space farms.

In fact, as early as the 1960s and 1970s, researchers began to try to build this kind of "artificial biosphere", but unfortunately they all ended in failure. Therefore, scientists have to settle for the next best thing: to build a system that has a certain connection with the outside world (such as electricity, energy, etc.), which is the Controlled Ecological Life Support System (CELSS) currently used by the International Space Station.

This system requires that plants can produce enough oxygen. At the same time, these plants must meet people's daily food needs in space and be able to utilize waste such as urine and feces produced by people.

Professor Liu Hong's team at the Beijing University of Aeronautics and Astronautics has built a controlled ecological life support system, the "Moon Palace 1". From 2017 to 2018, eight volunteers entered the "Moon Palace 1" one after another and survived for more than 370 days, setting the world's longest record for a closed survival experiment. This provides an excellent template for the construction of future lunar exploration bases.

Maybe in a few years, the space base in science fiction works will become a reality thanks to the efforts of scientists!