Biological life support systems, or biospheres, could now recycle enough oxygen, water and food to keep people alive for years. Two groups of four people lived in a sealed environment in China called Yuegong-1, or Lunar Palace 1, for a total of a year, with one group spending a record-setting 200 days in the facility without needing any outside materials, and they could have gone longer. The project aims to help China establish bases on the moon.

Details of the experiment, which ended in May 2018, were revealed in a study posted online. The researchers say volunteers got 98 per cent of the materials they needed to survive from recycling, with just 2 per cent coming from the outside, including seeds, toilet tissue and cleaning materials.

These are the best results achieved so far. “Now we are reaching a level of closure that is good,” says Christophe Lasseur, who leads the European Space Agency’s effort to develop regenerative life support systems, called the MELiSSA Project. Such systems can’t yet sustain people indefinitely, he says, but they can now do it “for a long period”.

Read more: Chinese Chang’e 4 engineer explains how to garden on the moon

“If they have accomplished what they claim to have accomplished, that would be a huge step forward,” says Rob Suters at Semilla Ipstar, a Dutch company that commercialises MELiSSA technology.

There have been many efforts to create habitats that sustain people, starting with Russia’s BIOS experiments from the 1960s to the 1980s. The Biosphere 2 facility in Arizona is the most famous. One of the crewed experiments done there in the 1990s lasted two years, but extra food and oxygen had to be supplied, so it is regarded as a failure. Japan also did a series of crewed experiments in the 2000s.

Lunar Palace 1 was built in 2013, with the first crewed experiment in 2014. The facility consists of a small living cabin linked to two larger cabins filled with shelves of plants growing under LED lights.

In the latest experiments, all the oxygen generation and carbon dioxide removal was done by the plants, which included wheat, potatoes, tomatoes, carrots, cucumbers and strawberries. There were some fluctuations when the crews swapped but gas levels remained within safe limits.

Waste water was treated in a bioreactor and sterilised with UV light before being used for irrigation. Drinking water was obtained by condensation and also sterilised. Some plant waste was used to grow mushrooms and then fed to mealworms, which were made into a kind of protein-rich bread. Faeces were mixed with plant waste and fermented to produce CO2 for growing plants. Some residues left after processing urine and faeces were stored. All crew members stayed physically and mentally healthy, the study says.

Read more: Biosphere 2: Saving the world within a world

“A good measure of these systems is how many square metres do you need to support one crew member,” says Oscar Monje at NASA’s Kennedy Space Center in Florida. In Lunar Palace 1, there were 40 square metres of growing area per crew member, compared with 75 square metres in the Japanese experiments, says Monje. “That’s pretty good, and matches what NASA predicted from its crop testing.”

The main aim of the research is to create life support systems for space exploration. “It would make long-term space travel much more feasible, as you would not need to bring so much mass,” says Suters. But supporting people on, say, a lunar base remains an immense challenge. For starters, a moon base would have to be underground to protect it from radiation, says Monje. Then it has to be powered. “If you want to do it with solar collectors, it would be a huge area so you probably need a nuclear reactor,” he says.

The moon is especially challenging because a lunar day lasts an Earth month, says Lasseur, giving it a long period of extreme cold and dark. And a system that works on Earth won’t necessarily work in space. The European Space Agency is taking a different approach, focusing on testing small components on space flights rather than trying to build a complete system on Earth. But it has set up a “space greenhouse” in Antarctica.

NASA, meanwhile, has been studying how to grow plants in space, installing the Advanced Plant Habitat on the International Space Station in 2018. However, the aim of this work is just to supplement the diet of astronauts on long missions with fresh food rather than for life support.

Reference: bioRxiv, DOI: 10.1101/2021.01.12.426282