Tomorrow four volunteers are due to be released from a sealed capsule after living together in close confines for 180 days. The capsule is housed in Shenzen City in Guangdong Province in southern China. The four volunteers have been living in a space of 370sq m.

The experiment is a survival mission to test how people fare physically, psychologically and emotionally in a sealed "ecological life-support system" that simulates how they might travel for prolonged periods in space.

The volunteers, who are all scientists, have been tending to 25 varieties of plants, including wheat, potatoes, sweet potatoes, soybeans, peanuts, lettuce, edible amaranth plants and Chinese cabbage, according to the Chinese news site CCTV+.

"It's been a huge amount of work," says volunteer Tong Feizhou, who is responsible for data management and medical support in the capsule.

The volunteers have been living on Mars time throughout the experiment, with days lasting 24 hours and 40 minutes. They have been testing how much the astronauts can rely on recycling food, water and oxygen.

Tang Yongkang, another of the volunteers, says that he was looking forward to returning to the outside world. "I feel excited, since we are getting out of the capsule soon. We have finished about 177 days of the 180-day mission, only a couple of days left to go. I look forward to the completion."

Scientists from the Astronaut Center of China, Harvard University in the US and the German Aerospace Center have been collaborating on the project.