Four Chinese volunteers completed a survival experiment on Dec. 14, after living inside a sealed capsule in Shenzhen for 180 days.

The four volunteers, three men and one woman, finished their task of determining how well food, water and oxygen can be used and recycled under controlled conditions. The volunteers also cultivated 25 different kinds of plants in the capsule, including wheat, potatoes, sweet potatoes, soybeans, peanuts, lettuce, edible amaranth and Chinese cabbage, among others.

They further monitored how a hermetic environment affects physiological characteristics, biological rhythms, sleep patterns and psychological health. The volunteers will next undergo one month of medical observation.

The experiment was launched in Shenzhen on June 17. The sealed capsule has a total floor space of 370 square meters. Scientists will collect data and carry out experiments inside the capsule for another month to ensure the continuity of scientific data.

The results of the experiment are considered critical to determining the viability of long-term space travel.