Yesterday, the international team of six astronauts from China, Japan, USA, Spain and Russia returned to daylight after spending six nights underground simulating a mission exploring another planet.

The Sardinian caves certainly look extraterrestrial and the course designers recreate a space mission with as much fidelity as possible. From 'cavewalks' to daily planning conferences as held on the International Space Station, as well as food and equipment resupplies and running scientific experiments, the six 'cavenauts' were put through their paces during their subterranean adventure.

ESA's underground training course "Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills" - CAVES - focuses on multicultural approaches to leadership, following orders, teamwork and decision-making so astronauts can improve their skills.

This year's astronauts were each assigned a role for the underground expedition: Japanese astronaut Aki Hoshide shared commander and campsite duties with NASA's Ricky Arnold, exchanging command halfway through the mission. China's Ye Guangfu was the team's survey and data engineer, while Russian Sergei Korsakov took up photo and video engineering duties. ESA astronaut Pedro Duque was the expedition's scientist for environmental science, geology and microbiology, while NASA's Jessica Meir was the biologist.

The team explored further than any other CAVES course, mapping their progress and taking samples of the environment and life they found.

They tested new techniques for making accurate 3D models of objects and the environment using standard cameras - a technique that could be used in exploring other planets.

Mission director Loredana Bessone spent the six days underground with the crew: "In addition to preparing astronauts for spaceflight, this course teaches us how to move from the Space Station to more autonomous expeditions, where astronauts will be more responsible for safety, planning, and for the maintenance of equipment.

"They have been an exceptional team from the very beginning and I believe they are ready to explore the caves of our Solar System."

Loredana concludes: "There were no borders in this team, and the variety of organisational, professional and national cultures enriched the team with a multitude of skills and fresh perspectives."