Astronauts are training for future missions to the Moon and Mars in a massive underground cave that mimics the conditions they will face on in space.

The cave, located in Slovenia, contains "a labyrinth of passages mostly unexplored and rich in indigenous species,” according to course director Francesco Sauro.

It is "the closest you can get on this planet to the environmental, psychological and logistics constraints of a space mission,” explains course designer Loredana Bessone.

During the six-day training course, astronauts from NASA, the European Space Agency, the Canadian Space Agency and Russian space agency Roscosmos will live and work in the cave.

(Image: ESAÐV. Crobu)

Supported by a team of instructors and safety personnel, the six explorers will begin their descent into the dark to set up a base camp on 20 September.

The crew will learn how to follow air and trace water flows – the main link with life on Earth and a precious resource in space exploration.

The cave environment provides many space-relevant conditions, including isolation, confinement, minimal privacy, technical challenges, and limited equipment and supplies for hygiene and comfort.

The astronauts will have to make their own decisions and work autonomously, isolated from the outside world and coping with communication delays.

(Image: ESA Ð A. Romeo)

"This new space-caving adventure helps them to learn from each other, from themselves and from the cave, which always humbles you with its enclosing spaces and darkness," said Sauro.

Inhospitable and hard to access, caves are almost untouched worlds and ideal traps for scientific evidence.

During their time underground, the astronauts will carry out experiments and will be on the lookout for signs of life that have adapted to the extremes.

“We are really hoping to find new species,” said Bessone.

The astronauts will keep logs of their experiences and discoveries on a tablet, which they can also use to check procedures and cue cards.

(Image: ESA)

Meanwhile, above the ground, mission control will track the astronauts' progress on a 3D map as they explore the cave.

Scientists will be able to locate the astronauts' scientific observations paired with pictures, and send their comments back to the cave.

“It is augmented science. This technology saves crew and ground teams time and helps improve the scientific return of the mission,” said Bessone.

It is hoped that the astronauts will be able to transfer the learnings from their caving expedition to future space missions - particularly as space agencies prepare for further Moon exploration.

"ESA is taking the lead in subsurface expeditions to shape future missions exploring lunar caves," said Bessone.

(Image: ESAÐV. Crobu)

US President Donald Trump has set NASA the ambitious deadline to send humans back to the moon by 2024.

The programme, named ‘Artemis’, will allow scientists to examine the surface of the Moon up close.

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“This will teach us how to move safely across lunar soil, known as regolith; how to build infrastructure on top of it; and how to keep humans safe in space," NASA said.

In the long-run, NASA hopes that its work at the Moon will prepare it for the next big step - missions to Mars.