CAVES underground training exercise. Image: ESA–A. Boesso

An underground cave is precisely the wrong direction if you’re hoping to go into space—so why is the European Space Agency sending the latest batch of ISS-bound astronauts on a spelunking expedition? To practice for life in a sealed tin can, of course.


On July 1st, six astronauts—the ESA’s Pedro Duque, NASA’s Jessica Meir and Richard Arnold, Japan’s Aki Hoshide, China’s Ye Guangfu, and Russia’s Sergei Korsakov— are being sent deep into the caverns of Sardinia, Italy, for what has become a key training exercise before shipping off into the cosmic void. In many ways, caves are an ideal testbed for space, affording a similar sense of claustrophobia and sensory deprivation while also screwing with human circadian rhythms.

Away from the sights and sounds of the world above, the astronauts will spend six nights running experiments and moving about on a tethering system similar to that used during space walks, all the while interacting with the same smelly people every waking hour. They’ll also be test-driving a few new pieces of technology, including xFerra, a communications system that can transmit signal through 800 meters of solid rock.

Image: ESA–A. Boesso

Decades of astronauts have prepared for space by depriving their senses here on Earth. But in recent years, these exercises have become more elaborate and scientific in nature. On the barren slopes of Mauna Kea, Hawaii, an experiment called Hi-SEAS has spent the last few years sealing would-be Martian colonists inside inflatable domes to study the psychological response to confinement. Earlier this year, a doctor headed to Concordia Station in Antarctica to learn about how human physiology responds to prolonged periods of darkness, similar to those we’d experience on a deep space expedition.


So if you’re thinking of filling out NASA’s astronaut application, consider a spelunking course first. It’s not only a guaranteed resume booster, but a quick gut-check to see if you’re really ready to ship off to the Red Planet.