NASA astronauts study in aquarius underwater ocean lab

They may be astronauts, but first, they're aquanauts. Before they go to the International Space Station, NASA astronauts head the other direction -- to the bottom of the ocean.

They dive down to Aquarius the world's only undersea research station. It rests more than 60 feet below the surface in the Atlantic off Key Largo, Florida.

Seven people at a time fit in Aquarius and the living quarters can be tight.

The Aquanauts easily exit and enter the lab to do simulated spacewalks on the ocean floor and other jobs they might have to perform in orbit.

The water's buoyancy is a good approximation of the low-gravity environment of the moon or an asteroid or planet. Sometimes, they just chill with the ocean's other inhabitants.