Astronauts and other scientists are calling the Atlantic Ocean home for the next few weeks.
The NASA Extreme Environment Mission Operations — also known as NEEMO-21 — began July 21 and will last 16 days.
The underwater mission allows crews to prepare for deep-space missions by conducting research, testing new tools and even doing simulated spacewalks.
Aquanauts are stationed on Florida International University's Aquarius Reef Base. At 62 feet below the ocean's surface, it's the world's only undersea research laboratory.
Astronauts participating in the 21st mission are from the U.S., Ireland, Germany and South Africa.
Some will remain on the mission for 16 days, while others will rotate out halfway through.