An international team of aquanauts has begun training at a lab deep in the Atlantic Ocean for an eventual visit to an asteroid, NASA said.
The scientists, astronauts and engineers making up the 16th excursion of NASA's Extreme Environment Mission Operations (NEEMO) come from the United States and the space agencies of Japan and Europe.
They began their latest 12-day mission on Monday at the Aquarius lab, off the coast of Florida, which provides an environment similar to what it would be like to navigate near-weightless on an asteroid.
"Aquarius provides a convincing simulation to space exploration, and NEEMO crew members experience some of the same tasks and challenges under water that they would in space," NASA said in a statement.
The ocean-floor outpost is located three miles (4.5 kilometers) off the coast of Key Largo, Florida, where it has provided lodging and life support systems for underwater scientists since 1993.
NASA has been sending astronauts to the undersea lab 63 feet (19 meters) down for weeks-long space training missions since 2001.
The latest effort is a new push to get ready for an asteroid trip that President Barack Obama has said could happen by 2025.
The commander of the mission is NASA astronaut Dottie Metcalf-Lindenburger.
The crew includes European Space Agency astronaut Timothy Peake of Britain, Japan Aerospace Exploration Agency astronaut Kimiya Yui and Steven Squyres who is professor of astronomy at Cornell University and chairman of the NASA Advisory Council.
The last NEEMO expedition was in October 2011.
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