Fabien Cousteau, grandson of famed marine explorer and conservationist Jacques Cousteau, is four days into a 31-day stint in an underwater NOAA research base in the Florida Keys that would top his grandfather's underwater record by one day.

The expedition goes by the name of "Mission 31," in reference to Cousteau's target stay-duration. Via the project website:

[The Mission 31 expedition] breaks new ground in ocean exploration and also coincides with the 50th anniversary of a monumental legacy left by his grandfather, who is also credited with creating the first underwater habitats for humans and leading a team of ocean explorers on the first attempt to live and work underwater. In 2014, Mission 31 will commence to honor Cousteau's original experiment by going deeper, longer and further while broadcasting each moment on multiple channels exposing the world to the adventure, risk and mystique of what lies beneath.

NPR's Camila Domonoske has more details:

The underwater lab that's serving as the team's temporary home is called Aquarius Reef Base. The 81-ton steel structure is located 63 feet beneath the water's surface, according to the Mission 31 website. At that depth, Reuters reports, the water pressure is almost three times the pressure at the surface.

"The 25-year-old facility, built by the federal government, has hosted everyone from marine biologists studying endangered coral reefs to NASA astronauts training for weightless missions in space," NPR's Greg Allen reported in 2012, when the facility was grappling with the loss of its federal funding. (Currently, operations are supported by The Aquarius Reef Base Foundation.)

According to CNET, Cousteau will be accompanied by two technicians, who will be staying with him for the duration of the project. Two cameramen and four scientists also will be involved, but the lab only has room for three of them at a time; they will swap out halfway through.

You can watch a live stream of the ongoing underwater attempt at the Mission 31 website.

[M31 via NPR]