Earlier this summer, a team of international astronauts descended more than 2,400 feet underground to train for a week in conditions that mimic the sensory-deprived, alien-esque setting of space. Now, another team has embarked on a 16-day training mission off the Florida Keys, living in a world of blue 62 feet down that will help prepare them for future deep space missions and, with luck, an eventual journey to Mars.

“NEEMO 21 astronauts and crew will pioneer complex tasks on the seafloor utilizing the most advanced underwater navigation and science tools which are methodically choreographed to mimic a Mars exploration traverse,” said project lead Bill Todd in a statement about NEEMO, the acronym for NASA Extreme Environment Mission Operations.

Luca Parmitano, leader of the NEEMO 20 mission, explains what it's like to train at that depth in the video below:

Home for this international crew, made up of NASA and the European Space Agency astronauts and researchers, is the world's only undersea laboratory dedicated to science and education. Known as "Aquarius," the habitat includes three compartments, can accommodate six people, and closely mimics conditions aboard the International Space Station.

“This unique opportunity will result in me becoming one of less than 800 people around the world that have lived underwater like this‚” NEEMO 21 team member Dr. Noel du Toit told the Times Live. "My stay will include five 'spacewalks' and a multitude of habitat-based science tasks and human physiology studies."

In addition to simulated spacewalks and experiments with various underwater robots, NASA is preparing astronauts for the time delay in radio communications between Earth and Mars.

The NEEMO 21 exercise is also an opportunity for astronauts to try out the latest advancements in gear that may one day accompany them on missions deep into the solar system. That includes a DNA sequencer, a medical telemetry device, and a HoloLens virtual reality headset to assist in "the operational performance for human spaceflight cargo transfer."

As you might expect, NASA isn't shy about promoting these incredible training exercises. For an agency that recently received a record 18,300 applications for its latest astronaut class, it's safe to say there's plenty of interest from the American public.

You can follow the NEEMO 21 team's progress through Twitter and Facebook.

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Deep-space astronauts train under the sea
For 16 days, these NEEMO 'aquanauts' are experiencing life aboard a space station by living 62 feet below the surface of the Atlantic Ocean.