Just slightly behind schedule, the Aquarius Reef Base reopened for business June 13. The NASA Extreme Environment Mission Operation (NEEMO) 23 team of four women swam down to the world’s only functioning undersea laboratory last Thursday to begin a nine-day mission that simulates conditions in a space flight.

While there, the crew will conduct experiments on physiological and psychological stress, tests equipment suitable for space and makes time for planting new corals in the closed research waters, 62 feet down at Conch Reef. “The close parallels of inner and outer space exploration will be clearly demonstrated during this undersea mission,” NEEMO Project Lead Bill Todd said in a NASA report. “The daily seafloor traverses, or extravehicular activities in space jargon, are jam-packed with technology and operations concept testing, as well as complex marine science.”

NASA’s expedition marks the return of Aquarius missions after damages from Hurricane Irma in September 2017. The 43-foot-long main habitat, now owned and operated by Florida International University in Miami, largely escaped significant damage but some facilities on the sea floor were swept away.

The NASA team, headed by Italian European Space Agency astronaut Samantha Cristoforetti, got the signal to dive shortly after noon Thursday. The NEEMO 23 crew includes NASA astronaut candidate Jessica Watkins; Shirley Pomponi, marine research professor Florida Atlantic University’s Harbor Branch Oceanographic Institute; and Csilla Ari D’Agostino, research assistant professor at the University of South Florida and a manta ray researcher. Two Aquarius technicians also submerged with the NASA team for the duration of the mission.

As part of subsea assignments, the crew plans to install coral nursery trees near Aquarius for a research project in the FIU Medina Aquarius Program. Two species of endangered coral will be monitored by university staff for four years to study “effects of nearby fish communities on the composition, function and health of the corals and their interactions with assemblages of microorganisms and algae in the area.” After working on the bottom, the team will undergo lengthy decompression required after saturation dives while inside the 81-ton habitat. They are expected to surface Friday or Saturday.