This 2021 photo provided by ICON and NASA shows construction of the Mars Dune Alpha 1,700-square-foot Martian habitat, being made by a 3D-printer, inside a building at Johnson Space Center in Houston. To prepare for eventually sending astronauts to Mars, NASA began taking applications Friday, Aug. 6, 2021, for four people to live for a year in Mars Dune Alpha - a 1,700-square-foot Martian habitat, created by a 3D-printer, and inside a building at Johnson Space Center in Houston. The paid volunteers will work a simulated Martian exploration mission complete with spacewalks, limited communications back home, restricted food and resources and equipment failures. (ICON/NASA via AP)