"The long voyages in weightlessness are bound to substantially debilitate the crew," he added. "At Mars arrival, they must have a way to rehabilitate themselves

"The long voyages in weightlessness are bound to substantially debilitate the crew," he added. "At Mars arrival, they must have a way to rehabilitate themselves before going to work, a tall order for the first mission in a very hostile environment." Is that really a problem as gravity is much lower on Mars than on Earth?