Human mission to Mars propellant from the Martian Atmosphere. This proposal drew on concepts developed by the former "Case for Mars" conference series. Over the next decade, Zubrin developed it into a mission concept, Mars Direct, which he presented in a book, "The Case for Mars" (1996). The mission is advocated by the Mars Society, which Zubrin founded in 1998, as practical and affordable. In 1991 in Toulouse, France, the International Space University studied an international human Mars mission. They proposed a crew of 8 traveling to Mars in a nuclear-powered vessel with artificial gravity provided by rotation. On the surface, 40 tonne habitats
Mars to Stay become a two-planet species". In August 2015, Aldrin, in association with the Florida Institute of Technology, presented a "master plan", for NASA consideration, for astronauts, with a "tour of duty of ten years", to colonize Mars before the year 2040. The Mars Underground, Mars Homestead Foundation, Mars One, and Mars Artists Community advocacy groups and business organizations have also adopted Mars to Stay policy initiatives. The earliest formal outline of a Mars to Stay mission architecture was given at the Case for Mars VI Workshop in 1996, during a presentation by George Herbert titled "One Way to Mars". Since returning