"The earth is the cradle of humankind, but one cannot live in the cradle forever" ,
Russian rocket pioneer Konstantin Tsiolkovsky, 1895
"Earth is too small a basket for mankind to keep all its eggs in." ,
science-fiction writer Robert Heinlein
"Since, in the long run, every planetary civilization will be endangered by impacts from space, every surviving civilization is obliged to become space faring - not because of exploratory or romantic zeal, but for the most practical reason imaginable: staying alive.",
astronomer-author Carl Sagan, 1994
"The dinosaurs became extinct because they didn't have a space program. And if we become extinct because we don't have a space program, it'll serve us right!" .
science-fiction writer Larry Niven, as quoted by Arthur C. Clarke in 2001