"The earth is the cradle of humankind, but one cannot live in the cradle forever" ,

Russian rocket pioneer Konstantin Tsiolkovsky, 1895

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"Earth is too small a basket for mankind to keep all its eggs in." ,

 science-fiction writer Robert Heinlein

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"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

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"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

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