"In my own view, the important achievement of Apollo was a demonstration that humanity is not forever chained to this planet, and our visions go rather further than that, and our opportunities are unlimited." Neil Armstrong, Press Conference, 1999

"I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars." Stephen Hawking, Interview with Daily Telegraph, 2001

"Today the human race is a single twig on the tree of life, a single species on a single planet. Our condition can thus only be described as extremely fragile, endangered by forces of nature currently beyond our control, our own mistakes, and other branches of the wildly blossoming tree itself. Looked at this way, we can then pose the question of the future of humanity on Earth, in the solar system, and in the galaxy from the standpoint of both evolutionary biology and human nature. The conclusion is straightforward: Our choice is to grow, branch, spread and develop, or stagnate and die." Robert Zubrin, Entering Space, 1999

"In the long run, a single-planet species will not survive. One day, I don't know when, but one day, there will be more humans living off the Earth than on it." NASA director Mike Griffin, quoted in "Mars or Bust," Rolling Stone, 2006

"The crossing of space ... may do much to turn men's minds outwards and away from their present tribal squabbles. In this sense, the rocket, far from being one of the destroyers of civilisation, may provide the safety-value that is needed to preserve it." Arthur C. Clarke, The Exploration of Space, 1951

"Once the threshold is crossed when there is a self-sustaining level of life in space, then life's long-range future will be secure irrespective of any of the risks on Earth... Will this happen before our technological civilization disintegrates, leaving this as a might-have-been? Will the self-sustaining space communities be established before a catastrophe sets back the prospect of any such enterprise, perhaps foreclosing it forever? We live at what could be a defining moment for the cosmos, not just for our Earth." Martin Rees, England's Astronomer Royal, 2003

"As a race, we survive on planet Earth purely by geological consent." Bill McGuire, Apocalypse, May 2000

"The penetration of humankind into the universe, into its study and mastery, is not an expression of the inability of human beings to grapple with earthly difficulties and problems, not flight from them, but a qualitatively new and often even unique, irreplaceable means of solving many of the most important tasks of science, technology and the economy." A. D. Ursul in The Human Being and the Universe in Sov. Studies in Philosophy, 1978