In a Reddit IAmA. http://www.reddit.com/r/IAmA/comments/r62jp/iama_nasa_astronaut_that_recently_returned_to/c437ubd (2012)
An earlier similar quotation can be found in:
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!
By Larry Niven As quoted by Arthur C. Clarke in "Meeting of the Minds : Buzz Aldrin Visits Arthur C. Clarke" by Andrew Chaikin (27 February 2001) http://web.archive.org/web/20010302082528/http://www.space.com/peopleinterviews/aldrin_clarke_010227.html
“People should be travelling to Mars and doing it in our lifetime.”
Page 9
Conversation: Elon Musk on Wired Science (2007), Foreword to Marc Kaufman's Mars Up Close: Inside the Curiosity Mission https://books.google.com/books/about/Mars_Up_Close.html?ido6XaCwAAQBAJ&hlen. National Geographic. ISBN 978-1-4262-1278-9.
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Elon Musk 91
South African-born American entrepreneur 1971Related quotes
“Why should we hate the people we once loved because of a war that mars even our memories?”
Source: Frouzanda Mahrad (an Arabic poem, translated by Mike Maggio in: Buckley, Jorunn Jacobsen (2002). The Mandaeans: ancient texts and modern people. New York: Oxford University Press.)

“… I plan to travel to Mars and make it my home.”
Page 9.
Conversation: Elon Musk on Wired Science (2007), Foreword to Marc Kaufman's Mars Up Close: Inside the Curiosity Mission https://books.google.com/books/about/Mars_Up_Close.html?ido6XaCwAAQBAJ&hlen. National Geographic. ISBN 978-1-4262-1278-9.

A Study of American Liberalism and its Relationship to Modern Totalitarian States (1938)
p. 42
Dorothy Thompson’s Political Guide: A Study of American Liberalism and its Relationship to Modern Totalitarian States (1938)

Page 10
Conversation: Elon Musk on Wired Science (2007), Foreword to Marc Kaufman's Mars Up Close: Inside the Curiosity Mission https://books.google.com/books/about/Mars_Up_Close.html?ido6XaCwAAQBAJ&hlen. National Geographic. ISBN 978-1-4262-1278-9.
“Someday I'd like to read a story about competent people on Mars.”
[c3i93p$iu$1@panix3.panix.com, 2004]: About First Landing by Robert Zubrin:
2000s

“Dead is the travel of all our travels.”
Thinkings

Turning down an offer of payment from Irénée du Pont in 1954 for a second mural after one he had finished in 1933 began to deteriorate because of improperly dried paint; as quoted in "How Maxfield Parrish Fulfilled a Warranty" by Seth W. Mattingly in Valley News [Lebanon, NH] (10 February 1982), p.2.