Poynter said the husband and wife need to be even-tempered. Clark said they should be post-childbearing age because of exposure to radiation. Poynter is 50, MacCallum 48.
For the 30 years NASA has been flying men and women, it has avoided the question of sex in space. MacCallum said it will happen: "It's a man and wife. Private time. Let your imagination run wild."
In a statement, NASA spokesman David Steitz said the venture validates President Barack Obama's decision to rely more on private sector ingenuity to explore space, and is "a testament to the audacity of America's commercial aerospace industry and the adventurous spirit of America's citizen-explorers."
He said "NASA will continue discussions with Inspiration Mars to see how the agency might collaborate on mutually beneficial activities."
Stanford University professor Scott Hubbard, NASA's former Mars mission chief, said the team's technical paper outlining the flight is "long on inspiration, short on technical details. What is there is correct."
Other outside experts praised the expertise of the team but worried about the lack of testing.
Former astronaut and current MIT aerospace engineering professor Jeff Hoffman said: "Since they don't plan to land on Mars, it's really a question of keeping people alive for 501 days in space, which is not an impossible task."
Inspiration Mars: http://www.inspirationmars.com
Seth Borenstein can be followed at http://twitter.com/borenbears
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