"The number of people who will be willing to move to Mars is much greater if they know that they have the option of returning, even if they never actually return. Most of the people who went to the original English colonies in North America they never returned to Europe even once. But some did, and just knowing that if you don't like it there you could come back I think makes a big difference in people's willingness to go there in the first place.
"In any case, we need the spaceship back, so it's coming. You could jump onboard or not. You get a free return trip, if you want," he said.
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Once the ships start flying, Musk figures it will take 40- to 100 years to relocate 1 million people to Mars, at which point the colony would be self-sustaining and autonomous. Eventually, the colony could decide to terraform Mars to make it more suitable for human life, such as by warming the planet and creating oceans.
"Terraforming would take place over a long period of time and I think ultimately would be a decision for people of Mars. We need to get there in the first place," Musk said.
Musk unveiled his colonization plan to attract partners -- he figures development costs will be about $10 billion -- and push along other companies and organizations interested in Mars and other space settlements.
"It is really a decision as to whether we want to become a multi-planet species in a space-faring civilization or not. Some people think its fine to stay on Earth forever and some people don't but I think a future where we are a space-faring civilization and out there among the stars is infinitely more exciting and inspiring than one where we are not," Musk said.
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The SpaceX founder, who also runs Tesla Motors, is unsure he'd be part of the first crew to travel to Mars.
"I would definitely need to have a very good succession plan because the probability of death is quite high on the first mission and I'd like to see my kids grow up, so some pros and cons there," he said.
"I would like to go to orbit, maybe visit the space station and then ultimately go to Mars. I've got to make sure that if something goes wrong on the flight and I die that there's a good succession plan and that the mission of the company continues and that it doesn't somehow get taken over by investors who just want to maximize the profitability of the company and not go to Mars," Musk said. "That would be my biggest fear in that situation."
SpaceX is planning to launch an unmanned Red Dragon capsule to Mars as an initial test flight in 2018.