SpaceX CEO Musk to present plans for Mars colony

SpaceX chief Elon Musk is set Tuesday to unveil his ambitious plan to build a human colony on Mars, an endeavor that experts say requires tens of billions of dollars. SpaceX plans to send an unmanned Dragon cargo capsule to Mars as early as 2018, paving the way for a human mission that would leave Earth in 2024 and arrive on the Red Planet the following year. "It's unlikely that (Musk) will be able to get humans on Mars by 2025," said John Logsdon, former director of the Space Policy Institute a