Engineer and daredevil explorer Bill Stone is obsessed with discovery. After years of crawling through the deepest unexplored caves on the planet, he's building robots to go where he can't. His company Stone Aerospace built DepthX, an autonomous robot, which descended 1,099 feet down Mexico's deepest watery sinkhole. In 2009, Stone and his team completed a successful mission to Antarctica. ENDURANCE, an expedition sponsored by NASA, was developed to explore and map under the ice of Lake Bonney in Antarctica. But this was just a test for the real mission (which is explained in a  National Geographic documentary, Journey to an Alien Moon): building a probe with NASA to bore through miles of ice on Jupiter's moon Europa, then swim through the buried Europan sea in search of alien life.

He's also hoping to singlehandedly jump-start commercial human space exploration by offering spacefarers affordable fuels and consumables extracted from the moon. His new Shackleton Energy Company, or SEC, intends to raise $15 billion (as he points out, this is about the cost of a North Sea oil production platform complex) to mine ice thought to be trapped on the moon's southern pole at Shackleton Crater, and to sell derived products (including propellants and other consumables) on the moon and in low earth orbit (LEO) to international consumers.

Read about his 2014 expedition to the Chevé system, perhaps the deepest cave on Earth.