The nominee for NASA’s top job is outlining his vision for space exploration. President Donald Trump nominated billionaire spacewalker Jared Isaacman to become NASA’s 15th administrator. In written testimony, Isaacman said he would prioritize sending astronauts to Mars. The Senate Commerce, Science and Transportation Committee held its nomination hearing for him in Washington on Wednesday. Isaacman has flown in space twice, buying his own trips from SpaceX, and last September performed the world’s first private spacewalk. He made his fortune with a payment processing company he started as a high school dropout in his parents’ basement.