"When scientists discovered the first ocean beyond Earth, they had two big questions: 'Is it habitable?' and 'How do we get there?' To answer the first, they had to solve the second, and so began a vivacious team's twenty-year odyssey to mount a mission to Europa, the ocean moon of Jupiter. Standing in their way: NASA, fanatically consumed with landing robots on Mars; the White House, which never saw a science budget it couldn't cut; Congress, fixated...