By MARCIA DUNN CAPE CANAVERAL, Fla. — A NASA spacecraft rocketed away Monday on a quest to explore Jupiter’s tantalizing moon Europa and reveal whether its vast hidden ocean might hold the keys to life. It will take Europa Clipper 5 1/2 years to reach Jupiter, where it will slip into orbit around the giant gas planet and sneak close to Europa during dozens of radiation-drenched flybys. Scientists are almost certain a deep, global ocean exists beneath Europa’s icy crust.