Video: Delta 4-Heavy tower rollback

A critical test firing Saturday of the four main engines powering the first stage of NASA’s gargantuan Space Launch System moon rocket is the final major hurdle before the fully assembled booster’s costly, oft-delayed launch late this year on an unpiloted test flight.

Completing a 2,700-mile journey across the United States, America’s inaugural Orion spaceship arrived back home at the Kennedy Space Center on Thursday, just under two weeks after its trial by fire.