Video: The launch of Orion

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.

A countdown dress rehearsal and rocket fueling exercise was completed at Cape Canaveral for next month’s launch of NASA’s Orion crew module atop a United Launch Alliance Delta 4-Heavy booster.

NASA is moving forward with a crucial test-firing of the core stage of the first Space Launch System heavy-lift rocket as soon as Jan. 17 after engineers were satisfied with the results of a fueling test last month.