Live coverage: Orion lands in Pacific

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.

Towering more than 30 stories tall, the mobile gantry structure at the Delta 4-Heavy rocket’s launch pad at Cape Canaveral was wheeled into position for liftoff of the triple-core launcher Thursday with a classified payload for the National Reconnaissance Office.

NASA and industry teams at Cape Canaveral launched an Orion capsule on a three-minute atmospheric test flight Tuesday to prove the spaceship’s ability to escape from an exploding rocket during launch, demonstrating a key safety feature before astronauts ride the vehicle into deep space. Liftoff occurred at 7 a.m. EDT (1100 GMT).