Live coverage: Kennedy Space Center to reopen Friday

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.

The U.S. Air Force’s fourth Advanced Extremely High Frequency spacecraft launched Wednesday from Cape Canaveral on top of a United Launch Alliance Atlas 5 rocket, expanding the reach of the military’s most secure, jam-resistant satellite communications network.

SpaceX rolled a fully-assembled Falcon 9 booster out of its hangar and lifted it on top of a launch pad Friday for the first time since an explosion grounded the commercial rocket last year, setting the stage for a one-second launch window Saturday to take off from California’s Central Coast and deploy the first 10 satellites in orbit for a $3 billion upgrade to Iridium’s globe-spanning message relay network.