The most powerful Atlas rocket to ever fly from the West Coast is poised for launch Thursday to deliver a secret payload into orbit while debuting a new upper stage engine.

SpaceX launch crews rolled out the company’s next Falcon 9 rocket to pad 39A at the Kennedy Space Center in Florida, then lifted the two-stage launcher vertical for a hold-down engine firing Thursday in preparation for launch next week with a South Korean-owned commercial communications satellite.

A Vega launcher lifted off Tuesday night from a spaceport at the edge of South America’s Amazon rainforest, climbed into orbit on the power of four Italian- and Ukrainian-built rocket stages, and successfully deployed a French-built, Moroccan-owned military surveillance satellite nearly 400 miles above Earth.