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.

Boeing’s first Starliner spacecraft designed to fly to the International Space Station rolled out of a converted space shuttle hangar before dawn Thursday.

Mission leaders Tuesday gave approval for rollout of the United Launch Alliance Atlas 5 rocket on Wednesday morning, leading to liftoff Thursday night of the Magnetospheric Multiscale science project for NASA.