Live coverage: Atlas 5 countdown and launch journal

A commercial Falcon 9 rocket in the final stages of launch preparations fired its nine Merlin main engines Saturday at Vandenberg Air Force Base in California, verifying its readiness for liftoff with a Taiwanese Earth-imaging payload Thursday.

Good weather for launching a rocket is forecast for Cape Canaveral and the Space Coast on Thursday morning when a United Launch Alliance Atlas 5 is scheduled to take flight.

The revised Atlas 5 rocket firing order includes two national security missions this summer before launching NASA’s daring asteroid sampler mission in September as originally planned.