Video: Weather causes Atlas 5 countdown hold

United Launch Alliance’s next Atlas 5 rocket moved to its launch pad Wednesday at Cape Canaveral, taking position for liftoff with the U.S. military’s sixth and final Advanced Extremely High Frequency secure communications satellite.

The United Launch Alliance Atlas 5 rocket, equipped with three strap-on solid-propellant boosters for added performance, was transfered from its assembly building to the pad at Cape Canaveral’s Complex 41 today for Sunday’s launch of the commercial EchoStar 19 communications satellite.

The mission, dubbed Cert-2 by United Launch Alliance, is the final mission required before the rocket can begin launching national security missions. Liftoff is set for the beginning of a three-hour window at 6 a.m. EDT (1000 UTC).