Video: X-37B payload mated to Atlas 5

The Orbital ATK’s Cygnus commercial resupply spacecraft, named the SS Deke Slayton II, is packed up and poised for launch to the International Space Station.

Running through a practice countdown and hold-down engine firing at NASA’s Kennedy Space Center, a SpaceX Falcon 9 rocket passed a key checkpoint Thursday ahead of liftoff next week with the U.S. Air Force’s fifth X-37B spaceplane flight, a mission that will come with several firsts.

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.