Snapshots from Atlas 5 launch

What began as a concept scribbled on a cocktail napkin in a Tucson bar 12 years ago — sending a spacecraft to an asteroid and retrieving a pristine sample to bring back to Earth for study — becomes reality Thursday with the launch of NASA’s OSIRIS-REx mission.

If all goes according to plan, engineers in southern Mississippi later this month will load cryogenic propellants into the core stage of a rocket NASA says will launch astronauts back to the moon, exposing its tankage and internal plumbing to extreme operating conditions hundreds of degrees below zero for the first time. The fueling test — a major milestone in its own right — is a precursor to a high-stakes eight-minute test-firing of the Space Launch System’s four shuttle-era main engines planned as soon as November.

United Launch Alliance teams loaded super-cold liquid hydrogen and liquid oxygen into an Atlas 5 rocket Friday at Cape Canaveral during a countdown dress rehearsal for a planned launch next month with the Solar Orbiter mission, a robotic spacecraft to study the origins of the solar wind and image the sun’s poles for the first time.