Watch a live view of the Atlas 5 launch pad with countdown audio (members only)

NASA’s robotic InSight Mars lander arrived at Vandenberg Air Force Base in California this week aboard a U.S. Air Force cargo plane, ready for final testing, fueling and launch aboard an Atlas 5 rocket May 5, two years later the originally planned.

Following delivery to the launch pad, the United Launch Alliance Atlas 5 rocket stands poised for the NROL-61 mission for the National Reconnaissance Office from Cape Canaveral on Thursday morning.

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.