Veteran astronauts Soichi Noguchi and Shannon Walker have been assigned to fly to the International Space Station on SpaceX’s second piloted Crew Dragon mission later this year, joining commander Mike Hopkins and astronaut Victor Glover on a planned six-month expedition in orbit.

Engineers believe super-hot gas from burning solid propellant impinged on the structure of the second stage on a European Vega launcher during a failed flight in July, causing the vehicle to break apart minutes after liftoff from French Guiana with a reconnaissance satellite for the United Arab Emirates, the CEO of Italian rocket-maker Avio said Monday.

The countdown began Saturday evening and will continue through the start of a simulated launch window opening at 9 p.m. EST Monday. The test started two days late because of predicted arctic weather along Florida’s Space Coast.