NASA engineers have called off Monday’s launch of the Starliner spacecraft due to a technical issue with an oxygen relief valve on Centaur, the second stage of the Atlas V rocket. The decision to scrub the launch from the Kennedy Space Center in Florida came just two hours before the scheduled liftoff time of 10:34 p.m. ET. NASA astronauts Butch Wilmore and Suni Williams had already been strapped into their seats inside the Starliner spacecraft at the time of the decision. The scrub is a big disappointment for the crew and launch team, but once the issue has been resolved, a new date for liftoff should be able to be arranged without too much delay.