Tom Clark, standing, a manager with contractor ERC, works with Quentin Jones and Emily Hadley, both mechanical engineers for the liquid oxygen system, with ERC, during a countdown demonstration event of cryogenic propellant loading April 12, 2019, inside Firing Room 2 in the Launch Control Center at NASA’s Kennedy Space Center in Florida. The practice simulation involved loading of liquid hydrogen and liquid oxygen into the Space Launch System rocket’s core and upper stages to prepare for Exploration Mission-1 (EM-1). During the tanking exercise, the team worked through surprise issues in real-time. The practice countdown events are training opportunities coordinated by EM-1 Launch Director Charlie Blackwell-Thompson with Exploration Ground Systems.