The launch control team is filling the Space Launch System’s interim cryogenic propulsion stage (ICPS) with liquid hydrogen (LH2) followed by liquid oxygen (LOX) loading. The core stage LH2 and LOX tanks, meanwhile, are being replenished as some of the supercool propellant boils off, meaning the propellant tank will be full through the rest of the countdown.
For the wet dress rehearsal, teams will conduct a test to demonstrate the capability to stop loading the core stage LH2 flow and will then resume with replenishment.
At L-40 minutes, the launch control team will conduct a planned 30-minute hold around 3:58 p.m. EDT prior to the start of the terminal count portion of the test. Mission managers will conduct a final poll on whether to proceed with terminal count at that time.
NASA is streaming live video and live commentary of the test on the agency’s website. Venting on the rocket is visible during these tanking operations.