After troubleshooting an issue with the temperature of liquid oxygen during early stages of propellant loading into the rocket’s core stage, launch controllers have resumed operations. Teams performed chill down operations again before liquid oxygen began flowing into the tank and adjusted pump speeds as necessary during flow to help ensure temperatures remain below limits. They also opened valves to bleed off any warm liquid oxygen.
Earlier in the count, teams began slow fill operations for liquid oxygen, but were automatically halted when temperature readings on the propellant showed it was warmer than intended. The liquid oxygen is an extremely cold, or cryogenic, propellant that is maintained at minus 297 degrees Fahrenheit and must be kept at super cold temperatures. As the super cold liquid oxygen fills the core stage main propulsion system, some venting may be visible.
Teams have now progressed to fast fill for core stage liquid oxygen and slow fill for liquid hydrogen.