The main event of the morning is now reaching its stride at Kennedy Space Center as propellant loading enters the critical slow-fill stage.
After successfully chilling down the transfer lines to prevent thermal shock, teams are now trickling liquid oxygen and liquid hydrogen into the SLS core stage at a controlled pace.
This deliberate speed allows the massive tanks to adjust to the cryogenic temperatures—-297°F for the oxygen and -423°F for the hydrogen—without causing structural stress to the rocket’s skin.
As the super-cooled fuel begins to fill the bottom of the tanks, observers at the pad can see the first signs of frost and condensation forming on the exterior of the orange insulation.
Once the sensors confirm the tanks have reached a stable temperature and a safe internal volume, the Launch Director will give the command to transition into the fast-fill phase, significantly increasing the flow to meet the 700,000-gallon capacity needed for tonight’s 6:24 p.m. ET liftoff.