Editor’s note: This blog post was updated at 4:09 p.m. EST on Feb. 2, 2026, to correct the status of liquid hydrogen operations at the time of posting.
Ground teams have resumed loading liquid hydrogen operations into the core stage of the SLS (Space Launch System) rocket. Operations were stopped twice after leak rates at the interface of the tail service mast umbilical exceeded allowable limits. Engineers will attempt to complete filling and then begin topping off the tank. Should that be successful, they will attempt to manage the hydrogen concentration, keeping it within acceptable limits during core stage hydrogen loading. Once the tank is full, the rocket will go into a replenish phase in which the flow rates are reduced; this is expected to help control the liquid hydrogen concentration level in the umbilical. Teams are reinitiating liquid oxygen flow into the upper stage.
February 2, 2026
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