"While loading liquid hydrogen (LH2) on the rocket’s core stage earlier this afternoon, engineers detected a leak on the tail service mast , which is located at the base of the mobile launcher and connects to the core stage," the blog said on Thursday.
Engineers then stopped loading liquid hydrogen and liquid oxygen (LOX) on the core stage. The launch director gave approval for teams to chill down the interim cryogenic propulsion stage (ICPS) liquid hydrogen lines to collect additional data and they have completed that activity, NASA said.
"Engineers will not load LH2 or LOX into the ICPS tanks, due to an issue with a helium check valve experienced several days ago. When teams paused propellant loading earlier today, there was about 49% of LOX on the core stage and about 5% of LH2 was loaded into the core stage tank prior to the hydrogen leak," NASA added.
The terminal countdown also did not take place on Thursday due to the modified configurations and delays with propellant loading. Teams are reassessing the next steps and will determine a go-forward plan, according to NASA.