Updated on: February 3, 2026
NASA’s wet dress rehearsal for the Artemis II Space Launch System was cut short early Tuesday after recurring liquid hydrogen leaks forced engineers to stop the practice countdown.
The team began loading more than 750,000 gallons of supercold liquid oxygen and hydrogen Monday evening, but the countdown was halted after a leak was detected at the interface of a tail service mast umbilical. The countdown had resumed at T-minus 10 minutes around 12:09 a.m. EST Tuesday and moved toward a simulated engine start. About four and a half minutes later it was stopped when elevated hydrogen concentrations were detected at the same tail service mast umbilical that had shown high readings earlier in the sequence, NASA said.
Tail service masts at the rocket’s base carry propellant lines and attach to pull-away umbilical assemblies at the booster engine compartment. Launch controllers worked to put the rocket in a safe configuration and begin draining the tanks after the leak was identified.
Whether Artemis II can still target as-early-as Super Bowl Sunday for liftoff will depend on an overnight review and post-test analysis. The nine-day, two-hour lunar mission would carry four astronauts — commander Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen. NASA has three available launch days this month (Feb. 8, 10 and 11); missing those opportunities would push the flight into March. Hydrogen leaks are notoriously difficult to repair on the pad, and officials said a Sunday launch would be unlikely unless the leak is deemed manageable without on-pad repairs. A news briefing was expected at 1 p.m. Tuesday.
The wet dress began Saturday evening after a two-day weather delay because of frigid conditions along Florida’s Space Coast. Following a Monday morning readiness review, Launch Director Charlie Blackwell-Thompson authorized remote fueling. The operation started about 45 minutes late but initially proceeded smoothly as liquid oxygen and hydrogen filled the core stage tanks and hydrogen flowed into the upper stage.
A leak was first seen at an umbilical plate where a pad fuel line connects to the SLS first stage when that tank was about 55% full. Engineers paused fueling, then resumed, and later cut off again at roughly 77% full. They continued, expecting the leak to subside once the tank reached full and entered replenishment mode. NASA reported the core stage had been filled with liquid hydrogen and that earlier concentrations at the tail service mast stayed within acceptable limits during parts of the sequence.
The 332-foot SLS, which uses two strap-on solid rocket boosters and four main engines burning liquid oxygen and hydrogen to produce about 8.8 million pounds of thrust at liftoff, first flew uncrewed on Artemis I in 2022. That mission experienced fuel leaks and propellant flow issues that delayed the program and prompted upgrades. Many fixes were applied for Artemis II, but the tail service mast umbilical leak seen in 2022 has reappeared in this campaign.