Updated on: February 3, 2026 / 2:17 AM EST / CBS News
NASA began a “wet dress” rehearsal for the Artemis II Space Launch System rocket Monday, loading more than 750,000 gallons of liquid oxygen and hydrogen, but the practice countdown was halted early Tuesday after recurring hydrogen leaks.
The countdown resumed at T-minus 10 minutes around 12:09 a.m. EST Tuesday, moving toward a simulated engine start. About four-and-a-half minutes later it stopped because of a liquid hydrogen leak at the interface of the tail service mast umbilical, which had already shown high concentrations of liquid hydrogen earlier in the countdown, NASA said.
The SLS mobile launch platform has two tail service masts at the rocket’s base that carry propellant lines to pull-away umbilical assemblies at the booster engine compartment. NASA said the launch control team was working to place the rocket in a safe configuration and begin draining its tanks.
Whether managers can clear the rocket to launch as early as Super Bowl Sunday for a nine-day, two-hour lunar mission with four astronauts — commander Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen — will depend on an overnight review and post-test analysis. NASA has three available launch days this month (Feb. 8, 10 and 11); missing those would push the flight into March. Hydrogen leaks are notoriously difficult to repair at the pad, and a Sunday liftoff appears unlikely unless the leak is judged 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. After 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 supercold liquid oxygen and hydrogen filled the SLS first stage tanks and hydrogen flowed into the upper stage.
A leak was detected at an umbilical plate where a pad fuel line connects to the SLS first stage when that tank was about 55% full. Engineers paused, then resumed fueling, cutting off again at about 77% full. They decided to continue, expecting the leak to decline once the tank reached full and entered replenishment mode. NASA later reported the core stage had been filled with liquid hydrogen and that concentrations at the tail service mast umbilical remained within acceptable limits earlier in the sequence.
The countdown had been timed to simulate a 9 p.m. EST launch but ran longer than planned and entered an extended hold at T-minus 10 minutes. After resuming just after midnight, it was stopped finally at T-minus 5 minutes and 15 seconds due to the detected tail service mast umbilical leak.
The 332-foot SLS is the launcher NASA will use to send Orion crew capsules and Artemis astronauts to the moon. It is powered by two strap-on solid rocket boosters and four main engines burning liquid oxygen and hydrogen that produce about 8.8 million pounds of thrust at liftoff. Its first flight was Artemis I in 2022, an uncrewed test that encountered fuel leaks and propellant flow issues that delayed that launch for months. Many upgrades were made for Artemis II, and officials said lessons learned from Artemis I informed fueling procedures. Still, the tail service mast umbilical leak that appeared in 2022 has recurred in this campaign.