Third Attempt of NASA’s Megarocket Rehearsal Foiled by Hydrogen Leak

NASA’s third attempt at a modified rehearsal of the Space Launch System (SLS) came to a halt on Thursday when a leak of liquid hydrogen was detected during tanking operations. The space agency is planning another wet dress rehearsal for the Moon rocket no earlier than April 21.

This is the latest in several setbacks to the rocket’s wet dress rehearsal, including delays due to weather, malfunctioning ventilation fans, and valve issues.

“All the issues that we’re encountering are procedural and lessons learned,” Mike Sarafin, Artemis mission manager, said during a press conference on Friday.

A wet dress rehearsal is when the 322-foot rocket is filled with fuel as it sits on top of a launch pad, and the team runs through a mock countdown to prepare for the day of launch. The rehearsal is critical for the launch of Artemis I, an uncrewed mission to the Moon and back, and the first step to returning humans to the Moon by the year 2026.

This wet dress rehearsal was first scheduled for April 1, but was initially delayed due to technical issues that prevented the crew from loading the rocket up with fuel. Before the next test date on April 11, the team discovered a faulty valve, which led them to modify the rehearsal and plan on only fueling the SLS core stage, and not its upper stage.

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Thursday’s third attempt was unfortunately not the charm, as the team discovered a leak of liquid hydrogen from the tail service mast umbilical, which connects the base of the mobile launcher to the core stage. Liquid hydrogen is one of two propellants used for the rocket, the other being liquid oxygen.

By the time the wet dress rehearsal was shut down, about 49% of the tank was filled with liquid oxygen, and only 5% of the other tank was filled with liquid hydrogen. The team successfully managed to cool down the lines used to load propellant into the upper stage, but were not able to flow any propellant to the stage due an issue with a valve.

Still, the team behind the SLS rocket say they aren’t giving up. “There’s no doubt in my mind that we will finish this test campaign, and that we will look into the hardware and the data will lead us to the next steps,” Charlie Blackwell-Thompson, Artemis launch director, said during the teleconference. “We will launch this vehicle… and we will be ready to go fly.”