Teams began chilling down the liquid hydrogen lines for the interim cryogenic propulsion stage of NASA’s Space Launch System (SLS) rocket. This critical step cools the propellant lines ahead of loading super-cold liquid hydrogen, chilled to minus 423 degrees Fahrenheit, into the SLS’s upper stage tank.

The Moon is seen shining over the SLS (Space Launch System) and Orion spacecraft, atop the mobile launcher on January 28, 2026, at Launch Pad 39B at NASA’s Kennedy Space Center in Florida. NASA/Sam Lott

The chill down process ensures the hardware is properly conditioned for cryogenic temperatures, reducing thermal shock and safeguarding system integrity. Once complete, teams will transition to fast fill of liquid hydrogen, followed by liquid oxygen operations later in the countdown.

During the Artemis II mission, the interim cryogenic propulsion stage, powered by an RL10 engine, will provide the in-space boost needed to send the Orion spacecraft into high Earth orbit before its translunar injection burn.

A 24/7 live stream of the rocket at the pad remains online, as well as a separate feed to capture wet dress activities.