NASA engineers and contractor teams successfully loaded more than 750,000 gallons of supercold propellants into the agency’s towering Space Launch System on Thursday, marking a major milestone toward launching four astronauts on a historic lunar flyby mission as early as March 6.
The fueling exercise, part of a full “wet dress rehearsal,” unfolded without the hydrogen leaks that plagued an earlier attempt this month. The smooth test has significantly strengthened confidence that the rocket and its ground systems are ready to support the Artemis program’s first crewed mission.
A full Moon is seen shining over NASA’s SLS (Space Launch System) and Orion spacecraft, atop the mobile launcher in the early hours of February 1, 2026. Credi: tNASA/Sam Lott
The practice countdown began Tuesday night and proceeded through a meticulously choreographed series of milestones, culminating in a simulated T-0 at 8:42 p.m. EST Thursday. Controllers then ran additional procedures designed to demonstrate they can recycle, hold, and restart the countdown — critical capabilities should technical or weather issues arise on launch day.
At 9:35 a.m. Thursday, Launch Director Charlie Blackwell-Thompson gave the “go” to begin tanking operations. Over several hours, teams pumped approximately 196,000 gallons of liquid oxygen and 537,000 gallons of liquid hydrogen into the rocket’s massive core stage. The upper stage was filled with an additional 22,500 gallons of cryogenic propellants.
Unlike the previous fueling test, when hydrogen leaks forced an early shutdown, sensors this time detected no significant leakage. The rocket’s tanks were filled and topped off as expected, with teams replenishing small amounts of propellant lost to normal boil-off — a common occurrence when handling ultra-cold liquid hydrogen and oxygen.
In the final 10 minutes of the countdown, engineers pressurized the propellant tanks as they would for an actual launch. Again, no major issues were reported — a crucial demonstration of system integrity under flight-like conditions.
Overcoming Earlier Hydrogen Leak Concerns
The success followed weeks of troubleshooting after hydrogen gas accumulations were detected during an earlier wet dress rehearsal. Sensors had picked up rising concentrations in a cavity between umbilical plates where fueling lines connect to the rocket’s core stage.
Engineers managed to complete much of that earlier test by adjusting flow rates and temperatures to keep leakage within acceptable limits. But late in the countdown, as teams began pressurizing the first stage, hydrogen concentrations spiked toward 16% within an inert nitrogen-purged cavity — a level approaching flammability risk. The test was halted before recycle procedures could be fully demonstrated.
Subsequent analysis pointed to faulty seals in the fueling umbilical system. Engineers replaced two suspect seals and conducted a smaller “mini” tanking test last week, pumping limited hydrogen into the core stage to confirm leak-free performance. Although a frozen ground-system filter restricted flow rates during that test, NASA said it gathered enough data to proceed confidently with the full rehearsal.
Thursday’s clean fueling run suggests the corrective actions were effective.
If post-test data reviews confirm preliminary results, Reid Wiseman, Victor Glover, Christina Koch, and Canadian astronaut Jeremy Hansen could be cleared for launch in just two weeks. The crew planned to enter pre-flight medical quarantine Friday in anticipation of a possible early March liftoff.
Artemis II will be the first piloted lunar mission since the final Apollo program landing in 1972. The astronauts will not land on the Moon but will travel farther from Earth than any human crew in history, executing a free-return trajectory around the lunar far side.
The mission will also mark the first time astronauts ride atop the 322-foot-tall Space Launch System — making only its second flight — and the first crewed voyage of NASA’s Orion spacecraft.
Beyond its symbolic importance, Artemis II is a proving ground for deep-space life support systems, navigation, communications, and re-entry performance ahead of the planned Artemis III mission, which aims to land astronauts near the Moon’s south pole in 2028.
NASA had initially targeted an early February launch but was forced to delay after the first fueling rehearsal exposed the hydrogen leak concerns. With Thursday’s successful test, the agency appears back on track — pending detailed engineering reviews — for a launch window that could open March 6.
For NASA and its international partners, the clean tanking demonstration represents more than a technical achievement. It is a critical step toward restoring human deep-space exploration capability and returning astronauts to the lunar frontier for the first time in more than half a century.
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