NASA has once again postponed one of the key milestones of its lunar program. The crewed test flyby of the Moon under the Artemis II mission, originally scheduled for early February 2026, has been pushed back until at least March. The official reason is a liquid hydrogen leak detected during fueling of the super-heavy Space Launch System (SLS) rocket in a wet dress rehearsal. But how critical — and how typical — is this for such systems? Alexander Bon, head of the Small Spacecraft Project at the Moscow Aviation Institute’s Space Technology Center, explained the situation to Gazeta.Ru.

What Happened at the Launch Site

On February 3, 2026, NASA engineers were conducting a final rehearsal of pre-launch procedures — fueling the rocket with cryogenic propellants and running a countdown. Everything proceeded as planned until sensors detected an elevated hydrogen leak in the aft section of the launch vehicle, near the Tail Service Mast Umbilical (TSMU) interface, while the core stage was being filled.

The automated system halted the countdown about five minutes before “zero,” once the leak exceeded allowable limits.

As a result, the test was not fully completed, and the February launch window (through February 11) was closed. NASA is now targeting March as the earliest opportunity — specifically the windows of March 6–9 and March 11 — with April options available if additional time is needed for refinements.

This is not the first such incident involving the SLS: similar hydrogen leaks in the same area affected the rocket ahead of Artemis I in 2022. The fact that the issue has not been completely resolved in three years raises questions among experts.

Why Hydrogen “Leaks”: Physics Meets Reality

Bon emphasizes that liquid hydrogen leaks are not uncommon in super-heavy rockets that use this fuel.

“Calling such situations ‘normal’ would be incorrect, but hydrogen systems are indeed prone to leaks. This is due to the physical properties of hydrogen: it is extremely fluid, can penetrate microscopic pores in materials, and can make the metals used in pipelines and tanks more brittle.”

Hydrogen is the lightest element, and its molecules can seep through even well-designed seals. At cryogenic temperatures (around −253°C), materials contract, seals lose elasticity, and microcracks become more pronounced. Predicting the exact location and timing of a leak is extremely difficult — which is why it is far better to detect the problem on the ground than during flight, when nothing can be repaired.

The expert adds that launch delays are rarely caused by a single malfunction. The decision typically reflects a combination of technical, organizational, and weather-related factors. The hydrogen leak may have been the “final straw,” while other minor deviations accumulated behind the scenes.

Safety Above All

After the Challenger and Columbia shuttle disasters, the approach to crewed spaceflight changed dramatically.

“Since the early days of the space race — and especially after the shuttle catastrophes — attitudes toward crewed flight safety have fundamentally shifted. In the past, the loss of a crew, tragic as it was, did not necessarily end a program. In the 21st century, society and governments are not prepared to accept that. Today, a launch can be canceled over even the smallest technical malfunction or unfavorable weather conditions. So the reasons can be numerous,” Bon notes.

For Artemis II — the first time in half a century that astronauts will head toward the Moon — risk is unacceptable. Even a minor leak that might have gone unnoticed during the uncrewed Artemis I mission is enough to halt the entire process when human lives are involved.

What Comes Next

NASA engineers have already replaced the seals in the problematic TSMU area, are analyzing the removed components, and plan to conduct another wet dress rehearsal. If everything goes smoothly, the March window remains realistic.

The Artemis program as a whole is not under threat — delays of a month or two still fit within the broader timeline of returning humans to the Moon by the end of the decade.

In Brief

NASA has postponed Artemis II — the first crewed lunar flyby — from February to March 2026 due to a liquid hydrogen leak detected during SLS fueling in a rehearsal. MAI expert Alexander Bon explains that such leaks are a typical challenge for hydrogen systems because of the fuel’s physical properties, and it is far better to find them on Earth. The delay is not a sign of panic but standard caution in an era of zero tolerance for crew risk. There may have been multiple contributing factors, but safety outweighs schedule.