Artemis II won't lift off for the moon this week after an overnight launch rehearsal revealed that NASA's mega moon rocket is leaking hydrogen fuel.

The Artemis II mission was scheduled to take four astronauts on a 10-day trip around the moon as early as Sunday (Feb. 8). But now NASA is targeting March at the earliest for the historic launch, which will be the space agency's first attempt to send humans back to the moon in more than 50 years.

"With more than three years between SLS launches, we fully anticipated encountering challenges," NASA administrator Jared Isaacman wrote on the social platform X. "That is precisely why we conduct a wet dress rehearsal. These tests are designed to surface issues before flight and set up launch day with the highest probability of success."

During a wet dress rehearsal, NASA's crew demonstrates its ability to fill the rocket with more than 700,000 gallons (2.6 million liters) of cryogenic propellants — super-cold liquid hydrogen fuel and liquid oxygen oxidizer. It's a delicate process at the best of times, but this time NASA has also been grappling with an Arctic blast of cold weather.

The blast delayed the wet dress rehearsal, which was originally scheduled for last week, and caused a late start yesterday because of a small hydrogen leak, which engineers resolved by warming up some components before they loaded the propellant, according to a statement released by NASA.

NASA's staff were able to finish fueling the rocket's tanks and began a countdown to a simulated launch. However, with around five minutes left on the clock, the ground launch sequencer (a software program that automates command and control procedures) halted the countdown because of a spike in the liquid hydrogen leak rate. The test was then scrubbed.

The leaks appear similar to the issues Artemis I experienced in 2022, Live Science's sister site Space.com reported. Liquid hydrogen was involved then and also occurred at an interface with the tail service mast umbilical, which carries propellant fuel from NASA's mobile launch tower to the SLS.

IN CONTEXT

IN CONTEXT

There's a reason why "blame hydrogen" is a common in-joke in the spaceflight community. The fuel has bedevilled NASA's launches and caused countless scrubs since the years of the space shuttle, the SLS's predecessor upon which its design is modeled.

As the smallest molecule, hydrogen can readily pass through solid metals by diffusing through atomic lattices. And with a boiling point of minus 423 degrees Fahrenheit (minus 253 Celsius, or 20 kelvins), it must be stored at extremely cold temperatures that freeze seals beyond safe limits. However, it remains the most efficient, clean-burning propellant, making it NASA's fuel of choice.

Teething issues

The hydrogen leak wasn't the only issue that occurred during NASA's two-day test. There were also audio communications dropouts, a recently replaced valve on the Orion crew capsule needed retorquing, and the cold weather affected cameras and other equipment that would have required attention on launch day, according to NASA.

However, the space agency said that its engineers "pushed through several challenges" during the test and met many of its objectives. NASA will now review the test data before attempting a second wet dress rehearsal.

Once Artemis II clears the wet dress rehearsal and simulated launch stage, NASA will conduct a flight-readiness review before committing to a launch date. The March windows include March 6 to 9 and March 11. If Artemis II doesn't fly on one of those days, it will be delayed until April. The mission is meant to launch no later than April 30.

If Artemis II makes a successful trip around the moon, then NASA will have tested systems and gathered data ahead of Artemis III, which aims to put people on the moon in 2028. Artemis II also marks the first time NASA is sending a woman and a Black man to the moon.

The Artemis II crew includes three NASA astronauts; Commander Reid Wiseman, pilot Victor Glover, and mission specialist Christina Koch, along with Canadian Space Agency astronaut and mission specialist Jeremy Hansen.

The crew has been quarantining in Houston since Jan. 21. Astronauts go into quarantine ahead of a launch to ensure they don't get infected by illnesses that could delay their mission. NASA said in its latest statement that the crew will now be released from quarantine for the time being, before reentering about two weeks before the next launch target.

"As always, safety remains our top priority, for our astronauts, our workforce, our systems, and the public," Isaacman wrote on X. "We will only launch when we believe we are as ready to undertake this historic mission."

NASA plans to host a news conference at 1 p.m. ET on Tuesday (Feb. 3) to discuss initial results from the wet dress rehearsal. You can stream the news conference on NASA's YouTube channel, which also provides a live feed of Artemis II sitting on the launch pad at the Kennedy Space Center.

Patrick Pester is the trending news writer at Live Science. His work has appeared on other science websites, such as BBC Science Focus and Scientific American. Patrick retrained as a journalist after spending his early career working in zoos and wildlife conservation. He was awarded the Master's Excellence Scholarship to study at Cardiff University where he completed a master's degree in international journalism. He also has a second master's degree in biodiversity, evolution and conservation in action from Middlesex University London. When he isn't writing news, Patrick investigates the sale of human remains.