The announcement comes as President-elect Donald Trump prepares to take office in January and could significantly reshape the direction of the US space agency.

Artemis, named after Apollo's twin sister in Greek mythology, was unveiled in 2017 as NASA's ambitious program to establish a long-term presence on the Moon and apply those lessons to eventual Mars missions.

Its first mission, Artemis 1, was an uncrewed test flight to the Moon and back in 2022 after multiple delays.

But teams reviewing the data later learned that Orion's heat shield eroded in unexpected ways, and there were also issues with its electrical and life support systems.

"We were able to recreate the problem here on Earth, and now we know the root cause, and this has allowed us to devise a path forward," NASA Administrator Bill Nelson told reporters during a press conference.

The problems have pushed back the entire Artemis timeline. Artemis 2, a crewed lunar flyby, has been delayed from September 2025 to April 2026. Artemis 3, intended to see the first woman and first person of color set foot on the Moon's ice-rich south pole, is now slated for "mid-2027."

"That will be well ahead of the Chinese government's announced intention that they have already publicly stated of 2030," added Nelson. "The safety of our astronauts is always first in our decisions. It is our North Star. We do not fly until we are ready."

NASA Deputy Administrator Pam Melroy elaborated on the heat shield issue, explaining that during atmospheric reentry, gases built up inside the shield, creating internal pressure that caused cracking and pieces to fall away.

In addition to Orion's troubles, NASA is awaiting a modified version of SpaceX's Starship rocket to serve as a lunar lander.

Although SpaceX is making rapid progress through flight tests, it still faces significant hurdles, including proving it can perform complex refueling in orbit. The spacesuits for Artemis, developed by Axiom, also remain under development.

Trump on Wednesday nominated Jared Isaacman to lead NASA, signaling a likely shift toward even greater collaboration with the commercial space sector in his second term.

Observers anticipate sweeping changes -- from possibly canceling the expensive Space Launch System (SLS) rocket used for Artemis to scrapping the Moon mission altogether in favor of Mars.

- 'Keep out' -

Nelson, however, defended the Moon-first strategy, citing the importance of prospecting its south pole for water ice deposits that could sustain human bases and provide rocket fuel for missions deeper into space.

"It's important, in an area where we think there is such promise...that we establish our presence there, so that China would not be there and say 'keep out.'"

Isaacman's nomination has raised concerns about potential conflicts of interest, given his close financial ties to SpaceX chief Elon Musk, who is both a key advisor to Trump and set to co-lead a government efficiency commission.

The 41-year-old founder of Shift4 Payments became the first private citizen to perform a spacewalk back in September during a SpaceX mission. He has also publicly advocated against NASA selecting Jeff Bezos' Blue Origin to develop a second lunar landing system, arguing that Starship alone is sufficient.

Nelson stressed: "We have contracts with two companies for landers -- as long as we're a nation of the rule of law, those contracts are going to be operative."

But he also struck a diplomatic tone, saying he had called Isaacman to congratulate him and remained "optimistic" about NASA's future under the new administration.