NASA on Tuesday announced that it will delay the launch of the Artemis II lunar moon mission, pushing it to next month.

The mission will send four astronauts into deep space for the first time since the Apollo program ended more than 50 years ago, CNN reported.

Postponing the launch was decided early Tuesday after NASA said it had completed a wet dress rehearsal, a test of the rocket system that will launch the astronauts around the moon. The mission had been expected to launch as soon as Sunday.

NASA said it encountered several issues during the test, which had a late start due to cold weather, including running into problems with hydrogen leaks while filling up Artemis II’s Space Launch System rocket with propellant. The delay would let teams review data and conduct a second launch rehearsal, NASA said.

“With more than three years between SLS launches, we fully anticipated encountering challenges,” NASA Administrator Jared Isaacman posted on 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.”

At 1 p.m. ET on Tuesday, NASA leaders will hold a news conference to discuss the initial results from the rehearsal.

The Artemis II mission will send four astronauts — NASA’s Reid Wiseman, Victor Glover, and Christina Koch, in addition to the Canadian Space Agency’s Jeremy Hansen — on a 10-day journey beyond the far side of the moon. The mission could set a record for the farthest distance that humans have ever traveled from Earth.

After entering quarantine in Houston on Jan. 21, the astronauts will now be released, but not travel to NASA’s Kennedy Space Center in Florida on Tuesday as tentatively planned.

NASA said the astronauts will enter quarantine again about two weeks before the next targeted launch date. The agency had previously said that March 6-9 and 11 were available dates for launch.

“With March as the potential launch window, teams will fully review data from the test, mitigate each issue, and return to testing ahead of setting an official target launch date,” NASA said.