NASA is gearing up for a simulated launch of the Artemis II mega moon rocket tonight after cold weather pushed back the mission's earliest potential lift-off to later this week.

Artemis II and its four-person crew will now leave Earth for the moon as early as Sunday (Feb. 8), two days later than the previous earliest window, according to a statement released by NASA.

"Over the past several days, engineers have been closely monitoring conditions as cold weather and winds move through Florida," a NASA spokesperson wrote in the statement. "Managers have assessed hardware capabilities against the projected forecast given the rare arctic outbreak affecting the state and decided to change the timeline."

NASA needs to get through a simulated launch before the space agency can proceed with an actual launch. The simulated launch is part of a "wet dress rehearsal," during which engineers test fueling the Artemis II rocket. This was originally scheduled for as early as Jan. 31, but NASA is now targeting Monday (Feb. 2), with the simulated launch window beginning at 9 p.m. ET. The space agency said that the test is expected to go on until around 1 a.m. ET (Feb. 3).

Any date that NASA targets for a test or launch is subject to change. The tricky nature of space travel means that delays are often part of the process, so we can expect NASA to postpone the earliest launch window again if weather conditions aren't favorable, or if technical issues emerge. The potential launch windows for Artemis II extend to no later than April 2026.

The Artemis Program is no stranger to delays. Artemis I returned to NASA's Vehicle Assembly Building twice in 2022 following issues during wet dress rehearsals. The uncrewed rocket ultimately took off during NASA's fourth attempt at a launch in November 2022. Artemis II has already been delayed multiple times, in part so that mission engineers can better understand issues that arose during Artemis I.

Artemis II's upcoming mission is the first time in more than 50 years that NASA is sending humans to the moon, and the first time that a woman will be part of the crew. The mission's Orion spacecraft will loop around the moon on a 10-day flight, testing systems ahead of the Artemis III lunar surface mission, which is scheduled for 2028.

NASA wheeled out Artemis II's Space Launch System (SLS) rocket and Orion spacecraft on Jan. 17. With a 212-foot-tall (65 meters) core stage and a total height of 322 feet (98 m) with the Orion crew capsule on top, the structure is taller than the Statue of Liberty.

Engineers have kept Orion powered on with its heaters running during the cold weather, according to NASA. The space agency previously noted that its engineers have been troubleshooting issues in the lead-up to launch. For example, they worked on leaky ground-support hardware that is needed to supply Orion with oxygen.

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.

NASA intends to send three of its astronauts on Artemis II: 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 in quarantine in Houston since Jan. 23. Astronauts go into quarantine ahead of a launch so that they don't pick up any illnesses that could delay their mission. NASA plans to fly the crew to Florida about six days ahead of launch. However, in the statement announcing the delay, NASA said its managers were "assessing the timeline" for the crew's arrival.

NASA hopes that the Artemis Program will lead to a sustained presence on the moon and serve as a stepping stone for sending humans to Mars.

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.