The launch of NASA’s unmanned Artemis 1 mission to the moon is now scheduled for September 27, with a fallback date of October 2. The agency initially considered retrying the launch as early as the 23rd, but decided to do so later after “careful consideration of many logistical issues,” reports The Verge.

The Artemis 1 mission will use NASA’s Space Launch System (SLS) megarocket to deliver an unmanned Orion capsule to the moon, the first step toward returning humans to the moon’s surface by 2025. Although the first launch attempt was stopped due to engine problems, the second attempt on September 3 ended prematurely after the Artemis 1 team discovered a liquid hydrogen leak that engineers were unable to fix.

The Artemis 1 team has now completed work to fix the problem, which involved replacing seals around the “quick disconnect” system that helps direct the cold liquid hydrogen fuel into the rocket. Engineers have scheduled a test for September 21 to see if the fast shutdown can work in the cryogenic conditions required for launch.

Also a big question is whether NASA will test the batteries in the rocket’s flight termination system, which the US Space Force can use to destroy a rocket if something goes catastrophically wrong during its flight. Testing the system will require NASA to return the SLS to the Vertical Assembly Building (VAB), a 6.5 km trip that will take hours. Ultimately, the Space Force will decide whether NASA can continue to operate without testing. NASA itself has already received a delay to extend the rocket’s certification from 20 to 25 days, but the US Space Force is still deciding whether to grant the agency another one.

NASA will attempt to launch the rocket on September 27 with a 70-minute launch window starting at 11:37 a.m. ET (6:37 p.m. Kyiv time). The launch date is between two other events: NASA plans to send an asteroid-crashing spacecraft as part of its Double Asteroid Redirect (DART) mission on September 26, and NASA and SpaceX crews will depart for the International Space Station as early as October 3.