Faced with stormy weather ahead of Tropical Storm Ian, which is expected to become a hurricane, NASA managers on Saturday ruled out a third attempt to launch the Artemis 1 moon rocket Tuesday but held open the option of making a run at blastoff on October 2, the current backup date.

That would require leaving the $4.1 billion 330-foot-tall Space Launch System rocket exposed to the elements atop pad 39B, assuming assurance from forecasters winds would not exceed 74 knots, the certified safety limit.

NASA Artemis 1 management team deferred making a decision on whether to haul the moon rocket back to the protection of the Vehicle Assembly Building in hopes of a more favorable forecast that would allow it to ride out the weather at the launch pad.

A decision is expected Sunday. If a rollback is ordered, the 4.2-mile-trip from pad 39B to the iconic Vehicle Assembly Building would begin late Sunday or early Monday.

That would allow the agency “to protect its employees by completing a safe roll in time for them to address the needs of their families while also protecting for the option to press ahead with another launch opportunity in the current window if weather predictions improve,” NASA said in a blog post.

The Space Launch System rocket is the most powerful ever built for NASA, a gargantuan booster that will generate 8.8 million pounds of thrust at liftoff, enough to propel Orion crew ships into lunar orbit.

The rocket’s upcoming maiden flight — the Artemis 1 mission — will be unpiloted. But NASA hopes to launch four astronauts on an around-the-moon trip in 2024 followed by a landing near the south pole in the Artemis 3 mission, optimistically targeted for launch in the 2025-26 timeframe.

The SLS rocket can only head for the moon during launch periods allowing carefully mapped out trajectories that take into account a wide variety of factors, including the ever changing positions of the Earth and moon, the desired lunar orbit, proper lighting for Orion’s solar arrays and optimized communications.

The current lunar launch period closes October 4, seven days beyond Tuesday. But two of those days — October 29 and 30 — are not available because of trajectory constraints and three feature launch windows less than an hour long.

NASA earlier reserved October 2 as a backup launch date and that’s the target the agency is protecting by deferring a rollback decision to Sunday. If forecasters can give NASA managers confidence the rocket will not be buffeted by winds gusting above 74 knots, the SLS booster may be able to ride out the weather at the pad, preserving the October 2 option.

But if the rocket isn’t off the pad by October 4, the end of the currently launch period, it faces rollback to the VAB anyway to service batteries in its self-destruct system that cannot be accessed at the launch pad.

The Space Force Eastern Range, which oversees all military and civilian launches from Florida, earlier extended a battery servicing waiver to allow launches through the end of the current period, but it’s not know what options might be available after that. The next launch period opens October 17 and runs through October 31.