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With just minutes remaining before takeoff, NASA and Boeing decided to delay the highly anticipated crewed launch of the Starliner spacecraft again.

Astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams were aboard the Starliner, which was set to launch from Cape Canaveral Space Force Station on Saturday afternoon. However, the mission was called off with 3 minutes and 50 seconds left in the countdown. The exact cause of this latest delay has yet to be revealed.

The original launch, planned for May 6, was postponed due to a valve problem. A second attempt on May 14 was also aborted, this time because of a propellant leak and additional testing requirements.

These delays add to Boeing’s challenges as it competes with Elon Musk’s SpaceX and Jeff Bezos’s Blue Origin, both of which were authorized for commercial space flights in 2014. Boeing has tentatively rescheduled the launch for Sunday at 12:03 p.m. EDT, pending the resolution of the latest issue.