Boeing’s new Starliner spacecraft’s maiden human trip has been rescheduled for May 25, an extra four days later.

The launch date for Starliner’s Crew Flight Test (CFT), which is scheduled to transport NASA astronauts Suni Williams and Butch Wilmore to the International Space Station (ISS) for an approximately week-long stay, had been set for Tuesday, May 21.

However, NASA said on May 17 that it is now targeting May 25 for the launch, which will occur from Cape Canaveral Space Force Station, located on Florida’s Space Coast, atop an Atlas V rocket operated by the United Launch Alliance (ULA).

“The additional time allows teams to further assess a small helium leak in the Boeing Starliner spacecraft’s service module traced to a flange on a single reaction control system thruster,” agency officials wrote in an update.

Following the discovery of the leak earlier this week, the mission team decided to postpone the scheduled launch of CFT until May 21. According to an update from agency officials, further investigation into the leak indicates that it may not be a major issue, but NASA, Boeing, and ULA want additional time to evaluate the matter.

“Pressure testing performed on May 15 on the spacecraft’s helium system showed the leak in the flange is stable and would not pose a risk at that level during the flight,” the update states.

“The testing also indicated the rest of the thruster system is sealed effectively across the entire service module,” it keeps going. “Boeing teams are working to develop operational procedures to ensure the system retains sufficient performance capability and appropriate redundancy during the flight.”

The launch team discovered a “buzzing” valve in the upper stage of the Atlas V a few hours before liftoff, which caused CFT to be canceled from its initial May 6 launch date. In the end, ULA chose to replace the valve, which meant moving the Starliner and Atlas V off the pad and back into an assembly facility. Due to the helium leak, the original launch date was shifted to today, which was not feasible.

Starliner is still inside the assembly facility, along with its rocket ride. Meanwhile, in Houston, Williams and Wilmore are under quarantine. When the intended launch date approaches, they’ll head back to Florida’s Space Coast, according to a NASA report.

In 2014, NASA’s Commercial Crew Program granted Boeing a $4.2 billion contract to develop and operate Starliner. A comparable $2.6 billion arrangement was made with SpaceX for the development of their Dragon capsule.

Currently, SpaceX is in the middle of its eighth contractual, extended-duration astronaut trip to the International Space Station (ISS) on behalf of NASA. The first crewed trip for Starliner, CFT will be akin to SpaceX’s Demo-2 mission, a test flight that was launched in May 2020.