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The Boeing launch already fun starliner spaceship will run for at least four more days, from next Tuesday until May 25, because of ongoing work to resolve concerns about a small helium leak in the capsule’s propulsion system, officials said Friday.

Mission Commander Barry “Butch” Wilmore and Copilot Sunita Williams are now aiming for a launch from Pad 41 at the Cape Canaveral Space Force Station in Florida at 3:09 p.m. EDT each week from Saturday, with docking established at The International Space Station day, May 26, at 4:12 p.m

Astronauts had hoped to take off on the first manned Starliner test flight on May 6, but the countdown was cancelled because of problems with an oxygen pressure relief valve in the Centaur upper stage of their Atlas 5 rocket.

Atlas 5, built by United Launch Alliance, was towed from the pad back to the company’s nearby Vertical Integration Facility, where the suspect valve was replaced and cleared for launch.

An unrelated helium leak in the Starliner’s propellant pressurization system was noted during the initial countdown to launch, but remained within safe limits for flight. After Atlas 5 and Starliner were returned to VIF for oxygen valve replacement, managers decided to take a closer look at the helium problem.

The leak was discovered in the plumbing making up Helium Manifold No. 2 inside one of the four “doghouse” modules located around the outside of the Starliner’s drum-shaped service module. Each doghouse features four Orbital Maneuvering and Attitude Control thrusters—OMACs—and four small reaction control system maneuvering nozzles.

Pressurized helium gas is used to push fuel to the rocket engines in each doghouse, as well as to four powerful launch abort engines, which would only activate in the event of a catastrophic problem with the Atlas 5 en route to orbit.

Engineers tightened the bolts in the flange where the leak was found, pressurized the lines, and then ran tests to determine if the leak was still present. Meanwhile, the launch has been rescheduled for May 21.

But as it turned out, tests showed that the leak was still there. Mission managers considered a range of options to resolve the problem, but decided Friday to move forward with the possibility of a May 25 launch, pending further data reviews and analysis to show that the leak, which is currently stable and within acceptable limits, will not deteriorate in flight.

“Pressure testing … showed that the leak in the flange was stable and would not pose a risk at this level during flight,” NASA said in a blog post. “Testing also showed that the rest of the propulsion system was effectively sealed throughout the service module.

“Boeing teams are working to develop operational procedures to ensure the system maintains sufficient performance and adequate redundancy during flight. While that work continues, (mission managers) will take the next few days to review the data and procedures to make a final decision before proceeding with the flight countdown.”

Wilmore and Williams, both veteran Navy test pilots and astronauts with four flights to the station between them, flew back to Johnson Space Center in Houston after the May 6 scrape to participate in additional flight simulations. They are expected to return to Florida next week.

The Starliner is one of two commercially developed crew shuttles ordered by NASA since the shuttle was retired in 2011. SpaceX won a $2.6 billion contract to develop the company’s Crew Dragon spacecraft and Boeing received $4.2 billion for Starliner development.

NASA wanted spacecraft from different manufacturers to ensure the agency would still have a way to get astronauts to the space station even if a problem grounded one company’s shuttle.

SpaceX launched its first two-person crew in 2020. Since then, the company has launched eight NASA-sponsored crew rotation flights to the station, three commercial research missions to the lab, and a privately funded two-man, two-woman trip to low Earth orbit. A total of 50 people have flown into space aboard Crew Dragons.

Wilmore and Williams will be the first astronauts to fly aboard the Starliner after a series of technical problems that included serious software problems during an initial unmanned test flight in December 2019 and corroded propulsion system valves that delayed a second test mission unmanned in May 2022

Engineers faced questions about the parachute harness connectors and the protective tape wrapped around the cables, which posed a fire risk in the event of a short circuit. Work to fix these issues and others delayed the first pilot launch until this month.