Boeing's troubled Starliner spacecraft is facing yet another setback, this time due to a persistent helium leak.

The leak, discovered during pre-flight preparations for the upcoming Orbital Flight Test-3 (OFT-3), has forced an indefinite delay in the launch.

This latest complication adds to a long string of misfortunes that have plagued the program since its inception, pushing back the timeline for the Starliner to become a fully operational crew transportation vehicle to the International Space Station.

While Boeing has not disclosed the precise location or severity of the leak, the fact that it involves helium – a crucial component for pressurizing and conditioning the spacecraft's systems – underscores the critical nature of the problem.

Helium leaks are notoriously difficult to pinpoint and repair, particularly in the complex environment of a spacecraft.

The delay is likely to involve extensive diagnostic testing to locate the leak's source and implement a reliable fix, potentially necessitating significant disassembly and reassembly of affected components.

This latest delay is a significant blow to Boeing and NASA.

OFT-3 is crucial for demonstrating the Starliner's capability to successfully dock with the ISS and return crew safely to Earth.

The mission's repeated postponement undermines confidence in the program's readiness and raises questions about its overall cost-effectiveness and reliability.

The delay also impacts NASA's broader plans for human spaceflight, as the Starliner is intended to provide an independent, commercial crew transportation system alongside SpaceX's Crew Dragon.

With the persistent issues, NASA might have to rely more heavily on Crew Dragon for future missions, potentially impacting budget allocations and mission scheduling.

The ongoing challenges faced by the Starliner highlight the complex engineering and logistical hurdles involved in developing and deploying reliable spacecraft.

While Boeing is working diligently to resolve the issue, the indefinite nature of the delay underscores the unpredictable nature of space exploration and the potential for unexpected setbacks even in advanced, well-funded programs.

The ultimate impact of this helium leak on the Starliner's future and NASA's broader plans remains to be seen, but it undeniably represents another significant hurdle in the program's already difficult journey.

The launch of Boeing's is slipping at least four more days, from next Tuesday to 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 co-pilot Sunita Williams are now aiming for launch from Pad 41 at Florida's Cape Canaveral Space Force Station at 3:09 p.m. EDT a week from Saturday, setting up a docking at the International Space Station the next day, May 26, at 4:12 p.m.

The astronauts had hoped to take off on the Starliner's first piloted test flight on May 6, but the countdown because of trouble with an oxygen pressure relief valve in their Atlas 5 rocket's Centaur upper stage.

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

The unrelated helium leak in the Starliner's propellant pressurization system was noted during the original countdown to launch, but it remained within safe limits for flight. After the Atlas 5 and Starliner were rolled back to the VIF for the oxygen valve replacement, managers decided to take a closer look at the helium issue.

The leak was detected in plumbing making up helium manifold No. 2 inside one of four "doghouse" assemblies spaced around the exterior of the Starliner's drum-shaped service module. Each doghouse features four Orbital Maneuvering and Attitude Control — OMAC — thrusters, and four small reaction control system maneuvering jets.

Pressurized helium gas is used to push propellants to the rocket motors in each doghouse, as well as to four powerful launch abort engines that would only be fired in the event of a catastrophic problem with the Atlas 5 on the way to orbit.

Engineers tightened bolts in a flange where the leak was detected, pressurized the lines and then ran tests to determine if the leak was still present. In the meantime, launch was re-targeted for May 21.

But as it turned out, tests revealed the leak was still present. Mission managers considered a range of options for resolving the issue, but they decided Friday to press ahead toward a launch opportunity on May 25, pending additional data reviews and analysis to show the leak, which is currently stable and within acceptable limits, will not worsen in flight.

"Pressure testing...showed the leak in the flange is stable and would not pose a risk at that level during the flight," NASA said in a blog post. "The testing also indicated the rest of the thruster system is sealed effectively across the entire service module.

"Boeing teams are working to develop operational procedures to ensure the system retains sufficient performance capability and appropriate redundancy during the flight. As that work proceeds, (mission managers) will take the next few days to review the data and procedures to make a final determination before proceeding to flight countdown."

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

The Starliner is one of two commercially developed crew ferry ships ordered by NASA in the wake of the shuttle program's retirement in 2011. SpaceX won a contract valued at $2.6 billion for development of and Boeing was awarded $4.2 billion for development of the Starliner.

NASA wanted spacecraft from different builders to ensure the agency would still have a way to get astronauts to the space station even if a problem grounded one company's ferry ship.

SpaceX launched its first two-man 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. In all, 50 people have flown to space aboard Crew Dragons.

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

Engineers ran into questions about parachute harness connectors and protective tape wrapped around wiring that posed a fire risk in a short circuit. Work to correct those issues and others delayed the first piloted launch to this month.