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The first crewed test flight of Boeing’s long-delayed Starliner spacecraft will not lift off as planned on Saturday and could face a longer delay as engineers assess a persistent helium leak from the capsule’s propulsion system.

NASA announced the latest delay to the Starliner test flight late Tuesday. Officials will spend more time considering their options for how to proceed with the mission after discovering the small helium leak in the spacecraft’s service module.

The space agency did not describe what options are on the table, but sources said they range from flying the spacecraft “as is” with a full understanding of the leak and confidence it won’t become more significant during flight, to removing the capsule from its Atlas V rocket and returned it to a hangar for repairs.

In theory, the first option could allow a launch attempt as early as next week. The latter alternative could delay the launch until at least late summer.

“The team has been in meetings for two consecutive days evaluating the flight justification, system performance and redundancy,” NASA said in a statement Tuesday evening. “There is still progress in these areas and the next possible launch opportunity is still being discussed.” NASA will share more details once we have a clearer path forward.”

Delays are nothing new for the Starliner program, but it’s not yet clear how this delay will compare to the spacecraft’s previous setbacks.

Software problems disrupted an unmanned test flight in 2019, forcing Boeing to fly a second demonstration mission. The Starliner was on the launch pad when pre-flight checks revealed stuck valves in the spacecraft’s propulsion system in 2021. Boeing finally sent the Starliner on a round-trip mission to the space station in May 2022. Concerns about the Starliner’s parachutes and flammable tape in the spacecraft ship’s crew cabin delayed crewed test flight from last summer to this year.

Boeing is aiming to become the second company to fly astronauts to the space station under contract with NASA’s commercial crew program, following the start of SpaceX’s crew transport service in 2020. Assuming a smooth crewed test flight, NASA hopes to enable the Starliner spacecraft for six monthly crew rotation flights to the space station early next year.

In the doghouse

Engineers first noticed the helium leak during the first launch attempt of the Starliner’s manned test flight on May 6, but managers did not deem it significant enough to abort the launch. Ultimately, a separate problem with a pressure control valve on United Launch Alliance’s (ULA) Atlas V rocket caused officials to abandon the launch attempt.

NASA astronauts Butch Wilmore and Sonny Williams were already strapped into their seats aboard the Starliner spacecraft on the launch pad at the Cape Canaveral Space Force Station in Florida when officials called a halt to the May 6 countdown. Wilmore and Williams returned to their homes in Houston to await the next opportunity to launch the Starliner.

ULA returned the Atlas V rocket to its hangar, where technicians replaced the faulty valve in time for another launch attempt on May 17. NASA and Boeing pushed back the launch date to May 21, then to May 25 as engineers assessed a helium leak. The Atlas V rocket and Starliner spacecraft remain at ULA’s Vertical Integration Facility to await the next launch opportunity.

Boeing engineers traced the leak to a thruster flange of a single reaction control system in one of the Starliner service module’s four doghouse-shaped propulsion pods.

There are 28 reaction control system thrusters – essentially small rocket engines – on the Starliner Service Module. In orbit, these thrusters are used to make small course corrections and point the spacecraft in the right direction. The service module has two sets of more powerful thrusters for greater orbit corrections and launch abort maneuvers.

The spacecraft’s propulsion system is pressurized using helium, an inert gas. The engines burn a mixture of toxic hydrazine and nitrogen tetroxide. Helium is not flammable, so a small leak is unlikely to pose a major safety problem on earth. However, the system needs enough helium gas to force the propellants from their internal storage tanks to the Starliner’s thrusters.

In a statement last week, NASA described the helium leak as “stable” and said it would not pose a risk to the Starliner mission if it did not worsen. A Boeing spokesman declined to provide Ars with any details about the helium leak rate.

If NASA and Boeing resolve concerns about the helium leak without requiring lengthy repairs, the International Space Station could take over for Starliner docking by part of July. Once docked at the station, Wilmore and Williams will spend at least eight days at the complex before undocking to head for a parachute and hovercraft landing in the southwestern United States.

After July, the schedule gets messed up.

The space station has a busy slate of multiple visiting crews and cargo vehicles in August, including the arrival of a new team of astronauts on a SpaceX Dragon spacecraft and the departure of an outgoing crew on another Dragon. There may be an additional window for the Starliner to dock with the space station in late August or early September before the launch of SpaceX’s next cargo mission, which will occupy the docking port the Starliner must use. The dock reopens in the fall.

ULA has other high-priority missions it would like to launch from the same pad needed for the Starliner test flight. Later this summer, ULA plans to launch the U.S. Space Force’s last mission using an Atlas V rocket. ULA then aims to launch the second demonstration flight of its new Vulcan Centaur rocket — the Atlas V’s replacement — as soon as September.