Boeing Starliner Launch Delayed to Test Helium Leak Repair

A United Launch Alliance Atlas V rocket with Boeing’s CST-100 Starliner spacecraft aboard is seen as it is rolled out of the Vertical Integration Facility to the launch pad at Space Launch Complex 41 ahead of NASA’s Boeing Crew Flight Test, Saturday, May 4, 2024 at Cape Canaveral Space Force Station in Florida. (Image: NASA/Joel Kowsky)

Boeing, NASA and United Launch Alliance (ULA) are targeting a May 21 launch date for the crewed flight test of the Starliner spacecraft to the International Space Station (ISS).

Crew Space Transportation (CST)-100 Starliner  is Boeing's reusable spacecraft developed to perform crewed flights in low Earth orbit (LEO), including carrying astronauts to and from the ISS for NASA service missions. Starliner is to be launched into orbit on ULA's Atlas V rocket. Both the rocket and spacecraft experienced problems in the previously scheduled attempt at launching Starliner into orbit.

The May 6 attempt to launch Starliner was canceled on the day of the scheduled launch due to a malfunctioning oscillating pressure regulation valve on the Atlas V’s upper stage. NASA released several updates about attempted launches of Starliner last week that were both canceled and delayed due to the problems discovered on the rocket and the spacecraft.

"Out of an abundance of caution for the safety of the flight and pad crew, we scrubbed the Crew Flight Test (CFT) launch attempt today due to an observation on a liquid oxygen self-regulating solenoid relief valve on the Centaur upper stage. The team needs additional time to complete a full assessment," ULA notes in a May 7 statement  posted to its X account.

When the attempted launch was cancelled on May 6, the ULA team was able to successfully command the identified valve close and the oscillations temporarily dampened, according to NASA. The oscillations then re-occurred twice during fuel removal operations.

After evaluating the valve history, data signatures from the launch attempt, and assessing the risks relative to continued use, the ULA team determined the valve exceeded its qualification and mission managers agreed to remove and replace the valve. ULA was able to get the valve replaced on May 11, and performed re-pressurization and system purges, and tested the new valve, which performed normally.

On the spacecraft itself, Boeing detected a small helium leak within Starliner’s service module that was traced to a flange on a single reaction control system thruster. Helium is used in spacecraft thruster systems to allow the thrusters to fire and is not combustible or toxic. NASA is currently working with Boeing to develop spacecraft testing and operational solutions to address the issue.

As a part of the testing, Boeing will bring the propulsion system up to flight pressurization just as it does prior to launch, and then allow the helium system to vent naturally to validate existing data and strengthen flight rationale. Mission teams also completed a thorough review of the data from the May 6 launch attempt and are not tracking any other issues.

The Atlas V and Starliner remain in the Vertical Integration Facility at Space Launch Complex-41 on Cape Canaveral Space Force Station in Florida.

Boeing, NASA and ULA are now targeting a launch date of “no earlier than 4:43 p.m. EDT on Tuesday, May 21,” according to NASA.