NASA has announced that two astronauts who flew to the International Space Station (ISS) aboard Boeing's troubled Starliner capsule in June will now return to Earth on a SpaceX vehicle early next year. This decision stems from ongoing issues with Starliner’s propulsion system, which NASA has deemed too risky for a crewed return. The move to rely on Boeing's rival, SpaceX, marks one of NASA's most significant decisions in recent years.

Boeing had hoped the mission would revive confidence in its Starliner program, which has been plagued by years of setbacks and cost overruns exceeding $1.6 billion since 2016. The aerospace giant is also facing quality control issues in the production of its commercial planes.

Veteran NASA astronauts Butch Wilmore and Sunita Williams made history on June 5 as the first crew to ride the Starliner to the ISS. Originally intended as an eight-day test mission, the flight quickly ran into problems. Just 24 hours after launch, Starliner’s propulsion system encountered multiple glitches, leading to months of delays. Five out of its 28 thrusters failed, and several helium leaks occurred, a critical issue since helium is used to pressurize the thrusters.

In a rare change in NASA’s astronaut operations, Wilmore and Williams are now expected to return to Earth in February 2025 aboard a SpaceX Crew Dragon spacecraft, which will launch as part of a regular astronaut rotation mission. Two seats on the Crew Dragon will be reserved for the pair. Meanwhile, Starliner will undock from the ISS and attempt to return to Earth without a crew.

Boeing has faced numerous challenges in developing Starliner, a capsule designed to provide a second U.S. option for ferrying astronauts to and from Earth’s orbit, competing with SpaceX’s Crew Dragon. In 2019, Starliner failed an uncrewed test mission to the ISS, though it largely succeeded in a second attempt in 2022, despite ongoing thruster problems. The June mission with Wilmore and Williams was meant to be the final test required for NASA to certify the Starliner for regular astronaut missions. However, the future of that certification is now uncertain.

Since Starliner’s June docking at the ISS, Boeing has been investigating the thruster malfunctions and helium leaks. The company has conducted tests and simulations on Earth in an effort to prove to NASA that Starliner is safe for crewed flights. However, the results of these tests have raised additional engineering concerns, ultimately failing to ease NASA’s worries about Starliner’s ability to safely complete its crewed return trip—the most critical and challenging phase of the mission.

NASA’s decision and the resulting uncertainty around Starliner’s certification add to the mounting challenges for Boeing’s new CEO, Kelly Ortberg, who took the helm earlier this month. Ortberg is focused on restoring Boeing’s reputation after a series of crises, including a dramatic incident in January when a door panel blew off a Boeing 737 MAX passenger jet mid-flight.