Which Boeing spacecraft experienced propulsion failures in June 2024, leaving two NASA astronauts stranded on the International Space Station?

In June 2024, the Boeing CST-100 Starliner spacecraft, on its inaugural crewed test flight, encountered significant propulsion system failures while en route to the International Space Station. This critical mission, carrying NASA astronauts Butch Wilmore and Suni Williams, was intended to certify Starliner as a second commercial vehicle for transporting astronauts to and from the orbiting laboratory, complementing SpaceX's Crew Dragon. However, the spacecraft experienced multiple thruster malfunctions and helium leaks, which severely compromised its maneuverability and ability to safely return to Earth.

These unexpected issues led to an dramatic extension of the mission. Originally slated for a brief 8-to-14-day stay, astronauts Wilmore and Williams remained aboard the International Space Station for 93 days as engineers on Earth meticulously analyzed the anomalies and conducted extensive ground testing. Ultimately, NASA made the unprecedented decision to send the Starliner back to Earth uncrewed in September 2024. The astronauts eventually returned safely to Earth in March 2025, aboard a SpaceX Crew Dragon capsule.

NASA later classified the Starliner incident as a "Type A mishap," its highest classification, reserved for incidents with the potential for severe consequences or significant financial damage. A comprehensive investigation into the failures revealed a complex interplay of factors, including hardware deficiencies, gaps in qualification testing, leadership missteps, and broader cultural breakdowns within both Boeing and NASA. This event underscored the significant challenges and rigorous safety standards inherent in human spaceflight, highlighting the ongoing efforts to ensure reliable and safe transportation to space.