NASA Scraps Crewed Starliner Return Due to Uncertainty Over Propulsion System

In June 2024, astronauts Suni Williams and Butch Wilmore launched aboard Boeing's Starliner spacecraft for an eight-day test flight. However, due to propulsion problems, they ended up staying in space for 286 days.

The mission was originally intended to last about eight days, but it extended far beyond that. The issue arose when five of the 28 aft reaction-control thrusters were automatically deselected after producing less thrust than commanded during the rendezvous with the International Space Station on June 6.

NASA and Boeing analyzed the problem and conducted hot-fire tests of the thrusters, studying helium leak rates and firing a comparable thruster through repeated duty cycles. They found that the heating could deform a Teflon seal in an oxidizer valve, restricting propellant flow and reducing thrust.

In August 2024, NASA decided to send Starliner back to Earth empty, citing uncertainty and a lack of expert concurrence on the system's safety and performance for human spaceflight. The spacecraft eventually made a safe autonomous descent on September 7, but this did not change the decision to keep Williams and Wilmore at the station.