What technical issue centered on the Boeing Starliner propulsion system causing the extended stay?

Problems detected with the reaction control system (RCS) thrusters

The core issue that led to the extended orbiting period for Butch Wilmore and Suni Williams involved vexing technical challenges centered specifically on the spacecraft’s propulsion system. More precisely, initial indicators of trouble surfaced regarding the performance of the reaction control system (RCS) thrusters, which are small engines critical for controlling the capsule’s attitude and orientation. Although the capsule was safe, the underperformance or outright failure of several of these thrusters raised significant concerns because a full complement of healthy engines is essential for executing the complex, precise multiple-burn maneuvers required for a safe deorbit and reentry sequence. The root cause analysis pointed towards leaks within the propellant lines feeding these RCS thrusters, which jeopardized the necessary pressure integrity for hundreds of micro-burns needed for departure.