Boeing said Friday that its Starliner spacecraft will be grounded indefinitely while it continues to investigate problems with the valves in the propulsion system.

In the 10 days since Boeing and NASA scrubbed the launch in Florida, technicians and engineers have sought to open 13 valves that control the flow of dinitrogen tetroxide (NTO) oxidizer through the service module of the spacecraft. There are 24 oxidizer valves in the propulsion system, which is critical both for in-space travel as well as launch emergency escapes.

Boeing has been able to open nine of the valves, said John Vollmer, vice president and program manager of Boeing’s Commercial Crew Program. The other four remain stuck. As a result, the company plans to de-stack the Starliner spacecraft from its Atlas V rocket and move it to the nearby Commercial Crew and Cargo Processing Facility deeper troubleshooting.