The target launch date for Boeing’s oft-delayed CST-100 Starliner capsule has been shifted again. The Crewed Flight Test of the vehicle is now targeted for May 21 at 4:14 PM EDT.

According to Boeing, “Starliner teams are working to resolve a small helium leak detected in the spacecraft’s service module traced to a flange on a single reaction control system thruster. Helium is used in spacecraft thruster systems to allow the thrusters to fire and is not combustible or toxic.”

Atlas V Valve Issue Has Been Repaired

This comes after a scrub on May 6 due to a valve issue with United Launch Alliance’s Centaur upper stage of the Atlas V booster. This necessitated the vehicle being rolled back from the launch pad to the Vertical Integration Facility (VIF) at Space Launch Complex 41. Boeing says that the valve repairs on the Centaur stage are now complete, which implies that the sole reason for the new delay is the new issue with Starliner.

“On May 11, the ULA team successfully replaced a pressure regulation valve on the liquid oxygen tank on the Atlas V rocket’s Centaur upper stage. The team also performed re-pressurization and system purges, and tested the new valve, which performed normally,” Boeing said in today’s release.

CFT Astronauts Are Back In Houston

Boeing also says that “NASA astronauts Butch Wilmore and Suni Williams, still in preflight quarantine, returned to Houston on May 10 to spend extra time with their families as prelaunch operations progress.”