Starliner has been plagued by issues even before launch. The flight test was originally tentatively scheduled for May 6, but was scrubbed after a problem with an oxygen valve on a rocket from United Launch Alliance (ULA), which manufactures and operates the rockets that launch spacecraft into orbit.

A new launch date had been set for May 25, but a small helium leak was discovered in the service module, which contains support systems and instruments for operating a spacecraft.

Helium leaks and a thruster issue then threatened to delay Starliner’s docking. Five days after docking at the ISS, NASA and Boeing said the spacecraft was experiencing five “small” helium leak sand, at the time, said enough helium was available for the return mission.

Last month, teams at NASA’s White Sands Test Facility in New Mexico performed ground tests of Starliner’s thruster, putting it through similar conditions the spacecraft experienced on its way to the ISS, to see how it would react upon undocking.