Already more than a month late getting back, two NASA astronauts will remain at the International Space Station until engineers finish working on problems plaguing their Boeing capsule, officials said Thursday.

Test pilots Butch Wilmore and Suni Williams were supposed to visit the orbiting lab for about a week and return in mid-June, but thruster failures and helium leaks on Boeing’s new Starliner capsule prompted NASA and Boeing to keep them up longer.

NASA’s commercial crew program manager Steve Stich said mission managers were not ready to announce a return date.

“We’ll come home when we’re ready,” said Stich, adding that the goal is to bring Wilmore and Williams back aboard Starliner.

Stich acknowledged that backup options are under review.

Engineers last week completed testing on a spare thruster in the New Mexico desert to try to understand what went wrong during docking. Five thrusters failed as the capsule approached the space station on June 6, a day after liftoff. Four have since been reactivated.

It appeared degraded seals are to blame for the helium leaks and thruster problems, but more analysis is needed. The team will test-fire the thrusters this week while docked to the space station to gather more data, said Boeing’s Mark Nappi.

After the space shuttles retired, NASA hired private companies for astronaut rides to the space station, paying Boeing and SpaceX billions of dollars.

This was the Boeing’s first test flight with a crew aboard. SpaceX has been ferrying astronauts since 2020.

(AP)