The astronauts’ return journey was first delayed until June 14 and more recently it was scheduled for June 26. Now, the NASA crew will reportedly stay aboard the ISS until some time in July as their window to return begins to close.

Two NASA astronauts are currently thought to be stranded at the International Space Station (ISS) after NASA delayed their return for the third time. The astronauts, Butch Wilmore and Suni Williams, were originally scheduled for a nine-day visit, but will stay aboard indefinitely until some time in July.

Engineers discovered numerous issues with Boeing’s Starliner spacecraft including thruster failures and leaking, Boeing reportedly said.

Following years of delays, the aircraft first launched on June 5 with a known leak no larger than a shirt button and reportedly “thin”, said one outlet. But during the 25-hour flight, engineers found that Starliner had encountered five separate helium leaks affecting its 28 maneuvering thrusters.

“Additionally, given the duration of the mission, it is appropriate for us to complete an agency-level review, similar to what was done ahead of NASA's SpaceX Demo-2 return after two months on orbit, to document the agency’s formal acceptance on proceeding as planned.”

Starliner’s return module is currently docked to the ISS’s Harmony module. NASA may be forced to launch a rescue mission to save the stranded astronauts, experts reportedly said, and that mission may prompt them to use one of SpaceX’s Dragon capsules and abandon Starliner altogether. However, Harmony’s fuel is limited which means Starliner can only stay docked for 45 days leaving a narrow window to rescue the astronauts.

“We are taking our time and following our standard mission management team process,” said Steve Stich, manager of NASA’s Commercial Crew Program. “We are letting the data drive our decision making relative to managing the small helium system leaks and thruster performance we observed during rendezvous and docking.”