New Delhi, Jun 26 (IANS): In a growing concern, NASA astronauts Sunita Williams and Butch Wilmore are stuck at the International Space Station (ISS) as engineers continue to fix the Boeing Starliner spacecraft that will take them back to Earth.

Originally slated to spend eight days on the orbiting space laboratory, the astronauts reached the ISS on June 6.

Twenty days later, NASA and Boeing leadership are still adjusting the return to Earth of the Starliner Crew Flight Test spacecraft which suffered a small helium system leak on its way.

Now, according to a Boeing spokesperson, four of the five thrusters that were previously shutting down are operating normally.

"This means only one thruster out of 27 is currently offline. This does not present an issue for the return mission," the spokesperson added.

According to Steve Stich, manager of NASA’s Commercial Crew Programme, "we are taking our time and following our standard mission management team process".

"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," Stich said in a statement.

According to the US space agency, the spacecraft requires seven hours of time to perform a normal end-of-mission and it "currently has enough helium left in its tanks to support 70 hours of free flight activity following undocking".