Washington: Two NASA astronauts Barry Wilmore and Sunita Williams have no planned date to return to Earth and they are waiting aboard the International Space Station (ISS) amid several mechanical issues with Boeing's Starliner spacecraft, ABC News reported.

The two NASA astronauts were scheduled to return on June 14. However, the pair has no set date to return to Earth as their return has been delayed multiple times.

In a statement, Steve Stich, manager of NASA's Commercial Crew Program, said, "We are taking our time and following our standard mission management team process," according to ABC News report.

Stich added, "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."

The Starliner with flight commander Barry "Butch" Wilmore and flight pilot Sunita "Suni" Williams onboard was launched from the Cape Canaveral Space Force Station in Cape Canaveral, Florida on June 5. The Starliner arrived at the ISS on June 6.

The mission is part of the larger Commercial Crew Program at NASA, which wanted to see whether Boeing's spacecraft could be certified to carry out routine missions to and from the ISS.

Boeing and NASA have said the crew is currently not in danger as they are aboard the ISS with plenty of supplies in orbit and the schedule of the station is relatively open through mid-August.

NASA and Boeing said Wilmore and Williams are "integrated" with the Expedition 71 crew aboard the ISS and are assisting the crew with operations of the station as needed and completing "objectives" required for NASA's possible certification of Starliner, ABC News reported.

In a statement, Mark Nappi, vice president and program manager of Boeing's Starliner program, said, "The crew's feedback has been overwhelmingly positive, and they know that every bit of learning we do on the Crew Flight Test will improve and sharpen our experience for future crews."

Starliner has faced several issues even before launch. The flight test was originally tentatively scheduled for May 6. However, it was delayed after a problem with an oxygen valve on a rocket from United Launch Alliance (ULA), which makes and operates the rockets that launch spacecraft into orbit.

The launch date was later set for May 25. However, a small helium leak was found in the service module, which comprises support systems and instruments for operating a spacecraft, ABC News reported.

Helium leaks and a thruster issue then threatened to delay the docking of Starlines. After docking at the ISS for five days, NASA and Boeing said the spacecraft was experiencing five "small" helium leaks. At the time, NASA and Boeing said enough helium was available for the return mission.

(With Inputs From Agencies)