Washington, DC [USA], Two NASA astronauts, Barry Wilmore and Sunita Williams, have no scheduled date to return to Earth and are waiting aboard the International Space Station (ISS) amid several problems mechanics with Boeing's Starliner spacecraft, ABC News reported.

The two NASA astronauts were scheduled to return on June 14. However, the couple does not have a set date to return to Earth as their return has been delayed several 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 an ABC News report.

Stich added: "We are letting the data drive our decision making regarding management of the small helium system leaks and thruster performance that we observe during rendezvous and docking."

The Starliner with Flight Commander Barry "Butch" Wilmore and Flight Pilot Sunita "Suni" Williams on board launched from 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 NASA's broader Commercial Crew Program, which wanted to see if Boeing's spacecraft could be certified to carry out routine missions to and from the ISS.

Boeing and NASA have said the crew is not currently in danger as they are aboard the ISS with plenty of supplies in orbit and the station's schedule is relatively open until 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 station operations as needed and completing required "objectives" for possible Starliner certification by NASA, ABC News reported.

In a statement, Mark Nappi, vice president and director of Boeing's Starliner program, said: "Feedback from the crew has been overwhelmingly positive and they know that every learning we do in the crew flight test will improve and refine our experience for future crews."

Starliner has faced several problems 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 United Launch Alliance (ULA) rocket, which makes and operates the rockets that launch spacecraft into orbit.

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

Helium leaks and a propellant problem threatened to delay Starlines' docking. 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 there was enough helium available for the return mission.