NASA has announced that astronauts Butch Wilmore and Suni Williams, who have been stuck in space since June, will have to wait until next year for a trip home.

After nearly three months, the agency decided Saturday that it was too risky to return the pair to Earth in the new, damaged Boeing capsule that had taken them into space, saying they would have to wait until February for a flight home on a SpaceX plane.

The experienced pilots have been stuck on the International Space Station (ISS) since early June. NASA’s decision to delay their return means the week-long test flight will now take more than eight months.

Their journey to the space station was marred by a series of annoying engine failures and helium leaks in the Starliner capsule, and they were put into a holding pattern while engineers conducted tests and discussed the return trip.

NASA’s announcement said the now empty Starliner will undock in early September and attempt to return on autopilot and land in the New Mexico desert.

The agency’s management said its decision was in the best interests of the pilots given the safety aspects of a test flight.

“Space flights are risky, even the safest and most routine. A test flight is inherently neither safe nor routine,” said NASA Administrator Bill Nelson.

“Our decision to keep Butch and Suni on board the space station and bring the Starliner home unmanned is the result of our commitment to safety: our core value.”

NASA: Astronauts support delayed return

The Starliner mishaps were a major blow to Boeing and heightened safety concerns that plague the company’s commercial aircraft operations.

Boeing had bet that the first astronaut flight would revive the troubled program after years of delays and skyrocketing costs. The company had insisted that Starliner was safe both in space and on the ground based on all of its recent engine tests.

The company did not attend NASA’s press conference on Saturday, but issued a statement.

“Boeing continues to place its primary focus on crew and spacecraft safety. We are executing the mission as specified by NASA and preparing the spacecraft for a safe and successful uncrewed return.”

Wilmore, 61, and Williams, 58, are both retired Navy captains and have many years of experience in space travel.

During their only orbital press conference last month, they said they had confidence in the engine tests being conducted. They said they had no complaints and were happy to help with work on the space station.

NASA’s Norm Knight said he spoke to the astronauts on Saturday and they fully supported the decision to delay their return.

Despite Saturday’s decision, NASA is not giving up on Boeing.

Mr Nelson said he was “100 percent” sure the Starliner would fly again.

Why can’t they return sooner?

The options were limited.

The SpaceX capsule currently parked at the space station is reserved for the four residents who have been there since March. They will return in late September, their stay extended by a month by the Starliner dilemma. NASA said it would be too dangerous to squeeze two more into the capsule except in an emergency.

The docked Russian Soyuz capsule is even more cramped, as it can only carry three astronauts – two of them are Russians who are just finishing their one-year mission.

Therefore, Mr Wilmore and Ms Williams will wait for the next SpaceX taxi flight.

The launch is planned for the end of September. Instead of the usual four astronauts, the space shuttle will launch with two astronauts for six months. NASA has withdrawn two astronauts to make room for Mr. Wilmore and Ms. Williams on the return flight at the end of February.

NASA said it had not seriously considered asking SpaceX to undertake a quick, independent rescue operation.

Last year, the Russian space agency had to provide a replacement Soyuz capsule for three men whose original spacecraft had been damaged by space debris. The switch extended their mission by more than a year – a US space record still held by Frank Rubio.

A decade ago, NASA launched its commercial crew program with the goal of contracting two competing U.S. companies to transport astronauts in the post-shuttle era. Boeing won the larger contract: it exceeded $US4 billion ($5.9 billion), while SpaceX received $US2.6 billion.

SpaceX has already completed supply flights to the space station and successfully completed its first of what are now nine astronaut flights in 2020. Boeing, on the other hand, was stuck with design errors that cost the company more than a billion US dollars.

NASA officials still hope that the Starliner’s problems can be resolved in time for another manned flight in about a year.

AP