Boeing is delaying the return of two NASA astronauts from the International Space Station (ISS), following problems with helium leaks and thrusters. NASA announced on Tuesday, June 18, that the efforts to get them home may have the two astronauts in space longer than anticipated.

The initial plan was for astronauts Barry Wilmore and Sunita Williams to spend around eight days in space. The Wall Street Journal reported that the latest delay will put them at closer to 20 days in space. The astronauts were originally slated to return between June 18 and June 22.

The Starliner faces two main problems. First, there is a series of helium leaks in the propulsion system, one of which was known of before the flight. The second problem is with five thrusters that temporarily failed as the vehicle made its approach toward the ISS.

Four of the thrusters are now back online, but one thruster will be turned off for the remainder of the mission, according to NASA. Starliner needs around seven hours of helium on board to finish the flight; the vehicle currently has approximately 70 hours of helium remaining.

NASA and Boeing also said that they will not let the crew return to Earth in the vehicle if there is any risk to their safety. The astronauts will need to be able to reenter Earth’s atmosphere and land under parachutes to get home safely.

If necessary, the ISS reportedly has at least four months’ worth of food and NASA said that the Starliner is capable of staying docked for 45 days. Eventually, the Starliner plans to have missions where it stays for six months at a time.

However, the Starliner delay is another setback for Boeing, which had planned for the mission to happen years ago. Boeing is under contract with NASA for six more crewed flights to the ISS.

Meanwhile, SpaceX has flown cargo to the ISS for years and successfully completed its first astronaut mission for NASA in 2020.

Former launch director for the space shuttle at NASA’s Kennedy Space Center, Mike Leinbach, who is not involved in the mission, told the Journal that the problems with Starliner are a bit of surprise to him.

“This one has a few more issues than I would have expected,” Leinbach said. “We hoped for a clean fight, but we didn’t get one, and we’re dealing with it. They’ll figure this out.”

The Starliner crew has reportedly reached 77 of 87 test objectives so far, according to Mark Nappi, a Boeing vice president overseeing the Starliner mission.

The announcement of the latest delay comes the same week that Boeing CEO David Calhoun testified before Congress over plane safety. Before he testified, Calhoun stood up and apologized to the families killed in two Boeing crashes that killed hundreds in 2018 and 2019, as they prepared to watch his testimony.