Two NASA astronauts who have been stranded in space since the beginning of June have finally booked their flight home: They will return to Earth in February on SpaceX’s Dragon capsule.

The decision is a vote of confidence for Elon Musk’s SpaceX, which not only won the race to transport astronauts by years, but now has the confidence to finish a job Boeing started. Astronauts Butch Wilmore and Suni Williams launched on June 5 on a mission that was never guaranteed to be without incident; they were the first passengers to ever fly aboard the Starliner, built by veteran contractor Boeing. Now their mission will be more complicated than originally planned – and take months longer than anyone expected.

“Space flights are risky, even at their safest and most routine,” NASA Administrator Bill Nelson said during an agency press conference on Saturday. “A test flight is inherently neither safe nor routine.”

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Wilmore and Williams also faced several delays before their launch earlier this summer. When they finally lifted off, they arrived safely at the International Space Station. But several small anomalies occurred during the flight, notably helium leaks and engine failures in the vehicle’s propulsion system. Since the pair reached orbit, NASA and Boeing have been working hard to troubleshoot their vehicle, a capsule nicknamed Calypso.

But NASA remains unconvinced that engineers understand the engine situation in particular well enough to trust the agency’s astronauts with the vehicle. Every NASA team that officials said was consulted on the Starliner’s return – about a dozen offices in total – opted for an uncrewed flight, said Ken Bowersox, NASA’s deputy director for space operations, during the press conference. “The engine prediction was just too uncertain,” added Steve Stich, program manager for NASA’s Commercial Crew Program.

For NASA, the decision represents a setback in its plans to have two reliable crew vehicles that can routinely carry astronauts into space. But despite the unpleasant optics of the new plan, changing the return trip is better for Wilmore and Williams than the alternative, says Wendy Whitman Cobb, a political scientist at the School of Advanced Air and Space Studies in Alabama.

“The attack would have been worse if they had made a decision that would have put the astronauts’ lives in danger,” says Whitman Cobb. “I think that’s probably the least risky option for NASA at this point.”

The reshuffle of plans shows how much faith NASA has in the SpaceX Dragon vehicle. Not only does NASA rely on Musk’s company to gain access to the International Space Station, but NASA has also entrusted SpaceX with launching a number of high-profile science missions, landing astronauts on the lunar surface – and even building the vehicle that will eventually destroy the space station in orbit.

For Boeing, NASA’s decision is likely to be painful, both in terms of the company’s reputation and its balance sheet. “I’m sure this is a big blow for them,” says Whitman Cobb. “Their balance sheets have already shown that they’ve taken a pretty big financial hit; this will be another one.”

But Nelson and other NASA officials stressed that both the agency and Boeing remain interested in making Starliner a regular visitor to the space station. NASA has stressed all along the importance of having two U.S.-built vehicles that can reach the orbiting laboratory, just in case a problem with one spacecraft causes it to be temporarily grounded. Asked how confident he was that Starliner would fly a crew again, Nelson said, “100 percent.”

No Boeing representative attended NASA’s press conference on Saturday, but the company issued a statement saying: “We remain primarily focused on crew and spacecraft safety. We are executing the mission as defined by NASA and preparing the spacecraft for a safe and successful uncrewed return.”

NASA is used to considering the lives of its astronauts in its decisions, and its leaders regularly talk about the way in which the disasters of the challenger Space Shuttle in 1986 and the Columbia Shuttle crashes in 2003 have shaped the agency’s “safety culture.” At Saturday’s press conference, Nelson referred to the lost shuttle crews and the way those incidents changed NASA’s culture. But both shuttles were operated entirely by NASA, and some experts have long wondered whether the start of commercial missions could cloud safety standards in space.

The way to earth

As things stand, Starliner will fly home empty in the coming weeks while Wilmore and Williams remain in orbit for another six months – a dramatic change in their work schedule. The duo will prepare the Boeing vehicle for departure and then bid it farewell in early September. The empty capsule will sail through Earth’s atmosphere and land in the Utah desert. (Crew-8, the Dragon vehicle currently docked to the space station, will be temporarily converted to hold six people in case an emergency requires the astronauts to be evacuated, NASA officials said.)

Then, in about a month, SpaceX will launch its planned Crew-9 mission, with just two of the previously assigned four crew members: NASA astronauts Zena Cardman, Nick Hague and Stephanie Wilson, and Russian cosmonaut Aleksandr Gorbunov. NASA has not yet decided who will remain on board, according to Norman Knight, chief of flight operations.

Wilmore, Williams and their two new companions will stay in orbit for the usual six months, conducting various scientific experiments before heading back to Earth in early 2025. (NASA has also confirmed that the two will train for spacewalks during an extended stay.)

A decade full of bumps

The return of the empty Starliner is another in a decade-long series of challenges for Boeing. In 2014, NASA commissioned Boeing and SpaceX to develop vehicles capable of transporting astronauts to and from the International Space Station. The agency had retired its shuttle fleet in 2011, just a decade after continuously occupying the station, and found itself in the awkward position of having to rely on Russia for transportation to and from the station.

Contracts with these private operators called for astronauts to be able to launch by 2017 – a timeline that neither company was able to meet. SpaceX built on its previous success using Dragon capsules for resupply missions to the orbital outpost, successfully and smoothly conducting a crewed test mission in 2020. Since then, SpaceX has conducted seven standard missions for NASA, with the eighth such mission currently in orbit and returning next month.

Boeing, on the other hand, had to start from scratch to build its Starliner spacecraft, an endeavor that has been rocky over the past decade. The company was finally ready to launch its unmanned test flight in December 2019. But the spacecraft – the same capsule that is now in orbit – burned too much fuel in the minutes after launch and was unable to reach the International Space Station.

After the incident, Starliner was grounded for two and a half years (due in part to a dozen faulty valves) before conducting a successful unmanned test flight in May 2022. But that mission wasn’t flawless either, with engine problems marring the flight to the space station. Last summer, Boeing lost another year due to a combination of parachute problems and the discovery that highly flammable tape had been used throughout the capsule.

In early May, Starliner was on its way to the launch pad to conduct the important crewed flight test – the final milestone between Boeing and regular flights to the International Space Station. However, the mission team canceled the launch due to valve problems that required a month-long pause before another attempt, which was aborted less than four minutes before liftoff due to a helium leak in the propulsion system.

So on June 5, Wilmore and Williams boarded the Starliner for the second time in less than a week, more than 100 feet above the launch pad, expecting a one-week trip to the space station—the third visit of each astronaut’s career. But during the trip to orbit, two more helium leaks occurred in the propulsion system, five of the vehicle’s engines failed, and the capsule’s cooling system used too much water.

None of the problems were particularly concerning on their own, but the combination made a big impression. Within days of Wilmore and Williams’ arrival in orbit, NASA began delaying their return flight. By mid-June, agency officials were discussing keeping the two in orbit while engineers collected as much data as possible about parts of the vehicle that burn up during reentry – not out of concern for the vehicle’s safety, but simply to better understand future missions.

Back to flight

How Starliner will return to flight is still uncertain. Although Boeing representatives were not present at Saturday’s press conference, Nelson said he spoke earlier in the day with Boeing CEO Kelly Ortberg, who took office just over two weeks ago. “He expressed to me his intention to continue working on the issues once Starliner is safe again,” Nelson said.

But questions remain. NASA officials declined to say whether they would be willing to approve Starliner for regular crewed missions without bringing Wilmore and Williams home, or whether they would consider using a full contingent of four astronauts for the next crewed flight. It’s also not clear what NASA’s international partners on the space station, particularly Russia, need to see before entrusting their own astronauts to a new vehicle.

All of these considerations will become clearer in a few weeks, when Starliner is back on Earth and in NASA’s hands, and as Boeing engineers assess the path forward. Whitman Cobb says the key factor in the vehicle’s future will be whether either organization requests changes to Starliner. “Any time you have to change something in the capsule, in the system,” she says, “it’s probably going to take a lot longer.”