Boeing and NASA are preparing to bring the Starliner back to orbit without a crew on Friday

NASA officials expressed confidence that Starliner would make a safe and successful return to Earth by late Friday evening, though they had enough doubts about the spacecraft’s performance that they concluded the trip should be made without humans on board.

This high-stakes mission is now officially set to end on Friday, when Starliner will attempt undocking around 6:04 p.m. EST. If all goes according to plan, the spacecraft will land at White Sands Space Harbor in New Mexico about six hours later.

These final maneuvers will cap off a troubled first crewed mission for the Boeing-built Starliner. It was to be the final certification mission before the vehicle went into operation as a regular transporter for astronauts to and from the International Space Station. But technical problems emerged shortly before an attempt to dock with the station on June 6, including some helium leaks in several of the spacecraft’s thrusters and propulsion systems.

The two astronauts on board, Butch Wilmore and Suni Williams, safely boarded the ISS. But the problems ultimately extended the mission by several months as NASA and Boeing engineers tried to figure out the root cause of the anomalies. After weeks of testing, both in space, using replica hardware, and in orbit, NASA ultimately decided on August 24 that Starliner should return to Earth empty, and Wilmore and Williams will return home using a SpaceX capsule in February 2025.

The return trip will have one big difference from normal return missions from the ISS, in that the Starliner will conduct a procedure called a “breakout burn” to quickly move it up and away from the station. This maneuver — which is actually 12 smaller burns, each with an orbital velocity of just 0.1 meters per second — will see the thrusters pulse for a shorter period of time than during the approach to the station. For this reason, the breakout burn is unlikely to cause the same problems as engineers saw at the beginning of the mission, and thus poses no safety threat to the ISS, Steve Stich, NASA’s commercial crew program manager, said during a news conference.

“We decided to do a breakout burn because it gets the vehicle away from the station much quicker,” he said. “Being able to take over manual control if needed if the crew is not there gives us a lot fewer variables to take into account when doing a breakout burn, and that allows us to get the vehicle on the road home much quicker.”

The next crucial maneuver will be a 60-second deorbit burn, which will take the Starliner into Earth’s atmosphere and on its way to White Sands. The spacecraft will deploy parachutes and airbags to make a soft landing on the ground.

“We are hopeful of a good result and we have ample surplus material and we are relying on that for a safe entry,” he said.

NASA and Boeing will spend a few months analyzing the spacecraft’s performance post-flight, but Stich said the teams are already considering system modifications or additional testing to get the vehicle fully certified by the space agency.

But it’s unclear what the final path to certifying the spacecraft will be like — how much more it could cost Boeing, which has already racked up more than $1.5 billion in costs related to the Starliner program. It’s also unclear whether Boeing will need to do another crewed test mission.

If NASA and Boeing’s joint flight control team doesn’t decide to undock on Friday, there will be several other opportunities in the coming days. Astronauts on the space station have modified the SpaceX Dragon vehicle that is currently attached to the station with temporary seats in case of an emergency.