Boeing’s Starliner is finally coming home, but the two NASA astronauts who traveled in the spacecraft to the International Space Station are not.
The mission, which launched in June, was the first time Starliner carried people to orbit. The flight was intended as a final shakedown before NASA certified the spacecraft for once-a-year missions taking astronauts to and from the space station.
The vehicle’s propulsion system experienced problems during its approach to the space station, including several balky thrusters and leaks of helium, a gas used to push propellant in the weightlessness of orbit. Although Starliner was able to dock successfully, the cause of the problems is still not fully understood, and NASA officials decided it would be safer for Starliner to return without anyone aboard.
When will Starliner return, and how can I watch it?
Starliner undocked from the space station on schedule at 6:04 p.m. Eastern time Friday. NASA continued broadcasting coverage as the spacecraft departed from the I.S.S., first pushed away by springs and then with series of thruster firings. By 6:10 p.m., the vehicle was outside of a “keep-out sphere” that defines a safety zone around the space station.
Coverage of the re-entry and landing of Starliner is scheduled to begin at 10:50 p.m.
What will happen during the undocking and landing?
A command sent from the ground retracted the hooks that are holding Starliner to the outpost’s forward docking port, and springs on the spacecraft then pushed it away. A minute and a half later, the spacecraft started firing its thrusters in short bursts to move away and above the space station.
At the higher altitude, it will be moving more slowly than the space station and the distance between them will grow quickly.
Several orbits of the Earth later, at 11:17 p.m., Starliner will fire its large thrusters to drop out of the orbit and back into the atmosphere, aiming for the White Sands Space Harbor, which is in the Chihuahuan Desert in New Mexico. Before re-entry, it will jettison its service module, the cylindrical piece below the capsule that contains the troublesome thrusters.
Landing is expected just after midnight Eastern time.
Why is Starliner traveling home with no astronauts aboard?
The Starliner mission carried two NASA astronauts, Suni Williams and Butch Wilmore, to the space station.
Lingering uncertainty about the cause of the vehicle’s propulsion problems led to unease that there might be a more serious underlying issue. A catastrophic failure of Starliner’s propulsion system during the return trip could leave the spacecraft stranded in orbit or it could burn up during re-entry.
Boeing officials have said that they believe the weeks of analysis and ground tests show that Starliner could have safely taken Ms. Williams and Mr. Wilmore back to Earth. But NASA officials decided it would be less risky for the two astronauts to remain on the space station instead of returning to Earth in Starliner.
Are there any risks during the undocking?
Any time a spacecraft approaches or leaves the space station, there is a danger of a collision if something goes wrong. A spacecraft travels very slowly as it approaches or leaves the I.S.S., and is designed with backup systems to avoid that possibility.
While Starliner was docked at the station, all but one of the 28 small thrusters were fired briefly to test their performance. (One thruster appears to be not working at all, and that one will not be used. Starliner was designed so that it can maneuver even if one or more of the thrusters malfunction.)
The undocking trajectory has been changed so that Starliner will be able to move away from the space station more quickly, and the thruster pulses that Starliner will fire to push itself away will not cause significant heating, which is thought to have led to the thruster problems during approach.
“We don’t really expect any issues with the thrusters near station,” Steve Stich, the manager of NASA’s commercial crew program, said during a news conference on Wednesday. “And then we get away very quickly.”
What happens to the astronauts now?
The two Starliner astronauts will become full-fledged members of the space station crew. NASA calls each rotation of crew members an “expedition,” and Ms. Williams and Mr. Wilmore will now be part of Expedition 72.
Later this month, two other astronauts, Nick Hague of NASA and Aleksandr Gorbunov of Russia, are scheduled to launch to the space station in a SpaceX Crew Dragon capsule, to also serve as part of Expedition 72. For Ms. Williams and Mr. Wilmore to have seats on the return trip to Earth next year, two other NASA astronauts who had been scheduled to serve on Expedition 72 — Zena Cardman and Stephanie Wilson — were bumped from the mission, known as Crew-9.
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