An empty Boeing starliner begins return to earth: How to watch

Boeing's Starliner is finally coming home, but the two NASA astronauts who traveled in the spacecraft to the International Space Station are not.

At 6:04 p.m. ET on Friday, hooks that held Starliner tight to the space station retracted, and springs on the spacecraft pushed it away from the docking port. At that moment, it was about 260 miles above central China.

Then a series of thruster firings gently nudged Starliner up and over the space station.

"Starliner is now on a path back to Earth," Anna Schneider, a NASA spokesperson, said about 20 minutes after the vehicle undocked and reached a distance far enough away that space station flight controllers no longer needed to keep an eye on it.

At the higher altitude, it is moving more slowly than the space station and the distance between them is growing quickly.

That was an uneventful beginning to the end of the mission, which launched in June, on a test flight that 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.

The big maneuver of the evening still lies ahead.

After several orbits of Earth, at 11:17 p.m., the large thrusters on Starliner will fire for almost a minute to drop Starliner out of orbit. It will reenter over the central Pacific, traveling to the northeast, crossing northwest Mexico en route to touching down around midnight at White Sands Space Harbor in New Mexico, part of the Chihuahuan Desert.

NASA's video coverage of the reentry and landing of Starliner is scheduled to begin at 10:50 p.m. The agency provided a guide to where people in parts of New Mexico, Arizona, Texas and northern Mexico might be able to see the spacecraft streaking across the night sky.

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 reentry.

Boeing officials have said that they believe the weeks of analysis and ground tests show that Starliner could have safely taken Williams and 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.

Before the undocking, Williams, who several years ago had given this vehicle the name Calypso, thanked the Boeing mission control team.

"It is time to bring Calypso home," she said. "We have your backs and you've got this. Bring her back to Earth. Good luck."

In turn, Chloe Mehring, the flight director, thanked the astronauts, who have spent years preparing for this flight. "We remember every setback and every revelation with you," Mehring said. "The teams on the ground have worked countless hours over the last few weeks, months, and, for a group of us, years to bring Calypso back, and we're ready to do that today."

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 Williams and 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 Williams and 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.