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After their weeklong journey turned into a monthslong stay on the International Space Station, two Boeing Starliner astronauts will soon be united with the spacecraft that will eventually bring them home.

The SpaceX Crew Dragon capsule, chosen by NASA to carry astronauts Suni Williams and Butch Wilmore back to Earth after their Starliner spacecraft was deemed too risky for crew, is approaching the space station. The vehicle, on a mission called Crew-9, is expected to dock at about 5:30 p.m. ET Sunday.

On board the SpaceX vehicle are NASA astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov. Alongside them are two empty seats, saved for Williams and Wilmore to occupy when the group returns to Earth next year.

Hague and Gorbunov launched aboard the Crew Dragon Saturday afternoon from Cape Canaveral Space Force Station in Florida. Though they reached their intended orbit without a hitch, SpaceX later revealed that the second stage, or upper portion, of the Falcon 9 rocket that powered the first part of their journey experienced an issue after it broke away from the capsule.

“After today’s successful launch of Crew-9, Falcon 9’s second stage was disposed in the ocean as planned, but experienced an off-nominal deorbit burn,” the company shared in a post on X, the social media platform formerly known as Twitter. “As a result, the second stage safely landed in the ocean, but outside of the targeted area.”

SpaceX indicated it would pause flights using Falcon 9 — the world’s most frequently launched rocket — as it explored the anomaly. “We will resume launching after we better understand root cause,” the company said in the X post.

CNN has reached out to the Federal Aviation Administration for comment.

Meanwhile, Crew-9’s SpaceX Crew Dragon capsule has spent about one day traveling through orbit as it prepares to dock with the International Space Station. Once safely attached to one of the station’s docking ports, the spacecraft will open its hatch, allowing Hague and Gorbunov to join the other astronauts already on board the orbiting laboratory.

Months in space

Together, Hague, Williams, Wilmore and Gorbunov will complete SpaceX’s Crew-9 team. The group will spend about five months on board the space station before returning home no earlier than February.

Williams and Wilmore first traveled to the International Space Station in early June aboard a Boeing Starliner spacecraft for what was expected to be a weeklong test mission.

But issues with helium leaks and malfunctioning thrusters left engineers scrambling to figure out what went wrong — and NASA ultimately decided the Starliner’s problems were not well enough understood for the space agency to allow Williams and Wilmore back on board.

The Starliner instead flew home empty on September 6.

After deciding not to return Williams and Wilmore to Earth on the Starliner, NASA opted instead to rearrange SpaceX’s flight plans, booting two other astronauts — spaceflight veteran Stephanie Wilson and Zena Cardman, who was set to make her first trip to space — off the Crew-9 mission to make room for the Starliner team.

But that meant Williams and Wilmore would have to fulfill the duties of the original Crew-9 staff, taking up months’ worth of routine work on the space station before their return trip.

Both Williams and Wilmore — veterans of earlier missions to the space station — have said they easily adjusted to the idea of staying in space until next year, with Williams noting the microgravity environment is her “happy place.”

Rounding out the staff currently on board the International Space Station are NASA’s Don Pettit and Aleksey Ovchinin and Ivan Vagner of the Russian space agency Roscosmos. The three arrived at the space station aboard a Russian Soyuz vehicle on September 11.

Pettit and Gorbunov rode aboard spacecraft developed outside their home countries as part of a seat-swapping agreement between NASA and its Russian counterpart.