Three NASA astronauts and a cosmonaut blasted off on a flight to the International Space Station on Sunday, the first of two launches by NASA and the Russian space agency to replace five of the lab’s seven crew members and to deliver a fresh Soyuz ferry ship for two cosmonauts midway through a yearlong flight.

During the final minutes of the countdown, SpaceX told the crew engineers had spotted a small crack in a seal around the Crew Dragon’s side hatch. That raised concerns about how re-entry heating might affect the seal during the ship’s return to Earth six months from now. But after an analysis, the engineers concluded the crack was too small to pose a threat and the team pressed ahead with the countdown.

And so, after launch scrubs Friday and Saturday, Crew 8 commander Matthew Dominick, co-pilot Michael Barratt, Jeanette Epps and cosmonaut Alexander Grebenkin thundered away from the Kennedy Space Center atop a SpaceX Falcon 9 rocket at 10:53 p.m. EST.

The Falcon 9 rocket’s reusable first stage, making its maiden flight, flew itself back to landing at the nearby Cape Canaveral Space Force Station after boosting the upper stage and Crew Dragon out of the lower atmosphere. The Crew 8 spacecraft was released to fly on its own 12 minutes after liftoff.

Dominick and company originally hoped to take off early Friday, but the flight was delayed because of high winds and rough seas in the Atlantic Ocean where the crew could be forced to make an emergency landing in an abort. More high winds Saturday triggered another scrub, but the weather improved enough by Sunday to permit a liftoff.

The launching kicked off NASA’s ninth Crew Dragon flight to the International Space Station since the agency began paying SpaceX to ferry its astronauts to and from the ISS in the wake of the space shuttle’s retirement in 2011. Four other Crew Dragon flights have been launched as purely commercial ventures, three of them to the space station.

Up to now, the Crew Dragon was the only flight tested and certified spacecraft available to NASA. But in April, during Crew 8’s stay aboard the space station, the first piloted flight of a Boeing-built Starliner ferry ship is scheduled for launch to the ISS in a major milestone for NASA’s Commercial Crew Program.

“Is this necessary for us to have this be successful in this mission? Absolutely,” Suni Williams, who will take off aboard the Starliner with fellow astronaut Barry “Butch” Wilmore, said in an interview with CBS News. “I think we need to have a couple of providers, so we’re not dependent on just one provider (for transportation) to the International Space Station.”

In any case, Crew 8 is expected to catch up with the space station early Tuesday. After looping up to a point directly in front of the outpost, the Crew Dragon will press in for an automated docking at the lab’s forward port around 3 a.m.

They’ll be welcomed aboard by Soyuz crewmates Oleg Kononenko, Nikolai Chub and NASA astronaut Loral O’Hara, who were launched to the station last September. Also on board: Crew 7 commander Jasmin Moghbeli, European Space Agency astronaut Andreas Mogensen, Japanese flier Satoshi Furukawa and cosmonaut Konstantin Borisov.

They were launched from the Kennedy Space Center last August and are nearing the end of a nearly 200-day mission. After briefing their Crew 8 replacements on the ins and outs of station operations, the Crew 7 fliers plan to undock March 11 and return to Earth.

“I truly can’t believe this adventure is almost over,” Moghbeli, a veteran Marine helicopter pilot, posted on social media. “This is what I’ve dreamed of since I was a little girl. I was afraid I might get here and be disappointed after having such high expectations my entire life but, if anything, this experience has surpassed all my expectations.”

A self-described “nerd,” Dominick is a computer programming hobbyist and Navy F/A-18 pilot with more than 400 carrier landings and 61 combat missions to his credit.

“You know, I’ve been a nerd my whole life, and the space program is kind of in the kingdom of nerds,” he said in an interview with CBS News. “I’ve always loved that.”

Barratt is a physician-astronaut who is making his third spaceflight. He’s a veteran spacewalker who co-authored a medical textbook during a 2009 stay aboard the station. He plans to work on an update during his latest mission and will celebrate his 65th birthday from orbit in April.

While he’s a quarter century older than his Crew 8 commander, he jokes that he still manages to hold his own.

“I am feeling great,” Barratt said. “This includes being spacewalk ready. I’ll be one of the primary spacewalkers with my crewmate Matt Dominick. Oh gosh, he’s almost 25 years younger than me. We go out in the (training) pool together and I hold my own just fine against him.

“I think the difference is, he’ll go home and do a workout, I’ll lie on the couch and cry for a little while,” Barratt laughed. “But we complement each other really, really well.”

Epps is a former CIA analyst with a doctorate in aerospace engineering who will become the second African American woman to make a long-duration space flight. She joined NASA’s astronaut corps in 2009 and trained in Russia for a Soyuz flight to the station in 2018. But NASA, without explanation, pulled her from that crew at the last minute.

After a stint training for flight aboard Boeing’s Starliner spacecraft, she was assigned to Crew 8, the last member of her astronaut class to get a spaceflight.

“You know, they always save the best for last!” she joked on arrival at the Kennedy Space Center.

Grebenkin rounds out the crew, named to the Crew 8 flight as part of a U.S.-Russian agreement to launch a cosmonaut on each Crew Dragon — and a NASA astronaut aboard each Russian Soyuz spacecraft.

The idea is to ensure at least one representative of each nation is always on board the station even if an emergency forces a Crew Dragon or Soyuz crew to depart early. Grebenkin is the fourth cosmonaut to fly under that arrangement.

The departure of Crew 7 on March 11 will set the stage for the Russians to deliver a fresh Soyuz ferry ship to the space station along with NASA astronaut Tracy Dyson, who is replacing O’Hara.

Dyson will hitch a ride to the station March 21 with Soyuz MS-25/71S commander Oleg Novitskiy and Belarus guest flier Marina Vasilevskaya. Twelve days later, on April 2, Novitskiy, Vasilevskaya and O’Hara will return to Earth using the Soyuz MS-24/70S spacecraft that carried Kononenko, Chub and O’Hara to the station last September.

Dyson will return to Earth next September, joining Kononenko and Chub aboard the Soyuz MS-25/71S spacecraft delivered by Novitskiy. While Dyson will log six months in space, the two Russians will have spent more than 373 days in orbit.

The record for the longest space single flight is 438 days, set by cosmonaut Valery Polyakov aboard the Russian Mir space station in 1994-95. The U.S. record is held by astronaut Frank Rubio, who logged 371 days aboard the ISS in 2022-23.