SpaceX is set to hit a milestone in human spaceflight as it aims to bring up another four passengers to the International Space Station.

The Crew-8 mission with three NASA astronauts and one Roscosmos cosmonaut will be riding in the Crew Dragon Endeavour when it launches atop a Falcon 9 rocket from Kennedy Space Center’s Launch Pad 39-A targeting liftoff at 11:16 p.m. with backup windows on Sunday at 10:53 p.m. and Monday at 10:31 p.m.

The first-stage booster is flying for the first time and will attempt a recovery landing at nearby Cape Canaveral Space Force Station’s Landing Zone 1, which could mean one or more sonic booms might be heard in parts of Central Florida.

Space Launch Delta 45’s weather squadron forecasts only a 40% chance for good conditions on Saturday, though. That improves to 70% if delayed to Sunday and 60% if delayed until Monday.

Once they launch, they will mark 50 humans flown to space among SpaceX’s four Crew Dragon spacecraft, with only one repeat flyer among the 50. Endeavour was the first to ferry passengers when it launched on the Demo-2 mission in May 2020 carrying up astronauts Bob Behken and Doug Hurley.

This marks its fifth flight.

“It’s our fleet leader,” said NASA Commercial Crew Program manager Steve Stich. “So we’ve taken a lot of extra time … to go through all of the systems and in particular the prompt system is to make sure we’re really ready to go fly.”

SpaceX launch this week could end NASA astronaut’s nearly 15-year wait to get to space

Flying up for NASA are commander Matthew Dominick, pilot Michael Barratt and mission specialist Jeanette Epps along with Russia’s mission specialist Alexander Grebenkin. They are set to join Expedition 70 on board the ISS docking on Sunday afternoon for about a six-month stay during which they will work on more than 200 science and technology experiments.

All but Barratt, who flew on both a Soyuz mission in 2009 and the last Space Shuttle Discovery mission in 2011, are spaceflight rookies.

“I can’t wait to fly this new spaceship, and I can’t wait to fly with this crew,” Barratt said when the quartet arrived to KSC last Sunday, noting it had been 13 years and one day since he flew on Discovery’s STS-133.

“Two more flights and our shuttle program was done. Most of us were hoping that there would be an overlap, not a big gap. But we did have a gap and when we came down here to watch Discovery be carted away from here, Kennedy Space Center was very quiet,” he said about when the shuttle was taken away to be put on display at the Smithsonian.

“It was so empty compared to what we were all used to for all this time,” he said. “We were all pretty sure that KSC was going to come back. But we had no idea how much. I would say KSC has come back with a vengeance.”

Now SpaceX is making its 13th Crew Dragon flight, the ninth flight for NASA as part of the Commercial Crew Program. The other four human spaceflights have been private missions for Axiom Space for short visits to the ISS plus the orbital flight Inspiration4 for billionaire Jared Isaacman.

Only former astronaut and now Axiom Space employee Michael Lopez-Alegria, who was on this year’s first human spaceflight on the Ax-3 mission that launched in January, has made the Dragon flight twice among the 50.

SpaceX has three more Dragon flights planned this year including Crew-9 as early as August and the fourth Axiom Space mission as early as October plus another flight for Isaacman on the Polaris Dawn mission that could fly this summer.

Meanwhile, the other company in the Commercial Crew Program, Boeing, is finally set to catch up to SpaceX with its first crewed test flight launching as soon as April 22 from Cape Canaveral. NASA’s goal was to have two active spaceflight providers to guarantee access to the ISS.

The five Dragon flights plus Starliner means 22 astronauts could make it to space from the U.S. this year, the most since 2009 during a busy year of the space shuttle program.

“It almost seems routine to the uneducated eye that SpaceX is putting them up one after another,” said NASA Administrator Bill Nelson this week. “You never want to get to the frame of mind that it is so routine that it’s like getting in your car and taking a Sunday afternoon drive.”