KENNEDY SPACE CENTER — A rocket, spacecraft and a pair of NASA astronauts are getting ready to fly today on Boeing’s CST-100 Starliner on its first ever human spaceflight.

Butch Wilmore and Suni Williams are set to return to the launch pad on the Crew Flight Test mission of Starliner sitting atop a United Launch Alliance Atlas V rocket at Cape Canaveral Space Force Station’s Space Launch Complex 41.

“The weather looks good. Atlas is standing tall, strong, and proud. The sun rises above. Feels like a good day to go to space,” said ULA President and CEO Tory Bruno on a post on X.

Liftoff is targeted for 12:25 p.m., taking the duo on a trip to the International Space Station, with a backup opportunity on Sunday. Teams began loading cryogenic fuel to the rocket just after 6:30 a.m.

“Butch and Suni are excited for today. As astronauts, especially Butch and Suni, consummate professionals, test pilots and they got their steely eyed game faces on but inside they are excited for today,” said NASA astronaut Mike Fincke during NASA’s live coverage that began at 8:15 a.m. on NASA TV and its social media channels.

“We’ve been, all of us, the whole team has been working for a long time. It’s not just Butch and Suni, they’re the literally tip of the spear, but they are very excited to go do their part for this test flight and to get Starliner certified and be the first of many Starliner flights,” Fincke said.

Space Launch Delta 45’s weather squadron forecasts a 90% chance for good conditions at the launch site for both Saturday and Sunday. Further backup opportunities fall to Wednesday and Thursday. The main concern that popped up Saturday morning are high winds along the Space Coast.

But the astronauts are on track to don their spacesuits and make the trip in the Boeing-themed Astrovan from KSC’s Neil Armstrong Operations & Checkout Building to the Cape to once again their seats in the capsule.

They made that trip already on May 6 coming within two hours of launch before teams scrubbed the attempt because of a fluttering valve on the Atlas V’s upper Centaur stage. That scrub led to the rollback of the rocket to ULA’s nearby Vertical Integration Facility for replacement. But teams also took the time to gauge the threat of a small helium leak found on the Starliner’s propulsion system, which managers ultimately decided to not fix before this second launch attempt.

“I mean it’s a really, really small leak and it’s well within the margin that we have,” said NASA Commercial Crew Program manager Steve Stich during a prelaunch press conference Friday. “And so sometimes for spaceflight, you plan for contingencies and you design the vehicle to have margin. And in our case, we have margin in the helium tank and we’ve worked really hard and worked really hard to understand that margin and understand maybe the worst cases.”

Stich said the spacecraft could handle a leak that was 100 times worse and still fly safely.

“We took the time to go through that data, and we really think that we can manage this leak both by looking at it before we launch, and then if it got bigger in flight, we could manage it,” he said.

So if all goes well, Wilmore and Williams will take flight and try for a rendezvous with the ISS at 1:50 p.m. Sunday. They will then stay on board about eight days before making the return trip to Earth for a parachute-assisted desert landing in the southwestern United States as early as June 10.

“Starliner is designed to land on land nominally, oh and with airbags,” said Fincke. “I landed on the land in the Soyuz and the shuttle and I’ll say that these airbags are going to be good. And I think that’s probably the first thing I’m going to ask Butch and Suni after they land it’s like how are the airbags.”

The CFT mission is the final key needed before NASA can certify Starliner so it can begin regular rotational crew missions to the ISS. Boeing is playing catchup to SpaceX, which just celebrated the four-year anniversary of its own crewed test flight, Demo-2, that launched from KSC on May 31, 2020.

SpaceX has since been the sole U.S.-based provider for human spaceflight for NASA. Its fleet of four Crew Dragons have launched 13 times carrying 50 people to space, including last February’s launch of Crew-8, who await the arrival on Starliner on the ISS.

The Commercial Crew Program was designed to end NASA’s reliance on Russia with its Soyuz launches after the end of the Space Shuttle Program in 2011. The contracts for Boeing and SpaceX were awarded in 2014, but both programs faced development delays.

Both of CFT’s crew are retired Navy and have flown to space two times previous each, both on the space shuttle and on Russia Soyuz spacecraft with stays on board the ISS. Wilmore is the commander for this flight and joined NASA in 2000. Williams is pilot and joined in 1998.

“We have been through quite the process over the years,” said Wilmore ahead of the May 6 attempt. “It’s been really a thrilling process. I mean, to be two Navy trained test pilots and be into the process of this first flight, and all that goes into that and all the discovery that we’ve had over the years and working together with our Boeing counterparts, test after test, evaluation after evaluation. Every single day is different, and that’s been intriguing, and thrilling along the way.”

Starliner is only the sixth ever U.S.-based spacecraft to fly with NASA astronauts following Mercury, Gemini, Apollo, the space shuttle and SpaceX’s Crew Dragon.

It also marks a return of human launches from Cape Canaveral’s launch pads, which last saw a crewed flight in 1968 with the launch of Apollo 7. Every Apollo mission afterward as well as the space shuttle and Crew Dragon launches have come from nearby Kennedy Space Center.

It’s the first time an Atlas V will fly with humans as well, although earlier iterations of the Atlas rocket flew several human spaceflights in the early 1960s including John Glenn’s historic trip to space as the first American to each orbit in 1962. This also marks the 100th launch of an Atlas V rocket.

Starliner will also become the first U.S.-based capsule to make a land touchdown as Crew Dragon, Apollo, Gemini and Mercury all made water landings, as will the Artemis program’s Orion capsule that has yet to fly with humans. Russia’s Soyuz, though, features land touchdowns.

The CFT mission comes more than two years since Starliner last flew on the Orbital Flight Test 2 (OFT-2), a successful trip to the ISS without a crew, just a mannequin named “Rosie the Rocketeer.”

The first human to ever venture into Starliner in space was actually NASA’s Bob Hines, a member of Crew-4 in 2022.

“Nobody stepped inside. I floated inside,” he said. “It was me. I got to open the hatch … We had agreed early on that as a new guy, this was a good project for me to kind of take on, and so I was the lead for when the Starliner mission was up there on space station.”

He is now part of the NASA’s joint test team for crews prepping for both SpaceX Dragon and Boeing Starliner, and has been working with the CFT crew leading up to this launch.

“I got to open the hatch and go in and kind of lead that mission,” he said. “It was pretty cool, and it’s almost coming full circle here being very involved in getting crew off the ground.”

Having flown up to the ISS on Dragon, he took note of the differences between the two capsules.

“One, it was very obvious that there are different philosophies in approaching human spaceflight, which is really neat to see as a test pilot,” he said. “A different cabin layout, a totally different capsule design, a different philosophy for operating the vehicle … So it was really neat and eye opening to see another solution.”

That mission was a do-over mission from the original uncrewed test flight, now referred to as OFT-1, that in 2019 saw myriad issues including not being able to dock with the ISS. But now nearly four years behind SpaceX, Boeing, which has spent more than $1.5 billion on Starliner’s development, looks to finally get its spacecraft certified to perform normal rotational missions to the ISS.

“It’s important that we’re making history. I feel that a lot as the Commercial Crew Program manager,” Stich said in early May. “It was just four years ago we brought the Dragon spacecraft online and the Falcon 9 launch vehicle, and then here we are now four years later bringing another system online.”

If all goes well with CFT, that first operational mission, dubbed Starliner-1, could fly with four astronauts to the ISS as early as next February and become the first of six Boeing missions that would share taxi duties with SpaceX to the station until the ISS is decommissioned after 2030.

“We have been striving in Commercial Crew to have two independent space transportation systems,” Stich said. “That’s been our goal since from Commercial Crew’s inception and we’re very close to reaching that goal.”