Scrub! NASA's Boeing Starliner crewed test launch postponed Monday night at Cape Canaveral

Scrub! Turns out NASA astronauts Suni Williams and Butch Wilmore will have to wait until Friday at the earliest to take Boeing's Starliner capsule on its first crewed test flight.

The astronauts were scheduled to lift off at 10:34 p.m. EDT aboard a United Launch Alliance Atlas V rocket for a historic trip to the International Space Station from Launch Complex 41.

However, about two hours before liftoff — and after the astronauts had boarded the spacecraft — ULA Launch Director Tom Heter III decided that launch operations would not continue.

Cape Canaveral: Is there a launch today? Upcoming SpaceX, NASA, ULA rocket launch schedule in Florida

Why? The mission was scrubbed so crews could work through the night evaluating a "buzzing" liquid-oxygen self-regulating solenoid relief valve on the Centaur upper stage, ULA President and CEO Tory Bruno said during a NASA late-night news conference.

Early Tuesday morning, ULA officials announced, "the team needs additional time to complete a full assessment, so we are targeting the next launch attempt no earlier than Friday, May 10."

For Starliner mission updates, visit floridatoday.com/space.

Following are FLORIDA TODAY Space Team live updates that chronicled Monday's unsuccessful launch attempt.

NASA administrator: 'We go when we're ready'

Update 8:57 p.m.: In a tweet, NASA Administrator Bill Nelson said the following: "Standing down on tonight’s attempt to launch #Starliner. As I’ve said before, @NASA's first priority is safety. We go when we’re ready."

Centaur oxygen valve was the culprit

Update 8:49 p.m.: NASA TV broadcaster Megan Cruz just announced tonight's mission was scrubbed so crews can evaluate an oxygen relief valve on the Centaur second stage.

Scrub!

Update 8:40: United Launch Alliance just announced that launch operations will not continue tonight.

Today to mark 100th Atlas V launch

Update 8:33 p.m.: ULA officials just announced today's upcoming Starliner crewed test mission will mark the 100th launch of an Atlas V.

"Did you know? Today is the 100th launch of an #AtlasV, which has demonstrated reliability spanning more than 20 years and successfully launched scientific spacecraft to Mars on five different occasions, plus the Sun, the Moon, Jupiter, the Asteroid Bennu and Pluto — all with bulls-eye trajectories every time," a ULA tweet said.

SpaceX Dragon, Boeing Starliner differences

Update 8:15 p.m.: FLORIDA TODAY spoke Sunday with NASA astronaut Bob Hines, who is leading astronaut development and testing of Boeing's CST-100 Starliner. Hines, who piloted the SpaceX Crew-4 mission, spoke about the differences between Starliner and SpaceX's Dragon.

“It’s very interesting seeing two different philosophical approaches to accomplish the same mission. They are fairly different. The Dragon is designed to be primarily operated from the ground. Mission Control in Hawthorne, the SpaceX mission control, they manage a lot of the vehicle there, whereas Starliner is designed to be more operated by the crew," Hines said.

"It’s (Starliner) a much more crew-centric vehicle,” he said.

Starliner astronauts enter the spacecraft

Update 7:58 p.m.: Boeing Space officials report the astronauts will "undergo a series of checks, including umbilical hook ups, communications checks and suit checks," along with spacecraft checks ahead of flight.

NASA astronauts en route to launch pad

Update 7:39 p.m.: Wilmore and Williams have departed NASA's Neil Armstrong Operations and Checkout Building, greeted well-wishers, boarded an Astrovan, and driven past the KSC press site to Launch Complex 41.

ULA: Starliner launch weather still 95% 'go'

Update 7:11 p.m.: Just under an hour ago, ULA officials announced weather conditions continue holding at a 95% "go for launch" status.

"Launch Weather Officer Brian Belson in his latest briefing indicates conditions are acceptable with little threat of lightning for the Blue Team's entrance into the launch pad and for the next few hours of work to load the flight crew into Starliner," the blog post said.

"The forecast continues to reflect a 95 chance of meeting the launch weather rules at liftoff time today with a few clouds, southeasterly winds of 12 gusting to 18 knots and a temperature near 73 degrees F," the post said.

Suni Williams saluted by Florida Tech

Update 7:02 p.m.: NASA astronaut Suni Williams, who earned a Florida Institute of Technology master's degree in engineering management in 1995, received well wishes from her alma mater less than two hours ago.

"We wish Sunita and Cmdr. Butch Wilmore a safe voyage to the International Space Station!" Florida Tech officials said in a tweet featuring a video message.

Starliner astronauts putting on spacesuits

Update 6:41 p.m.: NASA astronauts Suni Williams and Butch Wilmore continue suiting up for the upcoming launch with less than four hours to go before liftoff.

Their vehicle awaits:

NASA TV launch broadcast begins

Update 6:30 p.m.: NASA TV has kicked off its live broadcast of tonight's Starliner crewed test flight.

Awaiting the Starliner crew walkout

Update 6:14 p.m.: FLORIDA TODAY Space Reporter Brooke Edwards is in position waiting for the crew to emerge from the Neil Armstrong Operations and Checkout Building.

About the Starliner CFT mission patch

Update 6 p.m.: In a blog post, ULA officials said Wilmore and Williams added personal touches to the development of their mission patch.

"The prominence of orange, for example, surrounding the Starliner spacecraft and the Atlas V rocket is based on orange historically signifying flight testing. In fact, some refer to the color as 'flight test orange,' " the post said.

"The orange is also a nod to Wilmore and Williams’ experience in testing new vehicles. Both are experienced U.S. Navy aviators and test pilots, who combined have spent 11,000 hours in more than 50 aircraft, including the F/A-18 Hornet, T-45 Goshawk, H-46 Sea Knight and V-22 Osprey," the post said.

SpaceX Crew-1 pilot: Starliner crew is grateful

Update 5:35 p.m.: NASA astronaut Victor Glover is giving media interviews here at the Kennedy Space Center press site. He piloted the SpaceX Crew-1 mission, and he is set to serve as the pilot of Artemis II, which is slated to fly around the moon as early as fall 2025.

When FLORIDA TODAY interviewed Glover on Sunday, he said he has spoken recently with Williams and Wilmore.

“They are feeling grateful to the team that has worked so hard to get them here. Boeing, the Boeing Mission Operation Team, and NASA team who have worked so hard for so many years,” said Glover.

“I can also say, they are feeling ready,” said Glover. “That’s a huge note of gratitude and confidence in the team.”

Glover said he imagines how the crew is feeling: “I would speculate that they are feeling pretty relaxed. Once you go into quarantine, that’s when things start to really become clear. All the testing is behind you,” said Glover, explaining that now the crew can just soak in the moments before launch, and appreciate how far they have come. “It’s a calm and peaceful time before launch.”

As for piloting the first crewed mission following SpaceX’s Demo 2 certification mission, Glover said, “there was a lot of learning. It was great to fly a new spacecraft as a rookie. I’m a test pilot, just like Butch and Suni.”

ULA's Atlas V rocket: a closer look

Update 5:16 p.m.: ULA officials report that the Atlas V stands 172 feet tall, will weigh 979,000 pounds at liftoff, and will produce 1.6 million pounds of thrust.

The company shared this artist's rendering earlier this afternoon.

Atlas V liquid oxygen fueling begins

Update 4:56 p.m.: Fueling update from ULA:

"Filling of the Atlas V rocket's largest tank has begun. About 48,800 gallons of super-cold oxidizer for the main engine is flowing into the liquid oxygen tank on common core booster first stage," a blog post said.

For the latest news from Cape Canaveral Space Force Station and NASA's Kennedy Space Center, visit floridatoday.com/space.

Rick Neale is a Space Reporter at FLORIDA TODAY. Contact Neale at [email protected]. Twitter/X: @RickNeale1

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This article originally appeared on Florida Today: Scrub! NASA's Boeing Starliner astronaut launch postponed Monday night