'Buzzing' rocket valve pushes 1st astronaut launch of Boeing's Starliner capsule to May 10

a white rocket stands on its launch pad on a sunny, clear morning.
Boeing's Starliner capsule sits atop its United Launch Alliance Atlas V rocket ahead of the planned launch of the Crew Flight Test astronaut mission. (Image credit: ULA)

The first crewed flight of Boeing's new Starliner capsule has been pushed to the end of the week due to a technical issue.

Starliner was supposed to launch late Monday night (May 6) on Crew Flight Test (CFT), a roughly 10-day mission that will carry two NASA astronauts to the International Space Station (ISS) and back. But mission teams called the attempt off about two hours before Monday's planned liftoff, after identifying a faulty "oxygen relief valve" on the upper stage of Starliner's rocket ride, a United Launch Alliance (ULA) Atlas V. The valve was "buzzing," opening and closing rapidly, during the launch countdown, forcing the delay, ULA officials said.

NASA, ULA and Boeing initially expressed optimism that the issue could be resolved quickly, perhaps even in time for another launch attempt on Tuesday night (May 7). But, early Tuesday morning, the teams announced that CFT will lift off no earlier than Friday night (May 10). 

"The delay allows teams to complete data analysis on a pressure regulation valve on the liquid oxygen tank of the Atlas V rocket's Centaur upper stage and determine whether it is necessary to replace the valve," NASA officials wrote in an update on Tuesday

A launch on Friday would occur at 9 p.m. EDT (0100 GMT on May 11). There's an additional backup opportunity on Saturday (May 11), NASA officials said. Whenever CFT launches, you can watch the action here at Space.com.

Related: Boeing Starliner 1st astronaut flight: Live updates

It's too soon to know if Starliner and the Atas V will be ready to fly on Friday or Saturday, however. That depends on whether ULA decides to replace the valve, which would require rolling the rocket off the launch pad and back to its assembly facility. 

Teams would then apply "tooling to support the Centaur, and the Starliner on top, and then we'd take off all the pressure and simply remove and replace the valve, pressurize it, remove the tooling, and then we'd be ready to roll back," ULA CEO Tory Bruno said in a post-scrub press conference on Monday night.

"That procedure takes several days," he added. So, if valve replacement turns out to be necessary, "it's unlikely we would be prepared to make another attempt before Sunday." 

CFT's two crewmembers are NASA's Butch Wilmore and Suni Williams. After the scrub was announced, both astronauts disembarked from Starliner and headed back to the crew quarters at NASA's Kennedy Space Center, which is next door to Cape Canaveral Space Force Station, agency officials said.

In 2014, NASA awarded both Boeing and SpaceX multibillion-dollar contracts to fly astronauts to and from the ISS. 

SpaceX has been doing so since 2020 with its Dragon capsule and Falcon 9 rocket; Elon Musk's company has already completed seven such operational crewed flights for NASA and is in the middle of mission number eight. Boeing, however, has experienced numerous delays in Starliner's development and has yet to launch a crew.

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Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with Space.com and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.