Starliner Crew Flight Test Slips to May 17 at the Earliest

Starliner Crew Flight Test Slips to May 17 at the Earliest

The launch of Boeing’s Starliner Crew Flight Test has slipped to at least May 17. The United Launch Alliance, which builds and operates the Atlas V rocket, determined that the malfunctioning valve that scrubbed last night’s attempt needs to be replaced. That means rolling the rocket back to ULA’s Vertical Integration Facility. NASA astronauts Butch Wilmore and Suni Willams will remain in quarantine in crew quarters at Kennedy Space Center awaiting the next chance for a “go for launch.”

NASA said this evening the launch is now planned for “no earlier than” 6:16 pm ET on May 17 after ULA determined it needed to “remove and replace a pressure regulation valve on the liquid oxygen tank on the Atlas V rocket’s Centaur upper stage.”

Last night, the launch was scrubbed about 2 hours before liftoff because one of the oxidizer valves on the Atlas V’s Centaur upper stage was not behaving properly. Engineers heard a “buzz” or a “flutter” indicating the valve was not seating properly.


During the post-scrub news conference, ULA President Tory Bruno explained this wasn’t the first time it happened on a Centaur, but since they have always launched satellites, not people, they would simply recycle the value and continue with the launch.

In this case, however, ULA has established a flight rule that no changes can be made to the rocket’s fuel state when the crew is onboard. Wilmore and Williams were getting seated in the Starliner capsule when the problem was discovered so the flight rule required the scrub.

Bruno said the valves are rated for 200,000 full cycles and engineers would work overnight to determine how many this specific valve had experienced. If it exceeded the limit, the rocket would have to be returned to ULA’s Vertical Integration Facility (VIF) for repair.

NASA reported today that after the crew exited the spacecraft, ULA engineers closed the valve and the oscillations ceased, but they returned twice more when the rocket was being detanked.

“After evaluating the valve history, data signatures from the launch attempt, and assessing the risks relative to continued use, the ULA team determined the valve exceeded its qualification and mission managers agreed to remove and replace the valve.” — NASA

The roll back will begin tomorrow, returning the Atlas V with Starliner on top to the VIF.  They left the VIF on May 4.

ULA’s Atlas V rocket with Boeing’s Starliner capsule on top departs ULA’s Vertical Integration Facility on the way to the launch pad, May 4, 2024. Credit: ULA

The schedule for when the rocket will return to the launch pad was not provided today.

Williams was philosophical about the possibility of a launch delay when she and Wilmore arrived at Kennedy Space Center last week. She insisted there is nothing “magical” about any launch date and they will launch when everything is ready. The two are experienced Navy test pilots and NASA astronauts. Both have flown two space missions already.

NASA astronauts Butch Wilmore, left, and Suni Williams, right, walk out of crew quarters at Kennedy Space Center on May 6, 2024 to head to Space Launch Complex-41 at the adjacent Cape Canaveral Space Force Station for launch on the Boeing Starliner Crew Flight Test. The launch was scrubbed that night, however. Photo Credit:(NASA/Joel Kowsky

The delay is another setback for Starliner, but this time not because of Boeing’s commercial crew program. Four-and-a-half years after Boeing’s first uncrewed Orbital Flight Test (OFT) revealed significant flaws in the spacecraft’s design and software, two years after a successful second uncrewed OFT, and almost one year after Boeing indefinitely delayed this Crew Flight Test as new problems emerged, the spacecraft seems ready to go.

Now it’s the rocket. This will be the 100th launch of Atlas V and the first to carry people. The rocket has a 100 percent mission success record since the first launch in 2002.

Atlas V was designed and developed by Lockheed Martin in the late 1990s and early 2000s while Boeing was developing the Delta IV for what both companies anticipated would be a robust commercial market. That market did not materialize at the time. The government needed the rockets to launch its satellites, especially for national security, and, at government urging, the two companies formed ULA in 2006 as a joint venture to provide those services. The Atlas V first stage is powered by Russian RD-180 engines and following Russia’s annexation of Crimea from Ukraine in 2014, Congress directed ULA to stop buying them.

ULA decided to develop a new rocket, Vulcan, with American-made engines to replace both Atlas V and Delta IV. The first Vulcan launched in January 2024.  The final Delta IV was launched last month, but about a dozen-and-a-half Atlas Vs remain and will continue to launch through the end of the decade. ULA already has all the RD-180 engines it needs for those missions.

The Atlas program itself dates back to the 1950s and four Atlas rockets launched astronauts into orbit in 1962 and 1963. The first, Mercury-Atlas 6, sent John Glenn into orbit almost exactly 62 years ago on May 5, 1962. He was the first American to orbit the Earth. (Alan Shepard was the first American in space in 1961 on Mercury-Redstone 3, but the Redstone rocket was suborbital only). The last Atlas flight with an astronaut was in May 1963.  Since then astronauts have launched on Titan for the Gemini program (1965-1966), Saturn for Apollo (1967-1975), the Space Shuttle (1981-2011), and Falcon 9 for Crew Dragon (2020-present).

The Centaur upper stage, or second stage, also has a long history dating back to the 1950s and has been used with Titan, Atlas, Delta, and now the new Vulcan.

The version used with Atlas V has been in use for decades and in recent years typically has one Liquid Oxygen/Liquid Hydrogen RL10 engine. Two are needed to boost Starliner, however, so the ride is gentler and the astronauts can abort the launch at any point on the way to space.  The dual-engine design successfully launched the OFT and OFT-2 uncrewed test flights in 2019 and 2022.  RL10s are made by Aerojet Rocketdyne, an L3Harris Technologies company.

Atlas V-Centaur does not actually put Starliner into orbit, but flies a suborbital trajectory. Starliner’s own engines put it into orbit after it separates from Centaur. That maneuver was one of the problems on the first OFT because Boeing incorrectly set the timer for when the engine should fire. Everything worked fine on OFT-2.

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