Starliner launch delayed to at least May 17 to replace suspect valve in Atlas 5 rocket

After analyzing data following a launch scrub Monday, United Launch Alliance managers decided to haul the Atlas 5 rocket carrying Boeing's Starliner astronaut ferry ship back to its processing facility to replace a suspect valve, delaying another launch try to at least May 17, NASA said in a blog post Tuesday.

The new "no-earlier-than" launch target from Florida's Cape Canaveral Space Force Station — 6:16 p.m. EDT a week from Friday — will give engineers more time to carry out the valve repair while setting up a rendezvous with the International Space Station that fits into the U.S. Eastern Range launch schedule, which coordinates all rocket flights from the East Coast.

A United Launch Alliance Atlas 5 rocket carrying Boeing's Starliner crew capsule stands poised atop pad 41 at the Cape Canaveral Space Force Station in Florida. After a launch scrub Monday, the rocket will be hauled back to a processing facility where engineers can replace a suspect oxygen pressure relief valve in Centaur upper stage. The next launch attempt is targeted for no earlier than May 17. / Credit: United Launch Alliance

The Starliner, Boeing's long-delayed answer to SpaceX's Crew Dragon spacecraft, was grounded Monday just two hours before its planned launch on its first piloted test flight to the space station. On board were NASA astronauts Barry "Butch" Wilmore and Sunita Williams.

The culprit: a pressure relief valve in the rocket's Centaur upper stage liquid oxygen plumbing that failed to seat properly during the final stages of propellant loading. The valve repeatedly "chattered" as it attempted to seal, rapidly opening and closing so fast engineers at the launch pad reported an audible hum.

ULA engineers could have carried out a procedure to force the valve in place and likely would have done so for a normal satellite launch. But conservative flight rules in place for the Starliner flight ruled out any changes to the "fueled state" of the rocket while the astronauts were on board. As a result, the launch was scrubbed.

The valve in question was designed to "self regulate," opening and closing as needed to bleed off gaseous oxygen buildups in the Centaur's liquid oxygen tank. It was certified for 200,000 open-close cycles.

"The oscillating behavior of the valve during prelaunch operations ultimately resulted in mission teams calling a launch scrub on May 6," NASA said in a blog post. "After the ground and flight crew safely egressed from Space Launch Complex-41, the ULA team successfully commanded the valve closed and the oscillations were temporarily dampened.

"The oscillations then re-occurred twice during fuel removal operations. 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."

The ULA team plans to haul the Atlas 5 and its mobile launch platform back to the nearby Vertical Integration Facility on Wednesday. After the valve is replaced and tested, the rocket will be moved back to the pad for normal pre-launch preparations.

In the wake of the space shuttle's retirement, NASA funded development of two independently designed, built and operated crew transport craft, awarding a $4.2 billion contract to Boeing for its Starliner and a $2.6 billion contract to SpaceX for the company's Crew Dragon ferry ship.

The Starliner is years behind schedule after a series of technical problems that have cost Boeing more than $1 billion to correct. In the meantime, SpaceX's Crew Dragon has carried 50 astronauts, cosmonauts and civilians into orbit in 13 flights, 12 of them to the space station.

While Boeing has been under intense scrutiny in recent months because of problems with its 737 airliners, the Starliner program, while behind schedule, is a separate operation. The launch delay was not the result of any problem with Boeing hardware.

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