The Boeing Starliner flight for NASA astronauts has been cancelled

United Launch Alliance, the manufacturer of the Atlas V rocket, said the rocket will be returned from the launch pad to replace the valve that regulates the pressure in the oxygen tank in the second stage.

This led to the postponement of the first-ever crewed flight of the Starliner, a flight for NASA astronauts to and from the International Space Station, which has seen a series of costly delays over the past several years.

About three hours before the scheduled launch time of 10:34 p.m. ET, and once the astronauts reached the launch pad, the valve began buzzing at a rate of about 40 times per second. The crew on the launch pad described hearing an “unusual audible sound” to flight controllers.

Preparations for the flight continued with Mr. Wilmore and Ms. Williams boarding the spacecraft. But at 8:34 p.m. ET, two hours before the scheduled liftoff, United Launch Alliance, the company that manufactures and operates the rocket, canceled the flight.

This behavior has previously been observed during some other Atlas V launches, and typically opening and closing the valve stops the hum, ULA CEO Torey Bruno said.

But for astronaut launches, ULA made a rule not to do anything that might change the state of the rocket while astronauts were present, including opening and closing the valve. This in itself was not a dangerous act, but it would have increased uncertainty.

“Our philosophy is that we don’t need to change the state of the vehicle when people are there, so we won’t do that,” Bruno said at a news conference Monday night with officials from NASA and Boeing.

After the astronauts exited the Starliner and returned to their crew quarters, the valve closed and the buzzing stopped. But the oscillations were repeated twice when the propellant was drained from the tanks.

After reviewing the data, ULA engineers concluded that the valve had exceeded the maximum number of times it could reliably open and close and needed to be replaced.

Boeing was one of two companies to win a contract to build a spacecraft to transport astronauts to and from the space station several years after NASA retired its space shuttles in 2011. For nine years, astronauts could only reach the ISS aboard a Russian Soyuz spacecraft. . Missiles.

The other company was SpaceX. In May 2020, NASA astronauts Bob Behnken and Doug Hurley flew to the International Space Station in SpaceX’s Crew Dragon spacecraft. That capsule has since become the only way to reach orbit from the United States.

Development of Boeing’s Starliner took much longer than expected. Technical risks included inadequate software testing, corrosion of thrust valves, flammable tape, and a key component of the parachute system that turned out to be weaker than designed. Boeing fixed the problems, and it was finally ready to go. The delays have left Boeing facing unexpected charges worth more than $1.4 billion.

While the canceled flight on Monday was due to the rocket, the postponed launch attempt comes during a difficult 2024 for the space giant. Just days into the year, a panel on the fuselage of a Boeing 737 MAX 9 exploded during an Alaska Airlines flight. The pilots were able to land the plane safely, and there were no serious injuries, but the accident had wide-ranging repercussions for the company, especially its aviation department.

Neeraj Chokshi Contributed to reports.