Boeing’s First Astronaut Flight on Starliner Faces Further Delay

Last summer, before stuck valves caused Boeing and the National Aeronautics and Space Administration to postpone a planned launch, the agency and company said they believed the Starliner could carry astronauts to the International Space Station on a test mission by the end of the year.

Mr. Vollmer’s comments came at a briefing on Tuesday, where Boeing and NASA officials offered details about their work trying to identify why some of the valves on the Starliner propulsion system became stuck and botched the planned launch in August. Boeing and the space agency postponed that flight because of the problem.

Michelle Parker,

chief engineer for space and launch at Boeing, said Tuesday that the most likely cause of the valves problem was a corrosive substance created when moisture and oxidizer combined.

Humidity is the probable source of the moisture that interacted with the oxidizer, Ms. Parker said. She said the company accounts for humidity when sourcing parts from suppliers and has a purge system meant to keep the valves dry.

Boeing has wrestled with setbacks on the Starliner before. Almost two years ago, during the first attempted test launch of the ship without crew members, a software error prevented the Starliner from reaching the correct orbit. The company previously booked a $410 million charge tied to the do-over of the launch.

In 2014, NASA hired Boeing and Space Exploration Technologies Corp., the formal name for Elon Musk’s SpaceX, to develop spacecraft that could carry astronauts to the space station and return them to Earth. At the time, the agency didn’t have a way to transport people to the research facility other than purchasing seats on Russian government rockets.

SpaceX last year launched astronauts from the U.S. to the space station for the first time since NASA retired the space shuttle in 2011, and brought them back. The company has completed other crewed missions to the space station and is slated to launch four astronauts to the research facility this month and ferry others from there to the ground in November.

Steve Stich,

a program manager at NASA, said eventually the space agency would like Boeing and SpaceX to be flying once a year each, part of the agency’s goal of having two space vehicles that could reach the space station.

“We’re looking forward to the day that we get into those flights where we’re handing over from a SpaceX vehicle on orbit to a Boeing vehicle and vice versa,” Mr. Stich said.

Two of the valves that became stuck have been removed from the vehicle and will be sent to the NASA Marshall Space Flight Center for analysis, officials said Tuesday.

Write to Micah Maidenberg at micah.maidenberg@wsj.com