How corroded valves may have delayed the launch of Boeing’s Starliner

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Boeing says it is narrowing down the source of the issue that delayed the launch of its new Starliner spacecraft this summer, blaming the problem on excess water and humidity causing the vehicle’s valves to stick ahead of the flight. The company plans to extensively study the problematic valves over the months ahead and implement design changes, with the hope of launching Starliner again in mid-2022.

Boeing’s CST-100 Starliner is a new passenger spacecraft, designed to carry astronauts to and from the International Space Station for NASA’s Commercial Crew Program. Before Starliner can carry a crew, however, NASA wants Boeing to launch a successful flight of the vehicle without people on board, to prove the spacecraft can safely go through all the motions of a typical launch.

But Boeing’s attempts to launch an uncrewed Starliner have hit quite a few speed bumps along the way. The company launched the vehicle without a crew for the first time in December 2019, but a series of software glitches prevented the spacecraft from reaching the right orbit needed to meet up with the International Space Station, and flight controllers had to bring the vehicle back earlier than planned. Boeing hoped to try again in early August 2021, by launching another empty Starliner. But just hours before liftoff, the company found that a number of Starliner’s valves, used to transport oxidizer — a critical propellant needed for the flight — weren’t in the right alignment.

In an update today, Boeing officials said that 13 of the 24 oxidizer valves would not behave properly, sticking in the wrong position. While Starliner was still on the launchpad, Boeing was able to free up nine of the 13 sticky valves, but four stubbornly wouldn’t move correctly. That prompted Boeing to return Starliner back to the factory for a closer look. Since then, engineers have dissected three of the valves, which helped them figure out what happened.


Boeing’s CST-100 Starliner ahead of launch.
Photo by Gregg Newton / AFP via Getty Images

“We were able to eliminate a number of those items such as wiring or bad instrumentation of giving a faulty reading,” Michelle Parker, vice president and chief engineer at Boeing, said during a press conference on Tuesday.

Ultimately, Boeing thinks that some of the oxidizer inside the valves actually escaped, leading to the stickiness. The valves are sealed with Teflon, and it’s known that oxidizer can sometimes permeate through Teflon material, according to the company. Boeing said Teflon is “chosen because it’s compatible with the oxidizer,” while other seal materials are not. The theory is that when the oxidizer escaped, it mingled with extra moisture and humidity at the launch site, causing the valves to slightly corrode. And this corrosion is why Boeing couldn’t get the valves to move as they wanted.

Since the launch delay, Boeing says it has freed up 12 of the 13 stuck valves using a combination of extra heating and higher voltages. The Starliner team is keeping one valve stuck intentionally in the meantime, as they determine what kind of fixes they can put in place to ensure this doesn’t happen again. That might include the addition of extra heaters in the valves. Additionally, Boeing removed two of the valves and is sending them to NASA’s Marshall Space Flight Center, where they’ll undergo CT scans for even more stringent analysis.

Perhaps most concerning is that Boeing still doesn’t understand why the problem didn’t present itself ahead of the flight. The company claims that engineers did plenty of testing on the valves before the vehicle was on the launchpad, and the equipment worked as expected. “We had no indication that there was going to be any problem with these valves,” John Vollmer, Boeing’s program manager for Starliner, said. Vollmer claims Boeing added oxidizer into Starliner 46 days ahead of the flight, but they expected to be able to add the liquid up to 60 days ahead of the mission without any problems.

If Boeing does fly Starliner in the middle of next year, the company hopes to fly the vehicle with its first passengers toward the end of 2022. “[Our objective] is to get back to flight safely — and I stress safely — as soon as possible,” Vollmer said. “So everything we’ve done up to this point, and the path that we’re developing going forward, is going to enable us to meet that goal and getting back to fly safely.” Meanwhile, NASA’s other Commercial Crew provider, SpaceX, has already begun regularly flying astronauts to and from the International Space Station, with another launch coming up on October 31st. When Starliner starts flying, the plan is for SpaceX to fly crews once a year and for Boeing to fly crews once a year.

When asked what would have happened if Starliner had launched with the sticky valves, Boeing said that such a scenario could never have occurred, because flight controllers must check the valves before flight. “This was one of those things that had to absolutely work, or else we would not fly,” Vollmer said. “So, this is not an issue of, if we had launched and not known this. We absolutely knew that these valves would be in the right position before launch.”

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