NASA says helium leak poses no threat to the safety of Boeing’s Starliner capsule

After nearly three weeks of exhaustive testing and data analysis, NASA managers said Friday they are confident that Boeing Starliner crew capsule frequently delayed can safely launch “as is” on June 1, saying a small helium leak in the ship’s propulsion system does not pose a flight safety concern.

Steve Stich, manager of NASA’s Commercial Crew Program, said that even if a suspicious rubber seal the size of a shirt button in the plumbing leading to a specific thruster failed completely during flight – resulting in a leak rate 100 times worse than seen to date – the Starliner could still fly safely.

“If we’re wrong about something, we could deal with four more leaks,” he said. “And we could deal with this particular leak if the leak rate increased, up to 100 times in this (propulsion module).”

What will now be a nearly month-long delay in launch was necessary because “we needed time to work on this analysis and to understand the helium leak and understand the ramifications of that,” Stich said.

It also gives the workforce time off during the Memorial Day holiday weekend.

The Starliner’s two NASA crew, Commander Barry “Butch” Wilmore and co-pilot Sunita Williams, plan to fly back to Florida’s Kennedy Space Center next Tuesday to prepare for the launch from Space Force Station Cape Canaveral atop an Atlas 5 rocket at 12:25 pm EDT, June 1.

If all goes well, they will dock with the International Space Station the next day and return to Earth on June 10.

Wilmore and Williams were preparing for the May 6 launch when the countdown was aborted due to problems with an oxygen pressure relief valve on the Centaur upper stage of Atlas 5. Rocket builder United Launch Alliance transported the booster back to a processing facility and replaced the valve without incident.

At the same time, Boeing engineers began a detailed investigation from a small helium leak in one of the Starliner’s four propulsion modules, known as “doghouses,” which appeared when valves were closed as part of normal post-wash procedures.

The leak was eventually traced to a flange where the propellant lines feeding a specific reaction control system thruster in the port cabin come together. The Starliner is equipped with 28 RCS jets and helium is used to pressurize the propellant lines, opening and closing valves in each cockpit as needed.

Because traces of extremely toxic propellants could still be present in the plumbing, the seal could not be replaced or even inspected while the capsule was still attached to the Atlas 5. The Starliner would first have to be transported back to Boeing’s processing hangar at Kennedy. Space Center for invasive repairs that would cause a longer delay.

Instead, NASA and Boeing commissioned testing and analysis to fully understand the leak and what kind of problems it could cause during flight. The observed leak rate did not appear to be a concern, but engineers needed to gain confidence that it would not worsen dramatically. They also wanted to make sure that no other systems were affected.

Stich said the seal in question was likely bent or had a small defect allowing helium to pass through. But tests showed that even if the flange seal was removed, the Starliner could still fly safely. The helium collector in question could be isolated and many of the Starliner’s other thrusters could easily compensate.

Mark Nappi, Boeing’s Starliner program manager, said the May 6 launch had a “silver lining” because it brought the helium leak to everyone’s attention and “now we know exactly where it was, we’ve done all the work to understand the root cause, and this will help us improve the system in the future.”

“If we had launched…it would have been a safe and successful flight,” he said, “but we wouldn’t know as much as we do today.”

This includes an unexpected result, what Stich called “a design vulnerability.” The investigation shows that in the very remote possibility of major problems with two adjacent doghouses, including the one with the helium leak, the Starliner could lose redundancy for firing the thruster needed to deorbit for reentry.

Starliner is designed to support three redundant de-orbit capabilities. In one of them, the braking burn is carried out with four powerful Orbital Maneuvering and Attitude Control (OMAC) thrusters. The burn can also be carried out with just two OMAC jets running, or with eight smaller RCS boosters, firing them for longer than planned.

Under the right circumstances, with adjacent modules out of action, Starliner could lose full RCS deorbit capability from eight boosters.

“We worked with the propellant supplier, Boeing and our NASA team to find a redundant method for doing the in-orbit burn, to divide it into two burns of about 10 minutes each, 80 minutes apart, to get to a de-orbit burn of four RCS thrusters and to recover the capability of the original system,” said Stich.

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