It’s not the heat, it’s the humidity that grounded Boeing’s Starliner

NASA and Boeing officials said Tuesday that they have successfully removed two valves from the Starliner spacecraft and have shipped them to Marshall Space Flight Center in Alabama for further analysis.

The forensic examination—the two valves will be inspected with a variety of techniques, including a CT scan—is part of Boeing’s ongoing effort to diagnose the “stuck” valve issue that caused an abort of Starliner’s uncrewed test flight on August 3. With less than five hours remaining in the countdown to launch, during a routine procedure, 13 of the 24 valves that control the flow of dinitrogen tetroxide oxidizer through the service module of the spacecraft would not cycle between closed and open.

An initial diagnostic effort at the launch pad yielded no results, so the Atlas V rocket and spacecraft were rolled back to an integration facility. After more inspection and testing there, engineers decided to “de-stack” the spacecraft and return it to Boeing’s spacecraft processing building at Kennedy Space Center. This eventually led to further dissection of the vehicle and removal of several valves.

Corrosive humidity

Boeing’s chief engineer for space and launch, Michelle Parker, said during a news conference with reporters Tuesday that the company has a pretty solid hypothesis for what went wrong. At some point during the 46-day period when the vehicle was fueled—and when the valves were found to be stuck—humidity must have gotten into the spacecraft. This moisture combined with the oxidizer and created nitric acid, beginning the process of corrosion.

Parker said dew points at the launch site were high in August, and while the vehicle was designed to operate in Florida’s humidity, there is physical evidence that humidity is nonetheless the culprit. Boeing and NASA engineers now want to try to recreate the corrosive reaction in similar test conditions so that they can be confident of the root cause and any countermeasures they implement.

The company and NASA will press ahead with work in Florida, Alabama, and at Boeing’s test site in White Sands, New Mexico. All of this will take time, acknowledged Boeing’s program manager for commercial crew, John Vollmer. He said Boeing is now targeting the “first half” of 2022 for the uncrewed test flight of Starliner. (One source told Ars the “no earlier than” date is May 2022).

This mission is formally named Orbital Flight Test-2, or OFT-2. The company is flying OFT-2 at its own expense, $410 million, following an uncrewed Starliner mission in December 2019 that went awry due to software issues. The company’s technicians and engineers worked long and hard after the OFT-1 flight to fix the software, only to have these new hardware problems crop up during launch-day checks on the pad in early August.

NASA is hoping that Boeing can get Starliner up and flying so that it can have a second launch system, alongside SpaceX’s Crew Dragon vehicle, to get its astronauts to and from the International Space Station. Assuming that Boeing safely completes OFT-2, Vollmer said the company and NASA would like to have about six months to review data and prepare for a crewed test flight. That would put the earliest possible launch date for Starliner’s first mission carrying astronauts toward the end of 2022. More realistically, the mission may not fly until early 2023.

After this flight, NASA will certify that Starliner is ready for regular, operational astronaut flights.

Buying more Dragons

As part of its commercial crew program, NASA ordered six “post-certification” missions from SpaceX and Boeing. SpaceX successfully completed its demonstration crewed mission in 2020 and is set to launch its third certified crew mission, Crew-3, to the International Space Station on October 31. A fourth and fifth mission are scheduled to follow in 2022.

During Tuesday’s news conference, NASA’s commercial crew program manager, Steve Stich, said the agency is negotiating additional flights for SpaceX—and possibly Boeing. He said details about those contract extensions could be announced within the next few months. Given the issues discussed Tuesday, It now seems possible that SpaceX could complete its initial six-mission contract before Boeing flies its first certified mission. But Stich is confident that Boeing will get there.

“I have no reason to believe that Boeing won’t be successful in getting Starliner operational,” Stich said. “We’ll get this problem solved, and then we’ll have two space transportation systems like we want.”