WASHINGTON – Boeing says it is considering redesigning the propulsion valves on the future CST-100 Starliner commercial spacecraft as a long-term solution to the corrosion problem those valves suffered from last year.
In a May 11 briefing on the upcoming Orbital Flight Test (OFT) 2 mission, Boeing’s program manager said that while a solution to prevent valve corrosion is working for the upcoming mission, a valve redesign is “definitely on the table”. as a long-term solution, something the company had not previously recognized.
The OFT-2 launch last August was called off and ultimately called off when more than a dozen oxidizer valves in the spacecraft’s service module failed to open when commanded during pre-launch tests. An investigation by Boeing and NASA concluded that nitrogen tetroxide (NTO) propellant was leaking through the valve’s Teflon seals and reacting with ambient moisture, creating nitric acid that corroded the valve’s aluminum.
Boeing developed a solution to prevent that corrosion that doesn’t make any changes to the valve itself, aside from sealing an electrical connector that provided a path for moisture to enter the valve. That solution includes loading NTO into the spacecraft later in spacecraft processing to reduce the time it can leak through the valve and dry purging the valves with nitrogen gas to remove moisture.
Mark Nappi, Boeing’s vice president and commercial crew program manager, told the briefing that the solution, which also includes cycling the valves once every several days, is working. “We cycled [oxidizer] valves four times so far,” he said. “They are working very well.”
However, Boeing said in a statement to Reuters that the company was working on “short-term and long-term design changes to the valves.” The statement appeared in a May 11 story about a dispute between Boeing and valve supplier Aerojet Rocketdyne over the cause of the corrosion, with Aerojet claiming it was caused by a cleaning solution Boeing used in ground tests. from valvule.
Boeing had not previously disclosed plans to redesign the valves. In a May 3 briefing, Michelle Parker, Boeing’s vice president and deputy general manager for space and launch, said there were no changes to the valve design for the OFT-2 mission. When she was asked later about the long-term changes, she was noncommittal.
“We have a usable solution for OFT-2. We don’t expect to have any problems,” he said at that earlier briefing. “As always, we will look long term and see if improvements can be made, as someone mentioned the aluminum casing may be a part of that, but at this point we are confident in the solution we have, and will continue to look at future missions.”
Nappi said at the May 11 briefing that Boeing had been considering a valve redesign for some time. “The short-term solution has been not to have a redesigned valve,” he said. “For the long-term solution, we have been looking at options for at least a month, if not longer, and have included a valve redesign as an option.”
Those plans, he said, depend on ongoing testing. “We are already looking at different options for CFT,” the crew flight test mission that would follow OFT-2 and be the first mission to carry people. “It hasn’t been decided yet what we’re going to do, but I can tell you that a valve redesign is definitely on the table.”
Steve Stich, manager of NASA’s commercial crew program, said the agency supported Boeing’s focus on a short-term fix for the OFT-2 mission while it continues to study long-term changes to the valve. Those changes, he said, could include the use of different materials or different ways to seal the valve.
“We chose to implement the mitigations that Mark talked about and stick with the qualified valve design,” said Stich. “We can fly the flight with this. We know that this flight is safe to fly. We know the valves are working.”
The briefing came after a flight test readiness review that confirmed plans for OFT-2 to launch at 6:54 p.m. ET on May 19, with a backup launch date. by 6:32 p.m. dock with the International Space Station about 24 hours later. Starliner will remain at the station for several days to carry out tests and transfer more than 200 kilograms of cargo before undocking. The spacecraft’s primary landing site is White Sands Space Harbor in New Mexico, the landing site of the original OFT mission in December 2019.