As a long-term fix to the corrosion issue that hampered the propellant valves on the CST-100 Starliner commercial crew spaceship last year, Boeing is exploring rebuilding the valves. While a method to prevent valve corrosion is working for the forthcoming mission, Boeing’s program manager claimed that a valve redesign is “absolutely on the table” as a long-term repair, something the firm has not previously acknowledged.

When over a dozen oxidizer valves found in the spacecraft’s service module ended in failure to open when instructed during pre-launch tests, the launch of OFT-2 was postponed and subsequently aborted. Boeing and NASA concluded that NTO propellant seeped via Teflon seals that are in the valve and reacted together with ambient moisture to produce nitric acid, which corroded the valve’s aluminum.

Boeing devised a method of preventing corrosion that involves sealing an electrical link that allowed moisture to enter the valve. This method entails loading NTO into the spaceship later in the processing process to decrease the amount of time it can leak through the valve and performing a dry purge of the valves using nitrogen gas to remove the moisture.

The approach, which also entails cycling the valves once every several days, is working, according to Mark Nappi, program manager and the vice president (VP) of Boeing’s commercial crew program. He said, “So far, we’ve cycled the [oxidizer] valves 4 times.  They’re doing an outstanding job.”

According to Reuters, Boeing is working on “short- and long-term design adjustments to the valves.” The statement was made in a May 11 piece regarding a disagreement between the valve supplier, Aerojet Rocketdyne, and Boeing, over the origin of the corrosion, with Aerojet stating that it was caused by a cleaning solution used in ground tests of the valve by Boeing.

Boeing had kept its intentions to modify the valves a secret until now. Michelle Parker, Boeing’s vice president (VP) and deputy general manager in charge of the space and launch, stated there had been no changes to the valve design for the OFT-2 mission during a May 3 briefing. She was noncommittal subsequently when asked about long-term changes.

“For OFT-2, we’ve got a workable answer.  We don’t expect any problems,” she stated earlier. “As always, we’ll examine long-term to see if there are any improvements that can be made — as someone noted, the aluminum housing could be one of them — but for now, we’re confident in the remedy we have and will continue looking at future missions.”

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