Boeing was forced to scrub its launch of the CST-100 Starliner OFT-2 mission in early August, only hours ahead of its scheduled launch. The problem was that 13 valves that control propellant stuck in the off position wouldn’t activate. Boeing tried to troubleshoot the issue on the launchpad, but eventually, the rocket was removed so it could be disassembled for investigation.
Boeing has confirmed that the delay in launch caused by the sticky valves will extend well into next year. Boeing also shed some light on how the testing process is going. While the investigation into what caused the valves to stick in the closed position is ongoing, the main focus is now related to moisture and created nitric oxide in the nitrogen tetroxide (NTO) propellant corroding the valve.
Boeing believes that the nitrogen tetroxide propellant leaking into the valve reacted with moisture to create nitric oxide, which led to valve corrosion. Boeing officials say they developed an extensive flow chart and have looked at every possibility that could have caused the stuck valve issue. Currently, they are 75 percent through that flow chart and are continuing to click off boxes.
NASA is working along with Boeing on the investigation as well as Aerojet Rocketdyne. The latter company provided the propulsion system for Starliner. Marotta produces the valves in question and are participating in the investigation as well. Boeing has removed several valves from the spacecraft for analysis, and they will be sent to the Marshall Space Flight Center for CT scans and additional testing.
One significant mystery is why the corrosion showed up on this spacecraft but wasn’t seen in the first uncrewed flight test flight or other ground tests. Boeing points out that the valves are the same units and part numbers used in the module hot fire and other testing. No changes have been made to the valves. Boeing is investigating how long the propellant was in the tank of the spacecraft before launch and how humidity could have contributed to the formation of moisture. They are clear that the previous Environmental Qualification Testing performed with the same spacecraft is not a cause of the sticky valves.