WASHINGTON – NASA and Boeing say they are confident they have solved a problem with the valve that delayed the test flight of the company’s CST-100 Starliner crew last year and are ready to try again later this month.
Boeing moved the Starliner spacecraft from a processing facility at the Kennedy Space Center on May 4 to a United Launch Alliance vehicle processing facility at Space Launch Complex 40. The Starliner will be installed on the Atlas 5 rocket there for final preparation for the orbital flight test (OFT) 2 mission scheduled to launch on May 19 at 6:54 p.m.
The company was hours after the launch of OFT-2 last August, when it cleaned up the issue due to problems with the opening of the fuel valves in the service module of the spacecraft. The company later canceled the launch after finding that 13 valves had corroded closed when nitrogen tetroxide (NTO) interacted with moisture to form nitric acid.
Speaking to reporters on May 3, Boeing officials said that months of investigation with NASA confirmed their earlier assessment that the NTO, penetrating Teflon valve seals, had interacted with ambient moisture to create nitric acid and to corrode the aluminum housing of valves. That assessment included extensive tests at NASA’s White Sands test facility and analysis of corroded valves at the Marshall Space Flight Center.
“There was a significant amount of testing and analysis of the root causes that was done by the whole team,” said Mark Napie, vice president and program manager for Starliner at Boeing. “We are confident that we have the right mitigation.”
This mitigation involves “dry cleaning” the valves with nitrogen gas to remove moisture and sealing an electrical connector, which can be a pathway for moisture to absorb. The NTO was loaded into the spacecraft later during vehicle processing to reduce the time it could penetrate the valve. The valves will also activate every two to five days to confirm that they can move properly.
The valves themselves have not been redesigned, said Michelle Parker, vice president and deputy general manager for space and Boeing launches. “We have a workable solution for OFT-2. We do not expect to have problems, “she said. “We will look at the long term to see if there are any improvements that need to be made. The aluminum housing can be part of it. But right now we are confident in the decision we have. “
The upcoming OFT-2 mission will be Starliner’s second unmanned test flight. The initial OFT mission in December 2019 suffered technical problems, including an incorrectly set mission timer that caused problems after the spacecraft reached orbit, as well as a software problem discovered during the shortened flight that could have caused a collision with the operator. spacecraft module crew module after separation just before re-entry.
“We certainly learned a lot with OFT-1,” Parker said. Key tests for OFT-2 will be to confirm software changes made to deal with problems during the first flight, as well as to approach and dock with the International Space Station, which it was unable to do during OFT. “Those areas that we have not yet demonstrated will be of particular interest to us, although the whole mission has criteria that we must meet.
Starliner will deliver about 225 kilograms of cargo, mostly food, to the station and will stay attached to the station for several days. It will return with about 270 kilograms of cargo, as empty tanks for refueling with nitrogen-oxygen.
The successful OFT-2 flight will allow Boeing to continue its Crew Flight Test (CFT) mission, the first flight with a spacecraft crew. Napi said Boeing could be ready to fly the CFT later this year. “We understand that we will learn a lot from OFT-2,” he added. “This, as well as many other variables, will dictate where the final timetable will fall with the launch of CFT.
Steve Stitch, NASA’s sales crew program manager, confirmed that the CFT could be ready to launch as early as the end of the year. “We are taking it step by step,” he said. “The best way to CFT is a successful OFT-2 flight.”
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