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WASHINGTON — The first crewed flight of Boeing’s CST-100 Starliner will be delayed at least another week and a half to replace a faulty valve in its Atlas 5 launch vehicle.
NASA announced late May 7 that the Crew Flight Test (CFT) mission, whose launch was scrubbed May 6 because of a malfunctioning valve in the rocket’s Centaur upper stage, had been rescheduled for no earlier than May 17 at 6:16 p.m. Eastern.
The lengthy delay will allow United Launch Alliance to roll the rocket back to its Vertical Integration Facility (VIF) hangar near the pad to replace a liquid oxygen pressure regulation valve in the Centaur. That valve started oscillating after the stage was loaded with liquid oxygen, creating a buzzing noise noticed by launch pad crews.
At a briefing after the May 6 scrub, Tory Bruno, president and chief executive of ULA, said the concern was that the vibration could have caused the valve to approach its rated life of 200,000 cycles. The valve was vibrating at 40 hertz, he noted.
He said then that engineers would examine if those vibrations involved full cycles of the valve. If so, then ULA would have to replace the valve. However, if the valve was only partially moving, then it was possible the valve was not nearing its design life and could be retained. Officials said at the briefing that they could try to launch again the next day, but later revised the launch date to the next opportunity, May 10, before this latest delay.
In NASA’s statement about the new delay, the agency said that while the valve vibration was dampened once the valve was closed after the scrub, that vibration returned twice while propellant was being offloaded from the rocket.
“After evaluating the valve history, data signatures from the launch attempt, and assessing the risks relative to continued use, the ULA team determined the valve exceeded its qualification and mission managers agreed to remove and replace the valve,” NASA stated.
The new date is somewhat later than projections given at the briefing. Bruno said the procedure to replace the valve, which involves installing tooling to support the stage, takes several days. “It’s unlikely we would be prepared to make another attempt before Sunday [May 12],” he said.
That was not one of the days NASA had identified as a launch date, with backup dates for the original launch attempt of May 7, 10 and 11. Steve Stich, NASA commercial crew program manager, estimated the next available launch opportunity after May 11 to be May 14 or 15.
There are no near-term schedule conflicts for a launch on the International Space Station, to which Starliner will dock. “We did clear our summer schedule intentionally to give us plenty of runway for this CFT mission,” Dana Weigel, NASA ISS program manager, said at the briefing.
The two astronauts flying the CFT mission, Butch Wilmore and Suni Williams, will remain at the Kennedy Space Center in pre-flight quarantine for this latest delay, NASA said.