A malfunctioning valve in its Atlas 5 launch vehicle will cause Boeing’s CST-100 Starliner to postpone its first crewed flight for a minimum of an additional seven and a half weeks.

NASA revealed late on May 7 that the Crew Flight Test (CFT) mission, which was originally slated for May 6 but was postponed until May 17 at 6:16 p.m. Eastern due to a failing valve in the rocket’s Centaur upper stage, had been rescheduled.

Due to the extended delay, United Launch Alliance will be able to roll the rocket back to its hangar at the Vertical Integration Facility (VIF) in close proximity to the pad in order to replace the Centaur’s liquid oxygen pressure regulator valve. After the stage was filled with liquid oxygen, that valve began to oscillate, making a buzzing sound that the launch pad operators heard.

Tory Bruno, president and chief executive of ULA, expressed worry at a briefing following the May 6 scrub that the vibration may have brought the valve closer to its 200,000 cycle rated life. He saw that the valve was vibrating at 40 hertz.

Then, he stated that engineers would investigate whether such vibrations included the valve operating through its full cycle. In that case, ULA would need to swap out the valve. If the valve was only partially operating, though, it might not be close to the end of its design life and could be kept in place. During the meeting, officials indicated that they would try to launch again the following day. However, they later changed the launch date to May 10, which is the next available date before this most recent delay.

NASA said in a statement regarding the latest delay that although the vibration in the valve was reduced when it was closed following the scrub, it reappeared twice during the rocket’s propellant dump.

“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 revised date is a little later than anticipated. According to Bruno, changing the valve requires establishing equipment to sustain the stage, which can take many days. “We don’t think we’d be ready to try again before Sunday, May 12,” he stated.

NASA did not designate that day as a launch date; May 7, 10, and 11 were the backup dates for the initial launch attempt. After May 11, Steve Stich, NASA’s commercial crew program manager, predicted that May 14 or 15 would be the next launch window.

Starliner will dock with the International Space Station when there are no upcoming scheduling conflicts. NASA ISS program manager Dana Weigel stated, “We did clear our summer schedule intentionally to give us plenty of runway for this CFT mission.”

NASA announced that due to this most recent delay, the two astronauts flying the CFT mission, Butch Wilmore and Suni Williams, will stay in pre-flight quarantine at the Kennedy Space Center.