LAS CRUCES, N.M. — Boeing is delaying a series of test flights of its CST-100 Starliner commercial crew vehicle by up to six months, pushing back the first operational mission of the capsule until the end of 2018.

Boeing spokesman William Barksdale said Oct. 11 that a number of development and production issues with the spacecraft led the company to reschedule the test flights that are part of its Commercial Crew Transportation Capability (CCtCap) contract with NASA. News of the delay was first reported by Aviation Week.

Under the revised schedule, a pad abort test of the CST-100, previously scheduled for October 2017, is now planned for January 2018. An uncrewed CST-100 flight, called the Orbital Flight Test, has shifted from December 2017 to June 2018.

A crewed flight test of the CST-100 to the International Space Station, carrying a NASA astronaut and Boeing test pilot, has been delayed from February to August 2018. If that schedule holds, Being anticipates flying its first operational, or “post-certification,” CST-100 mission to the ISS in December 2018.

Barksdale said that several issues prompted the schedule changes. They included “development to production” delays and minor component qualification test issues, both of which Boeing is resolving. He said the program also suffered delays when a spacecraft dome element was damaged during the manufacturing process.

“Based on those challenges, we stopped and took a hard look at our schedule moving forward and made the adjustment,” he said. “As we learn these hard lessons, we’ll continue to incorporate them throughout the build and test campaigns.”

Just a month ago, Boeing officials believed that the CST-100 would be ready for ISS missions by the middle of 2018. Speaking at the AIAA Space 2016 conference in Long Beach, California, Sept. 14, Chris Ferguson, deputy program manager for commercial crew at Boeing, reiterated a schedule that included a crewed test flight in February 2018 and the first post-certification mission in June 2018.

He acknowledged at that time, though, that it was a “very aggressive” development schedule. “We’re optimistic that we’re going to meet the deadline, but we’ll fly when we’re ready, and that’s really what it comes down to,” he said. “And if it takes a couple of extra months to ensure we have a safe vehicle, we’ll do just that.”

This latest delay comes on the heels of a Sept. 1 report by NASA’s Office of Inspector General that warned that additional delays were likely on CCtCap contracts held by both Boeing and SpaceX. That report said that technical problems, and not a lack of funding, were causing delays in both companies’ programs.

“Notwithstanding the contractors’ optimism, based on the information we gathered during our audit, we believe it unlikely that either Boeing or SpaceX will achieve certified, crewed flight to the ISS until late 2018,” the report stated.

This latest delay could put more pressure on NASA to purchase additional Soyuz seats to avoid a gap in access to the ISS. NASA’s existing contracts with the Russian state space corporation Roscosmos cover flights to the station through 2018, and past contracts have required a lead time of two years or more to acquire additional seats.

NASA Administrator Charles Bolden, asked about the commercial crew program during a Sept. 26 press conference at the International Astronautical Congress in Guadalajara, Mexico, said he was “relatively confident” that the companies would be certified to carry NASA astronauts by late 2018.

He added that, given that schedule confidence, NASA was not thinking about buying additional Soyuz seats. “We are not presently looking at any additional seats beyond those that we have already purchased,” he said.