Virgin Galactic told analysts on an August conference call it was targeting its first private astronaut flight for “late Q3” next year.

Shares of the company fell 14% in postmarket trading to $20.59.

A recent lab test identified a possible issue with the strength margins of certain materials used to modify joints that will require further analysis but have “no impact” on its space vehicles, Virgin Galactic said.

“Our decisions are driven by detailed and thorough analysis, and we fly based on the most accurate and comprehensive data available,” Michael Colglazier, the company’s chief executive officer, said in the statement.

Virgin Galactic, founded by entrepreneur Richard Branson, has been working to commercialize space flight since 2004. It received regulatory approval from the Federal Aviation Administration to fly customers into space in June.

The rescheduling is unrelated to an internal probe into a potentially defective part, Virgin Galactic said. Last month, it delayed the flight window for the research mission to mid-October due to a possible problem with a flight control actuation system component.

The upcoming research flight is scheduled to include two members of the Italian Air Force, an aerospace engineer and a Virgin Galactic employee.

The FAA lifted a ban on the company’s test flights last month after concluding an investigation into Virgin Galactic’s failure to inform the agency of an errant trajectory in a July 11 launch, which carried Branson and three others. The regulator had grounded it on Sept. 2.