Entrepreneur Elon Musk’s Space Exploration Technologies Corp. has decided to delay to 2018 from 2017 the first manned launch of its Dragon capsule intended to carry U.S. astronauts into orbit.

The company privately reported the slippage to the National Aeronautics and Space Administration earlier this year and confirmed it on Monday. The nearly one-year delay, to the second quarter of 2018 from the spring of 2017, comes in the midst of top-priority efforts to develop new launchpad fueling procedures affecting the company’s entire fleet of Falcon 9 rockets. A company spokesman initially described it as a slip of several months, but a NASA document indicates the initial manned mission had been targeted for April 2017.

Problematic loading of supercooled fuels is believed to be the cause of a catastrophic explosion that destroyed an unmanned Falcon 9 during routine ground tests in September and, according to critics, also poses significant safety hazards for future crews destined for the international space station.

More than a year ago, a NASA advisory committee quietly raised concerns about possible dangers stemming from SpaceX’s novel plans to fuel rockets while astronauts are strapped into capsules loaded on board.

The committee recently received an updated agency briefing about the issue amid unusual secrecy, but people familiar with the meeting said details about the most likely procedural changes weren’t shared.