Experts concerned by SpaceX plan to fuel rockets with people aboard

The recovered first stage of a SpaceX Falcon 9 rocket is transported to the SpaceX hangar at launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida May 14, 2016. REUTERS/Joe Skipper

A proposal by Elon Musk's SpaceX to fuel its rockets while astronauts are aboard poses safety risks, a group of space industry experts that advises NASA has told the U.S. space agency.

"This is a hazardous operation," Space Station Advisory Committee Chairman Thomas Stafford, a former NASA astronaut and retired Air Force general, said during a conference call on Monday.