The space shuttle Discovery won't be blasting off tonight because engineers have found a problem with a fuel sensor.
"We will not fly today" said commentator George Diller.
This is not the first problem that Discovery has had, a window cover recently fell off, damaging the craft.
This would have been NASA's first space shuttle mission since the Columbia disaster in 2003.
The shuttle was set to take-off from the Kennedy Space Center at 8.51pm UK time.
When re-scheduled, the mission will take 12 days, during which time Discovery will carry a crew of seven to the International Space Station with supplies and parts.