SpaceX has postponed for at least 24 hours the scheduled Florida launch of a Falcon 9 rocket on a satellite-delivery mission and attempted return-landing at sea to allow extra time to chill the rocket's propellant, the company says.
Blast-off of the 23-storey-tall booster and its payload, a SES SA communications satellite, was rescheduled for 6.46pm local time on Thursday from Cape Canaveral Air Force Station, SpaceX said.
"Rocket and spacecraft remain healthy," the company said in a message posted on Twitter as the delay was announced.
Hours earlier SpaceX had described weather conditions at the launch site as a "60 per cent go" and said it was tracking thick clouds and high winds.
Following the delay, the company issued a further statement explaining: "The team opted to hold launch to ensure liquid oxygen temperatures are as cold as possible in an effort to maximise performance of the vehicle."
The statement left unclear how much, if at all, weather was a factor in the postponement.
Meteorologists forecast an 80 per cent chance that weather would be suitable for liftoff on Thursday.
In addition to boosting the 5721kg satellite built by Boeing towards orbit, the rocket's first stage will attempt to turn around and fly itself back to a platform floating in the Atlantic about 645km east of Cape Canaveral.
The mission would mark the second of more than 12 planned launches this year by Space Exploration Technologies, the private rocket service owned and operated by high-tech entrepreneur Elon Musk.
It also would be the fourth attempt at a sea-based return landing of the Falcon 9's main stage, a milestone in Musk's goal to develop a cheap and reusable booster.
A returning SpaceX rocket successfully touched down at a ground-based landing site near the launch pad in December, but three previous attempts to land a returning rocket on an ocean platform failed.