SpaceX has called off its second attempt to launch a Falcon 9 rocket on a satellite-delivery mission because of technical difficulties.
The rocket was first due to launch on Wednesday, but this was postponed for a day to allow more time to chill the liquid oxygen needed to burn the fuel, amid speculation that bad weather also played a role.
On Thursday, the reattempted launch was abandoned again less than two minutes from lift-off from Cape Canaveral Air Force Station in Florida.
The launch team was overseeing the final loading of super-chilled liquid oxygen propellant into the rocket's first and second stages when the countdown was halted.
"Preliminary (information) is that we were... looking at how much time we had left in the count to finish loading the liquid oxygen and at that time the launch team decided that we would need to hold the countdown," said John Insprucker, SpaceX commentator, during a live launch webcast.
Perched atop the rocket is a 5,721kg Boeing-built satellite owned by Luxembourg-based network operator SES SA.
SpaceX is aiming to deliver the satellite as high as 39,000km above Earth and still have enough fuel to fly the first stage of the Falcon rocket to a platform floating about 645km off Florida's coast for a return landing at sea.
After a number of failed attempts, SpaceX successfully returned its upgraded Falcon 9 rocket to flight in December after an explosion earlier in 2015.
Meanwhile, NASA astronaut Scott Kelly is due to return to earth next week after nearly a year aboard the International Space Station (ISS).
His time spent in space is now the longest US spaceflight and he admitted that the secret to spending so much time aboard the station is marking individual milestones, not ticking days off the calendar.
Since arriving at the ISS in March last year, Kelly and Russian cosmonaut Mikhail Korneinko have served with eight different crewmates, unpacked six cargo ships, weathered two botched supply runs and participated in dozens of science experiments.
Kelly also made three spacewalks outside the $100bn station, which flies about 400km above Earth.
"I've tried to do this with a deliberate pace, looking not really at the end, but at the next milestone," Kelly told reporters during his last inflight press conference.
"I could go another 100 days; I could go another year if I had to," he added.