SpaceX has further delayed plans for a satellite launch just two minutes prior to lift-off on Sunday.
The Falcon 9 rocket was first due to launch on Wednesday 24 February, 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.
SpaceX then called off its second attempt at the satellite-delivery mission on Thursday because of last minute technical difficulties.
The 23-storey-high rocket, carrying a communications satellite for Luxembourg-based SES, was less than two minutes from blast-off at 6:47 pm (11:47 am GMT) on Sunday when the team aborted the countdown, SpaceX said during a webcast.
Elon Musk, founder and chief executive of SpaceX and CEO of Tesla Motors, said that Air Force safety officers stopped the countdown after a boat strayed into a restricted zone east of SpaceX's Cape Canaveral Air Force Station launch site.
"Scrambling (helicopter) to get them to move," Musk posted on Twitter.
SpaceX resumed the countdown a few minutes later, aiming for a 7:21 pm launch, but a technical issue automatically stopped the liftoff again, just a second before it was due to take off.
"Launch aborted on low thrust alarm. Rising oxygen temps due to hold for boat and helium bubble triggered alarm," Musk posted on Twitter. He said the launch team was reviewing data and would provide an update afterwards.
Although the California-based SpaceX has not said when it would make its next attempt to launch the rocket, the Air Force has said it will be no earlier than Tuesday.
The company is aiming to bring the main stage of its rockets back to Earth so that it can refurbish and reuse them, something that would make launches much more cost-effective.
SpaceX has already succeeded in landing a Falcon rocket on an on-shore site near the Cape Canaveral pad where it launched, but it has failed in three previous attempts to guide rockets back to ocean platforms.
Meanwhile, China has announced it will put a second space laboratory in orbit in the third quarter of this year as part of the country's plan to have a permanent manned space station in service around 2022.
Advancing China's space programme is a priority for Beijing, with President Xi Jinping calling for the country to establish itself as a space power.
The first space lab was launched in 2011 and has reportedly been working well.